4 barrel economy

[Roadhog]

Back in the '70s with the first gas crunch where gas reached almost $1.00 a gallon There was a lot of talk about a 4 barrel being more efficient than a two barrel IF YOU WOULD NOT OPEN UP THE SECONDARIES! I never could keep my foot out of it! Has any one experimented with this theory or maybe disconnected their secondaries to find out? Or was this an old wives tale!

[Guest brh]

Well kinda sorta. Had a 72 Buick Centurion with the 455 the carb was a quadrajet. Small primaries large secondaries. I did everything to this gas hog including chopping the linkage to the secondaries this car still ate gas 8-10 MPG in the winter!! I changed carbs to a Holley 4 bbl the performance of the car was better, however if memory serves me the gas mileage never really changed. Best ever was 15 MPG gassed up just before getting on the expressway and just as I got off. The weight of that car plus the engine had been mistreated (it always had a couple of hung lifters) I believe did not help the mileage situation. Now my little Skylark with the 300 and 4 bbl Carter AFB best ever was 21 hwy. As long as the secondaries were not open. I took this car on a trip and burned a quarter tank one way. On the way back I had my foot in it big time (following a truck 80-90 miles per hour). Same distance took me a half a tank. The secondaries open and stay open over 70 mph. These are my experiences your mileage may vary.

[JohnD1956]

The following is a rumor, at least I've never done this. I heard you can fine tune a Q-jet and get 18 or more MPG. I do have a 69 Electra which used to get about 17 MPG with the Q-jet. But I digress..

Anyway I heard you use a Tach under the hood, and when the engine is warmed up, reduce the overall engine idle to 500 rpm. THEN you start with one idle mixture screw and adjust till the RPM maxes out. THEN you reduce the engine idle to 500 RPM again and switch to the other idle adjustment screw to max engine RPM again. Keep this up till adjustments on the idle screws result in no increase in engine RPM.

Like I said, I never did this. I do recall someone here saying in the past that you had to be careful not to make the engine run too lean. But the person I heard this procedure from was my brother, who is a mechanic and said he has done this on his Oldsmobiles with positive results.

Personally I think the max milage from a Q-Jet or any carb is going to depend on the rear axle final drive being matched to the road conditions. For example I doubt a 2.97 or lower rear will ever do good milage in steep hills. And I doubt 3:31's or higher will ever do well on flat open Thruways. But it's for certain no 4 barrell will ever do good unless you get your foot off the floor.

( BTW, my 56 Super with the Rochester 4 GC and 129K will do 17 mpg on wide open flat Thruway, at 55 MPH. While my 69 GS with the original Q-Jet and 30K will only do 15 MPG at 60 on the same road. Both on radials.)

JD

[55PackardGuy]

'69 seemed to be a good year for Electra gas mileage. Maybe it was partly the carb, but 17 mpg was pretty typical highway mileage for our '69, and it would do even better at times--on bias tires. You certainly can unhook the secondaries on a Q-jet to artificially improve your "driving habits." The primaries are smaller than a typical two-barrel without progressive linkage.

Final drive ratio, ignition timing, camshaft, and so many other things also enter into it though. It seems like some setups just have a good "sweet spot" that gives better mileage. In my experience, you can "tweak" all you want but don't expect miraculous gains in mileage. Sometimes even identical cars will vary widely, and usually you can't get the "gas hog" to change its ways much.

[Smartin]

I can make my 455 very fuel efficient if I drive VERY cautiously, and run about 55 on the highway for long distances. Around town and just general driving, it goes in the toilet.

I managed (no joke) 23mpg on my way to Flint in 2003. That was on a stretch of road with construction, so speeds were reduced, as well as aggressive driving. I've never been able to match it.

[NTX5467]

In the later 1960s, when bigger air flow carbs were needed for more horsepower and larger displacement engines, the "spreadbore" 4bbl was born. In prior times, most 4bbls had just slightly smaller primary throttle bores than the secondaries (i.e., the 625cfm Carter AFB had throttle bores of 1.56/1.69, the Holley 600cfm was 1.56/1.56, Holley 780& Carter AFB 750 were 1.69/1.69) but the spreadbore 4bbls typically had 1.38/2.25 sizing for the QJet, TQuad, and similar Ford carb for about 750cfm flow specs. There were some QJets and TQuads with 1.50/2.25 that were rated at 800cfm.

The idea was to get higher velocity through the primaries (1.38") so that finer fuel metering could be accomplished. Yet the smaller size also restricted total air flow, hence the need for the larger secondaries to make up for it. I think they usually had "triple step" venturis to achieve the higher flow past the fuel outlet nozzle. Holley also came out with OEM spec and aftermarket spreadbore 4bbls too.

Also consider that many 4bbl engines were also considered "performance" engines, so they usually had rear axle ratios a little lower than the "highway" gears of 2bbl engines AND single exhaust engines back then. There is also an excellent book on Rochester carbs that came out in the later 1970s. It goes into fine detail of how to tune the carbs for better performance AND fuel economy at the same time--it all relates to which metering rod/jet combination is in the primary side of the carb AND the power piston spring that phases the metering rod position versus manifold vacuum (key point in fuel economy issues!). As you might suspect, the Rochester QuadraJet spreadbore carb is highly tuneable across a huge band of displacements (230 to 455+) and vehicle applications. ALL of these things are covered in the Rochester book.

As mentioned, some engine/carb/cam combinations just seem to work better than others. There were many road test reports of QJet-equipped GM cars getting 20+mpg in some highway cruise situations at approx 60 mph or so, not all of them with highway gears. Olds had a "Turnpike Cruiser" setup on some (approx) 1967 Cutlasses (400 V-8, QJet, hot air air cleaner, 2.56 rear axle, leaner carb calibration which was aided by the constant air inlet temp of at least 100 degrees F) that would break 20mpg at 70mph and still outrun a stock base GTO (article was in CAR LIFE magazine back then). Even as some of the '72 era Olds Cutlass 350s were "desmogged" (illegal but popular back then), ALL of them would consistently hit the low 20s mpg, just as later Olds 307s in Delta 88s (might not run fast or quick) would typically hit middle 20s mpg on the highway (typically 2.41 rear axle gears, 3 speed automatic).

It was mentioned, back then, that keeping cruise rpms in the 2000rpm range was optimum for fuel economy. If you take a current production vehicle and check the rpms, that's pretty typical in most cases (except in cases where the engine has enough lower rpm torque to efficiently pull the car at lower rpms--late model LeSabres would take 82+mph to get to 2000rpm in OD, for example and still not have to get into the "power mixture" or downshift to go up normal hills).

In the later 1970s, Chrysler published some highly technical fuel economy guides. They detailed the EPA ratings of each of their cars AND THEN went on to detail how certain options (a/c, rear axle ratio) would affect those ratings in the "real world". In many cases it took more axle ratio change to change ultimate cruise fuel economy than you might suspect--back then.

With respect to camshaft issues . . . by observation, best fuel economy will happen when "cylinder filling" is in its more optimum orientation. This CAN be related to engine size and rear axle ratio (affecting cruise rpm), but does not always have to be. When cylinder filling starts hitting the "sweet spot" (we used to call it "coming up on the cam"), power and response will increase as can efficiency. In some cars, you can really feel it happen as throttle response gets much tighter (at cruise rpms) and can well correspond with the meat of the torque curve "hump". Recall that 2bbl cams were generally milder (less duration and lift) than the 4bbl cams? 2bbl V-8s were more about general driveability and fuel economy than 4bbls were, historically (and pre-spreadbore). In other cases, where cams were more optimized for the particular engine size (yes, there IS a relationship there!!!--email for my devised formula of this very issue), all it took was a 4bbl and dual exhaust to make them run better (even with stock exhuast manifolds).

Key things in most any consideration of fuel economy at cruise . . . low load and high intake manifold to keep the metering of the carb/FI in the "max economy" orientation and ignition timing vacuum advance maximized, lower rpms (say, 2300rpm and lower, but can be affected by the cylinder filling situation mentioned above) that don't lug the engine and the engine still has enough torque to moderately accelerate or go up hills without the power mixture kicking in, lower drag (tires and aerodynamics) in the vehicle (but if you have enough engine, this is less of a factor, it would seem), and a reasonably steady cruise speed (modern electronic cruise controls can aid this greatly, but the earlier ones could too). Vehicle weight can be a factor, but not typically at steady-state cruise conditions--it CAN be a factor in roads that have elevation changes every so often. Aerodynamic drag (or lack thereof) can be a factor as higher speeds (or convertible tops being lowered!) come into play, with respect to available reserve engine power (that "power mixture" situation, again) as evidenced by the amount of throttle pedal travel left at those elevated speeds PLUS how easily the engine might want to accelerate the vehicle at those higher speeds.

For some of the early 1970s engines, emission controls seemed to add some items into the mix that did hurt fuel economy, other than just compression ratio decreases. How much the "hurt" was seemed to be dependent upon the particular engines and their manufacturers--and other parts of the spec combination. By observation, the fed-spec 1969 Buick 430-4 V-8 that many in here have raved about it's seemingly better-than-it-should-be highway fuel economy in Electras probably came in at the right time to be as good as it was. Compression ratios were still high for 4bbl engines, only basically "engine calibration modifications" for emission controls, the QJet calibration for power and efficiency that obviously hit the "sweet spot" of things, and a great torque curve that worked in combination with the highway gears expected to be in a car of that nature. Put the same engine in a Skylark GS with 4.33 rear axle gears and it could well lose all of those fuel economy advantages real quick, but it definitely would run very quickly!

As mentioned, driving style and how it's impacted by the various vehicle equipment items can be more of an issue rather than just the equipment specs themselves. Electronic fuel injected vehicles (as most everything is now) are ESPECIALLY critical to driving style and use of the cruise control--as evidenced by driving one with the "Instant Fuel Economy" readout on the Driver Information Center display! You might THINK you're doing things to drive economically, but the display will clearly point out that you are not--even at highway speeds, a little too much pressure on the accel pedal can knock about 7mpg out of the cruise economy real quick and you would never know it, until you punched the cruise control and watched how things happen.

Carburetors are not quite that critical, but when the power mixture is activated with lower levels of intake manifold vacuum, fuel economy decreases a good deal. In some carbs, the power mixture can start coming in at 10.5" Hg and full on by about 6.5" Hg. In some cases, 10.5" Hg is just lower than where some engines are at idle and in gear with the a/c going! Even if manifold might be the normal 18" Hg at idle and out of gear!

Regarding carb adjustments . . . many earlier model engines did idle at 500rpm out of gear. They'd tolerate that as they had milder cams and seemingly higher velocity intake manifolds and smaller carb throttle bores than in later years. But you might also notice that when a/c came into the mix, there were additional specs for engines with a/c, regarding idle speeds. Then, emission controls came into the mix and idle speeds were increased again (for better mixture control and handling).

The time honored idle mixture setting was done with a vacuum gauge (before dwell tachs were in wide availability) by simply setting the idle speed to what worked right and then maximizing the manifold vacuum at idle with the mixture screws. Smoooooth idle, but not the best fuel use.

In 1969, the "leaner" settings were in place, which typically required the use of a dwell tach to do "right". There were still basic rpm targets to hit, but now rather than use just the "max vacuum, max rpm" settings, you leaned the mixture out to get a "20 rpm drop" with each idle mixture screw and then kept going back and forth until the specified idle rpm and best mixture combination was obtained.

The method I devised on my father's 1969 Chevy C-10 pickup with a 350 4bbl V-8 seemed to work well. That year of GM pickup and Turbo400 transmission had the line pressure seemingly raised (or the accumulator spring was stiffer in the transmission) such that when the idle rpm was at spec, it went into gear harder than you'd expect--they were ALL that way that year, by observation. He didn't like that so he had his mechanic set the idle speed down. When it was "there", it felt as expected but the rpm was too low to sit in gear talking in the field (for longer than you might expect) and it not overheat (not enough air flow through the radiator).

Having a single exhaust, I discovered that when the idle speed was set as "they" liked it, there were individual exhaust pulses that could be felt at the end of the pipe (in gear). I discovered that just slight increase in idle speed would smooooth out the exhaust pulses until it was one even flow. At that point, I started going back to the idle mixture adjustments to get "no smell" (i.e., obvious hydrocarbon emissions) too. To do that, I'd put my hand at the end of the pipe, in the gas flow, and then smell my palm to check for the hydrocarbon smell. When there was none, basically, I then refinessed the idle speed. It took a few trips between the carb and the exhaust pipe initially, but when I got it set to my procedures, it would sit and idle in gear, smooooothly, and not get hot or cause any other problems.

What did seem to bother me was that when it was then put into "Neutral/Park", the idle rpm went to 780rpm--which by all other orientations as "too high", but it worked well. I then used the same procedure on other cars we had and usually ended up pretty close to their specified idle speeds in "Neutral/Park", but after I'd done the "sniff test" for the idle mixture.

Later on, I replaced the QJet with a 450cfm Holley "spreadbore replacement" carb with a plunger-operated power valve rather than the metering rods/power piston in the QJet. In that carb, I'd do the same procedure, but it was tougher to do the sniff test as it was a more efficiently-metered carb. Still, I could do it and ended up with the same 780rpm idle in Neutral/Park. I found it highly interesting that at that 780rpm idle, the sensitivity on the idle screws was very tight, but when the idle rpm was dropped below 750rpm, that tight sensitivity went away and things got really "spongy" in that respect. Who would have thought that 30rpm could make that much difference in air flow vs metering/adjustment characteristics?

Anyway, point is that if you're going to get the best carb adjustment of the idle circuit, it can take some awareness of what's happening and how it all interfaces and inter-relates to each other. It's not always a "set it to spec" and "lick-it-and-stick-it-it's done" situation by any means. Factory specs are usually pretty close, but sometimes there can be a little further fine tuning or finessing that might vary from the stated specs that will turn out a little better for the particular vehicle combination.

Every vehicle has their own "sweet spots" all though it--idle speed and mixture are just one--but when some or most of those sweet spots are found and exploited, it makes the vehicle operate THAT much better and knowing that you got it there is an obvious just reward all by itself. It will take some time and attention to detail, but the trip is worth it, usually.

Enjoy!

NTX5467

[Harley]

Hi, new to forum but very grateful that others are sharing good input. I am restoring a pretty rough 1951 Super convertible and have decided to 'modernize' it with a 1969 Electra front and rear suspension AND the 430 engine. I feel that this will make the car more desirable (that putting a 350 Chevy in it,etc). I hope that I can learn more so we can end up with a powerplant that will do a good job of moving this heavy car down the highway efficiently. I have a V6 from a 1980 Buick, but doubt going this route makes any sense from potential resale down the road or plain efficiency. I appreciate any and all suggestions! Harley in CO.

[Roadhog]

Having a single exhaust, I discovered that when the idle speed was set as "they" liked it, there were individual exhaust pulses that could be felt at the end of the pipe (in gear). I discovered that just slight increase in idle speed would smooooth out the exhaust pulses until it was one even flow. At that point, I started going back to the idle mixture adjustments to get "no smell" (i.e., obvious hydrocarbon emissions) too. To do that, I'd put my hand at the end of the pipe, in the gas flow, and then smell my palm to check for the hydrocarbon smell.

Enjoy!

NTX5467 Lets see now as I understand it you used to tune carbs by sniffing the exhaust, did any one ever tell you that that could be harmful? Did it have any lasting effect like have an unending desire to fondle old rusty Buicks? Ha!

[Roadhog]

Harley, Thank goodness you are going to keep it all BUICK!!!! WAY TO GO BRO!!!!! I would Love to plant a 455 under the hood of me Special, but it runs too durn good to mess with, do these ole' nail heads ever quit???? Wewlcome to the forum there is a WEALTH of info here!

[JohnD1956]

Do you already have a donor car? If not I have one for sale.

[NTX5467]

The "sniff" I did was to put my bare, warm palm in the exhaust flow out of the pipe for a few seconds and then quickly sniffing my palm for hydrocarbon smells. Had to do it quick, lest there be too many lingering smells to taint further tuning results. Of course, when it was really "bad", you could smell it just standing near it. When everything was optimized just a tad lean from max rpm, there was no smell to speak of. This, with the smooth exhaust flow, of course, which generally took the quiver out of the engine at idle in gear "under load".

What I ALSO discovered, at least on Chrysler 383s, was that the '66 383 2bbl (with a quoted 9.2 compression ratio) had a normally cool exhaust temp at idle. When the engine was enlarged to 400 CI in '72 and the compression ratio was 8.2, doing the same idle mixture/speed adjustment procedure resuslted in the discovery that the later model year's exhaust temp was much higher than that of the '66.

The only real explanation for that would be the lower compression ratio and the open chamber heads versus closed chamber heads. Same temp thermostat, not more than 5 degrees difference in basic ignition timing, a slightly larger cylinder bore. Cam specs on the '72 were a little more "wild" than on the '66, but not to the 4bbl HO cam's specs. A '70 383 4bbl with 9.5 compression ratio and open chamber heads did not have the same elevated exhaust temps, though. None of these engines had A.I.R. pumps either.

Getting into a discussion of lower compression ratios resulting in greater heat rejection to the exhaust gas flow might get us into a place we might not want to be here. It was proven that keeping "the cook" on the exhaust flow after it left the combustion chamber would result in fewer hc emissions at the end of the tail pipe. Nevertheless, you can add that "higher heat" observation into the mix of my carb tuning exploits.

When I discovered the sniff-tuning technique, it was in those times of yesteryear when "real" gas had tetraethyl lead in it (proudly proclaimed on each gas pump too!) at something like 3-4 grams/gallon of 97 Research Octane fuel. Rather than "regular" or "superunleaded", the pumps had jazzy names like "Phillips 66 Flite Fuel" (premium that later had a posted pump octane of 95.5, or about 101 Research Octane!), Gulf Oil Company "Good Gulf" (regular, which would have been 94-5 Research Octane), "Gulftane" (sub-regular), Gulf "No-Nox" (premium), Esso "Extra" (premium) with plain Esso being "regular"--in other words, EVERY oil company had their own separate blends and chemistry that was designed to make your vehicle run better than it would with anybody else's gas in it, or so they claimed. And don't forget about those free roadmaps!!! Those were the days!!!

So far, no health issues from my sniff tests. Once I got them figured out AND bought a good dwell tach (still have it too!), I used the sniff and feel tests of the exhaust flow as the final quality control checks of what I'd done. Might not work as well with our new-fangled "safe for the environment" fuels, but they sure did work good back then.

An alternative to using the palm of my hand was to use a red shop rag, placed over the end of the exhaust pipe, then quickly removing it and getting a whiff of it for the same hydrocarbon smell. Had to hold is reasonably secure and gently onto the end of the warm exhaust pipe, though.

Automotive Trivia for Posterity . . .

When you held a shop rag up to the end of an exhaust pipe of a running vehicle, what did it mean if the rag was sucked into the pipe every so often while otherwise being pushed outward by the exhaust's flow?

[[[[[[ Negative pressure pulses at the end of the exhaust pipe would indicate a "leak" in an exhaust valve's seating action on the intake stroke of the piston, when the exhaust valve is closed . . . i.e., "burnt valve" . . . which would also be indicated by a regular drop of the vacuum gauge needle when the negative pulse was generated. End result, "Valve Job"! ]]]]]]

Enjoy!

NTX5467

[BqUICK]

1969 Buick Electra 225 Custom Convertible, 4,700 lbs, 430, duals, quadrajet.

19-20 mpg 93 Octane

21 mpg Race 110

God Speed

[imported_buick5563]

Wow,

I'm printing this one... I want to get better than the 12 mpg on premium unleaded my Wildcat is currently getting. I'm thinking of putting a Q Jet on the 66 manifold I have, I just need to figure out the linkage. THEN, I think I will try to get Willis down here to sniff my pipes. <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" />

Mike

[NTX5467]

Mike, if YOU don't know WHAT "aromatic addition" you are investigating . . . you can learn, too, on YOUR OWN vehicles' pipes. LOL It doesn't take much to learn that "feat", just some time and a screwdriver.

BUT we can probably do some things to get your Buick to get more MPG, though. Generally, it's in the metering rod phasing via the power piston spring tension. SMartin's comment about road speed and conservative driving point to the possible need of a "lighter" spring than what's in there now--something to take more throttle input and lower manifold vacuum to move to the "power" portions of the metering rods' diameter. I think it details these activities in the HP Books "Rochester Carburetor" book, with part numbers!

This "new fangled gasoline" (version 1 or 2 or whatever) doesn't seem to smell the same way the old stuff did, it seems.

Some thoughts on 5563's statements (?????) . . .

NTX5467

[carbking]

For those interested in getting to know the Q-Jet better, there is a new book on the market by Cliff Ruggles that is much more "user friendly" than the Doug Roe book.

Jon.

[imported_buick5563]

While i was Driving Miss Daisy (my boss, not a car, last week) She kept trying to get me to drive faster. I then told her that I hadn't gotten a speeding ticket in 20 years. So I don't think that speed is an issue for my mileage woes (even though I know I drive faster than the other Texans when getting back from Nationals). So, I don't think leadfootedness is the issue. I WOULD like to know if someone has ever put a Qjet in an earlier Nailhead and what I need to know as far as linkage alterations. ??? Actual experience?

Mike

[NTX5467]

First thing would be to find a suitable intake manifold (front heat track or not)--AND the correct base gaskets. Might even end up with an aftermarket manifold with dual base plate bolt patterns?

Second would be an OEM-production application to use to baseline the metering specs.

After that, the linkage issues would probably be pretty easy to deal with. QJets have used throttle rods and cables so getting something to work might require a trip to the salvage yard and a little research.

Carb spacer/adapters are not recommended, not to mention the affect they would have on hood clearance!

Enjoy!

NTX5467

[Bill Stoneberg]

Mike,

If you dont mind mix and match some of the newer carbs do better then the old Q Jets according to the people on the Nailhead list.

The Dominator and Edlebrocks version are two I can think of.

BTW, I found that green shag. Bought a whole roll. I figured you need some for under your kit.

[imported_buick5563]

'preciate it, <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" />

Thanks Bill

Mike

[imported_buick5563]

Hi guys,

Just found a rebuilt 66 Qjet and I will install it in the Wildcat next week when it arrives. I've been acquiring parts for years waiting for the carb. I have a NOS air cleaner, 66 manifold and the aluminum valve covers that I installed yesterday. I was going to attempt to sell the Cat but I don't think I could get what I want out of it so after driving it last week (and totally loving it) I decided to get everything working and drive the snot out of it. I'll let you know if I know if I need sniff tests performed. The choke is currently stuck open so I imagine that could have been part of the problem. I need to figure out the AC so I can enjoy it even more months per year...

I'll keep ya posted.

Mike

[imported_buick5563]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">

BTW, I found that green shag. Bought a whole roll. I figured you need some for under your kit. </div></div>

One last thing, Bill, I also found that green shag (in stock) at Lowe's, No Lie.

Mike

[Bill Stoneberg]

Two questions......

Who in their right mind would ever buy that for any house, apartment or vehicle and how much was it <img src="http://forums.aaca.org/images/graemlins/cool.gif" alt="" /> ?

Good luck with your wildcat.. It has to be fun to drive. Cant wait to get the Riv running.

[imported_buick5563]

A.) I dunno <img src="http://forums.aaca.org/images/graemlins/confused.gif" alt="" />

B.) I can't wait to see the Riv. <img src="http://forums.aaca.org/images/graemlins/cool.gif" alt="" />

Mike

[NTX5467]

Mike, was that "NOS" or an accurate "repro" pattern in the carpet? Did they also have "the rake" for it too? LOL

Glad to hear you got your carburetor "found". Should be neat when you get it all installed.

Enjoy!

NTX5467

[imported_buick5563]

I don't know if it was an exact match on Bill's new Riviera drivers side floormat.

Of course they had "the rake". It was in gardening <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" />

Mike

[Greenelectra]

I was thinking this might be a good time to reopen this thread.

I just ordered a rebuild kit for my Quadrajet to go on my slightly built 430-4 thats in a 68 Skylark. With the Holley thats on there now I'm getting nearly six and a half miles per gallon. Amazing right ??????

The engine and trans came from my old 69 Electra four door hard top. At worst that got fourteen miles per gallon.

I'm hoping putting the Rochester rebuilt on instead of the Holley will get me back to the good old days of 14+ mpg.

[NTX5467]

Well, "A Holley is not always A Holley". WHICH Holley did you put on the motor? One of the more universal models or an OEM-replacement carburetor. Which one can make a HUGE difference in fuel economy!

What are the cam specs on the 430? What rear axle ratio? Tire size? All things which can have an effect on highway fuel economy.

Why "highway" fuel economy? Because on the highway, the speed is more "steady state" so the power system is not needed very much (for a richer mixture for accelerating and such). Plus, no "idle time" at red lights!

Many people perceive that all Holley 4bbls are "racing carburetors", hence "no fuel economy", BUT that is not always the case. When I upgraded my '77 Camaro 305 to a Cam Dynamics Energizer cam (210 @ .050, .440 lift, 110 centerline) from the stock cam (basically the old 300 horse cam, but with a shorter intake side), I used an emissions-spec Holley 4160 for a '76 Impala 350. With the cam and intake and carb change, after some advance curve tweaking, it dropped fuel economy about .40mpg from what the 2bbl did, with more power. That meant an average of 17.4mpg, combined highway (mostly) and suburbs. Then, years later, when I got an emissions spec Holley 4175 (Q-Jet replacement) for it, the mileage went up to 20mpg average . . . and up to 23.5mpg on a highway loop of 60 miles . . . surface freeways at night. Which is still 1.5mpg better than the 2bbl ever did on highway trips!

So, I was curious what the part number (stamped on the upper choke horn on the Holley) for the Holley might be? I feel that might better explain the fuel economy. PLUS, some Holleys were bad about blowing power valves, which greatly erodes fuel economy.

IF you increased the cam specs very much from stock, it could make your stock carb need some adjustments to the idle fuel/air circuits. Off-idle hesitation/flat spots are one possible issue, plus getting the idle mixture to be "clean" rather than "too rich and somewhat non-adjustable".

Please advise.

Respectfully,

NTX5467

[Greenelectra]

1761 and a seperate 1 were the only numbers I saw when I looked at it a moment ago.

The rear end is whatever was in the car when I bought it . The engine rpms are low and normal at highway speed I believe.

I've tried to attach two pics of the carb in question.

Woops almost for got the cam specs.

lobe center 118

duration 284 304

Valve lift .490 .490

The rear tires are ; BF Goodrich 275/60R15

Thanks for the help.

Paul.

Edited May 4, 2012 by Greenelectra (see edit history)

[carbking]

Think of the entire vehicle as a "system". One may optimize certain components of the system, but the system output is only as good as the weakest component in the system. For fuel economy on vehicles of the 1950's, 1960's, and 1970's, the weakest components are generally the driving habits of the operator and especially the automatic transmission.

I have upgraded several vehicles with automatic transmission to manual. I EXPECT to gain 25~35 percent increase in fuel economy, and a decrease of at least one number fuel octane requirement. So far, have never been disappointed.

But this link may help in optimizing the fuel economy on any given vehicle:

THE CARBURETOR SHOP / Troubleshooting

Jon.

[carbking]

Well, "A Holley is not always A Holley".

NTX5467

Willis - "Holley" is French for "gasoline leak" :p

Also, BMC once tested Holleys for use on British sports cars. They rejected the idea. They decided one pool of fluid under the engine was sufficient.

Jon.

Edited May 4, 2012 by carbking (see edit history)

[buick5563]

Willis - "Holley" is French for "gasoline leak" :p

Funny

Also, BMC once tested Holleys for use on British sports cars. They rejected the idea. They decided one pool of fluid under the engine was sufficient.

Funnier

[NTX5467]

Thanks for the cam specs. I'm not sure what brand of cam that is, but I looked (for general reference) on the Crane Cams website and found a cam with similar advertised intake duration and less lift. The description mentions a cruise rpm of about 3000rpm or a little more. With a 2.56 or 2.73 rear axle and the tire size you have, that equates to a road speed of about 85+mph. When looking at the power band rpm, the lower rpm would be about 60mph, which means the cam isn't "working" until you get to higher speeds . . . "working" used to be termed "on the cam", now it's when the engine makes its best "cylinder pressure".

I was looking for a carb number of the orientation R-1850 or 0-1850 (for example) stamped into the air horn, on about the same level as the choke horizontal pivot shaft, but on the front, flat driver's side quadrant of the choke housing. But, in general, I suspect the cam specs spell where any fuel economy might have gone. Even with a decent running 430, with that much cam and gearing, it would probably take enough throttle to get into the power mixture level of intake manifold vacuum for normal driving. Compounded, somewhat, I suspect, by a lower-stall speed stock torque converter. If the engine might have backfired for any reason, then "poof", there went the power valve . . . which means the engine is running on about 12.5 to 1 air/fuel ratio all of the time, rather than the much more fuel efficient 14.8 to 1 at cruise rpm (at any level).

I didn't notice any spacer/adapters under the carb, so I suspect the intake manifold is correct for the Holley carburetor? And that the correct for the QJet manifold will be reinstalled with the QJet?

Getting the QJet back on there might get you a fresh carb, so to speak, back on the engine. But with the cam specs you've got, there is a good chance that you'll not have the same performance and economy you previously had with the stock cam. I suspect the cam was changed after the engine was removed from the Electra? In other words, you'll have issues to deal with to retune the carb for that camshaft.

In many cases, in order to get the idle throttle plates to be correctly phased with the carb's "transition" and "Idle" fuel ports, you'll need to drill the primary throttle plates to have "a hole of a particular size" in the throttle plates to allow the extra airflow the cam needs, but still put the thorttle plates in the stock relationship to the transition and idle ports in the primary throttle bores. Otherwise, it'll probably take too much openning of the primary throttle plates to get it to idle at a reasonable idle speed. You'll probably also notice a heavy "essence of hydrocarbons" out the rear tail pipes. Evidence of the primaries being too far open, such that both the idle and transition ports are flowing fuel at the same time, a too-rich mixture, at idle. Then, as you open the thorttle to drive off, you'll probably have a hesitation or flat spot until the rpm is high enough for the carb's primary main system to become the main metering source.

A good many years ago, a friend had a '79 Corvette L-48. He upgraded the cam to "something bigger" and had these exact issues with his stock QJet carb . . . until he drilled the holes in the primary throttle plates. If you can find a copy of the HP Books book on Holley Carbs, it'll detail how this all works and why.

As for "leaking Holleys", my own experience has been a little different. I do know that in the later 1960s, there were probably more OEM Holleys removed from Chrysler products (and replaced with Carter AFBs or AVSs) for that reason . . . otherwise known as "The Yearly Carburetor Rebuild". The ones I've had since the later 1970s have the "glue together" gaskets, which are heck to remove . . . B-12 won't faze them. But, I guess it was a good thing that Harleys didn't use Holleys.

In any event, from my own personal experiences, I believe you'll be better off with the Holley 4bbl . . . a "fixed" one that's better tuned to the cam and intake you have. I suspect that with the QJet, you'd just be starting over again with some of the same issues, just a different carb.

If it turns out that the carb you have is a "universal fit" version that fits many engines and such than being specific to a '67 Buick 430, then it's certainly not quite a "bolt on and go" sort of thing . . . although it might work reasonably well out of the box, it most probably will not work as good as it might work with a little mixture-map retuning. AND a new power valve of the correct value. A little looser torque converter and (about) a 3.36 rear axle ratio might not hurt, either.

These are my gut suspicions, from what I've seen over the years. Others might have differing orientatios, whcih I respect.

Respectfully,

NTX5467

[Greenelectra]

I bought the cam from Poston , I don't remember who made it.

All this makes me want to go back to a stock cam:(

The intake manifold is a Buick Edelbrock aluminum one from 1970 I believe.

I'm surprised that rebuilding the engine,trans and installing a new set of duals with a hotter cam has reduced my MPG by more than 60% in a two door Skylark instead of a four door Electra .

Whoops ,I guess thats the last time I ever do that .

Paul.

:confused::confused:::confused::confused::confused::confused::confused::confused::confused::confused::confused::confussed::confused::confused::confused::confused::confused::confused::confused::mad:

[NTX5467]

I understand your situation . . . you wanted something "better than it originally was, power-wise". The Edelbrock intake is probably a good item, provided it's rpm range is not too high. In looking at the current Edelbrock intakes for 430 Buicks, there are two . . . the B-4B resto manifold from the later 1960s and the newer Performer 455. Both show rpm ranges of "idle - 5500rpm", which should be fine. They usually have more generous port sizes and cleaner castings than the factory manifolds did. Plus more power, generally.

If the cam came from Poston, I suspect it's much more performance oriented than "just a little hotter than the stock cam". Just my gut suspicion. From the specs, it'd probably be just fine with a 3.73 rear axle ratio and headers, but not with a 2.73 (or thereabouts).

I looked in the CompCams website and used their software kit to see what might be comparable to your Poston's cam. What came up was their "Thumper" series cams, which are "thumpier" at idle and needs looser, higher stall rpm torque converters, headers, "gears", etc. The "Great Fit" criteria cams were their popular 268H and 260H grings, which have the assymetrical lobe shapes for "more area under the valve lift curve" for more performance. The 268 works very well in almost every engine I've seen it installed in, with the 260 being just a tad smaller, for more torque and a slightly lower rpm band. But with the 110 degree lobe separation, you'll need to re-curve the distributor for more advance sooner than the stock curve supplies.

I still believe a certain amount of your fuel economy loss is in the carb, though. Was it new, rebuilt, or used when you got it? Just curious.

When I was contemplating a cam/intake/4bbl upgrade on my recently-new '77 Camaro 305 2bbl, I looked around at many camshaft comparisons. I configured my own camshaft comparison formula, biased toward engine size vs. cam specs. At that time, I'd also known of several friends who'd used the CompCams 268s in Chevy 350s and a 327. All worked very well. If you set the idle down to 500rpm (in neutral), the 268's idle sounded expecially mean, but with it turned up to where it needed to be, about 650 in neutral, it became very smooth and "stockish".

Due to my smaller 305 and my formula, I opted for a similar spec to the 260 (Cam Dynamics, now Crane, 266, with the same 210 degrees at .050 and .440 lift). As it turned out, that was about as wild as the stock converter would take and not put too much load on the engine at idle in gear. With a 2.56 rear axle and P225/70R-15 Radial T/As, 31mph/1000rpm at cruise, it really needed a little deeper gear to be happy at 55mph, but once over 60mph, the throttle response got tighter and it acted "happier". I originally had a Holley 4160, emissions spec for a '76 Chevy 350 V-8 on it. Mpg dropped slightly from the stock cam and 2bbl carb. I used the Holley 28-Z Z-Line 4bbl intake on it. Until I quickened the mechanical advance in the distributor, it was lazzzy, but I got that taken care of with some playing around. Then, I also had to play with the secondary springs in the Holley to even get it to open them, even on a 600 cfm carb. It took more to get things dialed-in than ANY magazine article had ever alluded to!!! I had the resources and knowledge base to assist in those activities, though.

I know that a lot of enthusiasts like to brag about how much fuel their "hot rod" might use, as an indicator of how much power it makes . . . just like some Chevy guys brag about how many times they've had to rebuild their motor . . . just too much power in there, it seems. But we know that the Buick 430, in Electras, would knock down some great fuel economy on the highway, with some reliable reports of 20mpg on trips. Consider, too, with the 2.7_ gearing, P235/75R-15 tires, it's not running much past 2300rpm while doing that, if that much rpm at all. We've determined that with the bore size, etc., the valve sizes, the particular cam specs, and the smaller primaries of the QJet carb, that particular rpm range is right in "the sweet spot" of the 430s efficiency curve. Plus, there were some air speed ranges through the primaries of the QJet where the metering got very precise . . . all of which would yield the mpg results many in the Buick forums have mentioned.

"Too much cam" is something that many have done in the past, just as many will do it in the future, too. It can be quite common, in some respects. All in the desire to make things "a little bit better" in the process, but ending up with something worse in the end. BUT if you want to change the rear axle ratio to about 3.73, get the carb mixture curve dialed in, then you might have what you wanted . . . at probably better fuel economy, too, than what you mentioned. But certainly not 20+mpg on the highway.

Or you can downsize the cam and get the carb dialed in, keeping your existing rear axle ratio and torque converter. Possibly closer to high-teens in mpg on the highway.

Personally, I like passing gears that string up to about 100mph before the WOT 2-3 shift happens. Knowing you have another gear left at 100mph feels better than a WOT 2-3 shirt at 75mph and knowing that high gear will wind out sooner. Even if it might take a little longer to get to 60 in the first place. And, I like cars that cruise effortlessly and reasonably economically in the 75-90mph range, too, which usually means 2.56-2.76 rear axle ratios. Just my personal preferences . . . provided the CHASSIS components are up to that sort of activity!

Just some thoughts,

NTX5467

[Greenelectra]

Swapping the Holley for the Quadrajet today . I'll keep you informed.

[Guest 54fins]

I don't think you can do much with milage with a dynaslush tranny. I'm going to build a 425 nailhead for cruising and maximizing mileage. Nice motor out of a 65 electra with the TH400. The first issue is an overdrive. The TH400 is nice, but an overdrive is more expensive than a 700R4 adaptor. Then there is always a 5 speed.

going to use a fuel injection carb with an oxygen sensor and possibly a mass flow sensor. The altitude changes in Denver are just too much for a carb and I want to do some mountain cruising. Old Buicks also have tons of steel and pot metal, but It's had to see a way to shave weight as I want to keep the original look. It's all that chrome that makes them such beauties. But driving with the front clip off, it's amazing what loosing 500 lbs off the front end does for the performance. Unortunately I cant figure out a way to shave weight and keep the look.

Ultimately, if I can cruise at 75 and keep the RPM around 2000 I suspect that pushing 20 MPG may not be unreasonable. Not that I'm expecting it, but 10 MPG on a 54 just doesn't cut it! A 322 with a Dynaslush at 5000 feet, it's just dumping gas down the carb. A re-jet is about impossible at altitude, I don't see any way around fuel injection for altitude.

[carbking]

A re-jet is about impossible at altitude, I don't see any way around fuel injection for altitude.

Makes one wonder how people were able to drive in Denver before the late 1980's

Jon.

[Greenelectra]

So when we pulled off the holley we discovered the float was set way too high and if you tilted the carb at all gas just poured out of it .

My Quadrajet was already rebuilt with all the nice parts from Cliff's high performance so we have installed it and i'm already happier just having it back on the car .

I'm sure I'm probably getting twice the gas milage i was but that wouldn't be hard considering the way the Holley had been set up.

If I can get my odometer working I'll figure out the numbers.

Thanks.

[Ben Bruce aka First Born]

Makes one wonder how people were able to drive in Denver before the late 1980's

Jon.

I like that, Jon. I just don't know what Buick was thinking back then!!!:D

Ben

[Guest 54fins]

At 5000 feet you have 20% less oxygen so you are 20% rich

Not a big issue but from there it gets worse. If you had a strong motor you can make pikes peak but many cars did stall out above 10000 feet. I have heard stories of barely making a pass or getting towed but running fine back in denver