GM LS7 engine with 3x4-barrel carbs?

[Matt Harwood]

I'm sure you guys have all experienced this--I call him "the Topper." No matter what story you're telling, something even more remarkable/scary/injurious happened to him. So a guy at my local auto parts store found out what I do for a living and started telling me about this amazing cache of one-off GM secret prototype cars sitting in some old guy's barn near him. He says there are 1000 cars stashed there, all ultra-rare GM cars that were never released to the public (never mind the sheer square footage required to store 1000 cars). He's going down this list of truly impossible things, starting with a 2016 Corvette which, for some reason, he claims was built without any roof of any kind and is some kind of special prototype for racing. Then he goes on to say there's a 1970 Chevelle there with a factory LS7 engine that's got an aluminum block and heads and THREE 4-barrel carburetors on top. I told him surely it was three deuces and he was mistaken, but he doubled-down and yes, 12 barrels somehow shoehorned on top of a V8.
 

I stopped him right there because I was starting to drown in bullshiat.

 

I told him there was no possible way GM was trying to cram three 4-barrel carburetors onto a 454--there's no need for that much carburetor on anything short of 900 cubic inches running at 8000 RPM. Ignoring the fact that the LS7 was a 425 horsepower iron block that never went into production because of the fuel crisis, I can't imagine GM would build such a thing, prototype or not, and if so, there's just no way this old farmer in Ohio ended up with it just sitting there rotting in his barn.

 

So I bet the guy lunch that it didn't exist. I went in today and he's demanding that I pay up because he saw this mythical "triple quad" intake for sale on Ebay for $13,000. I can find no trace of it. My Google skills, which are considerable, can turn up no photographic evidence of such a thing--not even a home-made contraption with three quads. Apparently, nobody has ever been stupid enough to try to make three 4-barrel carburetors work on a V8 engine, and that certainly seems to include GM engineers.

 

I'm not really sure how to prove a negative and that it doesn't exist, so I've asked him to produce photos, but at this point, I simply dread going back there because I'll have to listen to this guy's wild goose stories for 20 minutes every time I go to buy parts.

 

There's no way he's correct, right? I'm willing to give him the benefit of the doubt and cough up $100 for lunch for all the guys at the store just to make him shut up (and to buy myself some goodwill), but you guys also know how much I like being right.

 

Thoughts?

[joe_padavano]

Yeah, factory 3 x 4bbl carbs... 

 

The aftermarket HAS stepped up here, with a 3x4bbl adapter that only accepts AFBs.  This was on ebay last year.

 

http://www.ebay.co.uk/itm/Tripower-3x4-bbl-U-Fab-Supercharger-Tunnel-Ram-Adaptor-/191438783700

 

 

For the really insane, there was a 4 x Qjet intake.

 

 

 

[joe_padavano]

I should probably add that while I'm no Chevy expert, I do know that the factories did try some crazy experimental stuff in the 1960s.  For example, I own a factory-cast experimental intake for the big block Olds motors that is a cross ram set up for two Qjet carbs.

 

[keiser31]

I have (almost) learned to say, "Never say never".

[padgett]

Well there was an early '60s Pontiac 421 with three carbs, two big Carters and "something else" in the middle. That said by LS7 time I was deep into FI (900 cfm) and the only four barrel I had was a QJ on a Corvair.

 

ps never saw a manifold bolt in a secondary before, at least not deliberately.

 

pps a good QJ could flow 800 cfm stock (could tell by the almost a venturi ring). Why would anyone need more than two (wonder if that olds had a flat crank and was being treated as two 4 cyls.)

[capngrog]

I think that some of the old Ferrari V-12s had 3X4 barrel carburetors, but I've never heard of  such a set up on a V-8.

 

I know what you mean by a "topper".  We have a couple of those at the local pub where I hang out.  I make sure I have my high-topped boots on and just ease back and listen while sipping on a "cool one".  Some "topper stories" are worthy of the science fiction genre, and, while entertaining, it is occasionally difficult not to jump up and shout "Bullshot"!!! 

 

Cheers,

Grog

[nzcarnerd]

1 hour ago, capngrog said:

I think that some of the old Ferrari V-12s had 3X4 barrel carburetors, but I've never heard of  such a set up on a V-8.

 

I know what you mean by a "topper".  We have a couple of those at the local pub where I hang out.  I make sure I have my high-topped boots on and just ease back and listen while sipping on a "cool one".  Some "topper stories" are worthy of the science fiction genre, and, while entertaining, it is occasionally difficult not to jump up and shout "Bullshot"!!! 

 

Cheers,

Grog

I think those V12s actually had four three barrel carbs.  Quite different of course to anything from the US. 

[joe_padavano]

4 hours ago, padgett said:

Well there was an early '60s Pontiac 421 with three carbs, two big Carters and "something else" in the middle. That said by LS7 time I was deep into FI (900 cfm) and the only four barrel I had was a QJ on a Corvair.

 

ps never saw a manifold bolt in a secondary before, at least not deliberately.

 

pps a good QJ could flow 800 cfm stock (could tell by the almost a venturi ring). Why would anyone need more than two (wonder if that olds had a flat crank and was being treated as two 4 cyls.)

 

The Olds intake is a cross ram and the two plenums don't connect, thus the need for two carbs.  Also, note that 4bbl carbs are rated at 1.5" of mercury pressure differential. CFM rating changes with pressure differential - more pressure differential flows more air. As venturi area increases, pressure differential decreases, so CFM rating also goes down.  Two "800 CFM" carbs on a common plenum may only actually achieve 1200 CFM or less. 

[Guest]

2 hours ago, capngrog said:

I think that some of the old Ferrari V-12s had 3X4 barrel carburetors, but I've never heard of  such a set up on a V-8.

 

I know what you mean by a "topper".  We have a couple of those at the local pub where I hang out.  I make sure I have my high-topped boots on and just ease back and listen while sipping on a "cool one".  Some "topper stories" are worthy of the science fiction genre, and, while entertaining, it is occasionally difficult not to jump up and shout "Bullshot"!!! 

 

Cheers,

Grog

Most used the weber 2bbl carburetors before going to FI. See images;

Little Dino with it's six cylinder

Edited July 27, 2016 by helfen (see edit history)

[capngrog]

3 hours ago, nzcarnerd said:

I think those V12s actually had four three barrel carbs.  Quite different of course to anything from the US. 

 

The photographs I've seen of the old carbureted V-12 Ferraris showed three carburetor bodies on the intake manifold, not four.  With that said, it is quite possible that Ferrari also experimented with four 3-barrel carburetors for their V-12s. 

 

 

As I recall, Holley and a couple of other carburetor manufacturers produced what they called a 3 barrel carburetor.  These were basically 4 barrel carburetors with the two secondaries combined into one large oval venturi.  These carburetors were indistinguishable from a normal 4 barrel without looking down the throat of the carburetor.  The three barrel carburetors were reputedly not real happy in the street driving environment. I have a Chev 350 in a streetrod with 3X2 barrel carburetors, and they are a sufficient challenge, so I think that I will hold off on acquiring a couple of three barrel carburetors.

 

It's all good,

Grog

 

 

Edited July 27, 2016 by capngrog
wrong link (see edit history)

[Guest]

Pontiac was using a three barrel Carter in NASCAR in 1962-3. It flowed 939 CFM

 

 

Manifold to go with it;

 

[padgett]

Jon would know but think the Carter was a 3636. Note on the Olds each carb is feeding one bank (cross ram) which works best with a flat crank. Suspect there mustabin about a 2 inch riser between the carb and manifold in #11 else the secondaries would never open.

 

BTW I do know an engine that had two three barrels - early Porsche 911. And the three bolt carb was a Stromberg 97.

 

GM in 56 tried a lot of engines with 2x4bbls WCFBs then went to tripowers in 57. Those started with three 1.25" cabs, then the end carbs went to 1.5" and in 66 only Pontiac used three 1.5" carbs - 2Gs on the ends and a 2GC in the middle.

 

Fun thing was the Pontiac choked down the A-bodies (GTO) with small individual air cleaners that flowed much less than the carbs were capable. This enabled Milt to demonstrate that the single QJ on a 67 400 (much larger air cleaner) was faster than a 66 Tripower 389.

 

</ramble>

Edited July 27, 2016 by padgett (see edit history)

[nzcarnerd]

44 minutes ago, capngrog said:

 

The photographs I've seen of the old carbureted V-12 Ferraris showed three carburetor bodies on the intake manifold, not four.  With that said, it is quite possible that Ferrari also experimented with four 3-barrel carburetors for their V-12s. 

 

 

As I recall, Holley and a couple of other carburetor manufacturers produced what they called a 3 barrel carburetor.  These were basically 4 barrel carburetors with the two secondaries combined into one large oval venturi.  These carburetors were indistinguishable from a normal 4 barrel without looking down the throat of the carburetor.  The three barrel carburetors were reputedly not real happy in the street driving environment. I have a Chev 350 in a streetrod with 3X2 barrel carburetors, and they are a sufficient challenge, so I think that I will hold off on acquiring a couple of three barrel carburetors.

 

It's all good,

Grog

 

 

 

 

I knew I had seen three barrel carbs somewhere.  It was not Ferrari but the Lamborghini Miura that used them - look it up. I think some Porsches used similar carbs but of course only two per engine.

[Guest]

34 minutes ago, padgett said:

Jon would know but think the Carter was a 3636. Note on the Olds each carb is feeding one bank (cross ram) which works best with a flat crank. Suspect there mustabin about a 2 inch riser between the carb and manifold in #11 else the secondaries would never open.

 

BTW I do know an engine that had two three barrels - early Porsche 911. And the three bolt carb was a Stromberg 97.

 

GM in 56 tried a lot of engines with 2x4bbls WCFBs then went to tripowers in 57. Those started with three 1.25" cabs, then the end carbs went to 1.5" and in 66 only Pontiac used three 1.5" carbs - 2Gs on the ends and a 2GC in the middle.

 

Fun thing was the Pontiac choked down the A-bodies (GTO) with small individual air cleaners that flowed much less than the carbs were capable. This enabled Milt to demonstrate that the single QJ on a 67 400 (much larger air cleaner) was faster than a 66 Tripower 389.

 

</ramble>

Naturally a 400" Pontiac with the new valve angle and 2.11 / 1.77 heads and a 750 CFM Q jet with Ram Air exhaust is going to out run a 389 with restrictive 1.96 / 1.66 bathtub chamber head with tri-power and standard restrictive exhaust. Later, High Performance Pontiac magazine took a 66 tri-power and installed it on a 69 RA3 and the tri-power made more HP than the Q-Jet 4bbl.

[60FlatTop]

If I was working at GM and an engineer was retiring (especially one who screwed up a manifold design)I might drop by the nonferrous foundry and run off a 3X4 manifold as a gift. Things like get get out in public. It's better than getting an inflatable sheep for a gift.

 

I have a miniature 20,000 gallon bunker C fuel oil tank on my desk, accurate to the bolt holes in the flanges, so accurate I was afraid to touch the black puddle at one end. A guy could splash one of those manifolds out of aluminum pretty quick.

 

Bernie

[carbking]

Matt - there have been some "interesting" things produced over the years; however, I am unaware of a "factory 3 4-barrel set-up". Doesn't mean some prototype wasn't tried at some time or another. In the future, you might be better served to suggest the topper produce the proof.

 

Padgett - your memory is correct on the Carter 3-bbl as being a 3636s. Carter flowed it using both the 4-barrel criteria (939 CFM) and the 2-barrel criteria (1128 CFM). Somewhere, I have a copy of the actual flow test.

 

I am unaware of what 3-barrel carbs may have been produced outside of the USA. To the best of my knowledge, three manufacturers produced a 3-barrel in the USA:

 

Stromberg, then Carter, then Holley.

 

The Carter has already been pictured. Here is the Stromberg:

 

 

 

And no, gentlemen, that is NOT a photoshopped picture, I have possession of the carburetor.

 

The bottom of the Carter 3636s has already been posted, here is the top:

 

.

 

The secondary linkage on this carburetor is set up on basically a one-to-one. When the primary opens, so does the secondary. Not too friendly on the street. I have modified a couple of them to have conventional secondary linkage for the street. I have a letter from Carter stating that only 15~20 of these were built; however, that is incorrect. When I was researching the Pontiac SD carbs many years ago, I found the existance of 24. I currently have two in my possession.

 

Holley made both a 950 CFM and a 1050 CFM. I have had examples of both, but have them no longer.

 

Jon.

[carbking]

21 hours ago, helfen said:

Naturally a 400" Pontiac with the new valve angle and 2.11 / 1.77 heads and a 750 CFM Q jet with Ram Air exhaust is going to out run a 389 with restrictive 1.96 / 1.66 bathtub chamber head with tri-power and standard restrictive exhaust. Later, High Performance Pontiac magazine took a 66 tri-power and installed it on a 69 RA3 and the tri-power made more HP than the Q-Jet 4bbl.

In seemingly a different lifetime it has been so long ago, I took a graduate course in which one of the subjects was the creation of surveys. I was an adult at the time, and the instructor was a very good friend. I asked him during class what was the most important criteria in designing a survey. He thought about it a moment, and then stated: "the most important criteria in designing any survey is to remember who is paying for the survey". I knew what he meant, but for the benefit of the class, I asked him to elaborate. His comment: "If we are trying to determine the most popular non-alcoholic drink, and the two candidates are Nestle iced tea and Hershey hot chocolate, and Nestle was paying for the survey, we would NOT pass out ballots in Minneapolis in January"!

 

 

The Pontiac Super Duty Department tested, and rejected the tripower for racing about 1961. They even cast an aluminum intake. But it didn't come close to a single AFB (let alone the larger Q-Jet). Pontiac settle on the single 4, the single 3 (NASCAR), and the 2x4 for their racing efforts prior to the infamous "get out of racing edict".

 

Granted that this was the tripower with the smaller center carb and two larger ends, but it was competing against the Carter AFB 3010s, which was rated 625 CFM, not the larger 750 CFM Q-Jet. And of course, the manifold design was done at the same time.

 

Jon.

Edited July 28, 2016 by carbking (see edit history)

[Guest]

5 minutes ago, carbking said:

In seemingly a different lifetime it has been so long ago, I took a graduate course in which one of the subjects was the creation of surveys. I was an adult at the time, and the instructor was a very good friend. I asked him during class what was the most important criteria in designing a survey. He thought about it a moment, and then stated: "the most important criteria in designing any survey is to remember who is paying for the survey". I knew what he meant, but for the benefit of the class, I asked him to elaborate. His comment: "If we are trying to determine the most popular non-alcoholic drink, and the two candidates are Nestle iced tea and Hershey hot chocolate, and Nestle was paying for the survey, we would NOT pass out ballots in Minneapolis in January"!

 

 

Jon.

Jon, I'm a simple guy so can you explain exactly what you mean to say in regards to my post in the Kings English? 

[carbking]

OK - Pontiac PAID Carter to sabotage the secondary side of the Carter AFB used on the street Pontiac engines so the more expensive tripower street engines would not get beat by the 4-barrel engine! The more "exotic" and expensive tripower losing to the cheaper 4-barrel would have been embarrassing

 

Substitute "road test" for "survey" in my above post and yours.

 

Jon.

Edited July 28, 2016 by carbking (see edit history)

[Guest]

5 minutes ago, carbking said:

OK - Pontiac PAID Carter to sabotage the secondary side of the Carter AFB used on the street Pontiac engines so the more expensive tripower street engines would not get beat by the 4-barrel engine! The more "exotic" and expensive tripower losing to the cheaper 4-barrel would have been embarrassing

 

Substitute "road test" for "survey" in my above post and yours.

 

Jon.

You linked it to me and I was describing the transformation from Tri-power to the Q jet. The magazine was published long after not only Tri-Power was discontinued, but the Pontiac engine was long gone by 20 years. No skin in it for anyone.

[padgett]

Like the flange on Firebird QJs (one of the worst kept GM secrets) ?

 

<waning, gearhead stuff>

 

And along those lines I never thought the little AFB used on the Goat flowed more than about 550 (4 bbl rating) Meanwhile the 1.5" end carbs were good for about 360cfm each (corrected to 4bbl) and the center 2GC about 200 or about 920cfm for all (and if you took a Chevvy 396 2bbl (station wagon engine) with big (1.375" ?) venturis you could get over 1000 cfm out of a tripower & the high rise A body manifold flowed better than the flat B-body.

 

Also I would agree about the stock tripower, but the late XS engine with the 744 cam (I have a 744 in my Judge - would not want one with an automagic) flowed better than anything Pontiac had in 67 with 670 heads.

 

 

[Guest]

14 minutes ago, padgett said:

Like the flange on Firebird QJs (one of the worst kept GM secrets) ?

 

<waning, gearhead stuff>

 

And along those lines I never thought the little AFB used on the Goat flowed more than about 550 (4 bbl rating) Meanwhile the 1.5" end carbs were good for about 360cfm each (corrected to 4bbl) and the center 2GC about 200 or about 920cfm for all (and if you took a Chevvy 396 2bbl (station wagon engine) with big (1.375" ?) venturis you could get over 1000 cfm out of a tripower & the high rise A body manifold flowed better than the flat B-body.

 

Also I would agree about the stock tripower, but the late XS engine with the 744 cam (I have a 744 in my Judge - would not want one with an automagic) flowed better than anything Pontiac had in 67 with 670 heads.

 

 

Pontiac used the 744 for the first time in 1966. XS 389 block 093 heads Tri-Power 360hp M/T  Fed cars non California AIR.

Pontiac used the 744 in 1967 400" engine.

744 is basically a 535480 (7) with 1.50 rockers. although the #7 uses solid lifters. That's what I had in my 59 Catalina A/SA  

[carbking]

Padgett - the stock AFB's used by Pontiac were built on a 610 CFM frame, but after the "tripower insurance modification", were down to approximately 575 CFM.

 

The AFB's Pontiac used on the SD's were totally different, with the smallest (even the one used on the 4 cylinder Tempest) being 625 CFM, and other increments of 700 CFM, 750 CFM, and 939 CFM.

 

The CFM of the tripower is limited by the internal turbulence of the intake manifold where the number of plenums is not an even divisor into the number of cylinders; not the actual size of the carburetor. Pontiac found that the maximum CFM the 1966 tripower unit (with the improved higher manifold) would flow was 780 CFM, but this number DECREASED as the RPM increased - certainly NOT desirable in a high performance engine. 

 

Heflen - wasn't meaning to throw rocks at you, and sorry if you took it that way; was throwing rocks at the test. Lots of enthusiasts were (and still are) VERY annoyed that GM discontinued multiple carbs on everything but the Corvette, and replaced their beloved tripower with the Q-Jet. I believe the testers fit that category. As I stated, the Super Duty Department tried to make the tripower work for high performance work, and couldn't; thus it was rejected.

 

Here is a picture of that aluminum SD intake casting number 540510:

 

 

The SD people even modified one of the large aircleaners to use (MUCH less restrictive than the pie pans used for looks later on). The snorkels were removed from the large air cleaner, and seven oblong holes the same size as the snorkel holes were broached into the housing. But the tripower still could not compete. However, due to the "cool" factor, Pontiac continued to sell them to enthusiasts that wished the laws of physics could be ignored. And this is still very true today. We have done a very good job of rewriting much of history to suit our wishes, why not do the same with automobiles. But the facts still DID happen.

 

There is no doubt a tripower looks absolutely great on an engine, more so than the more efficient single quad. Personally, I like the look of dual quads (which work!) even better than the looks of the tripower. But if everyone had the same idea of what looked the best, we would all drive the exact same vehicles.....boring. 

 

Also, Pontiac tried (and rejected) a single 6-barrel carburetor.

 

And for those that truly believe the tripower is the greatest, I still have dozens of them available for sale.

 

And just to offer proof about the modifications made to the AFB:

 

Carter (as did other manufacturers) installed hot idle compensating valves on many of their carburetors. On the AFB, the hot idle compensator is located on the lower casting between the two secondary venturii. The valve is a temperature controlled valve which opens a metered vacuum leak into a passage right below the valve dropping down into the intake. This tended to lean out the mixture and prevent hot stalling in summer city traffic. In the picture below, part number 169-92 is used on non-Pontiac carbs, 169-66 on many Pontiac carbs with automatic transmissions, and 169-80 (DUMMY) used on many Pontiacs with standard transmissions EVEN THOUGH THE PASSAGE WAS NOT DRILLED! The wings on the 169-66 and the 169-80 reduced the amount of CFM available on the secondary side of the carburetor by about 35 CFM.

 

 

Jon.

Edited July 28, 2016 by carbking (see edit history)

[carbking]

Matt - going back to your original post:

 

There have been LOTS of really interesting things tried, many rejected, others modified over the years. With the internet, a lot of these things can be found, but even if they cannot be found, doesn't mean they didn't happen.

 

For those that are interested, look up the Adams-Farwell car.

 

Also, overhead cam engines were available in the early teens, don't remember exactly but 1913 seems to resonate in memory.

 

One company ran a small exhaust pipe into the gas tank to pressurize the gas tank and thus eliminate gravity feed for early cars. Not much information on their success!

 

One carburetor company built a capacitor out of a sheet of mica in the carburetor bowl to preheat the carburetor mixture! MUCH more common to either water-jacket or exhaust-jacket the carburetor, but like I stated, many things tried.

 

Two-barrel carbs were tried as early as 1916. I have one of them in my museum.

 

Probably the early equivilent of the 4-barrel/tripower discussion/argument would be the rotary throttle (Master, Winfield, etc.) carburetors versus conventional throttle valve carburetors. The rotary throttles were the rage for awhile, but what survived?

 

And the sleeve valve engines have always amazed me.

 

And or course, the super high mileage Pogue and Fish carburetors. Never was willing to spend the price for one of the Pogue's but have had (still have) a number of Fish. My mentor in the carburetor vocation did an extensive (1000 mile) comparison road test on the Fish versus the stock Holley on a 1963 Ford 6-cylinder.

 

Time for a cup of coffee  

 

Jon.

[Guest peter123wallace]

Awesome thread! 

The LS7 has always been one of my favorites

One example wont hurt: http://www.nocarnofun.com/1960-chevrolet-corvette-convertible-driven-by-ls7-at-2015-sema-motor-show/

[padgett]

Even better would be a Chevvy 495 (1969) with unequal  injector stacks. Also in a 'vette, the 435hp tripower made less real power than the single 4bbl 430hp. Chevvy was playing games for marketing.

 

 

ps 1913 Indy Peugot: DOHC/4valve

Edited July 30, 2016 by padgett (see edit history)