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Carb Size Advice


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I've got a 75' 455 that is going over a complete rebuild, heads, crank and all. Most likely going with the Hemi Killer Cam and JE racing pistons, headers, 2.5" exhaust. I've got a few questions. I want this setup to run about 450-500 hp and still burn pump gas, I figure 10.2-10.5 compression or so? The rear is getting a 3.55 posi and the tranny is a stock TH400. First question - what stall speed converter? This will be a mostly street car but I'd like to be able to throw on slicks and run her about 12.5 or so (in a 67 Skylark) Anyone happen to know the curb weight of this car offhand? Second question - What cfm carb? I'm thinking a Holley Double Pump between 750 - 850 cfm. What are the performance advantages of going to an 850 with the afformentioned setup, is it necessary? Thank you. <P>------------------<BR>67 Skylark 455

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The Holley is gonna kill you with gas milage (talking less than 7 mpg). My 750 vaccum secondary Holly was about 5.5 MPG, UHHHHHGGG!!!! I'm presently running a B4B with a '73 worked Rochester (approx. 840 cfm)over the top of a Hemi Killer w/110* Lobe Centers and seeing about 10 to 11 mpg. <P>I use the GSCA converter. 2800 stall, flashes to 3200. Probably should be a little higher, but it's fine for me. <P>------------------<BR>George C. Thomas<BR>70 GS 455 12.teens<BR>86 GN Low 13's/ high 12's

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The double pumper is great for drag racing, but it is not great for street duty. THe Q-jet will be easier on your pocketbook buying it and paying for gas, and driveability will be great. You can get T/A to build you one, specificly for your engine combo. But! Do what you want! Its all good stuff if you can tune it and make it work together! I love to drive my cars on the street, so I'm extremely biased toward the driveability side.<P>------------------<BR>Ted Nagel<BR>65 WildcatConvSuperWcat<BR>65 WildcatAutoSuperWcat<BR>65 Wildcat4spdSuperWcat<BR>65 Riviera Wildcat 445<BR>65 Special Wagon 455<BR>70 GS Stage1 4speed<BR>66 Fleetwood Brougham?

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The stock carb on your motor was rated at 800 cfm. I had a similar combo. i had a 3500 conv it worked well. I had a Q-jet by a reputable source . I got 13 mpg and went 12.30s. Drivabilty was fantastic. Later I switched to Holley 850 , lost mpg to around 5 and driveability stunk. I picked up no ET.Good luck .....Pat

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Thanks for the good advice. I also noticed a big change when i switched from a rebuilt Q-Jet on the stock setup to a 650 Holley. She seemed to have much more pick up but my fuel econonmy dropped from like 14 to 10 mpg, and that was a stock motor with low compression. The problem with my old Q-Jet was that it really seemed to bog down on me off the line, perhaps with the better inner engine goodies I wouldn't have that problem. Is there any technical difference between the two carbs besides the name - ie if the cfm's are the same why is there such a MPG difference? I know that my old Q-Jet was a major pain in the ass to tune so that's why I changed to Holley, having the side bowls made it really accessable, especially when still on the car. <P>------------------<BR>67 Skylark 455

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I have learned the 850 or 1000 CFM Compitition Thermoquad is the hot setup for these motors. I sold a 1000 CFM on the GS Club OF America site a while a go and there was much interest in it. <A HREF="http://buickgsca.com/cgi-bin/ubb/Ultimate.cgi?action=intro" TARGET=_blank>http://buickgsca.com/cgi-bin/ubb/Ultimate.cgi?action=intro</A> <BR><P>------------------<BR>buickfam@aol.com<BR>Life long Buick Fan.<BR>1965 Skylark H/T<BR>1965 Gran Sport Convertible<BR>1948 Chevy Pickup with 401 Buick.<BR>"Fan of anything that moves human beings"

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The Q jet has small primaries, helping your around town milage, just don't dump it too often. If yours was bogging off the line, it sounds like a bad accelerator pump. Easily repaired.<BR>I suggest that you get a copy of Doug Roe's book on Rochester carbs. <P>------------------<BR>George C. Thomas<BR>70 GS 455 12.teens<BR>86 GN Low 13's/ high 12's<p>[This message has been edited by Thundrr (edited 12-20-2000).]

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