Hey all, many of you know a little about my combination and I'm certainly into the realm of when a larger carb would benefit the rest of the combination. However, at what horsepower level do our Buicks really want more air? To attempt to use numbers and math, when would we begin to see vacuum approaching or above 1.5" when dynoing one of our big blocks?
Cliff Ruggles is using (tuned) 750 Q-jets at nearly 600 hp. 800 Q-Jets at or slightly above 600 hp. 'Course, that's on a Pontiac engine. It's likely more important to have the fuel curve right than to have the ultimate in flow capacity. And we haven't even considered the difference in carb size needed between a fully-divided "180 degree (2-plane) manifold vs. a single-plenum, single-plane manifold.
I certainly see that, but if you dropped a Holley 950 HP on the engine what would it make? I honestly thought flow capacity was more important than a perfect fuel curve, but I guess what do I know lol
Ok I missed it, is it a Qjet or a Holley or ?. The Qjet is more adjustable so cfm is not measured like a Holley. You could get a 600 Holley but if you needed a 750 then you need to buy the 750 Holley, where the 750 Qjet could be tunned to 600 or 750 and more settings.
John, youre on the right track. I would say if you hook up a vacuum guage and see 2-3 lbs vacuum at WOT, you need more carb. BTW I think I saw you today on West St, maybe around noon or so?
Yeah, it's good for 550-600 hp but I would change to a 800 at maybe 475-500 so you are not trying to run on the edge.
Ask Jason Line, stock eliminator requires the original carb. 10.015 @ 131 mph at Indy 2019. https://www.nhra.com/news/2019/jason-line-making-most-indy-experience-pro-stock-and-stock-eliminator
Orginal casting does not mean it's not highly modified......... I dont know qjet well but I'm sure they can get more cfm of of qjet, like they can almost any carb.
At whatever rpm your test motor is pulling 1.5 Hg of vacuum then you have maxed out that Carbs flow capacity. Builders who do purely race motors do not want to see anything over 1 Hg of vacuum at the rpm of peak hp, but for a street / strip motor if I only saw 1.5 Hg show up at 400 rpm before peak hp Cam in I would not sweat it!
The harder the engine sucks, the more they flow. But you can go beyond the RATED cfm with additional vacuum; and the vacuum overall hurts power. Or less, maybe. Which is how folks wind up with Dual Dominators.
I can guarantee you NHRA inspectors know quadrajets very well by now. Absolutely no airflow mods are allowed. Fuel circuit mods are allowed. People like Jason Line aren't going to risk getting thrown out because of a bogus carb. There are many superstock cars running much faster than Jason with quadrajets. Enjoy!!!!
You need to think along the right lines to make the most power if that's what we are indeed talking about here and the bottom line is that a tuned Exh system along with the proper placement of the Cams overlap will draw a vacuum level in the cylinder many times higher the the suction that the cylinders make during the Intake stroke At the start of the Intake cycle to assist in getting the air flow moving again thru the Intake runner. This is added cylinder depression is also directly related to the quality of low lift flow the Intake port has at .200" lift. In effect you are using the Intake port during down time so to speak when the Intake flow would just starting to move in the runner as the valve began to open on the Intake stroke or going the wrong way due to reversion and the wrong overlap placement.
My 70 350 factory replacement gs350 carb is the best qjet I have had. 12.40 108.6 1.70 60 ft. I plan on going thru it as it just flat crapped out one day when I arrived at e town for their stock super stock shootout in 017. Have a fresh 800 built and plan to play w it when time n weather permit.
