How much vacuum?

J

JJRJR

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Hey guys,

I'm trying to choose the best carb and size for my set up. Engine still at Dyno Shop. I've read a few articles that a "hot" street car should be running no more than 1"HG of vacuum. My understanding is that at 5,500 rpm my 383 is "never below 2 inches of vacuum" according to the Dyno operator.

In the articles it seems to indicate that if you're pulling any vacuum, your carb is restricting your engine's performance. What do you think?

Thanks,

John
 
Theres more to it than just vacuum. Yes it is true that if you see more than 1 inch of vacuum the carb is a restriction. We dont race dynos though and probably the car will accelerate faster with the smaller carb. I am sending you a pm here in a minute.
 
while you are reading there is a hot rod article on carb booster,streight/downleg and there effect and that may help you pic your next carb.
 
Thanks. I misheard what the dyno guy said about the vacuum. He said it never approached 2"HG. Once the CR and heads are fixed; I'm going to test with an 850 and see how it runs.


Thanks,

John
 
John,

I think something wrote earlier is something to consider. The larger carb might get you higher top end, but a smaller carb will get you better lower end. That doesn't mean starve the engine, but how often are you going to be driving at top end?

Good luck,
Barry
 
nicanor said:
John,

I think something wrote earlier is something to consider. The larger carb might get you higher top end, but a smaller carb will get you better lower end. That doesn't mean starve the engine, but how often are you going to be driving at top end?

Good luck,
Barry
Click to expand...


Thanks Barry, this will be a low end power car for sure. With the 3.91's, I'm not going to be doing 120 MPH on the highway very often. Just want to show those Mustangs and Camaros what a Mopar can do. LOL. Thanks again, John.
 
I would think a stock stroke 383 with ported eddy heads you would be looking for horse power in mid to higher RPMs, the dual plane intake will make it more street happy but hurt the top end a bit, I'm not sure where your going. You have low enough gears that bottom end should be no issue. Just my :cents: Some one correct me if I'm off base
 
69hemibeep said:
I would think a stock stroke 383 with ported eddy heads you would be looking for horse power in mid to higher RPMs, the dual plane intake will make it more street happy but hurt the top end a bit, I'm not sure where your going. You have low enough gears that bottom end should be no issue. Just my :cents: Some one correct me if I'm off base
Click to expand...


I think I understand what you're saying. By using the 3.91's, it will compensate for the low end loss of a single plane intake. Dyno guy said for sure I will gain HP in the higher RPM range with a single plane. Something to consider for sure.

Thanks.
 
Just something to remember JJ the stock 383 was not a single plane :) There was a reason why the engineers had the 391's with a 4 speed in the A12 cars ;) I would either get a stock manifold or go with the edddy rpm air gap dual plane you will get the best of both worlds.
 
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