Too big cam too little vacuum

pdk255e · 06-18-2005

Can any of you creative gear heads come up with a solution for my 69 coupe with a 302 4v. I bought this from a guy who had put a very big cam in and I dont even know which cam. My problem is that this very big cam is creating a very low vacuum condition. Car needs to idle fast to stay running, the power brakes dont work great due to low vac. I am looking for a solution that would avoid ripping the cam out and starting over. Thanks for any good options you can give.

STONECOLD · 06-18-2005

I dont know if you can use this but I thought Id put the link up and let you take a look for yourself.

http://store.summitracing.com/defaul...=egnsearch.asp

Quick66 · 06-19-2005

the problem with running too much cam is that your car is not built around it. What I'm saying is that even if you increase your cylinder / manifold vaccum with a pump or canister, you still have a cam who's powerband is way above the operating range of the rest of the car's components and the typical intended use of the car. If you want to really enjoy the car and experience some fun to drive on the street, then the only plausible issue is to change the cam. I ran a comp cam .500/.493-270/280 flat hydraulic and it was a blast. The car had tons of bottom end torque, and even pulled fair through the midrange, it just ran a little weak above 6000 rpms. If it were me , and I was driving the car, not seriously racing, and I was more concerned about fun to drive than lope, I would call comp cams up and pick out a cam.

67coupe · 06-19-2005

What carb are you using, brand and model?

pdk255e · 06-20-2005

I am running witha Holly 850

67coupe · 06-20-2005

850cfm is way to much for a 302. That could be some of the trouble at lower RPMs. Less cam and less carb you would be a lot happier with the way it drives.

Putt · 06-21-2005

Quote:

Originally Posted by 67coupe

850cfm is way to much for a 302. That could be some of the trouble at lower RPMs. Less cam and less carb you would be a lot happier with the way it drives.

EGADS!!!

My 10:1 CR 428 only needs a 750 cfm, I would replace that 850 with a 600-670 cfm Holley before trying to crutch your low vacuum problem.

bstyluz · 09-05-2009

i bought an 88 mustang with motor already built not sure what size cam but has serious hesitation when i get on it and just doesnt run right, wont even do a burn out , it sounds good at idle but thats all, could it be the computer

andrewmp6 · 09-06-2009

Try asking in the 5.0 part of this forum.

The Greek · 09-06-2009

There's always the option of using a set of Rhoads Lifters. They're designed to make more vacuum with a large cam.
www.RhoadsLifters.com

Tominator · 09-06-2009

A properly jetted 850 CFM carb will work fine....

Change the cam....that is the ONLY viable solution!