Must Pull 17" Vacuum
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Senior User
Joined: Oct 2001
Posts: 306
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From: West Monroe, La
Must Pull 17" Vacuum
Hey all,
My son and I are getting into mud truck racing this summer. We were given a 79 F150 4wd with a 351m. It is bone stock with a 2150 2v. It had a short block installed about 20k ago, and it has set up for a couple of years. Got it running and sounds good, but we need to upgrade. The only rules in the 1/2 ton stock class are a cubic inch limit (385 ci-I think), no single plane manifolds and 17" vacuum at 1000 rpm.
Plan on an edelbrock intake/carb combo, headers and cam. Not rebuilding the motor--this is a budget buildup. My question is--How large can I go on a cam and stay over the 17" rule. Just talking off the shelf cam/spring combos.
Thanks for your help.
My son and I are getting into mud truck racing this summer. We were given a 79 F150 4wd with a 351m. It is bone stock with a 2150 2v. It had a short block installed about 20k ago, and it has set up for a couple of years. Got it running and sounds good, but we need to upgrade. The only rules in the 1/2 ton stock class are a cubic inch limit (385 ci-I think), no single plane manifolds and 17" vacuum at 1000 rpm.
Plan on an edelbrock intake/carb combo, headers and cam. Not rebuilding the motor--this is a budget buildup. My question is--How large can I go on a cam and stay over the 17" rule. Just talking off the shelf cam/spring combos.
Thanks for your help.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
First don't use the Edelbrock cam. It will be a mild cam to get 17" vacuum, but I can't give you a definite answer. I suggest that you call Comp Cams Tech help and ask them.
A couple of other suggestions is to get a good double roller timing set and set the cam timing 'straight up'. Another is to do some light porting work on the bowl and exhaust ports.
A couple of other suggestions is to get a good double roller timing set and set the cam timing 'straight up'. Another is to do some light porting work on the bowl and exhaust ports.
Thread Starter
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Senior User
Joined: Oct 2001
Posts: 306
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From: West Monroe, La
Good sugestions, thanks. I know there are a lot of variables that would make the vacuum number change. I am running Crane dual pattern cams in my 390 and 351w and am satisfied with them. Calling tech support is a good idea.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
I have an agressive custom grind HR cam from Comp cams in my 434. In order to keep the vacuum high enough for power brakes, I have a Lobe Seperation Angle of 114 degrees. This reduces the overlap. It is overlap the reduces vacuum. What you want is a long duration high lift cam with minimum overlap. These are called 'Cheater Cams', because they don't lope as much as a similar cam with more overlap. Unfortunatly a custom HR cam might be to many $$$, but you should talk to Crane or Comp Cams tech help.
Elder User
Joined: Feb 2000
Posts: 775
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From: Temperance,MI
I would get ahold of camcraftcams(.com) he does a lot of circle track car cams that have to do the same meet vac. requirements. My 400 cam is from him great power intake is just under .500lift ex is over and at idle it pulls 20" I just got home and don't feel like digging through the file for my cam card.
Curtis
P.S. if you like I can find it.
Curtis
P.S. if you like I can find it.
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