what does vaccuum restrict?
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Senior User
Joined: May 2003
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From: South Dakota
what does vaccuum restrict?
I started mud racing this year and some rules for the class I race just dont make sense. The club I race with started off with rules from a different club but butchered them so that they are unreckognizable! First Im gonna say that roller cams dont belong in superstock but thats my idea, But the rule is all superstock motors must pull a steady 15 inches of manifold vaccuum at 800 rpms. I have my 400 built the the old rules, and when it was fresh I could barely pull 15 altho now that its broke it will do it. with how my motor is built it probly has 325-350 hp and 450 torque acording to the builder. But to my suprise theres guys running double the power i have and still pull the required vacuum. The club is already talking about changes for next year including aftermarket blocks. That made me very angry as the only rule that separates supperstock from prostock is the vacuum but many of the top guys can compete in prostock easily.So I spoke and the vice president said with the vacuum in place the restrictions are still there. but if theres guy that have double the power i do and pull the vacuum what can it possibly restrict????
FTE Legend
Joined: Jun 2006
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From: Ottawa, Ontario
Engine vacuum is an oldschool indicator of camshaft overlap and it could be used to gauge how radical a cam is installed. But as you have seen it is no longer a good indicator and that's because cumputer modeling has made it possible to design cams that produce more power without reducing engine vacuum.
Of course the cam tells you nothing about the airflow capacity of the motor and it's a well known fact that the Ford heads are very restrictive compared to the GM and Mopar versions, so these guys will get more power with smaller cams.
Of course the cam tells you nothing about the airflow capacity of the motor and it's a well known fact that the Ford heads are very restrictive compared to the GM and Mopar versions, so these guys will get more power with smaller cams.
More Turbo
Joined: Jan 2008
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From: in the middle of nowhere
As Conanski stated, the vacuum indicates camshaft lift and duration. but this rule is from a different era, from guys who could set a dual points distributor in their sleep and meanwhile their kids are adjusting their timing and boost in their Acura with the laptop that their daddy bought them for Christmas. I don't know about your sanctioning body, but when I raced in a stock class just once, they were more worried about tire size and snuffed a little on the vacuum reading. But that was just stock. You get into super and pro, it's another story. BTW there is no sight like a redneck with a clipboard
More Turbo
Joined: Jan 2008
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From: in the middle of nowhere
Just saw your gallery, Dell Rapids huh? I know you didn't win that burnout 'cause your name's not Dearduff. I think I see myself in the stands 
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From: South Dakota
That burnout was some years ago I havent competed in it for about2 or 3 years. Highest i got was 2nd place. Now youll find me at the burnout wearing bunker gear n holding a fire hose.
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