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Author Topic:   Vacuum rules
Dirt Newbie

Total posts: 2
posted January 25, 2003 06:09 PM
Our track has a vacuum rule that states you must pull 10" of vacuum at 800 rpm. Does anyone have a cam recommendation for this?

Dirt Full Roller

Total posts: 37
posted January 25, 2003 06:38 PM
Our rules have a simaliar rule on Cam,however alittle higher.I believe this is a minimum,to keep you from pushing the cam to far.Its my understanding you can run a good cam it just cant be pushed.I overheard someone the other day talking about tweeking something to show a lower valcum reading.

Dirt Forum Racer

Total posts: 89
posted January 25, 2003 07:15 PM
10 inches isn't very much vacumn. A Lot of cams could hit that. Lock your timing advance so all the timing is always in at idle. Wider lobe seperation should produce more vacumn too.

Arkie Dirt Racer
Dirt Full Roller

Total posts: 69
posted January 25, 2003 10:23 PM
wow, I wish our vacuum rule was like that. does anyone have any recomendations for a cam that'll pull 16" at 1000rpm in a flat top 350 with stock 487X heads? I'm thinking about a .480 lift, about 225* duration@.050, does this sound about right to get 16"?
also, not having a really radical cam, would there be much advantage to running solid lift over hyd.?

"Dirt is for racing, asphault is for getting there"

Dirt Forum Champ
Total posts: 620
posted January 26, 2003 08:32 AM
arkie, yes a solid lifter cam will pull more vacuum than an similiarly ground hydraulic. the ramps on a solid cam are faster and the overlap would be less, thereby creating more cranking compression and more vacuum. you can run a bigger solid cam and get the same vacuum as you would get from a lesser hydraulic.

if rules allow, go with the solid. a specially ground roller cam could also pull a lot of vacuum and still have some big top end power.

Arkie Dirt Racer
Dirt Full Roller

Total posts: 69
posted January 26, 2003 10:19 PM
thanks outlaw.
our rules do allow solid lift, but no rollers. if I can go with a bigger solid lift and have about the same big should I go? any ideas?

"Dirt is for racing, asphault is for getting there"

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