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Author Topic:   pulling vacum
Dirt Full Roller

Total posts: 41
posted December 13, 2002 09:11 PM
where i race there told us we had to pull 12" of vacuum. An i don't have a clue how to check it. are what i can do to a motor to pull it. i need any help and what will it do. are there any tricks.

Dirt Full Roller

Total posts: 61
posted December 15, 2002 12:13 PM
you check it with a vacuum gauge attached to
a vacuum port at the base of the carb or on
the intake manifold. Your rules should be
easy to pass .*Depending on idle speed*
The first thing I would suggest is that you
get a real good gauge and see where your
motor reads when it is warmed up to racing
temperature. At this point, even if you are
passing, you can adjust the idle mixture on
your carb by reading the gauge . It will
drop off when the mixture screws are not
right . Make sure you check the idle speed
after adjustments. Another way to increase
vacuum at idle is with more ignition timing.
But you need to make sure your timing is correct at higher RPM also. If you have a
hydraulic cam motor, setting the valves at
.005 lash will help ,also. Hope this helps.

Dirt Full Roller

Total posts: 41
posted December 15, 2002 10:30 PM
idle speed is 1000

rico 08
Dirt Freak

Total posts: 372
posted December 16, 2002 01:54 PM
That's an easy rule,ours is 18" at 1000,some tricks are using bleed down lifters with hydraulic cams,specially ground cams,zero gap rings etc.But the cam is the most important try to keep the overlap low as this kills vacuum,most circle track cams have a low lobe center(106-108)this really kills vacuum and makes the engine lope,try some thing in the 112-114 range i beleive crane has some or about anyone can do it with a custom grind,i was reading where the new ls-1 type engines have a 116 degree lobe center and even when the cam is reground and more duration is added they still idle smooth.

Dirt Full Roller

Total posts: 41
posted December 16, 2002 08:48 PM
WE run solid lift. 547 isky and 292 comp.
2bbl. carb. 355cu in. the rest has to bet stock.

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