How much vacuum do you need??
Thread Starter
Intermediate
Joined: May 2008
Posts: 26
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From: Santa Maria CA
How much vacuum do you need??
Hey everyone!! Getting ready to drop my new 383 stroker in next week, but need help deciding on a CAM. I have a few in mind, but one important question I need answered. How much Vacuum do I need to ensure continued operation of the headlight and wiper systems on my 75 l48? Thanks!! I will post pictures of it when it gets assembled. Oh, and by the way, be careful when you hit your frame with a hammer, SOMETIMS it goes all the way through and reveals a rats nest :-)
Safety Car
Joined: Oct 2007
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From: Austin Texas
Corvette of the Year Winner 2017
2016 C3 of Year Finalist
20 " is a good value for a motor with min. cam or /orginal engine.
the bigger the cam, the less vacuum you can pull.
Radical cam 5-7"
I personaly think 5" is too low of vacuum to shoot for.
I would guess 12" vacuum would be closer to your target.
all this requires good plumbing and a 1 -way check valve also.
also the lower the vacuum, the slower your acc. will move.
69VETT
the bigger the cam, the less vacuum you can pull.
Radical cam 5-7"
I personaly think 5" is too low of vacuum to shoot for.
I would guess 12" vacuum would be closer to your target.
all this requires good plumbing and a 1 -way check valve also.
also the lower the vacuum, the slower your acc. will move.
69VETT
Thread Starter
Intermediate
Joined: May 2008
Posts: 26
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From: Santa Maria CA
Thanks for all the replies everyone!! I am looking at a CAM that will roll out about 14" vac.
Now, a little off topic, but what is the adverse effect of having the intake stay open longer during the compression stroke to reduce your dynamic compression ratio?
Now, a little off topic, but what is the adverse effect of having the intake stay open longer during the compression stroke to reduce your dynamic compression ratio?
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Joined: Jun 2008
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From: Murphy Texas
Now, a little off topic, but what is the adverse effect of having the intake stay open longer during the compression stroke to reduce your dynamic compression ratio?
Last edited by rham; Sep 4, 2008 at 09:52 PM. Reason: add more info
Racer
Joined: Oct 2006
Posts: 306
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From: Burnaby BC
Here are my cam specs and I get 8-9" at idle if I have the timing at 14-15* at idle.
RPM Range: 2500-7000 Advertised Duration: 290/300 Duration @ .050: 235/245 Lift: .490/.510 Lobe Center: 112c
Any lower timing and my vac dropped and the lights go up right first then left, but they still worked.
I also had to change all my lines so I have no leaks.
Wiper door on my 69 works great at this setup as well.
Vacumm goes up when you drive it so your brakes will be ok as well.
Unless you stall your engine going down a big hill, them it is good old leg muscles or do a Fred Flinstone.
RPM Range: 2500-7000 Advertised Duration: 290/300 Duration @ .050: 235/245 Lift: .490/.510 Lobe Center: 112c
Any lower timing and my vac dropped and the lights go up right first then left, but they still worked.
I also had to change all my lines so I have no leaks.
Wiper door on my 69 works great at this setup as well.
Vacumm goes up when you drive it so your brakes will be ok as well.
Unless you stall your engine going down a big hill, them it is good old leg muscles or do a Fred Flinstone.
Thread Starter
Intermediate
Joined: May 2008
Posts: 26
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From: Santa Maria CA
Thanks for all the responses guys!! This is plenty of info for me to work with. Definitly like the look of your big cam tristan!! This one wont be that big, but should be fun! :-)
Instructor
Joined: Apr 2006
Posts: 212
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From: Woodland Park Colorado
My 383 pulls 10 at idle and 6 in gear and thats at 8000 ft above sea level where I live. Everything works fine head light come right up. I also had to put a 4.5 power valve in the holley due to the low vac at idle in gear. If you have a manual trans you should be ok.
