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Old 05-19-2004, 10:25 PM
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how much vacuum at idle?

i just got a vacuum gauge today, and i was wondering how much vacuum do u think i should have at idle with valve lift .443/465, .050 dur. 214/224 and adv dur. 280/290.

thanks

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Old 05-19-2004, 10:29 PM
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Super Chevy,

Now you have the gauge and you want me to tell you what it reads? Let me think a bit. I got it ,18-20 inches on the gauge. Needle will bounce like a pulse indicator.

How did I do?
Scholman
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Old 05-19-2004, 10:31 PM
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well the engine isnt running yet, its just sitting in the chassis.
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Old 05-20-2004, 02:19 AM
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Vacuum

Hi!

Doc here

18 to 20 hg is proper for your engine.

I'm not sure on a Cam of that lift / Duration about the pulse...

However on a Stock Setup, they say (Whoever "They" really are...) If the needle bounces on Idle look at valves, Valve train...This, again may go out the window with a non~stock cam.

My Vette pulls 20 at Idle, drops to about 16 on throttle, Then returns to 20...and all is Happy and well in "General Mystery" land...

Sooo I'd say if your in the ballpark , and it runs good ... It should be All Good!

Doc

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Old 05-20-2004, 06:31 AM
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thanks, i didnt know if id loose a little with the lopeyier cam.
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Old 05-20-2004, 03:57 PM
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I have a 560 lift hyd roller cam, the vacuum in gear at idel is between 9-10
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Old 05-20-2004, 04:30 PM
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I ran a very similar cam in a 351W, initial vacuum upon installation was 10-12. After serious carb tuning and timing adjustment/tweaking I managed to get 16-18 running a 750 Holley DP on an open plenum manifold. Since this engine was equipped with an automatic the extra vacuum I got from tuning made a big difference in driveability and mileage. This engine actually got 16mpg in city driving with a 3.25 axle in a 3200 pd car afterward.
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Old 05-20-2004, 09:35 PM
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Quote:
Originally posted by 4 Jaw Chuck
I ran a very similar cam in a 351W, initial vacuum upon installation was 10-12. After serious carb tuning and timing adjustment/tweaking I managed to get 16-18 running a 750 Holley DP on an open plenum manifold. Since this engine was equipped with an automatic the extra vacuum I got from tuning made a big difference in driveability and mileage. This engine actually got 16mpg in city driving with a 3.25 axle in a 3200 pd car afterward.

Same here. Before, 15 hg in park, now, 17-18 hg in park.
If I give it gas it goes down to 10 hg.
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Old 05-20-2004, 09:44 PM
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I'll agree with 15-17 inches with that cam and a 350'ish engine. The size of the engine has a lot to do with it. It would act like a larger cam if you stuck it in a 283.
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Old 05-20-2004, 09:50 PM
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16-18, ok cool, thats what ill try and shoot for. you got some pretty good gas mileage, im going to be running a 3.36 gear, through a 4 speed manual. hopefully ill get desent gas mileage.


thanks for your replys
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Old 05-21-2004, 04:07 AM
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As far as the automatic tranny goes--, do you have the tranny vac. hooked up seperate or teed off with another vac. line.?
I have it teed off into the manifold with the brake booster?is this bad? still shifts hard...400sb---turbo350
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