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engine vacuum with comp 270 magnum

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Old 07-21-2002, 11:04 AM   #1
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Join Date: Dec 2000
Location: Chattanooga, TN
Posts: 92
Car: 1984 Z28
Engine: 350ci

engine vacuum with comp 270 magnum

I've been looking at many websites and magzines for a future build-up for my car. I ran across a 355 on the AFR website that looks sweet. Basic rundown of the engine:
AFR 190 heads
RPM type manifold
9.5:1 compression
comp 270 magnum cam (224* int/exh @ .050 .470" lift 110*LSA)
1 5/8" headers
My question is about the cam. It's a bit bigger and has a tighter LSA than I'd like for idle/vacuum. I currently have an L-82 cam (yeah, i know it sucks) i my 350 with similar duration numbers and it doesn't give me enough vacuum at idle to run my power brakes very well. I was also looking at an XE 262 cam also from comp that has slightly less intake duration to help that out. Surely several people use these cams, what kind of vacuum numbers do they put up?
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Old 07-21-2002, 11:25 AM   #2
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Join Date: Mar 2002
Location: Coushatta LA
Posts: 266

I have put together two 355 chevys using stock vortec heads,the XE262H cam and a rpm intake. I love this combo for the street, slight lope at idle, good vacuum, excellent drivability. I personally saw this combo run 14.20's in a 4000lbs trk with 3.42's and slicks and a stock converter. The AFR 190 heads you mentioned are hard to beat.

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Old 07-21-2002, 01:57 PM   #3
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Join Date: May 2001
Location: Tucson, AZ (deployed to Saudi Arabia)
Posts: 627
Car: 84 Z-28 Camaro
Engine: 383
Transmission: T-56
Axle/Gears: richmond 3.73, eaton posi

I have a comp 280H in mine and I pull 14 inches at idle and my brakes work fine
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Old 07-21-2002, 02:35 PM   #4
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Join Date: Jul 2001
Location: Pueblo Co
Posts: 3,974
Car: No more birdy

I used the 270H's in 3 of my 350's the last couple of years, there great for power but economy will suffer. The highest vacuum I could pull at idle was 10/11in with a conservative timing setting. Down the road in cruise it will pull around 17/18in of vacuum, not too bad but that equals around 12-14 MPG more 12 then 14. Power brakes work fine but under a fair amount of heavy accelration then braking they get touchy.
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