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engine vacuum with comp 270 magnum

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Old 07-21-2002, 12:04 PM   #1
Junior Member
Join Date: Dec 2000
Location: Chattanooga, TN
Posts: 91
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, 12:25 PM   #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, 02:57 PM   #3
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Join Date: May 2001
Location: Vilonia, AR
Posts: 624
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
84 Z-28 in the prosess of re-build:
383, steel crank, forged pistons 4 bolt block .040 over
comp cams nitrous XP 288HR
Adv dur 288/315
Dur@.050 236/248
LSA 113
valve lift .520/.540
"quiet" gear drive
polished and ported trick flow 23* heads
comp P/N 26918-16 beehive valve springs
steel full roller rockers
edelbrock pro-flow 1000 CFM EFI port mached to heads
Venom 36 lb injectors
edelbrock nitrous sys, 150 shot
hooker 2210 1 3/4 pri headers
powermaster starter
powermaster alternator, 160 amp
'97 T-56 transmission
centerforce dual friction clutch
pro 5.0 shifter
richmond 3.73 gears
eaton posi
spohn K-member
spohn "wonderbar"
spohn torque arm/crossmember
spohn lower control arms
spohn A-arms
spohn panhard bar
spohn subframe connectors
dual exauast, 3" up to cut outs
nordskog digital dashbord
trippel gauge pilar mount
digital fuel press.
digital nitrous pressure gauge
digital oil temp gauge

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Old 07-21-2002, 03:35 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.
1976 SWB C10 3/4 drop, gen VI 454/M3.
1973 Buick Apollo wifes play car. Chevy 383/S3.
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