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Discussion Starter · #1 ·
Well checked the vacuum on my 327 today...7" at idle and goes right up to 20" when I tap the throttle....Is this normal??..I know the size of the cam and the carb help determine Vacuum...What I know about the engine is as follows..It has real lopey cam,gear drive,Roller rockers,victor jr intake and a holley 750( I did not have the car when the engine was done)...It's sluggish untill about 3K then realy starts to pull hard...Is 7" of vacuum at idle OK???....I believe I might have to tune the carb...So vacuum might increase...

Also I read somewhere a tip on tunning your carb using your vacuum gauge..Can someone explain this for me..Thanks again guys

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Retored 76 LE Trans Am 455 4 speed..# matching FOR Sale or Trade for a 68 or 69 big block camaro in good shape
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Restored 68 Camaro R/S 327 4 speed

[This message has been edited by Badcaiman (edited 08-08-2001).]
 

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Badcaiman,
You are fine with 7" of vacum at idle with a large duration camshaft. I have a 331 that has 12.15:1 pistons, #140 service package mechanical cam using 1.6 rockers lift is around ..539 with duration 304 and 312 advertised or 257 265 @.050 valvelift. My idle is set at 1400 and is quite rough. Engine has 7" vacum at idle. It too goes up quite quickly when rpm increases. All of this is normal for the type of combination you are running. I forgot to mention I have a crossram on this engine also. Make sure if you run a Holley that you have a power valve that is about 1.5 to 2" rated below where your idle vacum is or you could be running too rich at idle if it offseats.
The problems with these large cams on the street is the lack of adequate vacum for brake boosters and vacum operated headlight doors at idle if the systems leak even a little bit. They sure are fun once you get the revs up above 4 or 5 grand though. An accumulator will help if you need more vacum at stop lights.
 

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Just to camp on what SY1 has said. I pull 9 inches of vacuum at idle (950 RPM) with fairly large cam. You need about 14 inches of vaccuum for your power brakes to work properly SO I bought an ELECTRIC vaccum pump (Master Power Brakes) that supplies the vaccum I need to operate the power brakes and those damn RS headlights.
 
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