Vaccum reading at manifold port??
10-02-2003, 02:16 PM
#1
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Vaccum reading at manifold port??
Can anyone give me an idea of what kinda vaccum reading I should see on the intake manifold port if I disconnect everything and attach a vaccum gauge? It's a 78 with a L-48. I'm going to change the intake this weekend (installing Edlebrock performer w/carb), but I'd like a before-after as well as what it SHOULD be! :crazy:
Thanks,
Rowdy
Thanks,
Rowdy
10-02-2003, 02:54 PM
#2
Drifting
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Re: Vaccum reading at manifold port?? (c3vettelover)
Don't disconnect everything. Just attach the V gauge to a full vacuum port.
Your before and after should read the same. That is once you set the new carb for highest vacuum.
The main thing that changes vacuum is a cam change and then to a lesser extent total plenum volume.
To get the best consistant vacuum readings and make idle a/f screw adjustments do it with your idle turned up to @1000 rpm with your vacuum advance attached and normal timing advance. once you get the highest inches of vac then turn your idle speed down.
Your before and after should read the same. That is once you set the new carb for highest vacuum.
The main thing that changes vacuum is a cam change and then to a lesser extent total plenum volume.
To get the best consistant vacuum readings and make idle a/f screw adjustments do it with your idle turned up to @1000 rpm with your vacuum advance attached and normal timing advance. once you get the highest inches of vac then turn your idle speed down.
10-02-2003, 04:52 PM
#3
Le Mans Master
Re: Vaccum reading at manifold port?? (Lt1er)
You should get about 18-22"hg. at idle in neutral. It will go down slightly in drive. The carb/intake swap should have no effect on vacuum reading but timing does .
10-03-2003, 09:50 AM
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Re: Vaccum reading at manifold port?? (c3vettelover)
Just checked mine yesterday. On my 78 with l 48 it was 17.5 at the vacuum port behind the carb on the intake. thats with an edelbrock cam,edelbrock intake,q-jet carb.