Vacuum pressure? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Mccoleman830 · 03-09-2010, 03:17 PM

I have a 78' K15 with Gm performance engine # 10067353. What should the vacuum pressure reading be at 800 rpm idle? Currently it reads at 15". Is this correct or should it be higher? Any help? Thanks.

MTCK · 03-09-2010, 03:37 PM

I show about 18-19" with the same motor. You are in the ball park. If a cam was swapped that would change it. You might pick up a little bit by dialing in your idle mixture and ignition timing.

68Timber · 03-09-2010, 03:42 PM

That cam is really mild, I'd expect north of 20" Hg.

Mccoleman830 · 03-09-2010, 05:23 PM

As of this point no cam swap has happened. So far i just have a Edelbrock 1400 smog carburetor and and manifold. I thought it would be higher, more towards 18-20in. It runs fine. Just tuning the carb I've seen the pressure towards the lower end of the scale. I checked the manual, its stating it should be around 18-22in.

64swb · 03-09-2010, 06:01 PM

I have the same motor in my '78 K2500 and I've never been able to get anything more than 15'' of vacuum. It has about 20k on it now, and never been any different.

Green Monster · 03-11-2010, 05:22 PM

I was wondering the same thing. I just installed a vaccum gauge on my 72 Blazer with a 350 ci. and I'm also showing 15". It runs great.

03-09-2010, 03:17 PM	#1
Mccoleman830 Registered User Join Date: Aug 2009 Location: Sacramento, CA. Posts: 57	Vacuum pressure? I have a 78' K15 with Gm performance engine # 10067353. What should the vacuum pressure reading be at 800 rpm idle? Currently it reads at 15". Is this correct or should it be higher? Any help? Thanks.

03-09-2010, 03:37 PM	#2
MTCK Registered User Join Date: Dec 2009 Location: Fairbanks, AK Posts: 1,830	Re: Vacuum pressure? I show about 18-19" with the same motor. You are in the ball park. If a cam was swapped that would change it. You might pick up a little bit by dialing in your idle mixture and ignition timing. __________________ -Marcus 1991 V3500 L29 454 4L80E NP205 D60/14 Bolt 4.56's 1984 K30 292 TH400 NP205 D60/14 Bolt 4.56's flat bed 7'6" Meyer Plow 2022 Silverado 3500 L8T Project Daily Driver Project Heavy Hauler Project Plow Truck

03-09-2010, 03:42 PM	#3
68Timber I know the pieces fit Join Date: Nov 2007 Location: MONTGOMERY, AL Posts: 5,523	Re: Vacuum pressure? That cam is really mild, I'd expect north of 20" Hg. __________________ John 79 2wd Blazer (Bruiser) 85 M1009 Blazer (Sarge) build 74 Honda Z50 build

03-09-2010, 05:23 PM	#4
Mccoleman830 Registered User Join Date: Aug 2009 Location: Sacramento, CA. Posts: 57	Re: Vacuum pressure? As of this point no cam swap has happened. So far i just have a Edelbrock 1400 smog carburetor and and manifold. I thought it would be higher, more towards 18-20in. It runs fine. Just tuning the carb I've seen the pressure towards the lower end of the scale. I checked the manual, its stating it should be around 18-22in.

03-09-2010, 06:01 PM	#5
64swb Registered User Join Date: Mar 2007 Location: Camino, CA Posts: 182	Re: Vacuum pressure? I have the same motor in my '78 K2500 and I've never been able to get anything more than 15'' of vacuum. It has about 20k on it now, and never been any different. __________________ 1978 Chevy C10, 1986 Chevy K20 'Burb, 1970 Chevelle, 1996 K2500 'Burb, 1977 Chevy K10, 1970 Ford F-250, 72 Ford F100 4x4, 1979 Chevy C30, 1982 Chevy C30, 1996 Chevy Dually 4x4 SAS, 1997 Chevy Tahoe, 1991 Ford F-350 cclb dually 4x4

03-11-2010, 05:22 PM	#6
Green Monster Registered User Join Date: Mar 2006 Location: Malvern, PA Posts: 951	Re: Vacuum pressure? I was wondering the same thing. I just installed a vaccum gauge on my 72 Blazer with a 350 ci. and I'm also showing 15". It runs great. __________________ Photo Gallery of 1972 K/5 Blazer CST



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