Vacum readings, opinions wanted - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

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post #1 of 2 (permalink) Old Nov 30th, 03, 04:09 PM Thread Starter
Join Date: Jun 2001
Posts: 57

On my parts car (which I can still drive, amazingly!), I was checking the vacum the other day, and it gave me a rock solid 17.5 vacum reading. My question is, when I gave it gas, the vacum dropped to about 7-9, but came back up immediately after I let off. I understand that revving the engine will 'subtract' vacum, but is this a bit excessive, and if so, what could it mean? I am planning on using this as a temp motor until I am done building the other one. Thanks in advance! The specs are as follows:

91 Z28
86 305 HO
4bbl q jet, no wiring (all wiring from computer has been stripped, as it was a TPI car originally)
416 heads, stock
stock intake and cam
all A.I.R. components removed/blocked

Also, while I have your guys ear, do you think that a Carter 625 carb, Holley Street Dominator Intake, port matched ported and polished 416 heads with 1.94int & 1.6ex, 1 3/4 headers, 1.6 aluminum roller rockers and a Comp Extreme 256 or 268 cam could make 375 hp? All but the cam is what I have left from a previous engine, and I saw a guy with a web page that had a similar setup and his 'pesimistic' graph boasted more than that, on a 305. Just wanting opinions on if it's a pot of poo or gold.
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post #2 of 2 (permalink) Old Nov 30th, 03, 06:58 PM
Senior Tech
Join Date: Mar 2002
Location: Austin, TX, USA
Posts: 5,277

As for vacuum your readings are normal. Imagine how the engine is sucking on the closed throttle blades at idle trying to consume air. When you pop the throttle, you let a rush of air into the intake which causes your vacuum to drop. It's not uncommon to hit 0"Hg for a moment. At WOT with the secondaries open, 0"Hg is very likely.

68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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