Intake Vacuum leaks? - Chevelle Tech
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post #1 of 9 (permalink) Old Aug 12th, 19, 10:38 AM Thread Starter
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Curtis
 
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Intake Vacuum leaks?

while tuning up my electric choke i noticed a sucking noise on the intake manifold. Its coming from four holes. Put you finger on them and its sucking, all four hole. Quick google and these are the four bolt holes on a edelbrock performer RPM 2 intake #7562. These four bolts are specified in manual as hand tighten only.

Mine have no bolts and you can see the gasket covering the holes between block and manifold. Never was a bolt in any of these four holes.

The question is this, is there any reason this would have been done intentionally? The car runs great, its dyno'd at 638 hp 652 torque. When i plug all four holes the idle drops way down and car barely wants to keep idling.
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Last edited by Curtis Chamberlain; Aug 12th, 19 at 10:55 AM.
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post #2 of 9 (permalink) Old Aug 12th, 19, 12:22 PM Thread Starter
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Re: Intake Vacuum leaks?

Anyone know of a good BBC forum or tech support type site? Im really concerned about this vacuum, leak issue
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post #3 of 9 (permalink) Old Aug 12th, 19, 1:17 PM
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Re: Intake Vacuum leaks?

Ya, put bolts in them holes! Unless those are some special race heads I am not familiar with , you are missing the four over port bolts. my lack of race head knowledge or not, clearly they are sucking unfiltered air, either from atmosphere or from the galley, so MUST BE squared away.

We dont know crap about BBCs here.

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post #4 of 9 (permalink) Old Aug 12th, 19, 1:24 PM
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Re: Intake Vacuum leaks?

Just doing a quick search, it looks like some heads use them and some don't. My stock heads do. If your heads do not have holes, I bet the intake port shape doesn't match either. Pull the intake and match the gasket to the intake and head ports to see what is not right. Maybe your head has the holes and it's just the wrong gasket.

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post #5 of 9 (permalink) Old Aug 12th, 19, 1:32 PM Thread Starter
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Re: Intake Vacuum leaks?

They are Patriot 320 CC heads with rectangular ports. Thats all i know about them. This engine came from the builder, Ross Automotive Machine Lapeer Michigan built in 2010 and has been this was since. Made me think it had to be intentional. Maybe the gasket without a hole for those bolts was sufficient to stop leak for a time and its slowed gained the leak? Very strange however as it runs amazing, has tons of power none of the typical vacuum leak issues you would expect.

I ordered some bolts for it. Just hope I don't need to change the gaskets all together and remove the intake.
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post #6 of 9 (permalink) Old Aug 12th, 19, 1:36 PM Thread Starter
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Re: Intake Vacuum leaks?

Quote:
Originally Posted by 69SS454 View Post
Just doing a quick search, it looks like some heads use them and some don't. My stock heads do. If your heads do not have holes, I bet the intake port shape doesn't match either. Pull the intake and match the gasket to the intake and head ports to see what is not right. Maybe your head has the holes and it's just the wrong gasket.
The heads and intake both have rectangular ports per specs. i guess i could poke through the hole and see if the block has bolt holes there.
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post #7 of 9 (permalink) Old Aug 12th, 19, 2:31 PM
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Re: Intake Vacuum leaks?

Even if they are the right gaskets and the ports match, they are leaking and need replaced. Pull the intake, get a new gasket set, and coat them with Gasgacinch Gasket Sealer.
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post #8 of 9 (permalink) Old Aug 12th, 19, 3:08 PM Thread Starter
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Re: Intake Vacuum leaks?

If i fix these leaks what are the adjustments that will need to be made to offset the adjustments made to counter the leaks? Just add more air at carb?
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post #9 of 9 (permalink) Old Aug 12th, 19, 3:35 PM
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Re: Intake Vacuum leaks?

Hopefully just open the throttle a little more. May need to go with smaller jets. Is this a recent problem or have you made air jet or other adjustments to fix it long ago?

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