Gain extra benefits by becoming a Supporting Member Click here find out how!

Classic Performance Products Classic Parts
American Auto Wire Classic Industries
Danchuk Catalog
Hellwig Products IncPerformance Rod & CustomJoin the Community today
Ecklers AutoMotiveNu-Relics Power Windows



Username Post: Intake Vacuum leaks?        (Topic#357630)
Go18Go 
Poster
Posts: 1

Reg: 08-12-19
08-12-19 10:19 AM - Post#2773039    

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 #75621. Heads are patriot 320CC both have rectangular intake ports. 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.


Manifold IMage



Edited by Go18Go on 08-12-19 10:48 AM. Reason for edit: No reason given.

 


Mel Foye 
*VIP* Founding Member
Posts: 4877
Mel Foye
Reg: 09-29-00
08-12-19 01:15 PM - Post#2773048    
    In response to Go18Go

Have never worked with a set up like you have but here goes. The bolts you have look far apart to me so I think that the intake holes are meant to have a bolt there.
If you are lucky all you need is a different intake gasket set and four bolts. Otherwise there is a mismatch with the manifold and the heads. With air coming in after the carb and it idles good, likely you are on the rich side of settings. Let us know the outcome. Mel



 
IgnitionMan 
Valued Contributor
Posts: 3667

Reg: 04-15-05
08-12-19 01:33 PM - Post#2773050    
    In response to Go18Go

I have never seen a big block head that did not use these hold down holes, and I would have added them in the process.

Yes, there is a vacuum leak, could be from two different places, one more serious than the other, both important.

The secondary leak, air in the engine chamber the PC valve controls.

Important, air/fuel mixture leakage from the tops of the inlet passages, because the heads and manifold do not have the bolt holes working.

If it were me, at this point, I would use UNLIT, UNLIT, UNLIT propane flowed over the leakage areas, to confirm just a mixture vacuum leak. With propane, no residue, nothing but rpm's going up, and the smell of burned propane where the leak(s) are.

As I said, me, I would have added the holes/threaded areas.



 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17389
grumpyvette
Age: 71
Loc: FLORIDA USA
Reg: 03-16-01
08-12-19 02:25 PM - Post#2773057    
    In response to IgnitionMan

yes you need to replace the intake gasket and install the correct length 3/8"/16 tpi bolts in the 4 holes
then re-adjust the carb to get the engine idle correct

http://www.gtsparkplugs.com/BBC-Intake-Torque-Seq u...

IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


Edited by grumpyvette on 08-12-19 02:28 PM. Reason for edit: No reason given.

 


Icon Legend Permissions Topic Options
Report Post

Quote Post

Quick Reply

Print Topic

Email Topic

244 Views
FusionBB
FusionBB™ Version 2.1
©2003-2006 InteractivePHP, Inc.
Execution time: 0.09 seconds.   Total Queries: 16   Zlib Compression is on.
All times are (GMT -0800) Pacific. Current time is 12:35 AM
Top