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Fresh 383 compression

6K views 35 replies 8 participants last post by  painted jester 
#1 ·
383 keeps blowing intake gasket

Fresh 383 keeps blowing intake gasket by distributor.
 
#7 ·
I would either install it dry with a dab at the ends or if you insist on coating the rubber gasket, let it setup/skin over before you install the manifold and cure for maybe 24 hours before you drive it. Sounds like it just slowly squishes out if the PCV is working/pulling a vacuum.
 
#10 ·
383 keeps blowing back intake gasket out. Ran compression test and all cylinders had from 120 to 145 of compression. I hear that's low but this motor always has had around that much. I didn't degree in the cam just lined up the dots. But it's still blowing intake gasket out. Any thoughts on any of this or opinions?? Any help is greatly appreciated.
 
#11 ·
Michael 9111 said:
383 keeps blowing back intake gasket out. Ran compression test and all cylinders had from 120 to 145 of compression. I hear that's low but this motor always has had around that much. I didn't degree in the cam just lined up the dots. But it's still blowing intake gasket out. Any thoughts on any of this or opinions?? Any help is greatly appreciated.
You need to run a PCV valve in one cover and a breather of some sort in the other or you got a lot of blowby somewhere.
 
#15 ·
A full bead of rtv should not leak if it is done correctly. Use lacquer thinner to clean the surfaces (not paint thinner). After you bolt down the intake, make sure to stick your finger down the distributor hole and press the fresh rtv away from the distributor hole. Then give it over night to dry.

with a breather and pvc valve there isn't that much pressure under the intake even on a poorly sealing engine. so the rtv should hold if every thing is clean before putting on the rtv.

to check for engine blow by, start the engine, pull off the pvc and breather and place you hands/fingers over the valve cover holes for 5 or 10 seconds. then release one hole and see how much pressure has built up.

how many miles on the engine now. What did you do to freshen it up?

what compression and cam size?
 
#19 ·
It was bored years ago. Has two sleeves in the block. Haven't had it checked for straightness since bored. It has a Lanati voodoo cam. 600 lift 110 love separation. Can't remember duration off top my head. My compression test I ran is all over the board. Goes from lowest cylinder being 110 and the highest being 145 and the rest inbetween. From what I hear there shouldn't b that much of a difference. And I checked my blow by. When I first crank it up it has no blow by. After it warms up it's has a little at idle but if raise the rpm to say 1500-2000 rpm there is no blow by. Im stumped. Maybe bad rings. Maybe worped cylinder. Idk. Besides it blowing the intake gasket it runs great in my opinion.
 
#35 ·
Seeing your blocks has been sleeved and it has not been plate honed there is a good chance ring seal is your problem, You need to do a leak down test at TDC which will tell you what going on.

Blocks that have sleeves the cylinders next to the sleeves will not be round more so once the heads are torqued on.

Plate honing is a must for good ring seal.

Here is a link on plate honing.

Values Of Torque Plate Honing - Team Camaro Tech
 
#20 ·
383 manifold gasket

I have always used the cork gaskets at the front and rear of the intake. I use 3M Super Weatherstrip and Gasket Adhesive, 5 oz. Tube - Yellow to glue the gasket to the block and a thin layer of Permatex Ultra Black Maximum Oil Resistance RTV Silicone Gasket Maker between the gasket and manifold. Be sure and put a bead of Permatex at the gasket ends. I let it set about 24 hours. I always had problems with leaks when I used the rubber gaskets on the front and back.
 
#22 ·
manifold gasket

Clean everything again and set the intake manifold in place with no gasket. Check the gap in the front and back. The gap should be smaller than the thickness of the gaskets. Like I said I tried glue with the rubber gaskets and they would always slip back out. I would throw them away and use Permatex. Are you torquing the bolts in sequence? Do the bolts have flat washers installed with them? Also after warm up re-torque bolts again.
 
#24 ·
The Right Stuff

The best trick i have for sealing the front and rear of the intake manifold is to use a spring loaded punch and punch about 100 or so holes throughout the length of the front and rear walls then use the Right Stuff (1/4" bead) and that seems to seal up the best and prevents blowouts. Good luck that is a weird issue.
 
#25 ·
Michael 9111 said:
383 keeps blowing back intake gasket out. Ran compression test and all cylinders had from 120 to 145 of compression. I hear that's low but this motor always has had around that much. I didn't degree in the cam just lined up the dots. But it's still blowing intake gasket out. Any thoughts on any of this or opinions?? Any help is greatly appreciated.

120 to 145 is a big differance on a freshened eng a 20 percent difference isn't except able take a wet compression check and see if pressures increase and level out, my guess is your rings are shot. And the blow by is pushing your gasket out!

Jester
 
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