billytuffnuts
Well-Known Member
I have a 5.9l magnum in my 72 demon that I swapped out the efi stuff for a air gap intake and holley 750 carb and I'm having a problem with the intake manifold gaskets blowing out. Its got a stock bottom end, stock heads with 1.6 roller rockers, hughes 1110 valvesprings, and I think its a comp cam, specs are: .487" intake @231* and .497 exhaust @234* duration.
Earlier last summer I probably put on a couple hundred miles before both the front and rear of the intake had leaks in it. When I put the intake on I did use black rtv on both of the end rails instead of the cork gaskets. I figured I had a PCV problem that had caused it but now I dont know. I had a PCV valve for a stock 5.9l hooked up to the back of the carb in one valve cover and just a regular push in type oil cap in the other.
I thought maybe because of the aftermarket cam and non-vented oil cap maybe the crankcase pressure was building up and blew them out. So what I did was I found a PCV valve that seemed to be used a lot in lower than normal vacuum applications with aftermarket cams with a lot of duration (even though mine doesn't have a whole lot) and also got rid of the oil cap and installed a push in breather in the other valve cover.
Well again after about 1000 or so miles I noticed the front of the intake looked a bit oily and while not nearly as bad as last time there is a small leak there.
What could be causing these leaks??? I'm definitely going to use a straightedge on the manifold and where it sits on the block to make sure they are flat and I'm also going to use "The right stuff" RTV instead of the normal black stuff. Anybody have any other suggestions??
Earlier last summer I probably put on a couple hundred miles before both the front and rear of the intake had leaks in it. When I put the intake on I did use black rtv on both of the end rails instead of the cork gaskets. I figured I had a PCV problem that had caused it but now I dont know. I had a PCV valve for a stock 5.9l hooked up to the back of the carb in one valve cover and just a regular push in type oil cap in the other.
I thought maybe because of the aftermarket cam and non-vented oil cap maybe the crankcase pressure was building up and blew them out. So what I did was I found a PCV valve that seemed to be used a lot in lower than normal vacuum applications with aftermarket cams with a lot of duration (even though mine doesn't have a whole lot) and also got rid of the oil cap and installed a push in breather in the other valve cover.
Well again after about 1000 or so miles I noticed the front of the intake looked a bit oily and while not nearly as bad as last time there is a small leak there.
What could be causing these leaks??? I'm definitely going to use a straightedge on the manifold and where it sits on the block to make sure they are flat and I'm also going to use "The right stuff" RTV instead of the normal black stuff. Anybody have any other suggestions??
