FAST manifold permanant air leak fix
02-20-2006, 11:31 PM
#1
TECH Enthusiast
Thread Starter
FAST manifold permanant air leak fix Since there was interest in the thread I posted for help I thought it would be great to post the info I got from a non-forum location.
I opened my FAST to do some porting and once it was opened, I wanted to insure that there were no leaks once reinstalled as some have reported. As many of you know, unmetered air results in wild A/F ratio problems that manifest it self as elevated idle and surging.
The fix came from an aircraft mecahnic ad is an o-ring concept.
For those that remove the top cover, you are fmailiar with the orange RTV silicone gasket in there. If you use too little...air leak. If you use too much then you get a blob of it that forms in the runners and you have an airflow disruption.
The silicone issue is that once trying to make a new one, there is the desire to try to get it back together and back on the car in one easy step. If you are willing to make it a 2 step/24hr process you the extra protection of a home made o-ring that will allow repeated removal and installation of the top cover without air leak issues.
The fix:
1-Completely remove and discard all the silicone gasket in the channels between the top and bottom cover.
2-Completely fill all of those channels with high temp, O2 friendly, RTV silicone.
3-Spray the top cover with a mold release agent in the areas where the lip will contact the RTV. This comes in a spray can that once applied looks like the powered sugar film on a peice of gum.
4-Using .015 thick metal shims as washers, about the thickness of a fingernail, bolt it back together off the car and with the shims between the top and bottom covers for all bolts. Snug all the bolts down and the RTV will seep out all over the place, even in the runners and out the sides.
5-Wait 24hrs. (This is the hard part.)
6-The next day separate the two halves and using a sharp razor blade or exacto knife, trim away all the excess RTV that seeped out between the two covers. You will be blown away at just how much there is. The resulting RTV remaining in the bottom half of the manifold is now a perfect O-ring that is .015" higher than the channels and when you now replace the top cover, it will compress like an o-ring and give a repeated perfect seal for multiple cover removals and yet have the maximun contact area to the top cover resulting in perfect seals every time.
7-Optional but you can reinstall the top cover with a slight amount of release agent and a touch of RTV on the tips of the lips that touch the o-ring if you are **** about this seal.
When you TQ it down on the car this time it will compress the extra .015" of the custom o-ring to allow the two to touch.
This fix came from my uncle who is a inspector authorization certificate holder and aircraft and powerplant mechanic for 30 years and has never touched an LS-series engine in his life. When he actually saw the manifold and the engine he said..."cute design".
I have pictures of the process and will supply them if someone can host/post them.
I hope this helps even one guy.
Impressions of the ported manifold and throttle body to come as soon as I get the chance to actually drive this car. I live down south and it stays here in NY for when I come back from time to time. I should have picked up 2.20768 rwhp and my butt-dyno can easily pick that up....
.
Drive safe.
I opened my FAST to do some porting and once it was opened, I wanted to insure that there were no leaks once reinstalled as some have reported. As many of you know, unmetered air results in wild A/F ratio problems that manifest it self as elevated idle and surging.
The fix came from an aircraft mecahnic ad is an o-ring concept.
For those that remove the top cover, you are fmailiar with the orange RTV silicone gasket in there. If you use too little...air leak. If you use too much then you get a blob of it that forms in the runners and you have an airflow disruption.
The silicone issue is that once trying to make a new one, there is the desire to try to get it back together and back on the car in one easy step. If you are willing to make it a 2 step/24hr process you the extra protection of a home made o-ring that will allow repeated removal and installation of the top cover without air leak issues.
The fix:
1-Completely remove and discard all the silicone gasket in the channels between the top and bottom cover.
2-Completely fill all of those channels with high temp, O2 friendly, RTV silicone.
3-Spray the top cover with a mold release agent in the areas where the lip will contact the RTV. This comes in a spray can that once applied looks like the powered sugar film on a peice of gum.
4-Using .015 thick metal shims as washers, about the thickness of a fingernail, bolt it back together off the car and with the shims between the top and bottom covers for all bolts. Snug all the bolts down and the RTV will seep out all over the place, even in the runners and out the sides.
5-Wait 24hrs. (This is the hard part.)
6-The next day separate the two halves and using a sharp razor blade or exacto knife, trim away all the excess RTV that seeped out between the two covers. You will be blown away at just how much there is. The resulting RTV remaining in the bottom half of the manifold is now a perfect O-ring that is .015" higher than the channels and when you now replace the top cover, it will compress like an o-ring and give a repeated perfect seal for multiple cover removals and yet have the maximun contact area to the top cover resulting in perfect seals every time.
7-Optional but you can reinstall the top cover with a slight amount of release agent and a touch of RTV on the tips of the lips that touch the o-ring if you are **** about this seal.
When you TQ it down on the car this time it will compress the extra .015" of the custom o-ring to allow the two to touch.
This fix came from my uncle who is a inspector authorization certificate holder and aircraft and powerplant mechanic for 30 years and has never touched an LS-series engine in his life. When he actually saw the manifold and the engine he said..."cute design".
I have pictures of the process and will supply them if someone can host/post them.
I hope this helps even one guy.
Impressions of the ported manifold and throttle body to come as soon as I get the chance to actually drive this car. I live down south and it stays here in NY for when I come back from time to time. I should have picked up 2.20768 rwhp and my butt-dyno can easily pick that up....
.Drive safe.
