I have recently bought a 91 RS with pretty stout LT1 swapped into it that came SLP 1 3/4 shorties. I have tried, and tried, and tried to keep my driver side header from leaking but it's just not happening. First I cleaned the old burnt up gasket off the header flanges and the head. Then I put one fel-pro on it, then two fel-pros at the same time, a copper gasket, and I've even tried putting high temp silicone on the gasket to try to get it to seal and nothing is working. I'm thinking that the D shaped exaust ports not matching the headers is the problem. Is there any header out there that will fit a thirdgen, has d-shaped flanges, and can support over 400hp? Or maybe there is some kind of adapter or gasket that I haven't tried yet that would fit/seal the header better? I just spent probably over 70 dollars on gaskets over the past week and nothing has worked,

 

i have slp's and they also have a small leak but it goes away after the car warms up a bit, not really sure if its on the header flange or at the collector...

 

The copper gasket I used sealed ok once it got warm, but the first time I got on the throttle it started leaking really bad and I couldn't get it to seal back up again. After every gasket I put on I tried driving the car for a little bit to give the leak a chance to fix itself but it never happened. I'm just really stumped on what to try next.

 

Old trick is to cut the flange in between the #1 and #3, and between #5 and #7

This lets it flex a lil more when its warming/cooling

Something ive found to work awesome...
Get a good header gasket (composite is fine) and some RED (high temp) RV sealant
Coat both sides of the gasket
Its messy but worthwhile

Got a set with 60,000 runnin strong no leaks

 

The SLPs I have already come with seperate flanges, so that's one thing I have going for me. I'm glad the sealant actually works, I just saw it laying around and thought it couldn't hurt to try and use it to seal the header. I'll try it again and hopefully it will work this time. If anyone else has any suggestions, just incase it doesn't work out, I'm all ears.

 

Be sure to torque the bolts with the standard heat cycles

If you let it loosten enuff to break teh seal and leak you have to start over, as torquing wont help the sealant reseal

 

I'm not quite sure what you mean, could you explain a little bit?

 

After the car warms up the exhaust will expand....when it cools it will retract.....if you let this happen too much without retorquing the header bolts the gaskets will blow and you will have to replace them again.O.E.M exhaust gaskets work good too as they addhear to both the head and the header.Once you put your gaskets on start the car and let it idel for a few min....let the headers get some heat to them .......shut it off......let it set and cool down (open the hood to help) then retorque the header bolts......then retorque them after about 150-200 miles.......then once again about every month or so (depends on how much you drive).
Good luck,
Mike

 

Ok that makes sense. That might have been what happened to the copper gasket I tried. I let the engine get warm, then retorqued the bolts and that was the last time I checked them. They sealed good for about 200 miles and then all of a sudden it sprung a leak. I may try the other copper gasket, if the RV sealant doesn't work, and I will be sure to keep the bolts tight this time. Thank you all for all your help, hopfully I'll get it straightened out this weekend.

 

The high temp RTV sealant worked! I covered just about every place were a leak could occur with about a 1/8" of the sealant, tightened the header bolts, let it set for a day, started it up and it worked like a charm. I'll be sure to check the bolts again in a day or so and keep checking them every couple weeks to help it stay sealed up. Thanks again for all your help.