i have mack mids on my car (96 formula). the mids came off of a 94 car. Well i had them bolted up with some crappy gaskets and 3/4 inch bolts. They were leakin on my passenger side so ripped them off and bought the felpro 1406 and some 1 inch long header bolts. The problem is that the 1406s on the out side header tubes 1,2,7, and 8 do not have the extra material to extend to where the holes are on my header flange. there are 2 holes on the block, one that goes right next to the tube and one about 1 inch away, well my header flanges have the hole drilled for the one 1 inch from the tube and the 1406 wont reach but the first hole. do i just tighten the crap out of it and use a bunch of rtv? or am i risking another header leak?

thanks braden

 

I'm not quite sure if this helps but here goes...

I put MAC mids on my car in June and I used the same gasket you're using. The MAC mids I believe use the outer? hole to bolt up instead of the inner hole. As where the felpro gasket is designed to "hang" off the inner bolt. I just snipped the part of the gasket that wrapped around the bolt off and made sure everything that needed to be sealed by the gasket was sealed and it was fine.

So in short just take a good look at your gasket and if you need to snip some extra material that is in the way, go ahead. Just make sure that the part that needs to be sealed (the part around the exhaust ports) has gasket around it.

Hope that helped.

-Gabriel Terrel

 

hey thansk for the info. Do you think it is needed to cut the excess (the part that hangs over the bolt) or would it be fine just leaving it and putting mor rtv on it?

 

I thought the part # was 1407 for the LT1 maybe you got the wrong gasket.

 

What kind of RTV are you going to use that can handle that kind of temperature?

 

thought i would use high temp red 650

 

That sealant is good for 650*F. The exhaust gases coming out of the cylinder are in upwards of 1200*F. I don't think it will hold. I looked up it's recommended uses:

Valve covers, oil pans, timing covers, water pumps, thermostat housings, transmission pans, etc.

If you use it to try and seal the header gasket, it will eventually burn off or melt (not sure which one), and you'll have another leak to deal with. Just my thoughts.

 

Don't use RTV on header gaskets, it will burn off and cause leaks. Also, silicone content can fail O2 sensors if it gets in the exhaust.

 

good thing you guys told me i would have screwed that up

thanks alot, looks like we will just be using the header gasket

again thanks a million sweetred95ta and jp95zm6

 

honestly, if i was using headers that used all the same holes as stock, I would just get the OE gaskets

 

I personally believe that the OE gasket is the best to use. I've had a couple different brands of headers and never have had a problem with them leaking. I don't remember with the Edelbrocks, but with the Jet Hot LTs, I had to snip a triangle out of the ends so that they would 'hang'. Other than that (which wasn't a big deal), they have been great.

 

hmm whats the part number for the original?

 

They should have them in stock at Autozone (Felpro p/n MS95585 - $9.86), O'Reilly's, etc. Here is the GM part number from Shoebox's website:

Application - 1993-1997 exhaust manifold gasket (each)
GM p/n - 12552469
Price - $5.92

 

i actually had the felpro stock replacement on the car and it was leaking through them, i figure i will give these felpro 1406's a shot, it takes about 15 minutes to unbolt the headers and 5 to clean the surface, so if these leak i can test out other th ings, maybe the percys gasket.

thanks for all your replies!!!!

 

Lay a straightedge on the header flanges to make sure they are flat, too. A little bow TOWARDS the head between bolt holes is OK as that will just squeeze the gasket better, but any curve away from the head needs to be corrected. Softer gaskets would be more tolerant of this, but overtorqing the bolts on a soft gasket can pull the bolt holes towards the head. Softer being fibre type, harder being copper etc.

That is a good reason to keep gasket material all the way around each bolt, too, it will lessen the flange deflection/bending when you tighten the bolts.

I assume Percy's dead soft would be pretty crushable due to the raised beads, and thus pretty tolerant of any waviness, but I have never seen one put in to know how much it crushes on install.