I snapped 4 out of 6 of the y-pipe to exhaust manifold studs. They were rusted beyond hope at 90K miles. I was planning to put a new y-pipe and cat on the car 1995 M6 LT1.

I took both of the manifolds off of the engine and I am in the process of drilling out the studs and removing them.

I noticed what looked like warpage in both of the manifolds. I checked them with a feeler gage and a Carpenters square.

I have .020" to .030" of warpage measured with the center pair of ports as the base for the square and a feeler gage under the gap at the sealing edge of the outer exhaust ports.

I have a 95 GM shop manual and it doesn't list the allowable warpage on the exhaust manifolds.

The manifolds were not leaking at the time I removed them, some possible carbon traces on one port. I didn't hear any leaks at all.

I don't want to do this twice, does anyone have suggestions for what I can get away with in the way of warpage?

Has anyone had the manifolds ground to flatten them out?

Is it time to buy headers?

Thanks

 

I have ground the impala manifolds just to have them replace later by headers because the passenger side manifold was cracked.
Get the headers, you will sooner or later.

 

Headers are never a bad idea, and you already have the manifolds off.

 

Thanks guys I appreciate your input.

I was hoping to hold off on headers until I was ready to do the whole engine as a package with a new cam.

How much did it cost to have the manifold ground down?

I didn't see any cracks but I haven't hit it with dye or magnaflux.

I am still working on the studs, if I screw the manifolds up, then the choice gets easier.

I hate rust, enthropy sucks, I don't like systems going to greater disorder.

Thanks

 

I hate rust, enthropy sucks, I don't like systems going to greater disorder.

ah yes, the imutable law of the universe (or so I'm told). Great quote tho, made me laugh to read that...I'm a fan of order not chaos myself!

with regard to your exhaust manifolds, I don't know of any serviceable limits either. I think it's a question of can you get them to seal up & stay sealed or not? I would say you could probably put them back on as is...but as previous posts pointed out, you have it apart, why not go for the headers now, it sounds like they're on your mod list anyway. It's only money right?

 

Your half way their just get some headers. You won't regret the decision.

 

I agree with just going with headers now, worst part is done.

 

Thanks for the input guys.

I bought a "Mapp" gas hand torch, a big help for heat on stuck parts. "Mapp" gas burns 2000 deg hotter than propane. Still can't get the broken/ruined y-pipe studs out.

So I bit the bullet and ordered the SLP 30015 1 3/4" midlengths.

I should get them soon. I am expecting a major hassle to put them on, but the stock manifolds didn't look like fun either.

I didn't get them coated, but I had a reason. I looked up the specs on 409 SS vrs carbon steel. 409 has roughly half of the heat conduction that carbon steel has. So much less need to coat them and the steel can't flake off. I was also worried about O2 sensors getting ruined by outgassing from the coating.

Mac and others look like good products and my worries may have no basis in fact.

I have had ok luck with SLP stuff, so I decided to go with them. The project is getting out of control anyway. So another $650.00 down the drain bites, but it is a performance car and I have driven it for 10 years.

I have found my new little Mapp gas torch to be a good friend, I popped off a stuck rear disk in a total of 2.5 minutes of torch time. I tried for an hour with PB Blaster and large hammer. Yellow bottle with a special torch head $31.00 at walmart. Next best thing to Acetalyene.

Creating waste heat, happy little enthropy monkey.

 

Just FYI if those SLP's are single cats plan on pulling the motor mount bolt on the drivers side. My buddy did his first and he had to pull the motor mount bolt and jack it up. I figured i was smarter and a better mechanic so i wasted 2hrs trying to get the header in with out removing the bolt. In the end i removed the bolt jacked the motor up and it took 15 mins. People will tell you that you don't have to do it. I say try once to get the drivers side header in without removing the bolt, if it doesn't go just jack the motor up.

 

They are single cat headers. Thanks for the tip, I will pull the bolt as you suggest if they don't go in pretty easy. I guess that might be why some of the other MFG have the slip tube on #1?