divil

A few times I have tried to use an infra red thermometer to check my header temperatures. I have always noticed that the 2-3 headers read much hotter. For a while I put this down to the fact that it's difficult to get consistent readings from the thermometer - you can't hit each header in *exactly* the same place, and it's a somewhat shiny surface which makes it tricky. But it's been very consistent, and lately I have been thinking, could the 2-3 headers be cracked underneath the heat shield, allowing gas to escape and make that heat shield much hotter?

This might tie in to some other things I've observed. For a long time I've heard a strange rattle between 2500 and 3000 rpm, but only under load. Under light throttle it's not there. It sounds a lot like a heat shield, and I always assumed that's what it was, but from reading about cracked headers apparently it can sometimes sound like that. Additionally, my turbo is spooling up much too late - certainly at least 500rpm too late in some cases and maybe more. My AFRs are not affected so I don't think it's an intake leak. *But*, the spool up issue is not perfectly consistent. Every now and then the turbo will spool up quicker, though usually for only a day or less. So I don't know if that fits the theory - unless there is something about the way the metal expands that sometimes I just seals a little better?

Anyway is it common for headers to crack under the shield where you can't see it? And if so, is there any positive diagnosis you can do? Thanks!

Techno Duck

Many 2-3 headers i have come across were cracked at the Y where the cylinders merge. Find a place with an evap diagnostic machine (smoke machine) and pump the exhaust full of smoke, you will probably see the smoke come out from under the heat shielding...and a i bet a few other places like around the flanges on the cylinder head side.

mahoney944

Yeah the metal is strong but the welds leave much to be desired. Though vibrations and heat over 30 years definately has its tolls. It's worth an upgrade or at least a rewelded by a competent shop. I've re welded 2 sets of stock ones with 100% success. I opted to go to the lindsey header for a cleaner, better flow. The stock ones just merge the connection weird. Plus the one piece flanges seems like a solid thought in the design.

divil

I grabbed a few shots of the temp difference. Looks like 2-3 are around 140 C hotter than 1-4.

Headers 1-4, top to bottom:

MC Luc

Mahoney944 - how did the shop you used weld your exhaust manifolds/headers? I keep reading that welding doesn't work but clearly those people were wrong. Who would you take the headers to have welded, what type of shop, and what would you ask them to do (bronze, MIG, TIG, etc.)? Thanks.