Thick exhaust flanges vs thin flanges

[AutoXer23]

Can anyone tell me the difference between the thick and thin exhaust manifold flanges? From what I can see is that the thick ones will sit lower but is there any performance
benefit?

[Dpmulvan]

78 79 thin flange 80-83 thick flange usa cars
78-83 thin flange euro cars

[AutoXer23]

Originally Posted by Dpmulvan

78 79 thin flange 80-83 thick flange usa cars
78-83 thin flange euro cars

Thank you... I have a 74 with a 2.7. I take it is thin? Can I add the thick flange if I change the studs?

[catuck]

Correct, the 2.7 takes the thin flange. I put my thin flange SSI exchangers from my old 2.7 on my 3.2 by changing the studs with no issues. So I imagine you could do the opposite. I'm also curious why later cars had thick flanges.

[Jeff Higgins]

While early "thin flange" heat exchangers will fit later "thick flange" applications, it's really not a good idea. The thicker flange was added and the primary pipe was extended a bit into the exhaust port as a means to reduce heat buildup through the exhaust port into the cylinder head. This setup reduces cylinder head temperature on the later engines.



Thin flange for comparison:



It should be obvious that the later thick flange design will not fit cylinder heads that are not designed for them. This is more than an issue with the length of the studs. The exhaust ports must have the rebated recesses to accept the pipe extension. You cannot simply bolt up thick flange heat exchangers onto your 2.7.

[AutoXer23]

Originally Posted by Jeff Higgins

While early "thin flange" heat exchangers will fit later "thick flange" applications, it's really not a good idea. The thicker flange was added and the primary pipe was extended a bit into the exhaust port as a means to reduce heat buildup through the exhaust port into the cylinder head. This setup reduces cylinder head temperature on the later engines.



Thin flange for comparison:



It should be obvious that the later thick flange design will not fit cylinder heads that are not designed for them. This is more than an issue with the length of the studs. The exhaust ports must have the rebated recesses to accept the pipe extension. You cannot simply bolt up thick flange heat exchangers onto your 2.7.

Thank you !!! Makes lots of sense. I now know what to look for.

[pete3799]

Thick flange will work but requires grinding the flange flat.

[Aircooled4evr]

Originally Posted by Jeff Higgins

While early "thin flange" heat exchangers will fit later "thick flange" applications, it's really not a good idea. The thicker flange was added and the primary pipe was extended a bit into the exhaust port as a means to reduce heat buildup through the exhaust port into the cylinder head. This setup reduces cylinder head temperature on the later engines.



Thin flange for comparison:



It should be obvious that the later thick flange design will not fit cylinder heads that are not designed for them. This is more than an issue with the length of the studs. The exhaust ports must have the rebated recesses to accept the pipe extension. You cannot simply bolt up thick flange heat exchangers onto your 2.7.

I have a kind of silly question. Which I hope is ok with AutoXer23...
But since the thick flange was designed to remove heat from the heads... Has ANYONE tried pairing this with a 964 head?.. which is designed with a ceramic insert for the same..
The same problem will apply as in the 3.0 heads.. It disrupts the flow! And maybe that's also why porsche walked away from this solution? But.. how much..
The only (crazy) reason to do this, would be to build a VERY special setup, with a lot of bottom end torque.
I'm only thinking...

[Aircooled4evr]

Anyone know what the thickness difference is, between thick and thin flange?

[RarlyL8]

Thick flange exchangers were used on engines with emission control equipment such as thermol reactors or catalytic converters. These systems require extreme heat to operate optimally. Such heat reduces engine life so thick flanges were used to help dissipate the amount of heat at the port. The engine will run much cooler once these systems are removed, and the requirement for thick flanges goes away. Thin flange (3/4") headers can be mounted on the long thick flange studs but not on thin flange (3/8') shorter studs. We tack small spacers on are header so they can be used in either application. If not needed they pop off.

[Damon88]

Originally Posted by RarlyL8

Thick flange exchangers were used on engines with emission control equipment such as thermol reactors or catalytic converters. These systems require extreme heat to operate optimally. Such heat reduces engine life so thick flanges were used to help dissipate the amount of heat at the port. The engine will run much cooler once these systems are removed, and the requirement for thick flanges goes away. Thin flange (3/4") headers can be mounted on the long thick flange studs but not on thin flange (3/8') shorter studs. We tack small spacers on are header so they can be used in either application. If not needed they pop off.

Rarly8, Just wanted to confirm what you're saying.. I have a set of original thin flange SSI's. I would like to install the on a 1983 3.0 engine. I will be removing all emissions on engine. So with spacers on, would this be fine to use as a setup.. along with your awesome Steet muffler..