I made the mistake of buying the 6 into 2 into 1 header from MSA. The number 2 exhaust pipe actually touches the E88 intake manifold at the number 2 port. This will super heat that mixture before it gets to the cylinder. I told them about it and sent them a size huge picture. All they said was "we've never had that problem brought to our attention before, we've sold hundreds of them" They did offer to refund my money. I spent an entire weekend sandblasting the crappy paint job, repainting, bending tailpipe with a torch and welding the system in and then putting on the manifold to find out it's all ****!

 

What kind of carbs are they? You have two dual barrel downdraft Weber DGAV 32/36 carbs?

If so, the original round top SU carbs rebuilt and re-jetted are a better performance carb.

 

Here is a picture that shows where it touches on the E46 manifold. You can see the blistered paint (1200 degrees+). I changed to the N36 manifold to give about a 1/4" clearance, still a little to close.

 

I ran 2 1/4 pipe to a 18" supertrapp too and I must say it sounds fantastic! Like a V8 with a mild cam at idle and at high rpm a sound that only a Z can make. I am going to bring a tester from work to check on the amount of heat radiated into #3 intake compared to the others. Will post results.

 

Brought home an infra-red thermometer with a laser pointer. I drove home hard to get it good and warmed up. Poped the hood and turned the idle screw up to 2500 rpm. Checked all the intake tubes at various places all around and found that they all run between 170 on top to 200 on the bottom side except #3, 240 degrees! I'm going to wrap the header and the intake in that area on all six.

 

wow.....

thats a disturbing piece of data, thanks for the info... i have one of these headers im waiting to put onto my car, and now i will definitely make sure i wrap everything well first... we might should try to find a way to make this information more available than it will soo be, buried in this thread.....

thanks again

 

as was stated SUs will provide better performance . Headers on a stock engine wont increase the HP in fact you will loose low end torque. If you install a cam with the headers this is another story. If you want to increase performance with out a large price tag . Lower the rear end gear ratio , find a 3.90 to 1 differential. This help greatly.