Which exhaust manifold should I use?

[S2Jay]

Dan, thanks for that clarification.

While at first I was seriously offended at the thought of upsetting the delicate weight distribution balance designed in by the Master, I soon realized that this is just a fiendishly clever way to offset the asymmetric weight distribution of the Driver for those of us with LHD cars at the same time as making space for the Big Tube Headers which I crave. Well Done!

[Note: if you have a RHD car, or you carry a passenger who weighs more than you, please disregard.]

Regards, Jay

[S2Jay]

Concerning the choice of Header or exhaust system material mentioned earlier:

The 2 most common versions of Stainless Steel used by most aftermarket manufacturers of Header & exhaust systems [at least in the U.S.] are Austenitic Stainless Steel T304 [the expensive stuff], and Ferritic stainless steel T409, the cheaper type.

The 409 is classified at the lower entry level of Stainless Steels, and it does have less Chromium and less Nickel than the higher grades. The minor corrosion that occurs takes the form of a brown-ish discoloration acquired over time. T304 has nearly twice the Chromium as 409, 18 to 20% for 304 vs. 10.5 to 11.75% for 409. Nickel is a max of 0.5% in 409 vs. 8 to 12% in 304.

Maybe the easiest way to tell the difference between the 2 types is with a magnet. The 304 is non-magnetic and will not attract a magnet, where the magnet will be drawn to T409.

[elanner]

Ah, that makes sense.

When I purchased my car the backbone cutouts were very small. But the Weber-side engine mount was falling to pieces and the airbox was hitting the footwell during starting. After fitting a new mount the engine popped up an inch or so, canting over a bit. Enough to cause the manifold/headers to occasionally knock against the backbone. So I had to open up the cutouts a tad more (I just got the cover off the car to have a look and reckon that the total is not more than 1/4", less than the 3/8" I guessed before).

Nick

[twincamman]

Ok ....remove the studs and replace them with cap head bolts ...this allows enough room for the headers to slide into place ...Ed

[ricarbo]

My experience is that the mild steel manifold is quieter.
regards
Richard

[S2Jay]

My experience is that the mild steel manifold is quieter.
regards
Richard

The difference in sound attenuation is likely due to the thicker gauge of material generally used for mild steel systems. The thicker material, usually 12 or 14 gauge vs. 16 or 18 gauge with Stainless headers, helps compensate for the lower strength of mild steel vs. stainless, and to allow for some loss due to corrosion over time. A side benefit is that the thicker steel helps contain the exhaust noises.