Exhaust Materials; X-over placement
Mike had a couple questions:
"1. What are the better/best materials for the exhaust?
2. where is the optimum plce to put and X pipe in a '92?? (to minimize the resonance)?"
First, I'm basing my materials selection criteria on use in North America, where you get a significant amount of salt exposure, and a significant amount of sulphur in the fuels. In increasing order of desirability:
1) carbon steel - totally undesirable; rusts badly in days, perforates within a year of average use.
2) aluminized carbon steel - good for a daily driver, perhaps, since the aluminum coating provides a reasonable amount of protection against salt corrosion, unless it has been welded or the coating has been otherwise damaged. Then, in the presence of ANY salt, the steel substrate "sacrifices" to protect the aluminum! Thus producing rapid pitting leading to perforation. Lives maybe two to four years in average service.
3) 409 "stainless" - Not a true "stainless" steel, since it doesn't have any nickel in the alloy, but it does have good elevated temperature strength; carbon steel is like silly putty above 1000F. The 409 develops a rusty surface fairly quickly, although it will take a high polish if buffed. In Texas or Arizona, for example, this material might last just about forever unless the car is used only for short trips. In Detroit, this stuff will last probably 4 - 7 winters.
4) Then comes aluminized 409 (AL 409) - The aluminum coating here gives excellent salt corrosion resistance; due to the lesser activity of the 409, the aluminum coating if damaged will sacrifice to protect the steel substrate. The appearance will be far superior to uncoated steels, since no red surface rust will apear until every little bit of the aluminum is gone. This would be a "lifetime" exhaust system on cars that aren't exposed to enormous amounts of salt, and if not welded.
Sometimes, depending on the exact alloy content, a condition known as "intergranular corrosion" can cause 409 or aluminized 409 to fail in weld areas, where the heat of welding has 'sensitized' the alloy to intersticial salt corrosion. The solution to this is:
5) 439-Ti or 18 Cr-Cb, two alloys having both higher levels of chromium (18%) than 409 (11%), and either titanium or Columbium (Niobium if you're un-American) or a combination of the two to prevent chromium-carbide precipitation, and intergranular corrosion. The higher chromium content also provides greater high-temp strength. This material will still develop cosmetic surface corrosion. I'm just guessing, but in daily use this might be a 6 - 10 year system. Much longer without salt exposure. These ferritic stainless steels will also take a high polish.
6) Finally, the ultimate material for automotive exhaust (IMNSHO) is aluminized 439-Ti (AL 439-Ti or equivalent. The coating provides cosmetic corrosion protection, while the substrate provides temperature resistance and intergranular corrosion resistance. Nobody knows for sure, but the best guesses are that this will exceed ten year life in the most severe environments, such as places using calcium chloride road salt.
PS: I didn't mention any of the austenitic stainless steels like 304 because of the intergranular corrosion issue. The first exposure to salt, even just near the beach, will cause weld areas to crack like a glass rod.
As for the cross-over pipe for a '92: I'd say put it just behind where the left and right pipes begin to 'Y' apart, near the differential. Checking of course for clearances! Then you might want the 3-chamber Flowmaster muffs. Those sound fine on my son's '96 C*bra!
It's important to note that "quiet" and "horsepower" are not mutually exclusive. See the C5 for proof; its' total exhaust backpressure is less than half that of the C4.
if those are the same mufflers which you had on your car ! Well, I guess I will know for sure after a trip to the muffler shop ! RedBob, if you read this, what are your thoughts on my goal for the exhaust on my car ? Thanks All,
