Here's one that I haven't heard or read anywhere. I was killing time is a 4x4 shop that also dabbles some in diesel aftermarket products recently when I overheard one of the store's salesmen telling a prospective customer about EGTs and that he would realize a reduction of about 100-150 with an aluminum 4" exhaust and an additional 100 or so degree reduction by going with a stainless steel exhaust. His explanation was that the stainless steel would dissipate the heat faster than aluminum. I find this very hard to believe, as like I said, I've never read or heard anything anywhere to attest to this supposed virtue of a stainless steel exhaust, not even on exhaust vendors' web sites. Has anyone else ever heard or read of this being the case? If it's true I would think the exhaust vendors would be all over this and touting it whenever there's a comparison of the two. My suspicion is this particular sales guy was simply trying to get the customer to open his wallet wider to let more money flow out to the store than he would have gotten from pitching/selling an aluminum system. Either that, or from what I know, he was very ignorant of what benefits really are attainable from either of these exhaust systems.

Steve

 

this is a sales man trying too make an extra couple bucks...that is all.

 

First, it's not ALUMINUM exhaust, it's ALUMINIZED--- BIG difference.

 

and it makes no difference in EGT

 

actually aluminized exhuast are normally steel core which holds in slightly more egt then a stainless steel on most systems.............the aluminzed exhuast normally have the unfinished interior pipe which has little more resistance then the unfinished stainless steel.....soo on the highway the egt might be like 50-100 degrees different because there is a cleaner more less resistant path out the tail end of the truck.......especially if its one of those good companys with there hydro bended exhaust which when they run the water in the pipeing at that high of a PSI the inside tends to be a bit smoother.....

 

Your right about it being aluminized, Hohn. I started to write it that way and for whatever reason changed the wording to aluminum. My mistake as I do know the difference. Anyway, the question still stands; does a stainless steel exhaust really run cooler than an aluminized exhaust, especially to the extent this saleman claimed, all other things being the same? With all due respect storx, I'm having trouble with the analysis that an unfinished interior can make that much, if any difference, in EGTs. That's why I posed the question in the first place, saying I have yet to see any scientific data that factually gives credibility to this claim. I hope Mark from DPPI or someone else who deals in exhaust systems will chime in here to gives us their knowledge.

Steve

 

have you ever looked at the inside of a diesel exhaust pipe after about 100 miles?

 

the salesman must have a pretty special grade of stainless that we haven't even gotten in the aviation world yet with super heat dissipation characteristics. that's a bunch of BS. stay far far away from that shop, unless you have lots of extra money you don't want. can you find out who the salesman was talking to? maybe that guy would like to send some of his money my way, too.

 

Fun part is that the EGTs we are interested in are measured before the turbine. So the heat dissipation of the pipe won't be a factor. Flow will be a factor, but this boils down to diameter, bends and muffler design. The heat dissipation of the pipe after the turbo will just lead to lower exhaust tip temperatures, and AFAIK there's nobody mounting a pyrometer to the exhaust tip for some reason

AlpineRAM

 

well, cooler exhaust is denser and flows better, but there's still no difference here...

 

alpineram, you don't watch your ETT??!! how do you know if you're overtemping your muffler or not? got to be careful not to put too much heat on those muffler bearings!
like i said, stay far away from that shop with your money. it would be entertaining though if you went back and asked that salesmans opinions on different performance options, i'll bet he's got some good ones if he tried to pull that exhaust temp thing!

 

I always thought you wanted to keep the temperature up to maintain a higher velocity for the gases to escape. Maybe that was more for a scavaging effect in headers.

 

heat wrap will usually cause the car to "want" a larger dia primary

 

I've got my unobtainium muffler bearing lubed with high temp elbow grease..


sheesh, what a noob to the performance world.

AlpineRAM

 

I'm going with the smooth bore I.D. explaintion,

by the way I have a stainless system for sale,
I need.............................................. ......$2000 for it, It's really nice ! and it keeps the 5" tip cooler too.........................oh ya and the bumper corner cooler too....ya and it wont leave "black tracks" on your camper either!