Has anyone had the opportunity to revisit the aftermarket fasteners they used to install thier downpipe, after say.... maybe a year or two?
I used some stainless socket head screws from McMaster, in conjunction with nickel antisieze, on mine. The last thing I want to do, is to have to remove them and find them firmly corroded and unremoveable from the heat. I heard even Mazda was having problems with broken studs and went to a more heat resistant material.
I've been looking for a source of inconel socket head screws. They are kind of expensive to have made and there are several alloys available.
Will someone with an exhaust gas temperature gauge let me know what kind of temps they are seeing so I can select the appropriate alloy. In addition, is there any one else who might be interested.
I think they are going to be a little pricey and I've seen people squeeling about the six bucks each for factory studs.

 

You know I never bothered pricing a higher alloy bolt than stainless. I figured if I wanted inconel, I might as well buy the Mazda bolts which are inconel or monel or something like that. The EGTs on this car can exceed 1200f.

I have some high alloy bolt vendors I work with - it would be interesting to see what Inconel 686 would cost in M10 socket head style. I doubt they would be forged though - probably machined - which is lower strength.

Dave

 

I've seen peak EGTs as high as 1500 degrees F, this measured about 3 inches post-turbine in the downpipe. Steady state EGTs under cruise can get as high as 1100 on my car, but after some tuning to richen up the cruising AFRs a bit I can get under 900.

 

IF you nicklesieze them right, clean the threads with a tap, they will come out later. Stainless is a good alloy for this service.

later

 

Dave,
I would have used the Mazda studs too, but the Pettit pipe will only work with two of the three studs (three with a little grinding), that leaves one hole that requires a socket head.
I cut one of those factory studs and they are tough, but I can't imagine a properly hung downpipe (with an appropriate bracket supporting the rear) would overly stress those screws.
Mazda's studs are expensive but they are not dimestore hardware either. The nickel stuff is expensive, especially when ordered in low volume.
Rich

 

Used Mazda OEM with some copper anti-seize.

Have never had a problem taking it off. That is the way I would go, bolts weren't that expensive from Ray Crowe, it was awhile ago but I remember 4.50 shipped.

 

I went two years, used stock bolts w/ no sealants or lubricants, and never had a problem getting the bolts off.

oh wait, no problem with three of them. The other one, the DP had warped over the 4th bolt, had to sawzaw the DP off, wasn't pretty.

 

I also have a pettit downpipe, and the hardware fits for me. Make sure you use the replacement studs used to bolt on the turbos. They work a t the downpipe flange and fit better.

I called a couple of fastener suppliers. You won't get cheaper than Mazda it seems, without getting either a weaker or faster-corroding part.

A-286 (commonly used in aerospace) runs around $20/ea for a bolt this size, and that's assuming they'll cut an M10 for the same price an english size. Inconels will cost more. Nearly all will be a custom order.

While Mazda's price for this hardware may have jumped significantly in the recent past, the jump in raw material prices leapfrog way past that. So even a very strategic sourcing approach will probably not get you anything similar or better without costing a lot more.

David