rotarymike

iTrader: (4)

With airplanes we used titanium. With race cars we used stainless and bronze locknuts (top few threads are deformed). I have FI resonated cats (and catback) that I'm going to start working on late next month... I figure the demon bolt will get snapped off, and the studs are in the cats, correct? (IE, not threaded into the headers). I'd like to replace all that with bolts that won't gall or break on me. Any ideas?

Also - anyone know what sizes?

/Edit - with the racecars, the exhaust came off at the end of the season and they were alwasy leaking exhaust anyway so the stainless stretch didn't matter so much.

Justin Bailey

There is one stud anchored into both the header side and the cat side, then the demon bolt threads into the cat. The best you could look for is inconel studs, the oem stud has a 1.5mm pitch threaded into the flanges and the nut side is 1.25 pitch. The demon bolt is 1.5 pitch also. I'm using ARP stainless studs, decent enough if it isn't a turbo application I would believe, but I haven't run them yet. I'm not sure but 6Al4V titanium may or may not be better cost wise, but definitely good because it has a higher thermal creep stability than stainless which some people reports loosening issues with SS. There are high temp threadlock formulas good up over 1000 degrees out there that are still removable or just find an all metal insert lock nut or the distorted thread kind, but distorted thread is uncommon in all but steel nuts. The ARP studs come with non locking nuts that are frankly undersized for really getting the best flange friction to prevent loosening I always had thought. The need to use a good anti seize it profound to getting high enough clamp force on the fastener so it will stay tight I think also especially with galling metals like SS and Ti.

Justin Bailey

There is an inconel 625 and a 715 and I think an 815. The higher number alloys are stronger with above grade 8 in the 715 and 815. There are some header to cylinder head studs for sale but those are 1.25 pitch at both ends and won't work in the cat/collector flange joint. You may need to look for turbo studs to get the different thread pitch in each end. Before I would go to that level I am just trying the ARP stainless kind which claims to be over grade 8 strength, but I don't think that is true over a certain temp, not sure what that temp is, over 300F for example?

Justin Bailey

Oh yeah, M10 I forgot to mention.

Justin Bailey

I choose the Wagner Rock N Roll ceramic anti sieze product because it doesn't just melt and become sacrificial as easily as metallic kinds plus it can be used on the o2 sensor threads also.

Dzionassi

I had cooper anti-seize on my oem studs for almost two years, came of without an issue. There was no rust or damage on nut or on stud.

I have some m12 and m10 ss nuts and bolts, i will try to use it on my exhaust to see how it will perform

rotarymike

iTrader: (4)

I have a ceramic high-temp brake lube for sliding pins etc that is essentially high temp anti-seize (the purple stuff). I've used it before instead of the copper stuff on spark plugs and it seemed to work well. If it can handle 800* F brake parts it should be fine for a NA car's exhaust.

So one stud is threaded into the header, one stud is threaded into the cat, and then the demon bolt screws into the cat flange or has a nut?

Sounds like I could replace just the stud on the header, as the FI RHFCs don't have threads in the flange for stud or the demon bolt, and use bolts/nuts for the others. Or I could get a 1.5mm pitch thread bolt and thread through cat flange into header - like the demon bolt upside down.

Were I going turbo, I'd be interested in the inconel. I can't even imagine how much that would likely cost - upwards of $50/bolt I'd imagine.

I know the answer is cost as to why-don't-they, but I'd gladly pay an extra $200 per car if everything used v-band clamps like they should.