Alternative power-plants and transplants (GTi, Porsche, Subaru, Audi, diesel etc). Discussion and Q&A last answered over 2 years ago.
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I'd certainly agree about cheap MIG welders... and all MIGs seem to need a certain approach to welding properly rather than just 'sticking' - practice makes (near) perfect (eventually) !
I think forward running/side exit is the way to go as the total system bends through the best part of a circle at the moment and that cannot be good for the flow.
I think unless they are wickedly sharp this is far less of a problem than most think... the really important thing is getting the tuned lengths and interference patterns right - that you will notice, if its right, and esp if its wrong - for an NA engine that depends on it. Turbos have made exhausts so much simpler - just get that gas outa there! Though I think its possible to go too big on diameter... slowing the gas down prematurely.
Stainless helps to keep the heat in the gas though, and the speed up
Yes, the VW diesels have a similar scheme - one manifold bolt hole pair normal clearance, and the other 3 sets a good oversize to allow for expansion of the whole manifold.
Together with oval exhaust ports in the head that are very much smaller than the manifold ports, with individual port gaskets to allow for overlap as it expands: this seems to be their solution to the problem. The big step change from head to manifold in CSA of the port also fits with breaking up any swirl by forcing turbulent flow early on.
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Different stainless' have a wide range of expansion coefficients, ferritic ones being very low, nearly half that of mild steel. But most are not much more than mild or alloy steels. About 15~16 x 10-6 /C.
316L is 16, mild steel at highish temps is not much less, maybe 15
If they're even 20% higher I doubt if it drives a design change itself c.f mild steel? Larger and thicker wall pipes might be what's causing more problems these days though, by being less compliant when the thing does get really hot and stainless would retain its strength much better too.
Picture a bend in 3" 16swg Vs a bend in 2" 18swg, ones going to be more of a problem when it gets hot - I reckon that'd be the bigger thicker pipe, just a guess though, but due to material disposition rather than expansion coeff.
I ordered some bends/flexi/clamp/pipe from dynoflow on sunday, it all turned up tuesday, looked really good quality. I have made my exhaust today, welded really well, certainly as good as the welds vw did.
Cant wait much longer for the system I was promised elsewhere, so may as well go for it myself.. even if I only tack it together and get someone to weld it proper like!!!
well mines all done mmmmmmmmmmmm looks nice sounds awsome i got the real subaru grunt well post pics very soon but the drive back from cambridge yesturday has made it filthy!!!!
DJ at Dubdayz Summerfest Now cutting about in an LT35 MWB
The shiney bit is a clamp, wanted it so back section comes off easy, it looks really close to back panel in that pic but its not.
It took most of the day to weld it all up.
The silencer alone took a day, i cut my old jx silencer in half, gutted the insides, welded it back together, opened out ends to 3" and welded a 3"pipe inside. I wanted to do this so it looks like it has a silencer. The welds on the silencer are only just noticeable.
Well, job looks a good'un from here... flexibit appeals and makes the whole job a bit quicker maybe, lining up?
and apart from what must be a very throaty bellow when under power, has it made any difference noticeable from the cab, as in the seat pushing you in the back more/less.
