SS OE Replacement exhaust manifold
 

Since i've seen it come up not less than three times in as many months- how difficult would it actually be to fabricate an OE replacement manifold in stainless steel? Where would the main stumbling blocks be? Etc.

I am in the plainning stage for doing this ,after I get my K1 BMW motorcycle painted .I am borrowing a stock manifold from Herblenny to use as a set up .

Hmm, If you manage to do this... would the stock turbos be too heavy or would there need to be some sort of support bracketing? Those hunks of iron are pretty heavy...

I've wondered about an SS exhaust manifold also, with a better design the twins could probably produce some nice numbers.

My first design will use two thick plates and some heavy wall tubing ,it should work with out extra brackets .If I can not find the tubing with the wall thickness I want then I can bore a solid stock part on the wire EDM at work . Making the jig to hold the parts in place will be the hard part .Cutting the parts out should not be hard .

the way you describe it.. sounds like you're ready to make a bunch for cheap :icon_tup:

I assume this must be for strictly nonsequential turbo operation, since it'd be almost impossible to do the flapper doors and passages that the stock manifold has for sequential operation.

I have never understood why people put a lot of time and money into nonsequential twins. I am not saying there's anything wrong with NS...I am a proponent of it myself. But you're getting the worst of both worlds with that setup...slower spool than sequential, but weaker output/flow overall than even a small single. Not to mention you have to worry about boost creep/spike from the internal wastegate. And you have those heavy, massive heatsinks on the side of the engine. The plumbing and placement of a single looks so much better as well.

Nonsequential IMO is a mod to make the best out of what you have for not a lot of money. When the twins blow up, or when you want to quit messing around with poorly flowing heatsinks, then you should just put your 2 or 3 grand into a single, instead of some rebuilt/modded/nonsequential twins. Just my opinion.

Another issue with SS manifolds and headers is that they let a lot of noise through on a rotary. Lots of times I install thin downpipes, or headers on NA rotaries, and the owners think they have an exhaust leak. In fact, what they hear is the thin pipe letting the sound of the pulses through, even though no air is leaking. The sound kind of echoes off the frame and the ground and catches some people off guard.

I know about the noise with thin tubes and my plan does not use them .I will make my tubes from solid stock with the wire EDM at work . The heat sink part may be true but the stockers are working . I tend to think two small turbos will spool faster than one big one, maybe yes maybe no .I show the car some and most people are taken with the look under my hood. I like the complex look . My car does not break alot and with with the low power level the motor may last longer .It is by no means a race car .People who have driven it or ridden in it think it is very fast . The improvement over stock works for me ,I have done single for others and I will stay with my BNRs. If my customers want single setup then that is fine with me ,I can do that as well .

+1 for a badass new NS header :)

!!! Expensive !!!

Any reason you can't buy mechanical tubing stock in 316L and work with that?

(Although for a one-off project it's not a big deal)

Dave

yep! miata with headers and a stuck lifter, is the loudest weirdest thing

Anywya to make a more efficient sequential manifold? non seq isnt for me.

modify the Supra sequential turbo system to fit our car?? :)

The problem with the supra sequential system is that it's mostly ecu controlled. One turbo is on for low rpms and low load on high load the second turbo spools. (Rather than our change-over at 4k.) It's a more useful, versatile system but you'd need standalone to operate it.

Explanation

The supra system operates identically to ours. The intake valves might be operated differently, with less mechanical means, but the turbos are doing the same thing.

The 4500rpm "changeover" refers to the switch from primary turbo only to parallel mode with both turbos.

Dave

I saw a pic of this like 4 years ago.. It used to be on this forum. It was a smaller Japanese shop was selling them. It looked like a decent part though I would question the returns.

I agree with RotaryResurrection,
the twins in nonseq. are just a compromise. They are to get you through until the twins blow or you can afford a single. It is for those who cannot understand the seq. syst. or do not want to fix it when it breaks. They delude themselves into thinking nonseq. can spool faster than a single and just as fast as seq. twins.
There are countless reasons single is better than nonseq. - heat, costly rebuild, low flow, low boost capability, etc.
I'm not trying to start a seq. vs nonseq debate here, just trying to be realistic about putting loads of research and money into a manifold that will add 5hp (if you're lucky).
Good luck on your experiment Garco, I do appreciate people like you engineering novel parts for our cars.

I would question your choice of SS, simply due to thermal expansion differences between that and the cast iron turbos, and I believe the engine is as well. You would either have an exhaust leak when cold, or induce thermal stresses when hot.

I know SS manifolds are pretty common, but I always wonder about the thermal issue.

What's the benefit? Weight savings? Better thermal resistance, turbos stay cooler? Part life? The cast manifolds on the car since 93 seem to be holding up pretty well.

Weight savings (the tt assy and manifold weight 40lbs), better flow ergo less heat in the engine bay & more power. the cast iron also functions as a heat sink & has a tendency to crack.

All good questions IMHO.

True, but all turbochargers are a cast hot side, and they have no trouble being attached to a welded header. Welded SS downpipes have worked fine on the cast turbo manifold.

Weight savings, yes.

I do think that welded manifolds are MORE likely to crack since the cast ones hold up just fine (it's the turbo manifold that does the cracking, and this discussion has not been about redesigning the turbo manifold). Not that eBay welded manifolds are the benchmark to use, but many of them crack at the welds. So while I'm sure that anything Garco builds would be better than that, it does show that building a welded manifold is not trivially easy.

Plus there is the issue of the heat retention - cast manifolds keep heat in the engine bay much longer and that's not a good thing for many reasons.

Dave

+2 to that!

My main reason is for better flow .I am not worried about cracking because the tubes will be very thick and the attachment will not be butt and weld .The plain is to put the tubes through the plate and weld both sides, a mechanical fit .The one thing I need advice about is the inside dia of the balance tube that will feed the wastegate . The weight savings is a gift ,wanted but not a major thing .Flow and long service life are my main objectives .

so no sequential operation retention? I guess I am dreaming the impossible.

i want one sequential

there is a replacement manifold for parallel setup i can get a good deal on them.