Carpokes Porsche Forum

Bergerac wrote: Thu Mar 13, 2025 8:47 pm

chris white wrote: Sun Mar 09, 2025 8:17 am

Bergerac wrote: Sat Mar 08, 2025 9:11 pm

If you offered that with a Vband crossover and downpipe package you'd have my attention.

just might be something I am working on......

I sent you a PM Chris, not sure if theres a better way to get in touch

email - [email protected] or jsut call me at 315-263-2095

The annoying off center play in the steering was thankfully traced down to a slightly loose connection between the lower joint of the steering shaft and the steering rack input shaft. Retightening the nut and bolt fixed the issue and pleased to say the superb steering feel that makes our cars such a joy to throw into corners is back for good.
Nothing else to report and the car is now ready for the warmer season after replacing belts with all rollers, engine and gearbox oil.

Just curious, what does everyone think about this "semi twin scroll" set up (from JME IIRC) ?


Reason for asking is that I'll be paying a visit to a fine local exhaust shop on Saturday and I've been doing some man maths with several possible options.

Thom wrote: Thu Apr 03, 2025 11:35 am Just curious, what does everyone think about this "semi twin scroll" set up (from JME IIRC) ?


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Reason for asking is that I'll be paying a visit to a fine local exhaust shop on Saturday and I've been doing some man maths with several possible options.

I have that pic saved to my work computer desktop.

I think it’s pretty nice looking. Probably works well considering the source.

Whether this "works" or not shall not raise any question if this is a Milledge design but it raises questions on how pulse wave length affects exhaust scavenging. Knowing what sort of intake was used with this exact exhaust layout would be interesting.
I have been playing with the possibly ill-founded idea that the long stock intake runners and the 4-2-1 nature of stock headers have been thoroughly thought out by the factory and that slamming a short runner intake on an engine using stock headers and cross pipe may harm the amount of "cross flow" taking place during the cam overlap phase, certainly getting worse the higher the overlap. Short of using 4-1 headers to balance out short intake runners I was wondering if a twin scroll set up should actually improve scavenging without negating the higher rpm gains given by shorter intake runners?

Also, for some reason I have always miserably failed to grasp the point of 4-1 headers with a turbocharged engine. As the turbo will always act as a clogging device in the exhaust tract ultimately adding back pressure, what is the point using a turbo with 4-1 headers that should theoretically give their best with "nothing" downstream? I know Milledge does it but I just don't understand. Again it works but perhaps still isn't as good, at least theoretically, as a Twin Scroll set up?
FWIW my friend who built my 16V intake uses one turbo per bank on his 427ci V8 muscle car with 4-1 unequal length manifolds per side and sees more intake pressure than back pressure with "large" hotsides and a monster cam (with a 10:1 compression ratio and put down ~1,500 lbs.ft on the dyno).



Sorry for all the editing, required to put down more or less accurately what I have in mind.

I can’t remember if I asked but are you measuring back pressure on your car right now?

I was close to 1:1 with my stock headers and dump to atmosphere wastegate. 18psi boost and 20psi back pressure.

That was with the 5 inch exhaust and the older tech LR Super 75 and .58 AR

Guessing your current turbo does quite well in comparison.

On the previous 8V engine I got the same figures as you with a GTX3076R and 0.82 A/R turbine housing already, but that was with the stock intake. I never measured it again with the short runner intake and perhaps I should have, especially with one of the high overlap camshafts tested down the line.
I have no long runner intake to play with on the 16V engine but I am not too worried with what the ratio may be with what I have observed with the larger turbine housing and the massive top end delivery - bigger is definitely better in this instance.

What goes on between outlet ports on the head and the turbine inlet in terms of pulse waves doesn't seem trivial to me with such a 4-2-1 design, especially with the long cross pipe. Also I do not think that the pulse wave model may affect back pressure much, in the same way that fitting the short runner intake on the previous engine didn't require adjusting boost control. It really is only during the overlap phase that I'm curious about what goes on.

But you are right, knowing where back pressure is now would still be useful, if only to tick the corresponding box.

I feel like the 951 from factory never got close to limit but the 968 turbo RS blew some gaskets and could never run right from factory because of this very predicament Thom they just did there best parts bin setup and turbo setup and let customers figure it out. But we all know that any little change affects everything. I think that twin scrolls setup would be very responsive with a 3+ liter and 35ish+ turbo with a 16v head setup correctly with the right pistons and cam profiles. The owner of this said car would most likely have more power then knows what to do with……thus creating even more problems ha

The 968 turbo replica I drove with an original S engine with RS turbo ran pretty well for an 8V set up and felt as reliable as one could wish, though the old K27/11 hotside couldn't hold a candle in response and top end with the (now old too) GT30/35 hotside.

A Twin Scroll set up may perhaps increase the amount of cross flow during the overlap phase, and if this improves peak performance a little further then it also means to me this should improve relability as the whole engine should work a little less to pump the same amount of intake air and exhaust gases all the way through, as in reduce the overall pressure loss from the air filter to the exhaust tip.
At this stage anyway I can't think of any other "upgrade" worth some time on the drawing board so to speak. I have a spare Tial MVS and a fancy Garrett V-band divided housing that have been gathering dust for ~8 years now... As I believe the inlet tract is now as good as can get, "cleaning up" the exhaust side just makes sense to me now. This will mostly depend on how much the exhaust shop are willing to dig into this anyway, as I don't want to spend a fortune either considering how well the engine runs already, and "better" is sometimes an enemy of "good". Will see.

I hadn't brought my car to a professional shop for decades and visiting the exhaust shop today reminded me why : because of the relatively high level of mods on my car they seemed to be thinking I was full of money for having spent that much on such an old platform and quoted me a whopping 2500€ for welding the twin scroll tubing. They added that it was not worth it considering how much better turbos had got in the last years, but didn't seem to acknowledge that exhaust pulses didn't care about progress in turbine design. I guess I'll be looking elsewhere... Makes me want to learn welding.