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interesting. Does he have any public content on 993 turbo? Or should I just contact him with a question or two.
Don't know about content but he's an easy guy to chat with. When I spoke to him many years ago there was a cheap Chinese made exhaust system that boosted power but the fancy ones we'd buy - nada. I stuck with stock since I couldn't rationalize a power boost and "she who knows best" thinks mine's loud enough. BTW, you anywhere near the Cape? Except for the COVID years, we spend most Septembers at Lecount Hollow Beach.
Last edited by ronnie993tt; 08-30-2022 at 06:29 PM.
Don't know about content but he's an easy guy to chat with. When I spoke to him many years ago there was a cheap Chinese made exhaust system that boosted power but the fancy ones we'd buy - nada. I stuck with stock since I couldn't rationalize a power boost and "she who knows best" thinks mine's loud enough. BTW, you anywhere near the Cape? Except for the COVID years, we spend most Septembers at Lecount Hollow Beach.
Just an afterthought but if there was a system that offered significantly less weight without the power loss, I'd definitely consider it. Unfortunately Akrapovic doesn't make a system for 993tt's last time I checked.
Some nice diy exhausts in my old thread. Mine and some of the things I played with look funny/amateurish but I had fun. Still have this system on the car now but with different diy tips. Bent those dual tips when I went off roading at the track. https://rennlist.com/forums/showthre...ferrerid=28499
That system on eBay looks cool but might be a pain/may not fit easily at all as it looks to be pretty well one piece with no place to make adjustments for fit
That system on eBay looks cool but might be a pain/may not fit easily at all as it looks to be pretty well one piece with no place to make adjustments for fit
It’s not a real race exhaust, but it could be turned into a nice street exhaust.
I’d do three things to it. First, valved exhausts with long pipes always need bellows to deal with thermal expansion. Otherwise the unequal metal temperatures cause flexing and eventual cracking. Titanium bellows could be added to the long muffler pipes or the shorter muffler bypass pipes. Titanium bellows here: https://www.ticonindustries.com/coll...-joint-bellows This pipe leading to the muffler would be the best spot:
Second, since this is a street exhaust, it needs 200 cell HJS cats. This section needs a cat element inside a big titanium shell:
Third, I’d hook up the valves to intake manifold vacuum. The valves would be normally open bypassing the muffler, but intake manifold vacuum would pull them closed and force the small pipe circuit thru the muffler. This way, just opening the throttle fully will always open up the exhaust whether or not the turbos are fully spooled.
I think a single piece install on a lift is feasible, but everything has to be exactly right and you need a crew working on it. (Although I’m now speaking out of my a$$ as I’ve never done that with a 993 Turbo.)
Some nice diy exhausts in my old thread. Mine and some of the things I played with look funny/amateurish but I had fun. Still have this system on the car now but with different diy tips. Bent those dual tips when I went off roading at the track. https://rennlist.com/forums/showthre...ferrerid=28499
Nice thread.
What’s the current thinking on x-pipes or generally connecting the banks?
My current thinking is that if there is no noise limit, combining the banks does not benefit the power. Consequently, it shouldn’t be done as the simplest exhaust is a straight megaphone of the turbo that just fits under/thru the bumper.
If there are noise limits, however, then connecting the banks does help. One can probably reduce the sound pressure by a dB of two by combining the banks and that in turn allows for lighter and/or less restrictive mufflers and thus more noise-constrained power. However, one should not compromise the flow much at all for just one or two dB.
One noise reduction idea that I have and that I haven’t seen anyone trying out is combining the stock pipes against the direction of the flow. For sound waves, the path direction matters much less than it matters for mean flow. One could weld a 2” stubs with a bellows one one side and v-band clamp on the other side to connect the stock cat pipes in a counterintuitive angle. The connection would be really short, one side having a v-band clamp flange and the other side having a v-band clamp flange and a bellows piece. This would not flow much gas at all but would likely do a good job mixing and cancelling the sound waves to some extent.
Here’s a sketch of what I mean, ignore the arrow direction:
The other thing that I’d do with a full custom fabricated exhaust would be to dramatically alter the pipe size. I’d expand right from the turbine outlet to a four inch pipe with a cone, if possible. Then I’d run that 4” pipe to the cat and then step it down as the exhaust gas cools to about 2.5” tailpipe (to which the tips would connect). The same space budget and/or back pressure budget are more efficiently used by making the pipes much larger at the turbine outlet where the flow is swirling and hot and then smaller at the tailpipe where the swirl has died and gas is cooler.
There’s lots of theory x pipes and cross overs/connectors like you mention but for me it was for changing the 993 turbo “motorboat” sound from having two separate exhausts to a merged one (and perhaps sound cancellation) which turns it into a more ?refined sound like some other sports cars. Having done this tho I realize the 993 turbo “motorboat” sound is unique and perhaps shouldn’t be messed with.
btw I did add some bellows between the merge box and the first resonators after a year or two for the reasons you mention, I thought it needed a spot where it could absorb any expansion.
There’s lots of theory x pipes and cross overs/connectors like you mention but for me it was for changing the 993 turbo “motorboat” sound from having two separate exhausts to a merged one (and perhaps sound cancellation) which turns it into a more ?refined sound like some other sports cars. Having done this tho I realize the 993 turbo “motorboat” sound is unique and perhaps shouldn’t be messed with.
btw I did add some bellows between the merge box and the first resonators after a year or two for the reasons you mention, I thought it needed a spot where it could absorb any expansion.
I studied this in detail back in the day. (A rambling diary of one such project here: https://www.speed-talk.com/forum/vie...1bc4a9184d8fb3 ). In a cross-plane V8, there’s a real power benefit from combining the exhaust from banks at lower rpms even if there is no noise limit. With a straight six, boxer six, or V6 (with firing order and crankshaft designed by sober engineers and not shrooming ones), the benefit is marginal, because the equally spaced 240-degree-apart pulses can “fill in” the pipe almost perfectly. There still is a benefit in terms of sound reduction, but less so than with a cross-plane V8.
In terms of what is a desirable exhaust sound, almost all humans want the loudest frequency to be the primary engine order and the frequency thus moving proportionally with the rpm. They also want the overall sound pressure measure by any typical averaging function to be monotonically increasing in the power generated by the engine.
I’m sure someone has done some logging at one point but as far as I recall, no one has posted any specific logs with different exhaust set ups. It’s been said that removing the cats do improve turbo response by shifting the curves and allow boost to come on 500 rpm’s sooner. The stock heat exchangers are supposed to be good flow but can be improved on by doing some ‘work on them’. Before and after :
Do you or anyone else happen to have the factory header inside diameters at hand? How large is the pipe right off the exhaust port? Does the header outlet match the K16 (or K24) turbine inlet?
It’s my understanding that the stock 993 turbo exhaust manifold matches the K16 turbine inlet well.
For the K24 turbine hot side, one might consider 50mm collector headers along the lines of gt2 parts 993 111 039 83 R and 993 111 040 83 R?
More and more I look at this engine, the better the stock-size headers, the K16 hot side, and very low flow resistance / pressure drop turboback exhaust appear to match its needs for a nice street car.
08-30-2022, 06:20 PM
