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Porsche 993 twin turbo

General engine tech -- Drag Racing to Circle Track

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Porsche 993 twin turbo

Post by ptuomov »

Anyone on the board hot rodding these? The last air cooled Porsche turbo model. This was the hot number 25 years ago and now it's just expensive and nostalgic. Just got a high-miles one and was wondering if anyone knows anything about what to do and not do with the engine.
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Re: Porsche 993 twin turbo

Post by BLSTIC »

The inlet port looks like it could make a ton more tumble than it does. I'm not entirely sure how much help that would be, but the way the head is now it doesn't look like it has much charge motion at all. There's probably also a plug that reaches further in than stock too.

I'd love to hear what people do to these though. They certainly had a lot of development of the years...
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Re: Porsche 993 twin turbo

Post by ptuomov »

BLSTIC wrote: Sat Aug 06, 2022 4:56 am The inlet port looks like it could make a ton more tumble than it does. I'm not entirely sure how much help that would be, but the way the head is now it doesn't look like it has much charge motion at all. There's probably also a plug that reaches further in than stock too. I'd love to hear what people do to these though. They certainly had a lot of development of the years...
I think that in terms of charge motion and the burn process, these are some of the best two-valve heads and combustion chambers out there, provided that one uses turbocharging and pump gas and can (has to) thus live with a low geometric compression ratio. The intake runner comes from a direction that is naturally normal to the cylinder centerline, which produces a lot of tumble. The spark plug is fairly central and without a dome there isn't a huge benefit from a second spark plug. With high compression, either due to natural aspiration or race fuel, the dome starts getting in the way and there's more of a benefit from second spark plug. The head is very good, other than of course missing two valves and thus not belonging to this millenium.

Where the money is made with these engines is with the turbo system, from the cold air intake to the exhaust tip. The engine being air, oil, and fuel cooled, the most important thing is heat management. I'll be driving this car in the north and appreciate the heat management, so this car doesn't have the hard life of a Kuwaiti businessman's hot rodded 650hp aircooled Porsche turbo...
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Re: Porsche 993 twin turbo

Post by BLSTIC »

I found a better cutaway to look at. It appears better than I thought initially.

Screenshot_20220806-220707_Chrome.jpg
.


Still, I can't help but remember that Honda paper where they got half a point of compression, a few percent better economy and massively reduced timing from turning the tumble up to 11. There were other things going on that you couldn't easily replicate though, like the offset oversized inlet valve that was partially outside the bore.

I've heard of water spray in the cooling airstream rather than normal water injection. Have you heard of that?
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Re: Porsche 993 twin turbo

Post by mag2555 »

These old heads need to take a lesson from replacement Harley hemi heads that now have a squish area to make more power .
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Re: Porsche 993 twin turbo

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You can always get more boost but thermal dynamics come into play. They are very good in stock form. I was a tech at the dealer when these came out. My recommendation would be to leave it alone. High powered ones are known to straighten out the teeth on first gear also happens with hard launches even stock.
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Re: Porsche 993 twin turbo

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I have always had the thought that these engines would be great for e85 conversion. Idk if that’s a viable option but it certainly takes care of the heat issue and probably still allow a nice bump in compression. The other limiting factor is the k16 turbos, their is a good bit of wiggle there but somewhere around 450whp (stock is 408fwhp) they are done depending on supporting mods/tune. Rennnlist and 6speedsonline are good websites for Porche info, though not as technical as here. Sub 4 sec 0-60 is still pretty good stock numbers…
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Re: Porsche 993 twin turbo

Post by ptuomov »

mag2555 wrote: Sat Aug 06, 2022 11:11 amThese old heads need to take a lesson from replacement Harley hemi heads that now have a squish area to make more power .
I am skeptical. I think that even a quarter century later, these are pretty much the two-valve heads to beat for turbo application. They have just the right amount of tumble and fairly complex and well thought out squish setup with the piston actually protruding about 5mm into the cylinder head.
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Re: Porsche 993 twin turbo

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rp930 wrote: Sat Aug 06, 2022 12:08 pm You can always get more boost but thermal dynamics come into play. They are very good in stock form. I was a tech at the dealer when these came out. My recommendation would be to leave it alone. High powered ones are known to straighten out the teeth on first gear also happens with hard launches even stock.
The 993 Turbo transmission is fairly robust and parts to make them last exist. The completely opposite of, say, the 928 S4.

The nice thing about turbo is that in normal street and highway use (I'm not talking about drag strip), the power automatically only shows up under sustained load in higher gears.

I know the smart thing would be to leave it alone, but I don't think I can.
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Re: Porsche 993 twin turbo

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tt 383 wrote: Sat Aug 06, 2022 12:28 pmI have always had the thought that these engines would be great for e85 conversion. Idk if that’s a viable option but it certainly takes care of the heat issue and probably still allow a nice bump in compression. The other limiting factor is the k16 turbos, their is a good bit of wiggle there but somewhere around 450whp (stock is 408fwhp) they are done depending on supporting mods/tune. Rennnlist and 6speedsonline are good websites for Porche info, though not as technical as here. Sub 4 sec 0-60 is still pretty good stock numbers…
There are a number of constraints to deal with. Plus if one wants to do something as dramatic as changing the fuel, one is better off IMO picking up a non-turbo 993 and going to town with it in a turbo conversion project.

The K16 compressor runs out of steam way earlier than the turbine. US tuners who build for acceleration spurts like K16 turbos that have K24 or 16g compressor wheel with the (modified) stock K16 hotside. German tuners who build for sustained high-speed runs tend to use larger hotsides and start with K24 on both side of the center housing. The ECU is smart enough that it pulls boost and timing when temperatures get out of check.

Rennlist is great for model specific info, I agree.
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Re: Porsche 993 twin turbo

Post by dannobee »

The 993 GT2 "Evo" was the highest hp car that the factory produced (air cooled). 592hp IIRC. The cams were a big difference (248/236 deg @ 0.050"), although it also had better turbos (K-24's?) and a bigger intercooler.

The factory 993 turbo heads flow almost 300cfm at 0.500" on my bench.

The updated 1st gear and input shaft cost $3K (and that's with my industry discount) on my last G50 build. If you wanted to change the ratios on your gearbox, there are a LOT of different ratios available, but plan on spending $1500 for EACH gearset, with ring and pinions even more.

As they say, "What part of racing Porsche's did you think was going to be cheap, the racing part or the Porsche part?"
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Re: Porsche 993 twin turbo

Post by rp930 »

Keep in mind those cars are worth a lot and they are worth more unmolested. Really a great car as delivered.

If you want to modify get a 996 Turbo. Less expensive and easy to get hp.
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Re: Porsche 993 twin turbo

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rp930 wrote: Sat Aug 06, 2022 3:19 pm Keep in mind those cars are worth a lot and they are worth more unmolested. Really a great car as delivered. If you want to modify get a 996 Turbo. Less expensive and easy to get hp.
996 Turbo is a great car, but it's cheap mainly because it's ugly. Horsepower with 996 Turbo is cheap and easy because the engine is water cooled, the head has 4 valves per cylinder, the exhaust pulses are grouped to turbos in three 240-degree separated pulses, and ECU is better than in the older models. But the looks...

The car I bought is high miles car and it's not 100% original. https://www.instagram.com/p/Cg5rn38oO3G ... _copy_link

And it's a sickness, I'm not sure I can stop my self from spending a lot of EUR to make this car slightly less valuable.
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Re: Porsche 993 twin turbo

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I think there may be a couple of versions of the EVO. Regardless, I think they did follow a very sensibly engineered plan to produce more hp, with four main changes:
- The turbos where K27s, compared to the K16s of stock 993 Turbo and K24s of Euro WLS 2 / Turbo S.
- The intercooler (and associated wing) by Secan that is a little better than stock. I think they are like EUR 18,000.00 (not exactly cheap, right?) per unit and may require changing the engine control from mass air flow to speed density to fit in the engine bay (not sure about the details).
- GT2 Evo cams are those mechanical lifter cams you mention, they don't pass US emissions even with stock catalytic converters.
- The exhaust was "simplified" from the above to below:
Porsche_993_Turbo_1998_Stock.jpg
GT2EvoAftermarketExhaust.jpg
dannobee wrote: Sat Aug 06, 2022 2:03 pmThe 993 GT2 "Evo" was the highest hp car that the factory produced (air cooled). 592hp IIRC. The cams were a big difference (248/236 deg @ 0.050"), although it also had better turbos (K-24's?) and a bigger intercooler.

The factory 993 turbo heads flow almost 300cfm at 0.500" on my bench.

The updated 1st gear and input shaft cost $3K (and that's with my industry discount) on my last G50 build. If you wanted to change the ratios on your gearbox, there are a LOT of different ratios available, but plan on spending $1500 for EACH gearset, with ring and pinions even more. As they say, "What part of racing Porsche's did you think was going to be cheap, the racing part or the Porsche part?"
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Re: Porsche 993 twin turbo

Post by ptuomov »

Big issue with this engine is addressing the flow restrictions and pressure losses ahead of the compressor outlet and the turbine inlet. What's between the compressor outlet and turbine inlet is very good to start with.

Starting from the turbine inlet and moving downstream:

There are two choices for the turbine. The first is swapping to a K24 turbine as the factory did with the Euro WLS/Turbo S. This is a fairly safe option. The second is to stick with the stock K16 turbine but increase the capacity of the wastegate circuit to prevent boost creep while increasing the leverage of the wastegate actuator by finding an larger diameter can (and diaphragm -- I'll draw an x on the office wall when I learn to spell that word without a spell checker) to prevent the back pressure from blowing open the wastegate at high exhaust manifold pressures.

The first option will manage high rpm temperatures better, the second option will improve low-rpm torque by spooling the turbo at low rpms and exhaust mass flow rates. German tuners go for option 1 for autobahn, US tuners go for option 2 for pulling away from newer cars in high-way accelerations. Thoughts on the choice?

The factory stock turboback exhaust is a very competently executed compromise by Porsche engineers. The physical size/packaging, sound level, emissions, weight, cost, and backpressure all make sense and it would be difficult to improve on any of those dimensions without making some other dimension worse. For context, these cars left the factory with 204-225hp per pipe. The exhaust starts from the turbine outlet at 84mm/3.3" ID and expands to the cat. The cat has 135mm/5.3" OD, but the cell flow area diameter is only about 115mm/4.5" and the cell itself has almost no flow in the outer channels next to the casing and insulation. After the cat, the pipe shrinks thru a bellmouth of sorts to 56mm/2.2" ID. The muffler inlet is also that about 56mm/2.2" ID but then shrinks to muffler outlet of 53mm/2.1" ID. Thoughts on these dimensions?

For reference, the tuner consensus seems to be that the factor turboback exhaust gives about 0.7bar/10psi back pressure at the turbine outlet at peak power (of 204-225hp). That's high, but comparable to other 1990's turbo cars.

How would you build an exhaust for this car?

My thinking is that the pipes themselves aren't that small for the stock power level, so most of the restriction has to be coming form the 115mm ID 400 CPI ceramic cat element and from the two-chamber muffler that's not a see-straight-thru drop-a-golfball-thru-without-it-hitting-anything design. So I'd focus on addressing those issues, I don't know if you agree.
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