ptuomov

I don't think it will be generally definitive, as there are other people also experimenting with 928 S4 long blocks. Each system is a bit different, with different goals. What we're trying to build here is a turbo street car that is as "factory" as possible in system design style while still putting out a lot of power.

The goal is to blow up the engine in an interesting way. It would be easy to blow the engine up in an uninteresting way, they did that to many of the "clunkers" during the cash-for-clunkers government program. It's much harder to blow up the engine in a way that teaches one something, and that's the goal here.

We're getting a lot of useful data, which will be fed to the simulation software. For example, we now know the turbine shaft rpms, intake manifold pressures, exhaust manifold pressures, downpipe back pressures, intercooler efficiency, etc. at various boost levels. I can use that to calibrate the simulation to real data and hopefully get some accurate predictions about where the biggest bottle necks are. And the answers to your questions about limits can really be explored quickly and efficiently with that software, at least approximately.

The dyno experiments will hopefully show some physical strength limits of the engine. The engine breaks, and then the physical strength envelope for the next engine is some margin of safety less than where this engine blew up. My thinking here is that as long as we then stay within the limits of those physical strength limits, there are two main reasons why the engine would not live long and prosperous life under sustained power: Irregular combustion and overheating. Beyond those two things, the engine is not going to wear out just because it makes more power, as long as we stay comfortably within the physical strength envelope.

There are still problems to be solved, including how to keep the combustion regular as ambient conditions change and how to cool this damn thing making close to triple the stock power, but at least both of those (knock and overheating) can be easily observed with say Sharktuner.

That's my theory anyway. In theory, practice and theory are the same. In practice, not so much.

It is without a question that I am wasting my time! What are you thinking -- I am a grown man playing with cars?!

Gt3071rs are not small turbos and there's no evidence yet that we're finding the limits of the compressor or the turbine. Wastegate priority can be improved, that is known at this point.

Oh, one more note on the optimal mapping: With this system and 93 pump gas, optimized fuel map, optimized spark map, and 11 psi intake manifold pressure gives peak 550 hp at the rear axle. I think that's pretty efficient, don't you think? And there are still many steps on the ladder to 20 psi where this engine has already been -- and beyond. The pressure ratio that the engine sees is (14.7+23)/(14.7+11) = 1.47 exhaust to intake pressure ratio. That's pretty good for a street car, if it weren't an R&D project I might just stop here, set the boost profile to 11 psi up to 5500 rpm and kick it to 20 psi by 7000 rpm and run it like I stole it.

123quattro

Twin 3071 should get near 1000whp. I'd say that's a fair amount of turbo. Don't be afraid to push them hard. I'm run mine to 28psi with no issue. On a 2.3L engine it runs out of steam around 7500rpm. You should have a similar experience with two on a 5L.

U-928

I love this thread. Moar power!!!

Tony

very cool! now your talking in proper terms!(top gauge)

for reference.

pdejong

Fabio421 asked me to share my experience with John Kuhn's Twin Turbo system on my ;90 GT. I have never figured out to post pictures on this forum, but if you go to http://www.flickr.com/photos/928tt/ , scroll down to page 2 and 3, there are a bunch of pictures of the finished product.
The first page just shows parts I have for sale.

I did this about a year ago. Bought all parts from John Kuhn. INstallation was tight but it is amazing how John has engineered this system to fit and how detailed he is with parts supply, everything but the kitchen sink was there.
I had the car tuned by John in May last year. I will try to attach the dyno chart.
The car is a blast, 470 RWHP and 465 ft/lbs.r, Running it at 8 psi. I had it up to 14 psi, but that was way too wild: smoking tires on the interstate at 80 mph in 3-rd gear. I need to get better tires (It won't take many miles to wear the rears out), but I am not driving the car too much so that will be a while.

The only thing I wish I could do, is change the end ratio to 2.2:1 instead of the 2.7:1. (I would go to the saltflats to try the get 200 mph). I am running out of RPM's at around 180 mph.
I spent a bundle of dough but it was a lot of fun doing this. Refreshed the engine with new rod bearings, piston rings, belt, gaskets seals etc, Engine has 90,000 miles on it.


Dyno chart at 9 psi is attached.

Peter dejong

'83 Eaton blown (RIP)
'90GT -TT(kuhn)

ptuomov

Peter --

It would be really interesting to see what the GT with 10:1 compression and bigger cams does with boost. Do you have dyno graphs with different boost levels?

I really, really recommend you get an eboost2 for your car. Eboost2 costs about $600 and gets you the following two features:

First, you can program a rpm-specific boost profile. This will allow you to keep the torque at that 465 ft-lbs level for the entire rev range. In practice on a GT this amounts to running the low boost until about 4500 rpm and then gradually increasing it with rpm. Not kicking it up like crazy like what I am doing with my '87 S4, but more gently.

Second, you can program six of those profiles in eboost2 and use a different profile on different gears. For example, 400 ft-lbs may be a good torque level on the first or second gear, but on the fourth gear at speed you can kick it up a notch to say 550 ft-lbs level. This way you can have your cake and eat it too -- keep the traction manageable at low gears and speeds and still accelerate fast at high gears and speeds.

Best, Tuomo

ptuomov

Should I be so lucky...

There are actually a couple of different versions of the gt3071r. I have the internally wastegated one. It's the biggest turbo that fits under the v-wings, and even that requires surgery to fit there. The best analogy would probably be the feet of a Chinese princess.

More is never enough and too much is just right.

I am slowly learning about what matters and what doesn't matter for these turbines and compressors. I am no dummy, but going by high-school physics makes it slow going. That said, I think I now understand how to get the power required to drive the compressor from the location on the compressor map and the compressor efficiency curve. I am still working on understanding how to estimate whether a given turbine can drive the compressor at that point.

Roy928tt

Yeh that is a sweet dyno graph, mammoth mid range, I can see why Tuomo suggests cranking up the pressure later in the rev range.

And I can understand why 8 psi is enough, through that mid range.

Lovely!

pdejong

Tuomo,

No, I do not have different boost level graphs. I did lower my CR from 10 to about 9.25, by the way, by installing an MLSS head gasket. I am not really interested in the most power, but briefly cranked it up to 14 psi, just to see what happened. At that level, there;s hardly time to shift. I had read a lot of stories on rennlist about boosting the 928. And I wondered what my car would do with TT's. I think John Kuhn's system is by far the best engineered TT system for a 928. I went to see him and got to ride his car. I decided to spend the $12k. It was fun installing it and I do not regret that I did. The engine runs too fat at the moment. I had a fuel pump issue when we tuned it, so I need to retune. I just bought the Sharktuner and I want to fine tune it. I am looking for help from a good engine tuner in my area. I may dyno it with 14 psi after that, but I think that is too much for longevity of the drive train, so I'll keep it around 8/9 psi.
I like your idea of the Eboost2. This is what I would like: increase boost with groundspeed. Is that a possibility with Eboost2? There's no need for boost in 1-st gear with the GT and you don't need more than 3 psi in 2-nd. I measured my forward acceleration and at around 0.7g my wheels start spinning. I think I had wheelspin in 3-rd gear at about 12 psi and 70 mph. Some sort of traction control would be the best. Another thing: I wish I had a 6-th gear or an overdrive.

Peter deJong

ptuomov

If you are buying a St2, you should make sure that you get the EZK maps that have enough scale on the load axis. I pegged out the supermaf ignition maps on the first dyno run. St2 probably now comes with the wider scale supermaf EZK maps.

If you like tinkering, you should tune your car yourself. Find a dynapack that is the most repeatable chassis dyno and start optimizing the maps!

I don't like thinking about the boost in terms of psi. Instead, I would like to think about it in terms of torque. After the boost threshold is achieved and the torque is where you want it to be at 3000rpm, then just set the boost profile at higher rpms such that the torque remains constant to the redline. You can have a separate program for 400, 450, 500, 550, and 600 ft-lb, if you use eboost2.

I don't know how to hook up eboost2 to ground speed signal. Right now I just press a button after a shift if I am really trying to accelerate at the limit. One could probably use switches and have the programs change automatically based on the shifter position, I think eboost2 would allow two switches and four programs selected with those two bits.

If I screw up the launch, my car feels like it's burning rubber past 100 mph. I don't know if that's physically possible with these power levels, but it certainly feels like it.

17prospective buyer

Tuomov, have you explored pre-turbo water injection at all? I probably don't need to explain the benefits.

ptuomov

Dual Bosch 044's on now and controlled by eboost2. Fueling is finally predictable. The fuelab setup looked cool on paper, but probably the last time I buy a fuel pump from an "aftermarket performance" manufacturer.

696hp at the rear axle in the warm-up runs tonight. This is with the completely stock '87 engine (plus the turbo kit) and 93 octane pump gas. Turbos are running at 128k rpm, so there's significant headroom still for tomorrow.

Let's see if tomorrow's the day when we succeed in making the engine fail. The consolation prize is a whole lot of power.

Photos and dyno charts coming later this week.

Gregg K

I picked a good time to resubscribe to Rennlist. I had forgotten all about this thread.

I'm still reading, but when I did my propane turbo creation back in 1980, I had that fuel problem you mentioned where the intake pressures go from normally aspirated to boosted, and it was never solved before I did cartwheels with the vehicle. Man it was fast though.

Just wanted to chime in, and stay tuned for the show.

illini-heel

Anyone TT a 16v...for kicks and giggles? If so, what numbers on the dyno?

Fabio421

The same guy who built PTuomoV's system has built some 16V systems. He started with those cars but the 32V system is much more refined than those early 16v builds.