G Man

I'm watching and waiting to see how this develops

Imo000

I agree but there are many that don't have a working AC what I made is only for those or woud be ideal for a track car. It's a very simple setup so less things can go wrong.

Imo000

Roy,

Do you have any pics of your setup or build. I'd love to see them.

Fabio421

Roy is the LPG turbo guy. https://rennlist.com/forums/928-foru...red-928-a.html

RKD in OKC

Look at the 944 Turbo guys with half a 928 motor and what they are doing. My 2.5 liter 944 Turbo made 412 rwhp on the dyno at 20 psi. The limit of reliable boost on the 944 was the valve springs. The stock springs floated the intake valves at 18 psi. Guys that went above 20 psi had problems with the head floating.

My personal opinion is that if you are going to boost, drop the compression to around 8.5:1 if for no other reason than to take more advantage of the external air pump.

The other tip I offer is to size the turbo for the maximum flow at the limit of the maximum boost you can run. Assuming everything is done right maximum boost will typically be determined by choice of octane (detonation), or valve springs (boost float). You want the turbo to max out at your maxium boost, this will provide both faster spool at lower rpm and a wider effective rpm range on boost. It also helps save things if the boost control goes wacky.

entropy_engineering

Their are other factors to determine maximum boost like timing curve etc. You don't want a turbo exactly maxed out at full boost or the intake air temp. will be way high. At max boost and airflow you want it to be in the innermost island of the compressor map of the turbo where it will be at its highest efficiency. I hope you're all right that my horsepower estimates are accurate, because this turbo is big enough that I'll be flirting with the surge limit on the turbo if it doesn't pull enough. I have talked to someone (I can't remember his name) that seemed to be an engine guru at Lindsey Racing about pistons, valve springs, etc. I have the plans in mind for how I plan to build the more powerful engine. Again, I want to see what I can reliably do with the stock unit for other people's sake. So my question remains...If I turn out not to be a complete moron, or if I am a moron and stumbled on a nifty idea, is anyone interested in a copy built for them once I have pics, dyno, temp. testing etc.? I guess I will be bold enough to say that again I'm not talking numbers yet...(draw your own conclusions) but pound for pound of boost it will make more hp than any 16 valve forced induction kit. Oh, I'm not the twin turbo guy that's never been my thing for these cars...please tell more.

entropy_engineering

Here's a copy of the compressor map. I've actually ran one of these on a 3800 Grand Prix years ago. At the time it was one of three in the country until the kits came out. With an automatic (stock high-ish GTP stall) and decently built motor it made 19 psi by about 4000 rpm. Some usable boost hit around 2000 rpm. It was hard to tell just how low you could make it spool because it would downshift every time you punched or race thru first gear so quick. You could try to footbrake but couldn't hold it past a few psi anyway. With the same turbine housing on a 928 it should spool really nice. If any of you aren't sure how to read a map it's easy. Since it's lbs/min. across the bottom you just add a zero and that's horsepower (it does work out VERY close with the math). The pressure ratio is the boost you're running + 14.7 divided by 14.7 to come up with the pressure ratio. You'll notice my immediate plans are too run near the bottom. See how big the sweet spot is on this turbo? Look like room for growth like I was talking about.....

James Bailey

The potential market is even smaller , California smog police would never let that pass and there are more 928s in California than any other state....

entropy_engineering

True, but I'm only looking to sell a few to other people in non-smog police states.

ptuomov

Good luck with the project. I am also firmly in the turbo camp, but I have to say that turboing a 928 is neither cheap nor quick.

Here's some of the new additions to my project:

aggravation

I think the money you will spend to create it and the cost of your final product, if it is going to better than John Kuhn's already well done turbo solution, will price it out of the market.

The supercharger solution is popular because it's relatively easy to do and costs less.
Considering the shrinking market as someone mentioned earlier your research and development would be better invested in search of other engine/transmissions that could be "dropped in" by way of a kit you develop and market to achieve the power you want.

So...make us a kit that lets us drop in something exotic and create a third option! Find that perfect engine/tranny combo that would make us Shark owners want to buy another car and draw in new blood to the Shark owners pool too.

Just my .02 tossed outside the box.....

ptuomov

A quick summary of the piston design. I decide to go with the 968 style squish areas. The pistons are symmetric so the same unit can be used on both banks despite the piston pin offset. The valve reliefs fit the 968 intake valves at 12 mm lift if need be.

ptuomov

Apologies for the hijack, this is the last one I want to show you guys here in this thread on my turbo project.

- GTS cooling mod description from Greg Gray
- .4R heads in great condition that I scored from ebay for $500 for the pair. These have only one downside, namely that they don't have the GTS / .5R extra cooling passages
- .1R sacrifical R&D head that will be cut in pieces to see where the cooling passages can be best modified around the exhaust ports.
- The .4R's will get thermal barrier coating in the exhaust ports, valves, and combustion chamber. And as they said in "Scarface," "Flash, pizzazz. And a little port work doesn't hurt nobody."

entropy_engineering

Ptuomov, that's some sharp looking hardware. If you're starting with a 5.0l block you might want to ceraminc coat your pistons and block off the oil squirters (many forged piston manufactureres suggest it). Keep the oil pressure for the crank. Seeing as how you're doing a 32 valve I can't wait to hear the dyno results.

I like you're comment about a driveline swap. I'm showing my dad what I plan under the hood of my "junk" 928 because I've already stripped off the intake, air pump, and other unnecessary bits to mock up with. It wasn't ten minutes in he goes, "You know how much easier this would fit with an LS1?". Yes damnit I know...now shut up and listen.

Speaking of driveline swaps...you're all gonna hate me for this one...I thought about since I own more than one, and even though road racing is my passion, how would I set one up to handle drag racing. I have a friends 2JZ engine here from his Supra that makes an honest 1150 at the crank on C16. He has a built GM Turbo 400 for drag racing (I can't believe he took out the 6 speed). Then, it occured to me, you can buy a nine inch ford center section set up for cv axles...so...a heavily built TH400 with high stall, a special coupling to join it straight to the front of the nine inch, Mark Williams axles, big daddy torque tube, and a reworked rear suspension that's strong and gains almost no camber when squatted. I bet noone has seen a boosted 928 leave the line on a transbrake. I digress I would never do it.

We'll see what turns up. I'm doing this on my car because the incredible chassis and suspension geometry of the 928 (and because I can!). I think it's time they got some heavy bragging rights in the HP department as well. If I'm not satisfied I'm going to swap a motor. If I can't get the transaxle built like I want and fed up with everything, I'm going to start looking for a good deal on a Mkiv supra and give in. If any of you wonder if I'm a rambling idiot that can't turn a wrench, I've got a few interesting photos up on photobucket of a custom evo project under entropyengineering. More photos will be on the way there including the 928.

ptuomov

The extra 5.0 block that I have set aside for this project doesn't have piston oil squirters. I wish it did, because I believe the cooling benefits more than make up for the extra mass of the oil that hangs on the piston. I am not particularly worried about windage, because I have Simard pan spacer, I-J tray and scrapers, and the boost controlled crankcase vacuum pump (last picture of an earlier post).

The reason why I am going with new pistons and rods is mostly weight. The 928 pistons and rods would work very well with turbo motors. They are strong. However, I have been told that the manual transmission will only take something like 575 lbf-ft on the engine side reliably. So the engine will be electronically limited to 575 lbf-ft torque at fourth and fifth gear and to a lower numbers on lower gears. These torque numbers mean that to make a lot of power, one has to spin the motor. With the rod bearings the weak spot, all this hassle with pistons and rods is just kind of insurance.

Yes, the pistons tops will also get a termal barrier coating. The skirts will have moly coatings and the cylinders nikasil. I think this will help keep the heat in the combustion chamber and whatever makes it to the piston will go thru the rings to the oily nikasil surface pretty easily, right? For cooling reasons, I am not going with thinner rings, using stock ring dimensions instead.

Pistons are forged 4032 units, by the way. This and the thermal barrier coatings should allow me to run minimal clearances. With the 1mm offset and minimal clearances, this should be a very OEM-like, streetable short block.

Let's see if I luck out and the engine will actually run! At minimum, I'll get some ash trays out of the pistons and paper weights from the rods.