Geo

OK, now that I can buy into! Anytime you have an assembled kit that is proven and the engineering is done is a big plus that direction. You get zero, nada, none, no argument from me on this one.

FWIW, I give John big credit if he's been able to engineer a finished set-up and MAJOR kudos if he has kits. I know how hard it is to produce stuff that is more than a one-off and especially if you want to sell them. Check out the web site in my sig sometime. It's relatively easy to do a one-off. It's an order of magnitude more difficult to produce monkey-proof products.

I love doers. Most folks are just talkers, and I feel a bit odd talking about what I personally think is possible with the 944 because I have zero plans to do any of it because I'm just building to a set of rules. But I have done a fair amount with other platforms. Two thumbs up for those who take on a project that is not cookie-cutter and see it through.

Danno

" there will be greater pressure between the exhaust valve and the turbine wheel. I'm sure there are some issues here, and while I don't have the engineering knowledge to correctly address how this plays out in the mix. All I can say is I've never heard any issues over this in the past. My guess is that with proper sizing of the turbine wheel and housing, this is not a significant issue or you'd hear about it all the time."

The backpressure in the exhaust between the exhaust-valve and turbine is necessary because it the differential in pressure before and after the turbine that spins it. To prevent back-washing of the exhaust, "square" cams are used with very little overlap. When the exhaust valve opens, there's still an incredible amount of pressure in the cylinder. This pressure is more than sufficient to overcome the pressure in the exhaust. At the end of the exhaust stroke, the square cams close the exhaust valve fairly even with TDC and very little exhaust-pressure can make it back in.

Geo

Oh course! Danno, thanks. Now I just need directions to get my head out of my butt.....

It's so obvious (smack forehead with palm) I'm embarrassed.

Z

I made a fitting to put into the exhaust system up at the front of it. A line connects the fitting to a MAP sensor. The exhaust fitting has the same thread as most, if not all, O2 sensors. The setup can be easily transfered from one car to another by just temporarily replacing the car's stock O2 sensor with the fitting, and plugging into the car's cigarette lighter socket. I can measure the output of the MAP sensor at a resolution of 1kpa, 0.1psi, or .01bar. This can be done in real time, or data logged it at a rate of 12 samples per second, and can be done either on the dyno, or continually while the car is being driven. No numbers pulled out of thin air here.

The point I was trying to make was that superchargers can be a viable and successful alternative to turbos. There are some people who will tell you that absolutely under no conditions can that be the case, and even when their own performance measurements show the opposite will make statements like:
There are apparently a number of people around who think in that type of way. I was at a dyno day held at a local Porsche dealership a while back that was advertised in the PCA magazine for the area. As expected, there were a number of 911 owners there. The highest horsepower for the day was made by an air-cooled turbo 911 of some variety. And then a street driven supercharged 928 got on the dyno and beat that 911's number by over 200rwhp. Even after seeing it for themselves, and having the dyno operator explain it several times, there are still some of those that don't believe it's possible that a centrifugal supercharger 928 made more power than a turbo 911 did. It was a double whammy for them. A centrifugal supercharger car made more power than a turbo one, and a front engined, water cooled, Porsche made more power than the most powerful 911 there. They still think that the dyno must have been broken, or that it was some kind of trick, because it just can not be possible.

Some have.



The above is from a regularly street driven 928 with a Vortech supercharger at 12psi to 12.5psi of boost, and way too rich of an air/fuel mixture over most of the RPM range. The car is currently running 14psi of boost and has had some fuel tuning. Unfortunately there wasn't any time before the season ended to get it on the dyno again. The engine uses stock 928 parts, except for having the stock pistons machined to lower the compression ratio a little bit, and always runs pump gas.

Here's one of that car Hacker-Pschorr mentioned:



It really depends on the application and what you want it to do again. If I had a street driven 944 that I use like I do my current cars, I'd probably really be leaning towards a twin screw if it could be made to fit well.

Danno

Any dyno-charts of twin-screw SC on a 928? I just don't like the slow boost build-up and lack of low-end torque on the centrifugal SC. Personally, I like to have a symmetric torque-curve centered in the RPM-range I use the most. So on a street, car say... 3000-5000rpm with torque-peak at 4000rpm.

That dyno-chart above is great for a race car, 4500-6500rpm with a peak around 5500rpm. That must be quite a monster! Don't take no sh*t from Mustangs, Corvette or Vipers huh?

BC

I just love that pic Z. Thats not tims bracket right? That SC is too high - it comes over the rad.

BC

I don't know danno. I was actually pretty okay with 300-495lb/ft of tq from 2k-6300rpm?

Andy has a dyno chart around here, but I personally have not seen any Twin screw dyno charts over 8psi on a 928. They may exist.

hacker-pschorr

Its a daily driver - rain or shine on stock 16" 928 wheels. The owner/fabricator of the car wants to keep the exterior stock.
It also has 8 forward speeds - it's an automatic.
The design and dedication of this car and it's owner is nothing short of amazing.
The dyno chart listed does not belong to that engine pic. The engine in the picture has not been on the dyno.

The next phase of that motor is a 6.1 liter stroker with that supercharger setup. The crank, pistons and rods have been built. Engine #1 is underway as we speak. Parts and info of one of the cars can be seen here:
https://rennlist.com/forums/928-forum/166901-i-would-like-to-share-my-supercharged-928-project-car.html

Lead Foot 944

I remember seeing those bad *** 928's over the summer....NIce guys with nice toys....!

DAmian

Z

The shape of the torque curve can be kind of misleading. First and second gear are basicaly worthless in that car if the pedal's to the floor. It's nothing but wheelspin, so there's already way more bottom end than can really be used on street tires. The owner was telling me that with the way it's running now he can get wheelspin up to 100mph. On a car like the 944 with it's smaller displacement engine, I'd say you're absolutely right about wanting more of the torque curve down lower, because there's a good bit less torque down there to start with than with the 5 liter 928 engine.

I'm pretty sure it is Tim's bracket on the car in the picture, just maybe modified a little bit for the Novi supercharger. The radiator has been lowered in that car, and that's why there's room for the air intake to go over the top of it.

GoRideSno

This chart is on an automatic car with the only other mod being an X pipe in place of cats. Basically 498CHP

Really?
In the run represented below I didn't even spin the tires. It was with drag radials, not slicks just extra sticky tires. I have also run 4.3 0-60. I have done 12.7 with street tires and another with one of my twin screw systems has run 12.5 sec 1/4th and and 4.6 0-06 without spinning the normal street tires


Andy K

John..

Z, there you go again comparing an apple to an orange...of course it makes more power than a 3.4-3.6 liter 6, I mean you are starting with 316 HP 32V V8 out of the crate, some early turbo 911s don't even make that much on the bottle feeder.

You see, all that wheelspin you refer to on the SC car....set for 12 lbs you make 12 lbs in 1st gear...you can't use it, or as you say you can't. So the CS makes too much when you don't need it and not enough when you do. Look at the boost curve on those devices. Turbo probably won't make it there (and I don't need it), so off the line traction will not suffer....and if it does...guess what, I can install a 7 lb wastegate spring, then hold the gates closed longer in 3rd+ gears with the touch of a button from inside the car to get 14 or so lbs of boost. It is called cockpit adjustable boost... You can't do that with the CS. Buy some 87 octane fuel and turn the boost down....104 octane, and crank it up without ever lifting the lid. The advantages are clear and we all know that 1st gear ends pretty quickly in any fast car...you don't need all your boost there. Third gear is where the CS will really fall off against the turbo.

Not one of you knows anything about how easy or difficult it is to install my setup on a 928, nobody has seen the underside of the car except for me and a few friends. I will tell you this...it is easy, much easier than you think....you don't have to do much on the front side of the engine at all. Pressure in the exhaust, big deal, who cares.... if the car makes more power and is more streetable, why would you care? My Callaway has the same valves it left the factory with and not one was burned up in 20 years of turbocharged use.

Continue to mislead....the extra money for my top end setup will buy a full hot-wire conversion (the only one ever made for L-Jet 928 mind you) and programmable injection calibrator made to my specs. It gives crisp and fast throttle response. A lower priced example is on the way. Say, intercooled 6 lbs of boost for a small amount more than a super...it is true and I will prove it very soon. BTW how do any of you know what the performance is? I don't recall giving any specs for my new setup just yet.

StupEd05

John... Could you get us detailed pics of your TT setup? Im very interested to see how you snaked stuff around. My first impression of the 928 engine bay was, "Darn, I dont ever want to work on that thing!" Kudos on the setup.

944J

now how would you go about getting big numbers with a SC on a 951 engine? say 300-400rwhp? 500rwhp?

Tony

Heres mine at 7 psi..falling off to 5ish at the end.
My first dyno run with it, last month...Im way rich 10.4:1, give or take.




right click save as.
(some folks have had trouble getting them to play..others havent?)
http://members.rennlist.com/v1uhoh/DynoRun1at7psi.mpg

http://members.rennlist.com/v1uhoh/DynoRun2at7psi.mpg