Turbo vs Supercharger
#121
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Originally Posted by Hacker-Pschorr
Geo,
I -think- I got your point. I have nothing against turbo's, never have. But in my situation (and most 928 owners looking for power) the turbo vs SC argument leans a lot more in favor of superchargers almost on the basis of simplicity alone. The 3 main kits offered for 928's are so well designed and work very well and IMO very inexpensive. The percentage gain you could get from turbo's is not worth the extra effort for 95% of the 928 crowd. I give John all the credit in the world for the car's he has been able to build. If and when he has a full kit to offer, excellent - the more boosted 928's on the road the better.
I -think- I got your point. I have nothing against turbo's, never have. But in my situation (and most 928 owners looking for power) the turbo vs SC argument leans a lot more in favor of superchargers almost on the basis of simplicity alone. The 3 main kits offered for 928's are so well designed and work very well and IMO very inexpensive. The percentage gain you could get from turbo's is not worth the extra effort for 95% of the 928 crowd. I give John all the credit in the world for the car's he has been able to build. If and when he has a full kit to offer, excellent - the more boosted 928's on the road the better.
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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.
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#122
Race Director
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" 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.
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.
#124
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Originally Posted by Geo
Show me the data on the exhaust backpressure. I think that number is pulled out of thin air.
Originally Posted by Geo
>>Did any of you see the Acura NSX with the centrifugal supercharger that was racing in the SpeedVision series? When I saw it race in the SpeedVision race up at Road America, I think it was the only supercharged car in the field. It came in I believe third place, ahead of a good number of turbocharged cars.<<
OMG. Like the supercharger is what made a difference.
OMG. Like the supercharger is what made a difference.
Originally Posted by John..
Anybody who seriously thinks a Vortech or Paxton or Powerdyne can make a better setup than a turbo on any given vehicle needs to have their head examined.
Originally Posted by Rich Sandor
I would have expected a supercharged 5L v8 to be making more than ~375rwhp/rwtq.
![](http://img79.exs.cx/img79/7867/78-Timschart.jpg)
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.
Originally Posted by Hacker-Pschorr
The 1987 928S4 running 22psi through a modified 951 intercooler (converted to air-water) is nothing short of a rocket. He has stock 9" tires on this car with LSD. He's still driving this car to work up here every day - once the snow flies he will park it.
He's running a Paxston supercharger.
I don't have any current photos of this engine to post at the moment.
He's running a Paxston supercharger.
I don't have any current photos of this engine to post at the moment.
![](http://img79.exs.cx/img79/3710/d2-EAAshow3.jpg)
Originally Posted by Campeck
which is a better s/c design though?
a centrifugal or a twin screw?
a centrifugal or a twin screw?
#125
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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?
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?
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#126
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I just love that pic Z. Thats not tims bracket right? That SC is too high - it comes over the rad.
#127
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Originally Posted by 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?![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
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?
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
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.
#128
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Originally Posted by Danno
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? ![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
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
#130
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Originally Posted by Danno
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?![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
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?
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
Originally Posted by BrendanC
I just love that pic Z. Thats not tims bracket right? That SC is too high - it comes over the rad.
#131
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Any dyno-charts of twin-screw SC on a 928?
![](http://928supermodel.com/album/images/fullsize/7192199a93dab4bd04a0ef8cb7337a87.jpg)
This chart is on an automatic car with the only other mod being an X pipe in place of cats. Basically 498CHP
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.
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
![](http://928supermodel.com/album/images/fullsize/947645bd5d8730216d79d83661b82055.jpg)
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Andy K
Last edited by GoRideSno; 12-03-2004 at 05:49 PM.
#132
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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.
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.
#133
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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.
#135
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Originally Posted by 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?![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
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?
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
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
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