So which Supercharger is better?
10-04-2003, 08:21 PM
#1
Burning Brakes
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So which Supercharger is better?
I am hearing things about the whipple, roots, and centrifugal blowers.
The guys who have complete kits are running vortech. It seems to be the least intrusive and has a long track record. Some are saying that these units heat up the boosted air more than a roots blower, yet I have heard 7psi on an S3 motor would be acceptable by FAST's standards but not by corky bells temperature theory? Im confused...
Nest we've got the roots and whipple that being developed for the 928. I have heard mentioned that this type blower will produce more torque ( and HP?) at lower RPMs, but how much are we talking? How many changes are needed? I can see that the intake manifold is gone and the roots sits in its place. I have noticed how the vortech seems to not kick in very much until 3.5k RPM, how much sooner will these models? I used to be under the impression that they would kick in better off the line than a turbo, but again the dyno charts speak for themselves.
Will the vortech be a bad decision on an automatic S3?
A side by side comparision is not available yet but would be quite helpful. Good luck you boostards and please let me know what you think.
The guys who have complete kits are running vortech. It seems to be the least intrusive and has a long track record. Some are saying that these units heat up the boosted air more than a roots blower, yet I have heard 7psi on an S3 motor would be acceptable by FAST's standards but not by corky bells temperature theory? Im confused...
Nest we've got the roots and whipple that being developed for the 928. I have heard mentioned that this type blower will produce more torque ( and HP?) at lower RPMs, but how much are we talking? How many changes are needed? I can see that the intake manifold is gone and the roots sits in its place. I have noticed how the vortech seems to not kick in very much until 3.5k RPM, how much sooner will these models? I used to be under the impression that they would kick in better off the line than a turbo, but again the dyno charts speak for themselves.
Will the vortech be a bad decision on an automatic S3?
A side by side comparision is not available yet but would be quite helpful. Good luck you boostards and please let me know what you think.
10-04-2003, 08:45 PM
#2
Nordschleife Master
Here's the deal.
Centrifical, typicaly the easyest to set up. Also typicaly the most efficent. This is a good thing as the more efficent the supercharger, the less it heats up the charge air. This can make a sigificant diffrence on a non aftercooled engine. The boost builds at a geometric rate compared to the rpm. So 4,000 rpm is about 4 times the psi of 2,000 rpm. As you can see, you have to set up the pullys so that you don't go over your boost pressure limit at max rpm. This means like you said, you won't get much of any boost under 3.5k rpm. This can be a bad thing, if your running the stop light special, it can also make your car more driveable around town, so your not so hard to the transmittions and tires.
Roots are cheaper than the Wipple, or twin screw, but IIRC, a bit more expensive than a centrifical unit. They are a positive displacement unit. This means the boost supplyed is almost not related to the rpm of the engine. If you set up the pullys for 10 psi, you'll get about 10 psi of boost at 1,000 rpm, and about 10 psi of boost at 6,000 rpm. They are typicaly the least effecent. Like I said this can make a big diffrence for an unaftercooled system. The more efficent, the cooler the charge air, the more boost you can run. They also require modifications to the intake. IIRC, GoRideSnow mannaged to fit one under a nearly stock hood, which is cool.
The twin screw units are the most expensive supercharger design out there. They are positive displacement units, similer to the roots. They are nearly as efficent as the centrifical units. They have similer mounting constraints as the roots. If you've got the money, I'd say this is the way to go, supercharger wise
Turbochargers come in many diffrent types. There are single turbo 928s, twin turbo 928s. They can also be hooked up to the engine is number of diffrent ways. Boost is controled by the use of a waste gate. Once the engine is moveing enugh exaust gas to spool the turbo up, the waste gate vents the excess exaust, keeping the boost level fixed. Turbos don't make boost linked to the rpm, like the superchargers, instead it's controled by the exaust gases. The more exaust gas the engine makes, the more boost is avalible. Twin turbos can be arranged together, so they both start makeing boost at the same time, or in a serices, so that one take care of the low end, and they both run for the top end. The pipeing can be difficult to build for a 928. Also becuase of their proximity to the exauste heat they are inclined to not be as cool as the centrificaly suprechargers. But they should have high effency, so they should edge out the roots.
OK, the reason that the S3 and S4 can get away with breaking Corky's rule of thumb is they have a realy good cylinder head design. The rule of thumb seems to have been designed as a blanket for all engines, includeing the wedge shaped iron heads from days of old. The 928 S3 and S4 uses a pentaroof combustion chamber, with an all aluminum block, and aluminum head. This is pretty good arrangement for controling detonation. As a result, the engine can run a higher theroetical peak combustion chamber tempeture w/o suffering from detonation. The FAST kits where designed for a 928, they take into account the engines design, and tested how high they could go.
What ever you want to do is pretty much a personal choice.
Good luck.
Centrifical, typicaly the easyest to set up. Also typicaly the most efficent. This is a good thing as the more efficent the supercharger, the less it heats up the charge air. This can make a sigificant diffrence on a non aftercooled engine. The boost builds at a geometric rate compared to the rpm. So 4,000 rpm is about 4 times the psi of 2,000 rpm. As you can see, you have to set up the pullys so that you don't go over your boost pressure limit at max rpm. This means like you said, you won't get much of any boost under 3.5k rpm. This can be a bad thing, if your running the stop light special, it can also make your car more driveable around town, so your not so hard to the transmittions and tires.
Roots are cheaper than the Wipple, or twin screw, but IIRC, a bit more expensive than a centrifical unit. They are a positive displacement unit. This means the boost supplyed is almost not related to the rpm of the engine. If you set up the pullys for 10 psi, you'll get about 10 psi of boost at 1,000 rpm, and about 10 psi of boost at 6,000 rpm. They are typicaly the least effecent. Like I said this can make a big diffrence for an unaftercooled system. The more efficent, the cooler the charge air, the more boost you can run. They also require modifications to the intake. IIRC, GoRideSnow mannaged to fit one under a nearly stock hood, which is cool.
The twin screw units are the most expensive supercharger design out there. They are positive displacement units, similer to the roots. They are nearly as efficent as the centrifical units. They have similer mounting constraints as the roots. If you've got the money, I'd say this is the way to go, supercharger wise
Turbochargers come in many diffrent types. There are single turbo 928s, twin turbo 928s. They can also be hooked up to the engine is number of diffrent ways. Boost is controled by the use of a waste gate. Once the engine is moveing enugh exaust gas to spool the turbo up, the waste gate vents the excess exaust, keeping the boost level fixed. Turbos don't make boost linked to the rpm, like the superchargers, instead it's controled by the exaust gases. The more exaust gas the engine makes, the more boost is avalible. Twin turbos can be arranged together, so they both start makeing boost at the same time, or in a serices, so that one take care of the low end, and they both run for the top end. The pipeing can be difficult to build for a 928. Also becuase of their proximity to the exauste heat they are inclined to not be as cool as the centrificaly suprechargers. But they should have high effency, so they should edge out the roots.
OK, the reason that the S3 and S4 can get away with breaking Corky's rule of thumb is they have a realy good cylinder head design. The rule of thumb seems to have been designed as a blanket for all engines, includeing the wedge shaped iron heads from days of old. The 928 S3 and S4 uses a pentaroof combustion chamber, with an all aluminum block, and aluminum head. This is pretty good arrangement for controling detonation. As a result, the engine can run a higher theroetical peak combustion chamber tempeture w/o suffering from detonation. The FAST kits where designed for a 928, they take into account the engines design, and tested how high they could go.
What ever you want to do is pretty much a personal choice.
Good luck.
Last edited by ViribusUnits; 10-04-2003 at 09:41 PM.
10-04-2003, 09:28 PM
#3
Burning Brakes
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I appreciate your response Viribus.
GoRide,
I know you'll be on this one soon enough... Do you have numbers yet on the potential low end torque gain for your models over a Vortech?
Is there a sacrifice on the top end for that low end gain?
Who has a supercharged automatic 928 out there? Calling all boostards!
GoRide,
I know you'll be on this one soon enough... Do you have numbers yet on the potential low end torque gain for your models over a Vortech?
Is there a sacrifice on the top end for that low end gain?
Who has a supercharged automatic 928 out there? Calling all boostards!
10-05-2003, 12:46 AM
#4
Drifting
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Hahahaha, Yes Warren I'm all over it.
I doubt that a centrifugal heats up charge air more that a roots from what I have read.
I don't knbow the exact temperature limits of the 928 but I am willing to bet they are quite a bit higher than Corky's arbitrary standard of 1075 degrees F. Corky deals with any old car that is getting SCed, anything from an iron block, iron head sparkplug on the side engine (think skillet, storing heat) to an engine w/ an all aluminum engine with hemispherical combustion chamber (think radiator, disipating heat). It is safe to say the S4 combustion chambers were designed for boost, since they are the same as the 959. The 85-86 can't be too far off.
I'll be back, girlfriend getting mad.
Andy K
Some are saying that these units heat up the boosted air more than a roots blower,
yet I have heard 7psi on an S3 motor would be acceptable by FAST's standards but not by corky bells temperature theory? Im confused...
I'll be back, girlfriend getting mad.
Andy K
Last edited by GoRideSno; 10-05-2003 at 10:59 AM.
10-05-2003, 10:55 AM
#5
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It looks like Viribus has a pretty good grip of the situation. My roots system fits under a completely stock hood. FWIW The Technical Director from Whipple told me that the Whipple is the most efficient blower available of any sort.
Warren,
Where did you hear that 7psi on the 85-86 is acceptable by FAST's standards? If you heard it from FAST then I would believe it. They have SCed over 30 928s, probably 10 times as many as anyone else.
These two types are disticnctly different. They both have the advantage of lowend torque and hp. Boost is related to throttle position. In general, as quickly as you open the throttle you will have full boost, wether it's 1k or 6k rpms. On the 928, under moderate boost levels the roots will not fall off at high rpms. On my 4 psi system the topend is very strong. I doubt you could spin the roots fast enough to make over 12 psi on the 32 valve 928. So boost would drop off at higher rpms at this level. 12 PSI would make well over 525chp, maybe more. The Jaguar roots also has the advantage of being very inexpensive. The Whipple provides lowend power and will be comfortable in excess of 20psi on the 32 valve 928. The power to drive the whipple is extremely low. So low that the Tech Director told me he used a 6rib belt to make 750 HP with the 2300.
Very true, I hope to have dyno charts available for a Roots and a Whipple setup before Sharktoberfest, within 2 weeks.
HTH,
Andy K
Warren,
Where did you hear that 7psi on the 85-86 is acceptable by FAST's standards? If you heard it from FAST then I would believe it. They have SCed over 30 928s, probably 10 times as many as anyone else.
Nest we've got the roots and whipple that being developed for the 928.
but again the dyno charts speak for themselves.
HTH,
Andy K
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10-06-2003, 06:08 PM
#9
Drifting
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Joe,
Do you have the stock engine HP and Torque curves in you owners manual? If so is it possible to scan them in and post them or give us a few rpm points on the curve with the HP and Tq #'s. I guess I haven't really thought about SCing an auto GTS.
Tony,
See you at STIM w/ 2 (cross my fingers) SCed cars.
Andy
Do you have the stock engine HP and Torque curves in you owners manual? If so is it possible to scan them in and post them or give us a few rpm points on the curve with the HP and Tq #'s. I guess I haven't really thought about SCing an auto GTS.
Tony,
See you at STIM w/ 2 (cross my fingers) SCed cars.
Andy
10-06-2003, 07:01 PM
#11
Developer
One of the ways the charged air package gains heat on the way to the intake is the heat of the lubricating oil itself (conduction) and the heat of the engine compartment (convection). The internal-compression units like the Roots operate at engine temperature because the integral - they become part of the engine. A centrifugal blower is an external-compression supercharger and naturally runs at a lower temp than the motor itself. That's a good thing. But the oil lines that bring in engine oil to lubricate it bring a certain amount of temp rise with them.
We offer two kits - a self-contained centrifugal blower with permanently lubricated bearings that produces the coolest charged air, and a race blower kit that requires an external oil line just like the Vortech's. We are a Powerdyne dealer.
Now before you reach for your keyboard to argue Powerdyne vs Vortech vs Paxton - you don't need to. The Vortech and Paxton's have more CFM and boost pressure available than the self-contained Powerdyne BD-11a. But, here at 928 Motorsports we are feeding the little 4.5L (273 ci) 928 - not the 5.0 liter and up like FAST and Tim Murphy are - so we do not need as big of a blower.
The belt-driven Powerdyne BD-11a with the self-contained bearings and no oil line offers an interesting and very streetable solution. Faster installation and no oil leaks too. But, it has a ceiling of reliable use of 9 PSI (believe me, we know). At 9 PSI we ran ours 2 years without maintenance. When we wanted more boost than that, we too had to go gear-driven - and with it in came that oil line form the engine...
The gear-driven blower from Powerdyne is the Xb-1a. It is designed for up to 18 PSI of boost. We gave run it at 15 psi on a stock 78 928 without detonation on pump gas (intercooler installed, of course).
We offer two kits - a self-contained centrifugal blower with permanently lubricated bearings that produces the coolest charged air, and a race blower kit that requires an external oil line just like the Vortech's. We are a Powerdyne dealer.
Now before you reach for your keyboard to argue Powerdyne vs Vortech vs Paxton - you don't need to. The Vortech and Paxton's have more CFM and boost pressure available than the self-contained Powerdyne BD-11a. But, here at 928 Motorsports we are feeding the little 4.5L (273 ci) 928 - not the 5.0 liter and up like FAST and Tim Murphy are - so we do not need as big of a blower.
The belt-driven Powerdyne BD-11a with the self-contained bearings and no oil line offers an interesting and very streetable solution. Faster installation and no oil leaks too. But, it has a ceiling of reliable use of 9 PSI (believe me, we know). At 9 PSI we ran ours 2 years without maintenance. When we wanted more boost than that, we too had to go gear-driven - and with it in came that oil line form the engine...
The gear-driven blower from Powerdyne is the Xb-1a. It is designed for up to 18 PSI of boost. We gave run it at 15 psi on a stock 78 928 without detonation on pump gas (intercooler installed, of course).
10-06-2003, 08:24 PM
#12
I suppose a separate oil cooler in-line to the SC would be a good idea to even further increase the efficiency of the unit and lower the air charge temp.
10-06-2003, 09:04 PM
#14
Burning Brakes
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Joe Dyer,
Thanks for the reply. How does your auto 928 perform with its vortech in place? Did you S/C supplier have any changes to the kit with the auto tranny? Did you end up teaking it to take advantage of the automatics gearing?
Go Ride,
I had heard from Mark at FAST that 7 psi is nearing the limit of a non intercooled S3.
Thanks for the reply. How does your auto 928 perform with its vortech in place? Did you S/C supplier have any changes to the kit with the auto tranny? Did you end up teaking it to take advantage of the automatics gearing?
Go Ride,
I had heard from Mark at FAST that 7 psi is nearing the limit of a non intercooled S3.
10-07-2003, 12:50 AM
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Good info Warren about the FAST said limits.
Remember that the GTS started w/ around 60 more HP and around 80 more lb/ft torque than the 86.5. This is a quite a difference in power. If the GTS has a lot of power down low then the difference will be magnified even more. The 86.5 auto I had felt peaky compared to my S4. The GTS also has lower gearing than the 86.5 (2.54? v/s 2.20) and I believe it will hold first gear longer. These things will add up to a very significant difference in low speed driveability. Hopefully someone with a S3 auto supercharged will come foreward as that would be the best comparison.
HTH,
Andy K
Remember that the GTS started w/ around 60 more HP and around 80 more lb/ft torque than the 86.5. This is a quite a difference in power. If the GTS has a lot of power down low then the difference will be magnified even more. The 86.5 auto I had felt peaky compared to my S4. The GTS also has lower gearing than the 86.5 (2.54? v/s 2.20) and I believe it will hold first gear longer. These things will add up to a very significant difference in low speed driveability. Hopefully someone with a S3 auto supercharged will come foreward as that would be the best comparison.
HTH,
Andy K