Random

About the Whipple link you posted.

They use a twin screw positive displacement supercharger. It is basically a variaton on the Lysholm style of supercharger popular as replacements for the VW Corrado G60's

For proof of concept to what cheuk posted, check out their boost maps for a twin screw vs centrifical.


You can see it quickly reaches max boost and stays there.

The Lysholm superchargers are very good, but they are also probably the most expensive. One of the other disadvantages to the Lysholm style of superchargers is their high noise. They are LOUD, much louder than a centrifical or roots type.

CAPA also sells a twin screw supercharger (Lysholm style).

I'm not sure who makes the Lysholm supercharger for the G60, but I'll post that link up here when I find it.

[ March 21, 2002, 07:18 AM: Message edited by: Random ]

Y2KTIBLTD

centrifugal isn't it? wink
But I see your point. Why does a supercharger max out though? Shouldn't it work the same way as a turbo? Is there a physical limitation on what it can push or something? BTW I bought both books from Corky Bell. They are on turbo, super, and NO2. I hope they help me with these decisions and questions as well so I don't have to bother you guys to much.

Also it seems to me that the PT cruiser kit from Whipple versus the CAPA or Alpine kit cost roughly the same (Mid 3G$). But if the amount of boost remains constant from say 2500 RPM on would that make your torque curve flat? Thus increasing HP dramatically as RPM's rise or would it start to diminish the torque as soon as your maximum boost as been achieved? Since in essence it is still pushing the same amount of air in but it needs to do it many more times (faster RPM's)? Am I making any sense here?

[ March 21, 2002, 07:32 AM: Message edited by: Y2KTIBLTD ]

Cheuk in Seoul

The torque curve will be similar to the stock curve except a little higher everywhere.

Since the boost... or amount of air taken in by the engine is steady at... let's say 1 atmosphere (14.7 psi) + 5 psi boost throughout the rev range. And since the power an engine makes is all dependant on the amount of air it can take in. You would theoritically make (14.7+5)/14.7 = 1.34 or 34% more power/torque throughout the entire rev range. Of course I am ignoring things like parasitic losses from the supercharger, thermal ineffeciencies....
That's why I say that a roots type supercharger acts very much like a bigger NA engine. Also quick spooling turbos fit this picture.

SickYellowG60

http://www.bahnbrenner.com/flash.html

http://www.bahnbrenner.com/main.html
look for the forced induction part of the main page.

This is the the G60 supercharger getting replaced. It is now down to $2,400. It is supossed to be a S/C that can equal a Turbo with the high revs and the boost is supossed to keep going up. The G60 compared to the Lysholm generally has equal low end and medium range power. But then the Lysholm is supossed to just be doing better in the High rev's and it is supossed to be cooler then the G60.

Since I have yet to be able to find a real Lysholm (twin screws sc) so I don't know if it really works as claimed. As far as I know, it can withstand 30 psi, my G60 would grenade in a heart beat.

Decker

I just volunteered myself as a guinee pig wink !
We really need a good S/C for the tibby. So build them up and i'll test them wink And if you see any shrapnel flying, you might have to change the design a little wink Although the idea of having a 30psi pushing sc strapped to my car, reminds me of when my parents told me not to blow a baloon up that bigger...

Do you think the pistons, rods and other components can handle 30psi? Or would you have to replace those?

Y2KTIBLTD

The stock internals can only handle so much power safely. It doesn't matter how you get there, turbo, super, nitrous. I wuld relace anything internal once you get up so high. I have no idea what that limit would be just that I'm sure it would need to be done eventually.

Random

Because the air delivery from a supercharger is linear in response to engine RPM, It can "create" boost fast, but spining the engine faster means spinning the supercharger faster at the same rate. As the supercharger pumps out more air, the engines air requirements increase as RPM increase, so the two go up by roughtly the same scale. (assuming the supercharger is sized right for the motor).

Superchargers also have "efficency" ratings just like turbos. to use an extreme exaple...10 PSI of 300 Degree air or 8 psi of 175 degree air? The 8 psi would make more power, and have less detonation problems. The supercharger has to be sized right for the motor in order to keep the supercharger in it's RPM range of peak efficency as much as possible.

Also the internal bypass is set for X PSI, no mater how much air the supercharger pumps out, the bypass will not allow pressure to rise above that set rate. The supercharger might be physically capable of 20 PSI at 3500 RPM...but if the bypass is set for 10psi...you will only get 10 psi.

The Alpine kit is a roots style blower. Much less efficent (creates more heat). The CAPA unit is the same as the Whipple...a twin screw or twin rotor design.

Stock rods and pistions start go go bad around the 250 Wheel HP range. It would be wise to replace them before that. Ditto to the stock axles.

[ March 21, 2002, 12:25 PM: Message edited by: Random ]

Decker

if random's right (which is normally the case wink
then wouldn't be a idea to design some sort of supercharger that can create 8psi all the time. Mabye some sort of centrifugal gears or something.
Then you can keep your S/C at a constant temp/pressure.

or, what if you had a blowoff valve set at 8.5psi or 9psi, so that it couldn't build up too mutch pressure and superheat the air?

Y2KTIBLTD

Would this work?
Supercharger

Probably to big huh? I figured there are more of these cars around running S/C than there are Tib's so it would make a good doner for my project. Thus also dramatically saving me money. wink

Veniston

You don't want to be dumping too much out your blowoff, you're doing the work to compress that air. Remember that the SC is parasitic--you're using your engine power to compress the air, wasting the extra work isn't very efficient.

Also due to efficiency, an "over-compressed" system will end up hotter than one that's tuned to the point you want it.