Which one puts out more pressure?

calereeves · Post by **calereeves** » Sun Sep 30, 2001 6:59 pm

At say 3000 rpm, on a respectable 2110, which would put out more pressure, a supercharger or the engine exhaust pressure? Would this change at say 5000 or 6000 rpm? I ask this because it seems to me that the super would put out way more than the exhaust pressure.
If you ran a nice sized turbo off of a supercharger, then
1.) You wouldnt get as much heat build up from the engine exhaust plumbing through the engine compartment.
2.) You would have more availible boost quicker because the super spins up just as fast as the engine RPM can go up because its belt driven. That would virtually eliminate turbo lag, right?
3.) The engine would not have to worry about exhaust back pressure screwing anything up, because it would be routed out just like normal.

If you ran a blow through system, with dual carbs, plumbing could get even tighter than just a turbo, but say a single progressive weber of nice size on a center manifold shouldnt be a problem.

Does anyone see a problem or flaw in my logic? All commments and input are absolutely welcomed!
Thanks,
Cale

67Junker · Post by **67Junker** » Tue Oct 02, 2001 10:04 pm

What do you mean run a turbo off a super?

Physically connect the compressor side of the turbo to the super?

Or will the air from the super be turning the turbo?

calereeves · Post by **calereeves** » Tue Oct 02, 2001 10:39 pm

I mean using the air from the super to spin up the turbo.

Cale

Trebor · Post by **Trebor** » Tue Oct 02, 2001 10:41 pm

It is my understanding that as you compress air you also create heat so you cannot eliminate all of it. You would not get the heat from the exhaust so maybe the air getting to the cylinders would be cooler but why not just connect the drive belt to the exhaust end of the turbo shaft and cut out the middle man. You could call it a low temperature supercharged pulley driven direct drive turbo highbred power fuel induction compressor system. You might even think of patenting it.

I think it's a great idea.

Robert Martinez

Lo Cash John · Post by **Lo Cash John** » Wed Oct 03, 2001 1:21 am

...or instead of "re-inventing the wheel", you could just buy a centrifugal supercharger, fab the brackets and plumbing and be done.

ray greenwood · Post by **ray greenwood** » Wed Oct 03, 2001 5:44 pm

Interesting conversation. What kind of supercharger were you actually thinking of using. There was a good comparative article last year in European Car mag. The gist was the comparison of efficiencies of differnt TYPES of superchargers...from the G-ladder, to the basic vane type roots, to scroll type Lisholm. The roots vane type...at very best is only capable of moving about 50+ percent of its available volume. It has too much loss through heat, friction and the fit of the components..., mostly due to the fact that it has two scrolls moving...but is still used because generally they are larger units and can supply the volume when compactness and efficiency is not an issue...like top fuel drag racing. The Lisholm or recirculating screw type...being the most efficient and least power robbing. This is much like the scroll type air-conditioning compressor..and if memory serves uses a single moving scroll..expensive..and they only get so big...and it needs intercooling. The G-ladder or G-chamber like the VW Corrado used is just a little less efficient...but only because the internal G-spiral can only be produced out to 70mm in length before the accuracy of the rotor starts to degrade due to minute heat distortion during running (hence the name G-70)...and it self destructs. It also needs intercooling. The G-ladder would be the best if they could make it large enough for more applications. Its design gives the most accuracy and longest reliability before rebuild (at about 70K miles it needs a new rotor and seal set) For trivia, they also produced a G-40 and a G-60. I havn't seen any mention of possibly ever using a turbo-supercharger...which is what many airplanes used in wwII (see P-38 lightning and P-47 thunderbolt). this is actually a turbine wheel...either gear or belt driven from the crank. It has the efficiency of a turbine (much better than a rotor/scroll)..but the constant torque/load of being driven by the crank...lots of torque! What you are speculating has actually been done...but I don't know if it has been done in the auto industry. In the last days of wwII...the FW-190 D and F (some of them) and the very last model...The TA series...used a 2-stage 3 speed super charger. The exhaust turbo was used a pre-charger to feed volume into the super charger. I'm not sure how speed was controled. For historical note, the intercepter versions of these aircraft used methanol water-injection at take-off, nitrous in high altitude zooms and generated max horsepower of 2800...with Bosch high pressure fuel injection and an electronic fuel mangement system for temperature and altitude compensation...talk about ahead of the times!! The final varient of this supercharged engine produced a sustainable top end of 479 mph at 32,000 feet...thank God they only built a few...there would be a lot more German restaurants on the planet. I'll see if I can find any more articles on the charger itself. Ray

calereeves · Post by **calereeves** » Wed Oct 03, 2001 7:11 pm

Thanks Ray,
I'll see if I can find some info on the Foche Wolfe, but I still dont know if every one understands what I'm talking about.

I mean: Have the crankshaft drive a supercharger(nothing new there) such as an Eaton M45, or something of the like that requires no intercooling. Route the compressed air from the supercharger to the compressor?/turbine? side of the turbo(the one the exhaust goes in). Then, the turbo acts just like normal and feeds the carb, like a regular blow through setup.

Thanks,
Cale

Trebor · Post by **Trebor** » Wed Oct 03, 2001 7:57 pm

Hey Cale, I knew what you were talking about I just felt the need to mess with you. I hope you didn't take it personally.

Robert

calereeves · Post by **calereeves** » Thu Oct 04, 2001 9:11 pm

Nope

I did like the creative name though! Imagine that painted in script on the side of the car!

Cale

Cam · Post by **Cam** » Thu Oct 04, 2001 9:22 pm

There was a conversion similar done on a SLK kompressor Benz a few years ago.
They left the standard blower and then fitted a turbo of some sort. I have it in a magazine somewhere (emphasis on somewhere!)

calereeves · Post by **calereeves** » Thu Oct 04, 2001 9:34 pm

Cam,
any possible way you could find that mag?! I would love you forever!( Or pay you, which ever one you want

)
Cale

Lo Cash John · Post by **Lo Cash John** » Thu Oct 04, 2001 10:08 pm

If you are really serious about doing things different, then I got one for ya'.
There was a brief 1/2 page write-up in an issue of KIT CAR or KIT CAR ILLUSTRATED back in the 80's that might interest you. Some high school auto shop teacher was having his students build a kit 427 Cobra (wish my school's shop teacher was that cool!!)powered by a turboed small block Chevy. The odd thing is the turbo was NOT powered by the exhaust, but instead by the exhaust from a propane fueled "burn chamber". The idea is simple: When you are not burning propane in this chamber the turbo is "off" and has little effect on the motor (perhaps some restricition in the intake). Flip a switch and the propane chamber lights up(sort of like a gas heater) and starts spooling the turbo up, so now the turbo is "on". The slick part to this is you can have positive manifold pressure at idle...talk about torque!!!!!! I'm affraid I can't recall what year that was published and there was very little detail about the workings. I have no idea how the "burn chamber" got air or how much. It seems like you would have to feed a lot of air into the the system.

Guy Gove · Post by **Guy Gove** » Fri Oct 05, 2001 2:55 am

Hello Cale

I understand what you are saying about using the supercharger to drive the turbo, however I do not think it will work.
For one (I may be wrong) I think that the pressure of the exhaust gasses will be higher than that produced by a supercharger. Secondly looking at the turbocharger from a thermodynamic point of view, it is not only driven by the pressure difference across it but by the kinetic energy that the hot exhaust gasses posess and transfer to the turbine.

Also if you look at the system you propose, you are compressing air from atomospheric pressure to a higher pressure using the super charger, this will require a certain amount of work (hp) lets call it W1. You are the expanding this high pressure air through the turbine of the turbo to create work again, W2. Due to friction and other inefficiencies W2 will be less than W1.
W2 is then used by the turbo's compressor to compress air again from atmos. to a higher pressure. But because W2 is less than W1 the pressure from the turbo will be less than that you are getting from the supercharger alone.

I hope this is not too long winded, and I hope that it makes things clearer for you.

Guy

calereeves · Post by **calereeves** » Sat Oct 06, 2001 3:57 am

Guy,
That was what I am trying to figure out, Which one puts out more pressure? I have started looking for actual flow numbers in CFM/PSI (thats my logical way of putting it, in cubic feet per minute related to pressure) I have found hard numbers from the Eaton company, now I just need someone to do some calculations for an engine. How many cfm and at what pressure are the exhaust gasses coming out at, at different RPM? My question is simply which one would spin the turbo faster. I'm not sure I follow you about the kinetics of the heat. It seems to me that the temperature of the incoming air to spin the compressor shaft would have zero effect, unless at extreme temperaures, on the rate at which the compressor wheel would spin. I do understand that the reason turbos are used in economical applications instead of superchargers is that the parasitic loss of power from the turbo is less than that of a supercharger. However, if the supercharger was slightly oversized for the engine you would be putting it on, it wouldnt matter, because that would mean it just moves more air for the turbo. At some point, when you are getting larger and larger for the supercharger size, the power output, if the power output vs. parasitic loss were plotted would have to overcome the the parasitc loss at some point. So, you just go one step beyond that point and you have a killer system like no other.

If I can find a cheap supercharger and another cheap turbo like the one i just sold...darn it... I will try to run some experiments with a side draft dell or something, with a draw through configuration on the turbo. Any donors

?

Lo Cash,
I think thats a pretty cool idea, with the propane, it would eliminate any parasitic loss, either from a super or from exhaust back pressure. That would be even harder, in my opinion, to set up than the super-turbo, because the carb would have to go sometimes with no boost, sometimes with tons. Cool idea though, maybe with EFI and a computer controller, that would kick some real ass!

Sorry so long, but Thanks,

Cale

Cam · Post by **Cam** » Sat Oct 06, 2001 9:59 am

The article is in a box in my basement somewhere.
I got it about four years ago or something, if your looking for spec's and stuff forget it! They were just using it as a promo for some company, so not much in the way of technical details.
I'll have a look and see if I can find it none the less.
I've moved since I last saw it, so the only question is which box it's in.