Spun

I am researching the idea of superchagring my 3rd gen and am looking for anyone that has experience in this department. Curently I am looking at prochargers' self contained models to run with my existing mods. If anyone has any ideas of who to talk to or where to look this is the place to post. thanks

Shad Laws

Hello-

You don't want a centrifugal supercharger... ESPECIALLY on a rotary. The engine will be a peaky little beast... which means a nearly-complete dog until very high rpms.

The pressure difference of centrifugal pumps (all of them!) is approximately related to the square of shaft speed. This means lots of high-end boost, and nothing down low!

Ever wonder why ZERO major car companies use centrifugal superchargers on their engines? That's why. It just isn't worth the money.

Prochargers are really expensive because the manufacturing numbers are so low (compared to mass-produced roots superchargers and whatnot). Some have come to like them because they add some "free" top end to a low-grunt V8. For a rotory, which doesn't have a bottom end, it'd pretty much suck. Sorry.

If you want a supercharger, go with a roots-style blower or a screw-style blower. They will give a good powerband. Of course, the screw-style is more efficient, but also costs a lot more money.

Take care,
Shad

peejay

Technically all 3rd gens are supercharged.

Turbos are superchargers too...

BTW - Both Studebaker and Ford have put centrifugal superchargers on their cars from the factory. Ah, the 50's and 60's...

cdk 4219

An SC takes power to turn, torque to be exact, something the rotary doesnt have a lot of to begin with. Turbo is much better for the application.

Shad Laws

Hello-

Yes, techincally true... in fact, to be particular about semantics, all FD's are centrifugally supercharged :-). The difference is that the turbosupercharged variety (slang terms being turbocharged or turbo'ed) use another centrifugal pump to drive the compressor, whereas a Procharger or like item uses a belt to the crank/eccentric shaft.


Yah... but the 50's also had flathead straight-8's :-). Talk about smooth... and godawful inefficient, heavy, underpowered, and large...

I should revise my above statement... I don't know of any OEM that has used belt-driven centrfugal superchargers for the consumer market within the last 20 years or so. Better? :-)

Take care,
Shad

Shad Laws

Hello-

Turbos aren't free, either... they cost power (it's eaten up in pumping losses... they have to pump exhaust gases out against a lot of backpressure). Whether you call it power or torque is irrelevant... at a given rpm, more of one is the same as more of the other :-).

Take care,
Shad

SPOautos

Your engine doesnt see all that turbo backpressure at the exhaust port. You exhaust is going to build pressure at the turbo if the wg is efficient and designed right. When the exhaust starts to build up at the turbo and create pressure that pressure would start to make its way back to the engine. When that pressure gets to the wg its going to get relieved and you dont see all that pressure at the exhaust port of the engine.

STEPHEN

peejay

The fact that the exhaust gas temperatures drop as they go through the turbo suggests that the turbochargers are reclaiming energy otherwise wasted.

cdk 4219

Please go to the dictionary and read the definition of torque and horsepower, if you are under the assumption that they are one in the same. Turbos are much much more efficient at what they do, and create a lot more torque than a supercharged engine. Supercharging a small engine is not that cost effective, and certainly not any more reliable. While it will work I suspect that you would be more than dissapointed with the end result.

rotarygod

iTrader: (1)

I think you interpreted him wrong and a were a little harsh about it. What he was saying is that you can not have more horsepower at any given rpm without having more torque at that same rpm and vice versa. He is absolutely correct. He never said they were the same thing. He merely stated it that way because some may say that in order to turn the supercahrger it robs horsepower while others may say it robs torque. Both statements are true.

How is supercharging not any more reliable or cost effective than turbocharging? How does it make less torque than a turbo assuming flow rate in cfm and boost pressures are the same? Those are blanket statements that may have different answers depending on how it is done.

You're response to him was a little harsh and lacked enough detail to even be relevant. How do you know HE wouldn't be happy with a supercharger?

KevinK2

Looks like a nice progressive torque build is possible with centrif super, even for high rpm applications.

http://www.comptechusa.com/images/dy...percharger.pdf

Would be unique, but nice clean singles are available.

Loss of effective VE and pumping losses due to exh backpressure make street turbo parasitic losses approach that of a vortech sc.

Shad Laws

Hello-

So long as there is notable intake manifold boost, there is notable (i.e. way above what cats/mufflers do alone) exhaust system backpressure.

Go back to what we said earlier - all centrifugal pumps have their pressure difference related to the square of the shaft speed. So, to get some intake manifold boost, you need the compressor wheel (a centrifugal pump) to be spinning fast. BUT, the opposite is also true! To get that shaft spinning fast, the turbine wheel (also a centrifugal pump) has to see a big pressure difference!

If there is essentially zero exhaust backpressure, then the shaft speed is essentially zero. That means that there is no boost. You can't have boost without exhaust backpressure (unless, of course, you don't use turbos :-) ).

Take care,
Shad

Shad Laws

Hello-

Not entirely...

A large part of that temperature difference is due to the drop in pressure. If you take a gas and suddenly decrease its pressure, it gets colder. If you removed the turbos (but, somehow magically, kept the same intake manifold boost), the pressure at the port would be about the same as the pressure normally seen after the turbos. It would also be MUCH cooler than normally seen before the turbos.

But, if you could make this magical 1:1 comparison, you WOULD see that the turbos still cool it a little bit more than a simple pressure drop would. This is because it does harness some of the energy that is normally wasted, but nowhere near 100% of the turbo's energy comes like this. A very large portion comes from increasing the amount of power the engine takes to push out the exhaust gases.

It is not for free, but it is taken more efficiently than a belt-driven supercharger.

Take care,
Shad

Shad Laws

Hello-

It is people like you that made me leave online automotive forums so long ago.

I see a technical discussion, and you see a chance to get into a belligerant argument. I see a chance to talk with people, and you see a chance to prove something to someone else.

I have nothing to prove. If you cared to know my credentials, you'd see why... suffice it to say that I can give far more descript defintions of torque and power than a dictionary :-). I don't need your "praise." I'm just here to help others out.

I'm not here to get into pissing matches. If you want to start one with me, I'll just let you win... I don't care.

I thought maybe I could chime in on this forum for fun... apparently, I was wrong. I'll leave now... I've no need to waste my time in places where people just get pissed off at one another because they don't understand concepts.

Take care,
Shad

peejay

I dunno about "MUCH" cooler... EGT tuning for turbos and for N/A is for about the same EGT, right? (about 1550-1600degF at the exhaust port)

Arguably, the temps *should* be cooler since they wouldn't be under as much pressure. However, without the backpressure of the turbos, volumetric efficiency would go up, and so you'd want less ignition timing, which will raise EGTs (and exhaust energy) back on up there... I realize that this is heavy duty hair splitting here, and I do see your point.

SPOautos

It seems like the pressure at the turbine housing would be much greater than the pressure at the exhaust port due to the wg basically being a "leak" in the system. It seems like it would be similar to having a 45mm whole in a IC pipe, your going to loose your pressure or at least the majority of it.

I dont understand how the wg couldnt be causing the exhaust port to not see a lower pressure than whats at the turbine housing

Someone please explain

STEPHEN

KevinK2

think of wot with both turbos online. the wg and the turbine inlets act like parallel restricting orifices to ehx gas pumped into the exh manifold chamber. Like intake manifold theory in reverse ... pressure in runners sane sa pressure in manifold.

at very high back pressures the wg door will tend to open more easily and drop boost, but this would be compensated for by any active boost controller.

SPOautos

Thats not really what I was saying though. I understand how the backpressure is created. What I was saying is it seems like the WG (think single turbo with a large wg) would relieve the back pressure. The wg is basically a hole in the exhaust to bleed off the excess pressure and exhaust.

Similar to the bov on the intake side. If your wot and all the sudden your bov opened up your pressure is going to drop cause your venting off the charge.

Why would the wg in the exhaust not be the same? Its a hole with low pressure on the other side of it so the pressure is going to bleed off thru the wg

STEPHEN

KevinK2

1) for most street applications, pressure in exh manifold is about the same or more than the boost in the intake manifold.

2) run short garden hose from home spiggot A (say 40 psi supply) to a sealed 5 gal tank, with similar but larger spiggot B on it to allow exit flow.

with A cracked open and B wide open, pressure at hose near A will be pressure in tank, about ambient.

with A wide open, B closed enough so 20 psi is in the tank, pressure in hose near A will also be 20 psi, ignoring slight pressure drop due to flow.

point ... pressure exiting the exh port will be about same as pressure in exh manifold that supplies the turbine and the wg. if big wg drops manifod pressure to ambient (first example) then no pressure at exh port exits, or in the exh manifold to spin turbine and boost drops to zip, consistent with point 1).

cdk 4219

Turbo charged engines will always make more HP and especially torque than an equal supercharger, because of the fact that a turbocharger doesnt create the parasitic drag that a supercharger does. Using exhaust gasses to spin the compressor wheel is much more efficient than using the crankshaft. To see a 50 HP gain on a rotary engine the torque lost could be in the 30 to 40 ft lb range at high rpm, and the turbo wont have this problem. For the same reason there is driveline loss in the transmission of your car there is also efficiency loss in a supercharger.Horsepower is a function of torque and is what makes your car move, and if given the choice of turbocharging or supercharging a small engine the choice is hands down turbo. The original thread asked about supercharging a 13b, and while it would be interesting, money would be better spent on a turbo. And being around the dyno would definately make your mind up, when a Honda makes 40 more HP and 20 more FT lbs of torque all for a $4000 supercharger.

SPOautos

I understand that completely.......

BUT how would it effect the pressure if you left A wide open, left B cracked and put a 45mm hole in hose A and let that dump out on the ground.

STEPHEN

KevinK2

in that case, the exh gas flow to tank is vented, and pressure beyond wg and to turbine can only be less than the pressure before the wg (ie at the exh ports) due to pressure drop as flow continues thru hose.

http://www.gothamracing.com/catalog/...x7%20turbo.jpg

for singles the wg is placed closer to the B point. you have engine exh ports and manifold runners which can be long (link), before the wg.

SPOautos

Yea, I know they are closer to the "B" its just that in our example there wasnt anywhere to put it .....ahhh this is rediculas lol

Anyway, I've been thinking about it and I've got it figured out. I guess the wg would change the pressure but what its going to do is lower the entire pressure overall between the port and the turbine outlet. Basically its going to lower it to about the same as the boost pressure. If the wg wasnt open it would make more and more and more back pressure (and boost) but then when you start to open the wg the entire system looses pressure and makes the turbo level off to where you need it at.

I've always understood how the wg works with boost, ect that wasnt the issue. I just never really thought much about its affect on the exhaust pressure. This thread got me thinking about it.

STEPHEN

KevinK2

bingo

Gene

iTrader: (1)

To clarify the problem with the centrifugal SC, it never reaches max RPM until the engine is at max rpm, so by the time you are making full boost, it's time to shift. Depending on your turbo setup, you can be making full boost with a turbocharger as low as 3500rpm.