awj

very interesting

Lex Luthor

Willard, you're okay with the parastitic loss associated with driving the unit off of the crankshaft, but venting the excess wasted energy via a wastegate is a no-no? Luv a good debate. I think the best compromise is a variable-nozzle VATN design, they've come a long way in the past few years, as opposed to 'a variable speed constant dispalcement SC driven by a hydraulic servo motor with the hydraulic pressure/flow supplied by the power steering pump and metered by an electronic servo valve so the SC rotation rate always exactly matches the engine's need for pressurized airflow throughout its RPM range' , but that's a real 'Buck Rogers' idea, which diesel manufacturer has adopted this system, i'm curious? If your assertion is that nothing is for free, and that even though that exhaust energy was headed out the tailpipe anyway, it somehow costs some hp to use it. I disagree, but if that were to be true, then it would certainly make sense that it would require plenty of hp to drive a pair of rotors with the fluid moved by the power steering pump, since it's driven directly off of the crankshaft. No, I don't feel an SC is a good choice for an SC, unless you're looking for a quick bolt-on 60-80hp, anything past that, and a smaller turbo can do anything a roots can do no problem, and can spool at least as fast as a centrifugal, at a much high efficiency. Where I will concede you're right is that although a turbine recovers wasted exhaust gas energy from the expansion of the hot exhaust gas, the kinetic energy of the flowing exhaust gas and the acoustic energy of the exhaust gas, the working turbine also causes an increase in exhaust gas backpressure, which can reduce the engine's volumetric efficiency. Your average street turbo kit has more exhaust backpressure than boost pressure and the power gains from these systems are due to the increase in the density of the intake charge, no from an increase in VE. This is only because the smaller turbine housings and turbine wheels that give you a quick spool also restrict exhaust flow. Excess backpressure can cause reversion, and we both know how bad that can be, but if your housing and wheel are large enough to the point that you actually are improving the VE and achieving 'crossover', and the spool-up time is reasonable, you've got it about as good as it's going to get with currently existing technology.

awj

So we are looking at two different areas of wasted energy. The hot exhaust gas, and the parasitic loss of the driven power steering pump. In either system, we are capitalizing on ineffeciency to improve performance. I must say that the hydraulic driven servo sc is a novel concept.

So, why can't we combine the two? Use the Hydraulic drive from the ps pump to drive the turbo turbine as well as the exhaust gas. There would be some logistical challenges to overcome as the hydraulic force and pnuematic force may fight each other. But then there is this backpressure issue.

Or we can underdrive the power steering. This would reduce system pressure and while requiring more effort to turn the vehicle - no sweat, reduce our waste loss. Hmmm, underdrive pulleys, mental note.

wwest

Hasn't Mazda, with the "miller cycle" engine, already proven that the wasted energy in the exhaust need not be wasted?

That's where they gain their improven engine efficiency, a longer "power stroke" (more use of the gas explosion expantion) vs intake/compression stroke. I doubt if you could even run a turbo at the high end of that engine's RPM range.

awj

you would have to shorten the stroke to run a lot of boost, but I'm sure a balance can be found there too.

Fantius

Has anyone ever tried a sequential supercharge-turbocharge solution? What I mean is to have instantly availible supercharger power at the low end and a big turbocharger at the high end. You would have to disengauge the supercharger once the turbo kicked in, to stop it's parasitic loss. Probably to much hardware to be worthwhile.

Here's another one:
Has anyone ever tried pushing air with a high speed electric fan? I don't know the parasitic implications of this b/c I don't know alternators. Probably a waste to go mechanical=>electrical=>mechanical.

Black94RX-7TT

I thought the Miller Cycle just had an intake duration that lasted into the compression event, and thus required a supercharger to keep stuffing the charge in while the piston started upwards....I don't remember anything about exhaust changes.

Black94RX-7TT

Nobody has mentioned that superchargers usually put a whole lot more heat into the charge air than a turbo at a given pressure delta. Of course hotter air is less dense, and you can't get as many air molecules in the cylinder, so you get a smaller boom....

awj

Good point. They do have intercoolers for that though, correct?

Black94RX-7TT

Correct, but intercoolers can only achieve so much temperature drop. Let's say our IC can achieve a static deltaT of 100 degrees F (neglecting ambient temperature, and assuming it has a linear deltaT across the whole range)

Supercharger: 350 - 100 = 250
Turbo: 225 - 100 = 125

Now that's not totally true, since the deltaT will get larger as the inlet temperatures go up and ambients go down, but you get the picture...the less of a deficit you have to work against to start with, the better off you are. Plus ICs create lag and introduce pressure drop....and impede airflow to the other components under the hood.

wwest

Given the same volume of ambient air (67F) to pump up to 9 PSI why would the airflow temperature rise more in an SC than in a turbo?

And given the proximity of massive HEAT in the turbo wouldn't the turbo body run hotter?

4 cyl torque peaks are usually on the high end anyway so turboes aer more appropreate.

healerhand

Black94RX,

Most of the SC kit these days have IC. SC has lower intake temp. than turbo.

SC + IC = Lower intake temp
TT + IC = higher intake temp.
SC - IC = lower intake temp
TT - IC = higher intake temp.

I have a ATI Procharger F1SC with 18 psi (1550 CFM) with intercooler. It runs flawlessly. There will be pros and cons.

V8 = supercharged
4 & 6 = turbocharged

healerhand

Secondly,

If your car is not designed for turbocharge, go for supercharger. Because of the N/A, TT or ST heat will destroy all the surrounding none metal with 2-3 inches. If you are going for turbo, you make sure you take care of the heating problem associated with Turbo.

Lex Luthor

David, underhood heat is the smallest of the problems, that can be overcome with HPC coatings, thermal wrap, and you may have to relocate a couple wires, but regardless I disagree with your evaluation, you say 4 and 6 cyl are better for turbo, and 8cyl is better for SC. Actually, if anything, that should be reversed. An 8cyl is better for turbo because the higher exhaust gas volume will spool a turbo quicker than the 4 or the 6, which could benefit from an SC because these smaller engines wouldn't have to worry about spinning the motor to the point where you have sufficient exhaust pressure/volume to spool the turbine. Argue with that one!

Black94RX-7TT

From Corky Bell's web site:

The turbocharger, with 75% thermal efficiency, makes less heat in the intake charge per psi of boost and cfm of air flow than any other form of supercharging. Regardless of the 'data' published by a variety of supercharger kit makers, science and engineering have not yet devised another method of compressing and moving air as thermally efficient as the centrifugal compressor on the front of the turbo. Roots style superchargers, by contrast, inherently have the lowest thermal efficiency, ranging from 35% to 65%, of any type of supercharger, yet their sellers express claims from 84% to 129%. Thermal efficiency is but one of the reasons turbocharged Grand Prix cars, Indy cars, and Le Mans style endurance racers have won hundreds and hundreds of races. Supercharged cars have not won any of these races in the past forty five years! Further, this automotive engineer will suggest it is unlikely they will win any of these races in the next forty five years, if ever again.