BC

So do we have some info on this? Obviously we have large efficiency numbers for the centrifugal, as it is known to be efficient already, and its also very easy to install on our cars.

With the whipple, we hear quite a bit about the fact that it also is efficient - more efficient then other prositive displacement blowers.

Now I hope "John.." doesn't hear this, but I know that twin turbos would probably be a very wicked setup on a 928 - but its simply not feasible for anyone that wants to have a daily driver, and not add a huge amount of weight to the front of the car, infact much of it in front of the front axle.
Plus the heat, complexity of intercooler pipes, etc. I know its been done, but for what cost and time?

Anyway, thats off topic. My point was I wanted to get some info on the efficiency of boosting applications for the 928, and it doesn't include turbos as an option.

Thanks.

Tony

http://www.lysholm.se/en/p_2300.asp

download the PDF files on the link

BC

Thanks Tony.

John..

http://www.aerocharger.com/tech1.htm

I would be less concerned with peak efficiency and more concerned with boost as a function of RPM. To me, the chioce in supercharging or forced induction is quite obvious...I won't say anything else.

Thanks for inviting me to post Brendan , maybe we can talk over a beer someday?. It is a shame Aerodyne is down and out for now, it is one of the most clever forms of forced induction out there, but some quality issues and legal issues have it shelved right now... Check Bell's Maximum Boost and the performance of the NSX with the dual aerochargers, on just 5-6 lbs of boost and under 400 HP. It is quite impressive.

Garrett also had some VNT turbines used on Chryslers, but they are not making this unit anymore.

BC

SO 65% at the 1.7 to 1.9 PR.

Let me look for the T-Trim SQ chart. Hmmm..

BC

Those variable Vans DO work, but it seems very complex, and as you said, we can't even get them. I'm okay with letting the exhaust gasses leave unhindered out the ***-end if you don't mind

I see that they just LOVED the centrifugal.

While boost/RPM is a big deal, the efficiency and HEAT that is generated is a big issue, as this affects tunability, and its a variable that can kill an engine.

Tony

I converted the Pressure ratio values and M^3 to CFM
http://www.sciencemadesimple.com/conversions.html
you can do Kw/Hp...you name it. VERY HANDY PAGE

BC

I was going to do that Tony. Thanks.

Anyone find the T-Trim Vortech With SQ gears yet?

SteveM928

The maps for the Vortech ones are at maps

Besides the pressure ratio, you have to look across to the cfm of flow you want at that pressure ratio to find the efficiency there. Going by Tony's conversions on the posted chart, the Lysholm chart looks like maybe about 600cfm or a little less at that 65% efficiency and the 1.7 to 1.9 pressure ratio you mentioned. From the looks of the Vortech maps, they are about the same efficiency, or maybe a little better at that pressure ratio and cfm point. It al depends on how much cfm you want at that pressure ratio. The Lysholm efficiency seems to drop off at the higher cfm and that 1.7 to 1.9 pressure ratio. At 1,000 cfm it looks like it's at about 55% efficiency. The Vortechs look like they do a much better job up there. Looks like a little over 65% for the S-Trim, and over 70% for the T-Trim up there. Kind of surprising that there's that much difference compared to the Lysholm with the same pressure ratios and higher cfm flows, and that the Lysholm really falls off that much at those higher flows.

John..

I still think the aerocharger would be sweet on a 928. No wastegates, no oil lines or return lines. You could fab up a simple manifold and then run the pipes up the back to one of these crazy air to water units and into the plenum, from either side, like a twin inlet intercooler.

Last I heard they were $1,200+ for one unit and the 928 would need two of them for sure. The benefit is they could sit waaaay low and there is no concern for getting oil in and out of them. There is lots of information on failures of these units after a short time, such a shame because a typical turbo can go 100,000 miles easily. If they engineer it to be reliable, it would be a sure bet for maximum performance on a street car.

I think we will see this technology resurface in the future.

Don't laugh, but there is now a Brittish company making an electric supercharger, that draws some crazy amount of electrical power to drive, but it is limited in its airflow capacity and is only used on really small engines.

Tony

1000cfm would get ya a lot of ponies!


Lags..what CFM do you think your "blowing out" to hit 500 rwhp?

SteveM928

Wonder why they only show applications for motorcycles and snowmobiles? I'm not quite crazy enough to get into the motorcycles, and the snowmobiles sure aren't going to me any good around here.

Not long ago I saw where some place was selling an electricly powered roots or twin screw type supercharger. It had three starter motors connected to the front of the supercharger to drive it. It was designed for drag racing on imports or something like that. One run and it's battery charge wait time.

BC

Can't we figure out the CFM needs for the 928 engine at 6500rpm?

I think someone mentioned this to me a few months ago.

Lagavulin

Ok, here's how you do it.

Let's first calculate how much air in cfm is moving thru the engine while in normally aspirated (NA) mode at max RPM.

CFM = (cid x rpm x 0.5 x VE) / 1728

Where 1728 is the conversion from cubic inches to cubic feet, and VE is the engine's volumetric efficiency (..use whatever value you'd like).

CFM = (302ci x 6500rpm x 0.5 x 88%) / 1728 = 499.84 cfm

So, an S4 at max RPM, the engine is consuming 499.84 cfm of air.

I'm running 11 psi to hit 500+ rwhp. Using that information, we need to find the pressure ratio so that we can use it to compute the total cfm of air moving through the engine.

PR=(14.7psi + boost) / 14.7
PR=(14.7psi + 11psi) / 14.7 = 1.748 Bar

Finally,

New CFM = (Orig CFM x PR)
New CFM = (499.84cfm x 1.748 Bar) = 873.87 cfm

So, a 500+ rwhp S4 at 11psi is pushing 874 cfm of air through the engine.

BTW, moving 1000 cfm through the engine requires 15 psi of boost, which should generate 608.09 rwhp in an S4 with an exhaust.

SteveM928

So at that 500+ hp, 874 cfm, 11psi level, it looks like the Lysholm's efficiency is about 60%, the Vortech S-Trim about 70% , and the Vortech T-Trim about 72%. That means that a smaller amount of the power put into the Vortechs ends up being used to make heat instead of boost at that horsepower, boost, and cfm point. Since the goal is the amount of boost you want, it would mean that more power would be required by the Lysholm to get that level of boost, since more of the power being put into that one would be used producing heat. In order to run that much boost with the same detonation protection on otherwise equal engines, you'd also have to get rid of more of that heat with a better intercooler on the Lysholm than the ones on the Vortechs. You'd need either a bigger or more efficient intercooler with the Lysholm to get to the same intake temperature as the Vortechs, but even then you would have still had to be putting more power into the Lysholm initially. Interesting comparison of the different units for the specific goal or application used for the example. It also really helps to show that knowing the power level you want, or may want to someday upgrade to, can be pretty important when planning out the combination that will work out best for you.