gooseNSJ4

Geoffery,

Thanks for the info. By trading some efficency would you say at top end or through the continuing pull to the red line between gears.

Geoffrey

With a clipped turbine, you are not getting as much energy turning the turbine as a nonclipped turbine. You can think of it as having a house fan with 5" wide blades, now you shave the blades to only 4" blades. It has the same diameter, but less surface area to push air. Clipping is relatively old school, and with the wide options available today, you can match a turbine/compressor combination for most applications. I like to stay away from clipping, to me it means that you've not chosen the correct turbo.

gooseNSJ4

Thanks Geoffrey, very informative.

Regards, Goose.

Geoffrey

Let me clarify my statement about clipping being "old school". There are probably times when it can be useful, but those are probably few and far inbetween. The turbo on my 930 has a clipped turbine wheel which was done as we were developing the turbo and having difficulty with overspinning and destruction of shafts. It no longer needs a clipped turbine with the latest compressor wheel and I'm probably giving up some turbo performance by having it clipped.

Kevin

Goose.. If you are going to change to a smaller hot housing, and a different diameter turbine wheel, well you have the makings of a K16 already....

Clipping is not needed for the K16's at our displacement levels, most people will install no cat, or muffler bypasses... We want MORE energy to turn the turbine wheel... it's called LAG reduction.. IF someone is hell bent on having clipped wheels, that's not a problem, I clipped Geoffrey's.. The reason was that we were working with a very tight A/R.. You trade something and give up on something else... It has proven to be a good design!

hatchy

I was not referring to the dyno you posted. Someone posted a dyno not too long ago on a completely stock 993TT and there was a drop in both hp and torque at 4000 or 4500--that is the dip I was referring to.

The one thing in common between the dyno you posted vs what I remember seeing is that there is drop off shortly after 5K. If the K16 hybrids will hold 28psi to redline, and if the ECU is not pulling timing, I don't see why the car would not continue to make power to, say 6000 rpm.

TB993tt

Geoffrey
My motor has over 500fwhp between 4250rpm and 6800rpm (I am not at home so can´t post actual sheet) - The dyno run you posted shows what I have been talking about, that is the k16s cannot hold near the peak power to the red line. My K24s do and this is all I have been arguing about. I would love to believe that a K16 based turbo could do this as I would be first in the queue for a pair. When I was speccing my motor, RS gave me the option of K16 based hybrid turbos - they said the car would feel very fast since the K16s would spool up very quickly and put on a lot of torque/power between 3000 and 5000rpm making the car very fast in street driving. and the curves they showed me were similar to the one you posted with the power peaking at 5000 rpm (as high as 540hp in one chart) then dropping thereafter to the red line - I am not arguing that this is one way to go for a fast 993tt, and indeed is probably very suitable in the US where you may not get much opportuninty to get over 120mph, but a K24 car which will hold near its peak to 7000rpm will have much bigger area under the curve between 5000 and 7000rpm and will ultimately be quicker. Not to mention the thrill of taking the engine to the red line
I appreciate your continued posting and I am not in any way trying to put down what Kevin is doing, just trying to understand it better with a few more facts.
What I really want to see is a dyno of a properly specced 993tt with K24s which have been "breathed on" by Kevin that will have me reaching for my cheque book

KRA993tt

Kevin,

Thanks for the clarification. Great posts as always.

TB,

I would think with your engine internals and tuning your car would be a prime candidate for some of Kevin's turbo's. I bet that with help from the folks at RS Tuning you could ring out some additional power with more efficient Turbo's be it K16's or 24's and not much else.

The pound to dollar exchange would make the cost efficient as well.

Geoffrey

TB, the torque and power drop are NOT from the turbos not flowing enough air or not being efficient enough. As you can see from the datalogging, the turbos maintain boost pressure to redline. The engine falls of because that is the natural power curve of a 993tt engine. The car was also set to run at significantly less boost pressure than you are running.

hatchy

If that is the natural power curve of a 993tt engine, what is the point of turbos being able to hold that much boost to redline? Which line is the boost line again, the red line nearest the bottom?

ScottMellor

TB: I think Bob has k-24s that Kevin has done.

How's about it Bob? Any dyno runs on your beastie?

Geoffrey

Hatchy, I don't mean to sound argumentative, but I think you are not understanding fundamentals of how an engine works. Both the car I dynoed, and the Ruf Turbo R have peak power roughly at the same point 5100 give or take a little. I don't know of any car that produces peak torque or HP at redline. Redline is a function of engine stress, not HP or torque.

The point of having turbos that flow efficiently to redline is that it will produce more torque than a turbo that is falling off. The more torque at a given RPM will produce more HP at the same RPM. Remember HP = torque * RPM / 5250. Even though the torque is falling off after its peak, an efficient turbo, maintaining flow will lessen the torque drop.

hatchy

I don't understand a lot of things, so maybe you are right.
I am sure there is a perfectly good reason--one that I simply can't understand--why turbos making full boost to redline, doesn't make
any more power or torque after 5K with proper tuning. If the K16s
slow the drop off torque after 5K, it isn't reflected in the dyno you posted.




z06 seems to make peak power at redline



so does the yamaha r6



Honda B18C5



NSX



E46 M3

hatchy

Also, if the dip is natural in the 993TT motor, why does it sort of go away with K24s?

TB993tt

Surely maintaining boost pressure is not the same as having enough air flow - I used to run some hybrid K16s which would show 1.2bar all the way to the limiter, but they didn´t flow enough air higher in the rev range to maintain the power - I may be fundamentally incorrect here but I assumed a K24 at 1 bar would flow more air than a K16 (forgetting hybrids for the moment) at 1 bar ?
As hatchy has conclusively illustrated above, quite a few cars produce their peak power at the redline - I suspect you made a typo there

Scott
Yes, I would love to see Bob´s dyno but I think he has been too busy to get a run in.