Herr-Kuhn

Have any of you run a clipped turbine wheel on the K26-6?

If so, what were the results?

Mike1982

Man, what a mistake! Clipping the wheel from what I understand makes it spool quicker but not as effience, therefore you get say 15psi sooner, but it will not produce the same HP or even HP under the curve as a non-clipped. When the clipping the wheel you lose surface area of the turbo so it might spin faster at lower RPM's it can't push that much or compress as much as a non-clipped. That is just my guess though, I will let the REAL turbo guys tell you exactly why.

Porsche-O-Phile

Haven't (and wouldn't) bother doing it on asthmatic turbo like the k26/6 anyway.

badcoupe

you'll kill the top end power- not that a 26-6 has much. I wouldn't do it. buy a bigger one if your wanting to do anything a 27-6 or 27-8 is an excellent one for the money. Places like michigan turbo will sell you a new one for approx 550 shipped. or step on up and get a big-un

sweanders

Is this for the twin turbo 928?

Herr-Kuhn

Yes, they are going on the 4.5 liter 928. Clipping should delay the onset of boost by a few hundred RPM...the reason for the clip is to open up the top end by minimizing the back pressure and thus helping the top end flow. I don't know where you guys get the idea this will decrease the spool time and kill top end power...it does just the opposite on both counts. Considering I'm only looking for 450 HP out of these I believe it is a good match, but I'm looking to minimize back pressure up on the top side. With the V8 I don't need instant spool...if they are on full tilt by 3,500 I will be happy. My goal with posting was to hear from someone who has actually done this on a 26/6. If you study the new garret GT line of turbos you will see they have a "clipped" design turbine setup out of the box.

So...has anybody done this and if so what results have been documented?

snappy

clipping is a hidden secret in the industry. I doubt certain vendors will come forth and tell you their secrets, I can tell you this. clipping does indeed speedup the spooltime in more than 90% of the applications right out of the box. now if you start flipping a larger left with a smaller right and clip them large a tad then you can end up with a turbo that has as fast a spoolup time as you had with the smaller unit, but you can push the top-end way further. clipping should only apply to modifying the a current blade setup. i see manufacturers marketing department mention it these days cause every body hears that clipping reduces spoolup and wants it. the garret mentioned comes with a tad smaller / degreed vanes which just makes it a different version than the other ones they have.
I have a feeling that there is at least one major vendor on here that does that to their turbo's. It gives them the competitive edge, so I dont blame them from speaking about it.

i heard a rumor that clipped turbo's hate high end torque. there seems to be a correlation on dropping torque and really bumping up the top HP. for instance changing headers to equal lengths should drop high end torque but really boost the top end HP. This effect should get exaggerated by a clipped turbo.

Herr-Kuhn

I disagree that clipping will decrease spool time, unless the moment of inertia of the wheel is the much less due to the clipping. I did some reading over the weekend. Some examples of clipping the wheel causing a 15 HP increase up on the top end on a Toyota MR2. This was a 12 drgree clip on a twin scroll compressor.

I've marked up my turbines at 7, 10 and 12 degrees. I'll probably go 10 degrees, but I'm not sure yet. I've seen the 951 results with a K-26...250 RWHP, no turbo work. Since I'm running 250 less ccs per bank and I'm clipping a tad bit I think my back pressure will be in check. Additionall, I don't plan on exceeding about 14 psig with the car. 4.5 liters is a lot of displacement. I don't think I'll worry about having my boost come in 100 rpm later. It should all come into balance here in the next two weeks.

I'll bring my results back when I have them.

hosrom_951

It all depends on how it was clipped, doesn't matter if it was 5,7,10 or 12 degrees. If it is not done right, the turbo itself would be on it's knees in terms of holding itself together. Meaning it could become so unbalanced it would destroy itself, even while trying to balance it.

Experience, tools and techniques in clipping is the key and it will decrease spool time. I saw a decrease of 300 rpms in a 7deg clipping myself, and you should see how it's done.

hosrom_951

Depending on what sized wheel and the hot housing of the turbo to start with, since the #6 hotside already runs out of steam at high rpms, clipping it MAY improve it slighly (dont quote me, havent seen or tried this) but the housing would generate a LOT of backpressure.

Even in a larger housing (a #6 trim in a #8 housing), it would have limits, since the #6 would have reached a limit eventually.

sweanders

On what kind of turbo and what kind of car? When did you do this?

hosrom_951

60-1 Hifi

On my car

3 months back

sweanders

Care to post pics?

whakiewes

Just for reference sake, on a BMW M3 Turbo, 3.0 and 3.2L, before people moved to bigger 60-1, then T61, now GT35R and GT40R, we only had a kit with a TD06 20G. The turbo gave a very good curve for daily driving, i.e. people who wanted torque and power at 2000 rpms, etc... but it died at 6200-6400 depending on a lot. So the solution was the clip the turbine wheel, most guys did a 10 degree clip. This moved the shifted the entire powerband about 500-700rpms towards the right. Spool was about the same, but it flowed way more in the upper rpms. The turbo could sustain 15-17psi to 7000 rpms whereas before it would drop to about 13-14psi.

Wes

hosrom_951

No, because i am a liar, always the first one to post in a thread and care about my post counts and love to mis-lead people



I have my own data, and i would like it to be my own.


Now, let's try to keep this on topic a bit