BOTTLEFED

iTrader: (1)

I have searched the entire forum for info on turbine clipping and found one thread over 4 years old with no definitive answers. So I thought maybe this topic needed to be discussed more thoroughly.

I am currently rebuilding a set of Pettit "high-flow" twins for sequential operation. I was thinking of doing something to them that would give me more power on the top end. So I thought maybe clipping would be the answer, but I had never seen a post on this section about clipping the turbines on a set of twins. Is this not a good mod for the twins? Does anybody have any experience with this?

From what I've read, clipping reduces low-end response but gains in top-end power. There is some disagreement on this from the thread I saw however.
What I'm looking to do - somebody correct me if I'm wrong here - is to clip the turbine on the secondary turbo, thus retaining the quick spool-up of the primary, but gaining the top-end power from the clipped secondary as the primary "runs out of steam" at high RPM. Does anyone know of any draw backs for a setup like this - maybe a rough transition? Or will this just not show any improvement whatsoever?
Please only give advice if you know what you are talking about. I don't need any more confusion on this. I would have posted this in the archive section but I cannot seem to get in to it.

TIA,
Tim

G's 3rd Gen

iTrader: (11)

The only people that I know that have fooled w/ this is Pettit... Maybe call there tech support hotline??

BOTTLEFED

iTrader: (1)

Is that true, they are the only ones that have done it?
I called their tech. guys when I got this set of twins, and they couldn't even give me a straight answer on what they do to make the "high flow" twins flow more. He gave me answers like, "we ceramicoat the exhaust side" and "we do a full rebuild." What does that have to do with flow?
Anyway, I don't think they are very knowledgable about this stuff. In fact I heard they don't even work on the twins any more.

Wouldn't any respectable turbo rebuilder be able to clip the turbine wheel? How much science is there in it? Would they have to know the flow characteristics of the turbos?

DaleClark

iTrader: (55)

I've run a hybrid turbo in my old FC back in the day. Larger compressor housing, larger compressor wheel, and stock turbine wheel clipped 7 degrees or so.

Basically, clipping just removes some of the outer fin from the turbine wheel. This reduces turbine inlet pressure allowing more flow, but at the expense of spoolup.

It has been done on FD turbos - this is a pretty common route for upgrading a stock turbo. JUST clipping the exhaust side may or may not be worth it, though. Normally it's done with an upgraded compressor side, which is tricky on the stock twins. The turbine shafts are VERY thin, and the extra mass from larger compressor wheels can snap the shaft.

This is part of the reason why BNR Supercars spent a LOT of time and put a LOT of effort into developing their upgraded twins.

Clipping is definitely something you can't do at home - it has to be done in a VERY precise manner to each turbine blade, and the whole assembly has to be re-balanced.

IMHO, if you're looking to stay with the stockers, there are 3 options.

1) Do nothing. People have made 350-380hp with the stock twins with a cast of supporting mods, and that's a DAMN fast car.

2) Go with the 280hp 99+ Japan twins. You will lose some ultimate power since they're don't handle higher boost as well, but you gain a LOT of response and power under the curve. They're killer for a "conservative' setup.

3) Call BNR Supercars and get your twins upgraded. People have made some good numbers with these, and they work well.

Then, of course, there's going single. That's a whole 'nuther story.

Dale

GoodfellaFD3S

iTrader: (213)

call Bryan at www.BNRSupercars.com

He can help you out. The turbine wheels on my last set of 'old' stage 3s were clipped.

BOTTLEFED

iTrader: (1)

Thanks Dale, that was very helpful.

I'm looking to put down as close to 400hp to the wheels with seq. twins as I can. That is why I found this set of Pettit twins. However, they don't seem to be much of an upgrade from stock, so I'm looking for other ways to get more power out of the turbos.
I thought about the '99 280hp twins, but like Dale said, they have their drawbacks in design as well. I wanted some BNRs but they are way too expensive right now and I could not find a cheap used set.

BOTTLEFED

iTrader: (1)

I just thought that any turbo rebuilder could clip the turbine. I have a really good shop that balanced the last turbo that I rebuilt. They haven't done FD twins before, as far as I know, so I doubt they could clip the wheel and get the right setup for the car.
I will call BNR and see what they recommend.
Thanks GoodfellaFD3S

Kevin T. Wyum

I had mine clipped back in the mid 90's. Pettit is not the only one doing it, not only that they don't do it themselves either. With something that's going to spin at the silly RPM's of a turbo you can't simply take a die grinder to it. It needs to be balanced.

It will do exactly like you're thinking it will, except with open exhaust the low end response loss is really non existant. Keep in mind these wheels were designed for response with a stock exhaust system with cats. I had Turbonetics do mine back then and they did a decent job. Don't bother with clipping one and not the other, just do both.

Kevin T. Wyum

BOTTLEFED

iTrader: (1)

Kevin T. Wyum,
So do you think any good turbo rebuilder could clip the wheels, or does the rebuilder have to have direct experience with clipping FD twin turbo wheels?
Like I said, I have a good turbo rebuilder in SLC that can balance them but I'm not sure if they do clipping.
Maybe I'll call Turbonetics and see how much they would charge to clip them.

Thanks for the reply

GoodfellaFD3S

iTrader: (213)

Just bite the bullet and order the new stage 3s. You won't regret it, they are worlds away from any kind of 'modified' stock twins. Bryan can give you more info when you call.

BOTTLEFED

iTrader: (1)

Well I called around today to some different sources.

First I called Turbonetics. They gave me the short, sweet answer of, "we don't work on outside turbos anymore, period." Meaning they will only work on turbos they sell.

Then I called Pettit to maybe get some info from them. No one was there that was able to answer my questions, so they took my name and # and will have the right person call me, ...someday.

Next I called my local turbo shop. I have had them balance my rebuilds before and they do a wonderful job for a reasonable price. I just asked them if they had any experience with clipping. The guy said he does but they are only able to do a 5 degree clip or a 10 degree clip. And he did not have any experience with clipping FD twins.

So my last hope was BNR supercars. Bryan was a world of knowledge about FD twins and rebuilding turbos! He said he had experimented with clipping and it did not seem to have any positive effects on the FD turbos. He also gave me some very helpful advice on rebuilding the turbos and even offered to send me parts if I needed them. He was a very nice guy and was genuinely willing to help a fellow rotary guy.
After he told me about the stage3s and how many upgrades he did over the stock twins, I cannot wait to save up the $$ for a set!
Hey GoodfellaFD3S, do you want to sell yours?

Howard Coleman

iTrader: (6)

clipping won't help the fd turbo as the problem is on the cold side...

at 14 psi and above you are running in an area that the compressor wasn't designed to efficiently operate. and that is a huge understatement. the compressor is running 140,000 rpm and the air is getting superheated from shear. more boost from 14 on up equals less oxygen equals less power. if you are going to mod the oem turbos you need diff compressors and then you run into the shaft durablility problem... so Brian, who wrote the book on the subject, was right on the money as to clipping the turbine.

another resource you might discuss this w is Kevin Draper at Majestic Turbo waco... 800 231 5566. tell him i suggested you call.

good luck,

howard coleman

GoodfellaFD3S

iTrader: (213)

Yup, Bryan is a standup and very knowledgeable guy .

As far as selling mine, I am going to do everything possible to keep my FD running and running well, to include not yanking parts off it . I hope to dyno at 450 with these turbos soon, we shall see. Why not just buy a set off of bryan? modding with credit cards is fun

Rich

BOTTLEFED

iTrader: (1)

Thank you Howard,
that is some great info. All the info I have been getting is what you summed up here: the compressor side is the problem with the stock twins and the turbos are built to be too small and weak from the start. They were built for lightness and not to run any more boost than stock.
That is why Bryan redesigned the turbos to be more durable and so he could add a larger compressor wheel and modified the turbine blades.

I'll give Majestic a call and get their take on it,
thanks again Howard!

BOTTLEFED

iTrader: (1)

I was just kidding about selling yours Rich

Keep us updated with the project. I would like to know what components you use to get over 400hp.
Thanks again for your help.

BTW, Bryan said the same thing about using a credit card to get the stage3 set.
-Tim