After getting into discussion on turbine wheel clipping, this got me thinking...

I swore I read somewhere that turbine wheel clipping reduction in rotating assembly weight aids in faster spooling (but the reduction in turbine fin "area" is more significant).  This got me thinking about the relationship of weight of the RA versus ability of the turbo to spool...

In the Garrett series, we can run T61's, T66's, and maybe even up to a T70.  So what prevents us from using a T72 or T76?  The turbine sections are the same, should it should spool right?  The only difference is the larger compressor wheel.  This goes into the theory of running compressor upgrades or hybrids, which keep the turbine side the same by allow for larger compressor wheels.  Isn't the T76 just a T61 with a larger compressor wheel?  Or am I totalling missing something here - does a T61 P-trim turbine totally different from a T76 P-trim turbine?


-Ted

 

Ted

T series (T70,72,76) are usually based around the T51 family of turbocharger and mostly use much larger turbine wheels (diameters and tip widths) and housings.

I am running a T51 Garrett which has roughly a T72 (Turbonetic terminology 72mm compressor) sized compressor wheel in it with a VERY large turbine wheel and big exhaust housing. 79mm turbine with large back sweep and 1.22 /ar rear housing (this is well over a 1.52a/r in T04 family speak).

What makes a turbo too big ??? Basically if you close the WG and you cant make near full boost at revs below 6k rpm (in 2nd gear) then I would class that turbo too big for your rotary engine.

Basically the biggest turbo you can run while still be able to make boost "where you want it" the better, it means more VE% from the engine and far reduce back pressure which means less stress on the motor/turbo for a give power level. T51 sized turbo chargers are not "too large" turbos for 13B's they are very common here in Australia, are very streetable and make good power bands when coupled to an optomised street ported engine, for a stock ported engine they tend to be a little short on usable power.

HKS T51's (SPL & KAI) are more adaptable to stock ported engines as they use a smaller turbine wheel and a 1.00a/r single entry turbine housing, have seen a few of these on circuit FD's only running 1 bar of boost and going very hard indeed with little "lag" on a circuit application, in fact if you search you will find some incar footage of one on an English FD racing around Donington Park from memory ?

 

is a t78 too big for a half bridge?

 

Ah, that basically explains it.

I had a feeling the T76 had a totally different turbine section, although you can still get it in P-trim and Q-trim options, as Turbonetics charges significantly more for them.

I'm surprised the other T70 and T72 was in the same boat.  I think Turbonetics still charges the same price from T61 up to T72.



-Ted

 

yeah they are mostly the same price..

http://store.yahoo.com/cheapturbo/tsertur.html

 

There's a really good rule of thumb to use in cases like this. Measure
the compressor wheel exducer diameter and divide it by the turbine inducer diameter. This gives a wheel diameter
ratio. A good wheel diameter ratio is between 1.1 and 1.20 (good boost
response and low backpressure). Mediocre is
1.20 to 1.25 (decent boost response and moderate backpressure). Anything
above 1.3 is horrible (bad boost response and
very high backpressure). Anything above 1.4 is shitty (doorstop material).
This rule of thumb is invaluable for turbo sizing, you would be suprised how many are made that are doorstop material and people run around thinking they have great a turbo. Thought this might be useful to someone.

-Sean

 

That is interesting...

Just for kicks...

HKS T51R Kai
Compressor 94.0mm
Exhaust 82.0mm
Ratio ~1.15


HKS T51R Kai SPL
Compressor 102.2mm
Exhaust 82.0mm
Ratio ~1.25


Garrett GT3540
Compressor 3.22"
Exhaust 2.45"
Ratio ~1.31


Hmmm...
I think we just insulted all the GT3540 owners out there.



-Ted

 

Actually Ted your sizes are a little off.

GT35R
Compressor 82mm
Turbine 68mm

It comes out to 1.20

They can all sleep easier now.

-Sean

 

Hmmm...compressor is right, but the exhaust exducer is off.
68mm = 2.68", which I see listed as the exhaust inducer/major?

I'm getting the numbers from:
http://www.turbofast.com.au/GTseries.html

That GT35R might be a totally different turbine section than listed?


-Ted

 

does that formula factor in larger ports?

 

This is a conversation I have had a few times with a few people. The 35/40 is a 35R, believe me anytime I needed to order parts for a 35/40 it comes up 35R at Garrett. This has been like that for years. It gets called a 35/40 from the larger series style comp cover with the 4"inlet. A good example of this is the fact ATP even changed there listing from 35R to 35/40R, because so many people are calling it a 35/40.

-Sean

 

zero r: so the gt35/40 is really just a gt35r. i see.

razorback: people use t78s on smaller ports than yours. remember T78 is not a garrett turbo, it is smaller than a t72 or a t76. but i don't think i've ever heard anyone using it on a half-bridge.

 

This formula is irrelevant to the engine it is for the comp to turbine ratio only.

-Sean

 

All the T series(TS04-T76) use the same turbine sections O/P/Q trims. They are smaller than the T51 family turbine wheels. The T51 turbine wheels that I have seen are the same exducer size as Q-trim but have a slightly larger major.

 

Isn't that different than what RICE RACING said?


-Ted

 

this is what really bugs me, is that there are 9 different names for the same g$&*%#$mn thing. its like a nissan...

 

Yes it is. I know, I know, I wouldn't have posted if I hadn't held them both in my hands multiple times in the past and actually measured turbine wheels.

 

LOL we must have different turbo suppliers.

Last time I looked at a T76 from Turbonetics it definatley had a T51 based rear exhaust housing and T51 bearing cartridge assembly, These are bigger than TO4 components, A TO4 P trim exahust wheel fits totally inside the exducer of one of these turbos with lots of room to spare.

The one I saw was definatley bigger.

Are you sure your not thinking of Hybrid turbos with larger front compressors ?

P.S. My OEM T51 turbo has a turbine wheel minor dia of over 3.1" ! The one Turbonetics T76 I saw had a similar sized rear wheel (much larger than a Q trim wheel).... I could be wrong as I have not seen lots of examples of that particular brand. So just to clarify are you saying that all T76 etc turbo are based around TO4 turbocharger frames and exhaust wheels ? If so this sounds incredibly stupid.... suppose thats why we in Australia buy factory Garrett turbos that are sized correctly LOL

 

I found one thing that may be causing some of the confusion. Is the T51 you are speaking of like a TA51? They do use very large turbine wheels in that family of turbos. I am basing what I am saying off the T45/T51 style turbochargers. Regardless, the Garrett T series turbochargers that Turbonetics sells are based off of big shaft TO4 family turbine wheels yes. I would not doubt that what you have there may be different, and I believe better suited to a rotary. This is the main reason I like Garrett turbochargers above any other, because of the parts compatability.

RICE RACING you are my hero! Seems like everytime I read one of your posts I learn something new. Do you still have a website? Can you post the link?

 

Maybe that's why the experiences are varied...

Yeah, it's too bad all these turbo shops use similar model numbers, and we get all messed up!



-Ted

 

IGY, remember when you called me yesterday and asked me if my T45s CHRA was attached to the backplate with 4 bolts like the garrett turbo's are? It isn't. I looked at it at 9 pm in the rain with a flashlight, and didn't see how the T45s CHRA attaches to the backplate.

 

I can't remember what the exact arrangment was, but the TA51 backplate definitly doesn't bolt up the same as the conventional Garrett T04 stuff. I had a TA51 with compressor specs very similar to a T66 and I looked into it a while ago as I wanted to get rid of its monster exaust wheel and housing.