Im trying to make a decision on trying out another comp turbo after having horrible results from the first one I received.

Some of you have probably read my last thread on having a 4:1 back pressure issue on the dyno at speed inc.

I used a comp ct43 8079 billet wheel ball bearing turbo on a forged 370 and couldnt get over 11psi. I had horrible results with 45psi of back pressure at 11psi intake pressure.

I picked up the car yesterday and have to make a decision on what turbo next.
Joe at comp has been very nice and apologetic about the turbo they sold me. He said they simply sold me the wrong turbo for my application and want to send out another.

The turbo that they want to send out will use the same 100 trim straight cut turbine wheel as the one before. Im trying to figure out if that was the issue my car had on the dyno.

This turbo will have a 88mm turbine instead of the 79mm, it will use the same billet 80mm compressor wheel. They claim the reason for the back pressure was that the billet 80 comp wheel was flowing way to much for the slightly smaller 79 turbine to keep up with.

This doesnt make total sense to me. I was using a tc78 for the last 2 years and it has a 68mm turbine spining a 78mm comp wheel. Now I know that wasnt the lowest back pressure setup in the world but it worked well and made power.

How is is that the f168mm turbine can spin the larger comp wheel? Does any one have any experience with the 100 trim older ITS r trim turbine wheel? Thats what im assuming comp is using as comp is a couple guys from the old ITS company. Straight cut, good or bad?

Bottom line, Im getting this turbo swapped out for 0 cost and its easy to swap out so it wont cost me much to experiment with it. Should I do it or should I just ask for my money back and go another route?

ALex

 

Your bottleneck was the turbine wheel, turbine wheel get's bigger bottleneck goes away. The turbine wheel just wasn't big enough period for your motor.

 

Its a 79mm turbine, I guess I dont understand how all the gts 76mm guys and similar size turbine wheels get away with it. Im not using a 400 plus ci engine, its just a basic 370 with stock heads. How is 79mm not big enough? I could see if I have a 2:1 back pressure ratio but it was 4:1 with a 3.5 dp and an open cutout before the muffler.

 

From reading the other thread, it sounds like the Comp turbine is 79/79. As in the inducer and exducer are the same size. The TC uses and F1-68 which is a 68/xx. I'm not sure what the inducer size is on the TC. There's also the pitch of the turbine and the rest of the geometry that plays into how it will flow.

Basically I'm guessing that just because 79mm is larger than 68mm doesn't mean that the Comp turbine will flow better.

This is just what I'm guessing from what I see.

 

id say if you can do it at no cost to you, go for it.....you will learn alot about comps turbos from this lil experiment. It will also add to this great pool of knowledge we know as ls1tech.

 

lol.... at this point all you have to lose is backpressure.

 

Compressor wheel and turbine wheel are on the same shaft. It's like a see-saw, if one side flows more or less than the other it will be totally out of balance and not work to it's optimum ability.

 

So it is their z trim wheel,supposed to be their best. Not going to lie I have no confident in comp right now but they are being stand up guys so far. Im going to stick with the 80mm billet comp wheel and up the turbine to 88mm. Hope this isnt a waste of time.

 

The turbo they want you to try, do they have results of it on a similar combination?

 

No, its not an off the shelf. Normally their 88 turbine is in a larger mid frame. This will be their first in a smaller turbo. Not going to lie Jim, I dont think its going to work. I haven't lifted my car yet but where did you drill/tap for the back pressure fitting?

 

I think the back pressure will go down but I also wonder about spool time and how it will carry up top. What was the AR on the old turbine housing and whats the AR of the new one? Is it a divided housing or single?

 

It was a 1.32 undivided. The new one will be the same. I still think its crazy it was 4:1 back pressure. I mean how bad is that turbine wheel? Or is that just how it is on a 370.

 

Blade count on the old and new turbine wheels? Alpha height (no beta, on this blade as it's a '100' trim - odd) differences, also, old to new? Worth asking and noting if / when you get to run the comparison, as well as the different shaft / wheel masses.

 

I think there is something wrong with your setup or you have fried the bearings in the turbo. But you have speed inc helping you, why not just do what they suggest?

There is a guy on the bullet that runs twin comp 88's that is mega fast. You might do some checking over there?

 

Sorry for the F$rd reference but 438 ci engine with the comp 80mm made over 1k on the engine dyno?

http://www.musclemustangfastfords.co...e/viewall.html

 

Yeah I guess the only way to know would be to try it.

I measured backpressure from the drivers side o2 bung.

Oh, what do we have here, these might free up some power

 

Believe me I wish I could do a twin setup. I can only afford to make,my single setup work for me. How do you guys make an adapter to fit the housing with a fitting for a gauge? Is it somthing I can buy so when the turbo comes in I can test it?

 

I still think that something was wrong with that turbo. bearing, something of that nature. The F1 wheel is good for it size but a 68mm wheel stomping a 79mm seems off to me.

 

http://www.musclemustangfastfords.co.../photo_20.html

ford version of your build

 

Maybe something restrictive in your setup? Front mount Turbo? Rear mount? What size crossover pipes? Or if rear mount what size pipe into the Turbo. Headers or manifolds? Primary pipe size? I had 3:1 back pressure on a 383 SBC with a qtrim (68mm) wheel, 72 mm compressor.