Rb20 Turbo Issue

[traphead]

Firstly, I have a R32 with all supporting mods - pfc, avc-r, sard 550cc, bosch 040, intercooler, 3" exhaust, splitfires, pod.

I bought a new turbo - at GT3040 with a 0.48 turbine housing (It was recommended!).

This ended up being extremely laggy and would also drop off boost at higher rpm.

The turbo has since had smaller gt28 wheels put in on both the compressor and turbine side, as well as a smaller 0.64 a/r compressor housing. However it still has a 0.48 a/r turbine housing.

The response is now better, but the system is unable to maintain 16 psi of boost. The max it seems to be able to hold is 1 bar.

I'm thinking this is due to the small size of the turbine housing, can anyone help clarify this?

My car is currently at the shop and this issue needs to be sorted asap.

I believe the turbo is now basically a gt2871 with a small 0.48 turbine housing - what kind of performance should i be expecting from such a system??

Thanks

[Roy]

My 2c...its the exhaust housing...far too small. I looked at the Trust equiv sized housing for my turbo and it is simply too small to be flowign any real sort of air....bin it and move up

[The Dan]

I would like to know about the 0.48 turbine housing. This is EXTREMELY and does not come on the GT3040 (which doesn't exist anymore). Also the 0.64 comp housing doesn't make sense. I'm wondering if you are getting numbers mixed up. If not then that turbo is a very poor selection for anything above stock power levels.

[traphead]

I'm not getting my numbers mixed up.

This turbo was sold to me by a renowned company as a perfect solution for the rb20. It cost me a significant amount of money, let along the extensive modifications required to fit it (custom dump, spacer, custom elbow). Aparantly they have fit it multiple times to the rb20 with 'fantastic' results. I some how find this very hard to believe.

I believe the turbo was a complete mismatch. Large core had too much intertia and caused the laggyness (the 0.48 turbine housing was meant to compensate for this). The small housing then restricts air flow at high revs and causes the boost to fall off. Not an optimal solution in my book!!

[Roy]

Id be askign for evidence of the results which they used to sell you the turbo...then i woulf be politely saying the turbo does not go anywhere near delivering what you asked for. Wont change anything, but may help get it all sorted 2nd tiem round.

What is the std A/R of the Rb20 turbo? Have they just machined it out and fitted bigger wheels to the std turbo? Should not be expensive and based on the problems you had fitting it doesnt really sound to be the case?!?!

Anyway, best of luck with it...maybe do a search or read the RB20 resutls thread. May give you a better idea of what works and what doesnt work on RB20s

And im one to always stand up for the professionals as often they get the short end of the tick. So i still say you shoudl speak to them and make sure that next time roudn you get what you want...BUT more importantly work out whether there is another problem with your car. Be it tune, some of the other bolt ons, a problem with the engine itself etc etc

[traphead]

It has been established that the turbo is the problem. Many professional mechanics have looked at it and come to the same conclusion. To the companies credit they have attempted to resolve the problem by modifying the turbo (new smaller wheels, comp cover), but i have had enough now. I have been without a car for 6 months now while this problem has been worked on.

Yes the a/r of the housing IS the same as the standard rb20 housing, but the turbine housing is new. Its a funny looking thing. The wastegate is covered (not openly exposed to the dump). The dump has a simple circular inlet (similar to an external gate turbo). Looking from the back into the housing you can only see the turbine wheel as the wastegate is hidden by a cover. This means gas from the wastegate must flow into the stream of gasses exiting the turbine wheel. I'm not sure if this has any sort of effect, but it is the reason i needed a custom dump fabricated.

Thanks for the comments.

[The Dan]

It has been established that the turbo is the problem. Many professional mechanics have looked at it and come to the same conclusion. To the companies credit they have attempted to resolve the problem by modifying the turbo (new smaller wheels, comp cover), but i have had enough now. I have been without a car for 6 months now while this problem has been worked on.

Yes the a/r of the housing IS the same as the standard rb20 housing, but the turbine housing is new. Its a funny looking thing. The wastegate is covered (not openly exposed to the dump). The dump has a simple circular inlet (similar to an external gate turbo). Looking from the back into the housing you can only see the turbine wheel as the wastegate is hidden by a cover. This means gas from the wastegate must flow into the stream of gasses exiting the turbine wheel. I'm not sure if this has any sort of effect, but it is the reason i needed a custom dump fabricated.

Thanks for the comments.

Can you post up some pics coz I think you've been jipped.

The standard rear housing A/R on an RB20 is 0.63 so I don't know how you matched this up with your figure of 0.48.

If what you have described in the last part is the same thing I'm thinking of, it's a bolt on internal wastegate plate that garrett made so that the GT30R, 3071 and 3076 could be internally gated. This was the most dodgey setup on a turbo I had seen and I told my rep that it would not sell. I was right.

There are so many turbos to chose from and it sounds like someone may have given you the wrong advice.

[Roy]

...i have seen a few of those types of rear housings and i would lvoe to see a back to back test to see how much power they lose. Lookign at them they look terrible, and when combined with the small A/R housing im not surprised the thing has no top end. The back pressure and turbulence would be pretty ordinary...but this is all talk out my a55, so not an expert opinion.

[traphead]

Is that true that the stock rb20 turbine housing has an a/r of 0.63??

I always thought it was 0.48, or was told that anyway.

Sorry don't have pics of the housing, its currently on the car at a workshop. I cant imagine that diverting waste gate air into the path of the turbine within the housing can be all that good. I can only guess its adding to my current problems. Considering i paid 2.5k for the turbo and line kit you can see why i'm not too happy with the results i'm getting.

Can someone confirm this. Because if thats true, a smaller turbine housing has no chance of holding boost.

[Roy]

Have you been in any other modded RB20s? They are not the most responsive things getting around. Certianly not going to help mask any possible turbo problems

[discopotato03]

Some of those numbers quoted just don't add up . Firstly the smallest AR ratio GT30 exhaust housings are .63 from Garrett and .61 from HKS . I can only guess what you have in .48 AR ratio housing . The Cosworth Sierra (not RS 500) had a .48AR ratio housing with a single circular outlet that could be bored out and profiled to suit the GT30 turbine though why bother .

A GT3040R in any form will be very laggy on an RB20 because its compressor is too big for the shaft power that a GT30 turbine can develop . The HKS version is a bit better because it uses a smaller trim version of the same compressor ie 50 vs 56 trim .

If this is a propper BB turbo you must be way out of pocket if they have changed the compressor and turbine meaning housings as well .

I think we really need to see some pictures of the thing and its ID tag though that may not tell the story if its been fiddled with . I just can't understand how those cork heads could put something together with a large compressor , medium sized turbine and small AR ratio exhaust housing . It sounds like a 700Hp compressor with a 500Hp turbine and a 280Hp turbine housing . No way it can work properly .

Cheers A .

[traphead]

It is interesting to read peoples opinion on this topic. I just wish I was more informed when i purchased the turbo, although I was ASSURED that the turbo was perfect for my application.

After spending much time reading about the operation of turbos, I now realize what such a bad design I have been sold.

I'll let you all know that I don't want to disclose the company from which I purchased the turbo from at the moment, since I am still dealing with them to try and resolve the problem. I will let you know that they are quite reputable though.

The turbo was apparently custom made from all garrett parts. This is why they have custom machined out a garrett 0.48 exhaust housing to fit at GT30 turbine wheel. And yes it is ball bearing so I am way out of pocket. Add to this that my car has been sitting at workshops for over 6 months now while attempting to INCREMENTALLY come to a solution leads to a very disappointing and frustrating situation.

Oh what a beatiful thing hindsight is!!!