ST165 TURBO - Upgrade or not

[Fizzy]

Ive got a 1988 ST165 Turbo, was going to swap the exhaust side with a later ct26 so that the exhaust fittings are the same - is this version better than the later ct26? Am asking cos st165 only put out 180 or so BHP???

[MegatronUK]

http://www.alltrac.net/tuning/turbofaq.html

Don't say I never do anything for you!

Power difference was mainly down to compression ratio and engine internals, rather than turbo difference, as far as I can tell.

[Fizzy]

ping

[JJ]

Stick the MR2 actuator on if you can, the earlier 26's were really only setup to run 7psi or so... so you can imagine the springs not up to much !

If you can make a hybrid out of it nije ( swap one of your suplus compressor wheels over & housing ) these units can tend to flow more than the junky later twin scroll / twin entry setup.

Drawbacks on the earlier crapper turbo is the turbine housing is very prone to cracking between the impeller channel and the wastegate port.

You after another turbo chap ??

[Fizzy]

I am really after something that will pust a constant 1.4 bar all day - I know this one wont come close but at least I will be able to run the car - if youve any ideas then pm me!!! Thanks dude!

[Fizzy]

JJ - are you saying that the older exhaust housing/turbine is better than the later, and that the latter compressor housing is better than the early one????? Me bit confused?

[JJ]

JJ - are you saying that the older exhaust housing/turbine is better than the later, and that the latter compressor housing is better than the early one????? Me bit confused?

yup - older turbine housing flows more - more likely to handle 1.4 bar's worth of air flow through it, and a bigger compressor to hold things to the red + delivering mass of air.

As for being better, well the later twin scroll design spolls up quicker and isn't prone to cracking .... so although earlier one can flow more, its reliability is touch and go ... predicament !!

1.4 bar ... you'll probably get that through the mid range chap, but at the top end when the engines flowing a great deal more gas, thats when you notice the power drop off... otherwise known as the bottle neck in the turbine housing... simply can't rid of the air = excessive heat build up in the turbine / manifold and backlog of combusted gas that the engine cannot get rid off = excessive heat to the valves, cylinder temps go up and thats when its starts endangering the pistons.

1.3 bars probably about the limit and even then it'll tail off at the top end due to this limitation through the turbine.

Wanna try something new ?? clag an external wastegate to the manifold !! That will sort out gas flow problems... excess build up in pressure straight out of a screamer pipe instead of trying to squeeze through the turbine housing and heating every bloody thing up !

[Fizzy]

anyone tried this? bit of an engineering nightmare??

[JJ]

If I could get the damn turbine to mate up with the MR2 downpipe, I'd prove my theory !!

I've only tried it with a supra unit though, not a celica !

Just as a note, the supras compressor wheels larger than the Celica / Later MR2 designs.

Engineering nighmare ?? lol ! Pair of pliers, whip off the compressor housing, unbolt compressor, launch larger compressor wheel with machined compressor housing on = hybrid turbo !

Thats all these turbo remanufacturers do - bore / replace bearing housing, retain compressor and comp. housing ( if standard rebuild ) new shaft, carbon based seals, couple of oil seals, ring gaskets and there you go £500 !

If you fancy a challenge, theres some chap selling rebuild kits for the Ct-26 on ebay... think they're around £70 - but that assuming your shafts still good and the bearing housing - new collar bearings / thrust, oil seals etc etc... I'm tempted to try a couple soon.

[MegatronUK]

Are there any issues to do with balancing if going that route? Wouldn't particulary trust my own skills on something rotating at 100000rpm!!

[MR2Mania]

1.4 bar ... you'll probably get that through the mid range chap, but at the top end when the engines flowing a great deal more gas, thats when you notice the power drop off... otherwise known as the bottle neck in the turbine housing... simply can't rid of the air = excessive heat build up in the turbine / manifold and backlog of combusted gas that the engine cannot get rid off = excessive heat to the valves, cylinder temps go up and thats when its starts endangering the pistons.

I don't agree, mate. The main reason he may not get 1.4bar at the top end is due to the size/efficiency of the compressor.

The restrictive turbine housing issue of the Mk2 CT26s is NOT what stops you getting the boost, in fact the opposite. To see this, let's look at the issues of the hybrids...

...basically, the restrictive part is the wastegate route. At high revs, where a lot of the gas needs to escape out of the wastegate and hence stop spining up the turbine, since the wastegate doesn't flow so well, the gases continue on towards the turbine wheel and keep spinning it up. Result is the boost spike! In fact, you try STOP a hybrid CT26 from boosting like mad at the top end!

With regards to the compressor wheel in the ST165, it could possibly be larger than that in the Mk2 MR2 CT26, so it *could* be an upgrade. I know for sure that the UK spec ST185s have a slightly larger compressor wheel. Effectively, using one of these compressor wheels in a regular MR2 CT26 gives you an Owens Stage1.

[MR2Mania]

Engineering nighmare ?? lol ! Pair of pliers, whip off the compressor housing, unbolt compressor, launch larger compressor wheel with machined compressor housing on = hybrid turbo !

Thats all these turbo remanufacturers do - bore / replace bearing housing, retain compressor and comp. housing ( if standard rebuild ) new shaft, carbon based seals, couple of oil seals, ring gaskets and there you go £500 !

OUCH! I can tell you for sure that Owens do a fair bit more work than that for the money (ie replace the ceramic turbine wheel/shaft with a steel one, some porting, and all balanced with proper equipment that very few companies in the UK have). Also, they NEVER bore out the bearing housing - their thinking is that a 1thou off-centre bore will cause an inbalance that will eventually compromise the turbo. Other companies aren't so concerned.

Let's not forget 360 thrust bearings that are CNC machined from scratch - you ain't gonna make one with your Dremmel!

Basically, I'd say OD and TurboDynamics do a fair bit of work, unlike all the other UK turbo "manufacturers" I've heard of which may well use the approach that JJ says.

[MR2Mania]

Are there any issues to do with balancing if going that route? Wouldn't particulary trust my own skills on something rotating at 100000rpm!!

Some turbos spin at over DOUBLE that speed!

[JJ]

I don't agree, mate. The main reason he may not get 1.4bar at the top end is due to the size/efficiency of the compressor.

I should learn to type whats in my head sometimes !! I'm coming from the angle of once the compressor has been upgraded.

Though from what you've said, I'm more likely to get overboosting problems ?? bloody hell.. I've got through 9 turbos, all different in term compressors - all CT-26's and each one of them performed differenty. Though No matter what I did with the "larger compressor" hybrids, I always had a little issue at the top end of the rev range dropping off, regardless of what actuator was put on - then i'm always trying to get the best out of a bleed /grainger valve !!

I've settled with satisfaction from one of these hybrids.. and to be honest, the compressor is huge ( the largest out of the batch! ) - produced some good air mass and good all round, strong boosting - I'll get a picture of it along side a stocker one day... problem being.. the damn compressor started to pass oil too ! so I was dumping oil vapour !! So off it came for another one to be put in place for the time being until I fix it !

Got any superglue ??

OUCH! I can tell you for sure that Owens do a fair bit more work than that for the money

I'm generalising chap.. ! Most of these fly by night turbo companies just rebuild, opposed to rework !

[MR2Mania]

Though from what you've said, I'm more likely to get overboosting problems ?? bloody hell.. I've got through 9 turbos, all different in term compressors - all CT-26's and each one of them performed differenty. Though No matter what I did with the "larger compressor" hybrids, I always had a little issue at the top end of the rev range dropping off, regardless of what actuator was put on - then i'm always trying to get the best out of a bleed /grainger valve !!

Ah! So, we might have hit on a good point here!! The hybrids that I've seen boost creep have all had the exhaust housing entry machined out to match the manifold-to-turbo gasket. Obviously, this will improve gas flow into the turbo, and hence it's probably this extra gas flow that tips the wastegate over the edge and means that it can no longer flow enough air out to control boost at high revs.

I know that BenF cured his high RPM boost creep by going back to a non-machined exhaust housing, so this could be the answer.

I've settled with satisfaction from one of these hybrids.. and to be honest, the compressor is huge ( the largest out of the batch! ) - produced some good air mass and good all round, strong boosting - I'll get a picture of it along side a stocker one day... problem being.. the damn compressor started to pass oil too ! so I was dumping oil vapour !! So off it came for another one to be put in place for the time being until I fix it !

That may be down to NOT having a 360 degree thrust bearing? I personally think it's important to have one on a hybrid if you want to go over 17psi.

I'm generalising chap.. ! Most of these fly by night turbo companies just rebuild, opposed to rework !

I know you are, matey! I'm just trying to point that out to others, so that when they're comparing prices between the different companies, they can see what they're getting from the 2 better firms for their money.