im looking for a de cat/down pipe for my st205
ive a mongoose exhaust and stage 1 turbo
ive tryed putting on a aussie
but suffered high boost problems (could it be the avc-r)
i removed the aussie and replaced the cat as i needed the car
but i still want to get the de cat done
but unsure about what to use without any problems
TB devolopments down pipe seems to be the prefered option
but im unaware of anybody haveing problems mateing
a aussie to a mongoose system

Overboost problems are not uncommon when running a decat and large bore exhaust system.

The issue almost always results from the wastegate on your turbo rather than a boost controller.

What turbo is it you have?

Apart from quality there is probably not much to seperate the different down pipes, I am not sure that a different one will resolve your problem.

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GT4DC Events Co-ordinator
1996 ST205 UK

hi ive a fensport stage1 turbo
i bought the aussie of fensport also and when i asked them the same question, they also mentioned
similar, they said that if i sent the turbo back, they would re-work the waste gate
i dont really want to remove the turbo if possible
but as said im sure that others have run a stage1 and de cat with no issues

There is a little bit of luck of the draw.

I know of one car with a hybrid and 3" straight through and no boost issues.

However most cars mine included will get some boost creep with that setup.

I resolved it with a hybrid turbo that has a custom wastegate, the previous hybrid that I was running had been englarged at the wategate but there is only so much material that can be removed - it still wasn't enough and I ended up running with a restrictor at the bottom of the down pipe.

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GT4DC Events Co-ordinator
1996 ST205 UK

When Owen Developments fitted a 'Stage 1' CT26 hybrid turbo to my UK ST205 they found they had to re-profile the wastegate to eliminate the overboost. IMO this is definitely the best solution for those of us that don't have a Turbo Technics S148 single wastegate turbo.

The design of the downpipe can play a part in this if it is not allowing the wastegate to open fully. Some I have seen look to have very little clearance. I had a Hayward & Scott downpipe and that was fine.

If it was my car I'd get either Fensport or Owens to reprofile the turbine w/g and d/p as a complete system rather than sending just the turbo.

BTW putting a restrictor in the system rather defeats the objective of fitting a hybrid turbo in the first place. (....sorry Mike )

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Don
GT4DC Chairman
1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
1994 Toyota Celica GT-Four Special GT 590bhp @ 1.8bar
1989 Van Diemen RF88/89 Formula Ford 1600
2008 Nissan Patrol GU 3.0L ZD30DDTi 154bhp

thanks for the replys
ive considered the restrictor in the down pipe option
haveing being incontact with tim at TB developments, he said he could supply one
even asked on what revs the cars started to over boost (assumeing there are slightly different sizes)
how restrictive are these? would there be any if much of a gain in performance/spool of the turbo
obviously the weight advantage but mostly looking
on improveing the spool for the turbo, altho its not actually that bad as it come-in at 3 half to 4k
or should i leave the cat in

Edited for accuracy

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JP
GT4DC Treasurer

Grey St185 RC
Silver BMW E46 M3
Multicolour yawn Honda VFR400
Silver Honda Civic Type-R

Check the problem isn't wastegate hitting the DP and not opening fully, if so cure this first.

The best way of curing boost creep for efficiency / power is to improve the wastegate flow. Feasability rather depends on how bad it is & whether enough metal can be removed without the casting cracking badly in use.

A method commonly used to make the car drivable again is to fit a restrictor plate. This rather defeats the object of fitting a free flowing exhaust in the first place.

Restricting the exhaust means more power is lost pushing the gas out of the engine, plus it means more hot gas left in the cylinder to mix with the incoming charge. By my maths, 5% exhaust gas at 800C mixed with 95% intake at 30C gives a temperature of 68C - makes a bit of a mockery of chargecooling !!!

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If at first you don't suck seed, try drier grain.

...the best solution is Turbo Technics S148 single wastegate turbo.

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Vice Chairman
1990 White UK Celica ST185 - Project DTM
1997 Cream BMW R1200C (as seen in James Bond "Tomorrow Never Dies")
2005 Jaguar X-type 3.0 Sovereign AWD Automatic
Blood Bikes - https://www.freewheelers.org.uk/

so basically best left alone?
not worth the effort for little gain
as said, its only really the extra weight and possible extra spool up (or not)
but as said the turbo picks up fine

Yes - To clarify...
S148 is a hybrid but does not use standard turbine housing and hence is not prone to boost creep.

As Mike said "I know of one car with a hybrid and 3" straight through and no boost issues" he is referring to hybrids with standard CT20 or CT26 turbine housings.

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JP
GT4DC Treasurer

Grey St185 RC
Silver BMW E46 M3
Multicolour yawn Honda VFR400
Silver Honda Civic Type-R

Don - I agree completely, just this was the only solution I could find for the problem short of replacing the turbo - which was what I ended up doing eventually!

IMO the S148 TurboTechnics unit with the single wastegate is the one to go for.

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GT4DC Events Co-ordinator
1996 ST205 UK

I am glad my years of brain washing you lot has worked

There has been reported issues with the longevity on the Gt4OC but ..
Mine is still working after many years (now sold to steve).
Steves one on Hannibal is probably 8 years old and still working fine.
Nigel Muddys was bought used and has had no problems (unless that is the cause of a bit of burning oil rather than his suspected loose rings)
Nigel Cs is still going as far as I know without problems after a few years at 1.2 bar and he does seem to do some miles.
Mikes is still going after a 2-3 years and probably a fair few miles.

I haven't heard of a failure on the DC. Maybe we have some mechanical sympathy?

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JP
GT4DC Treasurer

Grey St185 RC
Silver BMW E46 M3
Multicolour yawn Honda VFR400
Silver Honda Civic Type-R

I think mine has at least 35,000 miles on it, I cant quite remember when I bought it but I would think its 3-4 years ago.



Are you suggesting that the average DC member looks after there car better?!?

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GT4DC Events Co-ordinator
1996 ST205 UK

I don't think that's a fair statement. Some of the failures have happened to poeple who know how to look after and maintain these old wrecks

More interestingly the peole round here were by and large the first to have bought S148s "before they were famous" and whill TT were still building the rep for them.........