BPU boosting issues

Looking for a bit of help as my BPU TT isn't boosting over stock levels.

Up until a few months ago I was running it on an aftermarket exhaust without a restrictor ring and was seeing just over 1bar of boost. Then I fitted a Miami GT intercooler. I took it out for a run after I fitted it still without the RR was very careful with the right foot, it started overboosting which I was pretty pleased about as I thought it'd be a case of fitting the 1.2 bar restrictor ring and that'd be it.

Sooo this week I had the car in for it's MOT had the 2nd cat put on then once passed put the decat pipe back on with the RR this time. However now I'm seeing stock boost level which has got me a bit confused. I know RR's aren't an exact science but I thought with a 1.2 bar ring I'd see at least 1 bar of boost.

Anyone got any ideas as to why the boost is so low?

Cheers

Johnny

Just to make sure I've understood this correctly (been on the cider ) - the car was overboosting, you then fitted a 2nd decat and now it's back to 0.8 bar? This isn't far off normal as the cat is a major restriction in the exhaust and therefore limits peak boost. The cats are the only thing that stop jspec cars hitting 1.6 bar.

If the decat is now refitted then "something" must have changed before the exhaust swap. Are there any signs of leakage from the IC pipes, etc?

Sorry Homer probably wasn't the clearest post, the timeline was:

Bodged intercooler (info here: http://mkivsupra.net/vbb/showthread.php?t=177574) + double decat & no RR = 1bar

Miami GT intercooler + double decat & no RR = Overboosting

Miami GT intercooler + double decate & 1.2 bar RR = 0.6 to 0.7 bar

how have you tested for boost leaks???

I haven't as yet. The car hadn't been used between the overboosting and getting the RR fitted. Would the fact that it was able to overboost and hold that pressure not rule out any boost leaks?

Appologies if that's a stupid question but still trying to get my head around the TT setup on the Supra.

When you say overboost, what were you seeing on the gauge?

Got up to just over 1.2 bar then I crapped it and took my foot off the go faster pedal.

Hi Jonny.

Its worth getting the leak test done, boost leaks can be very strange indeed.

At some pressures the hole/leak can be sealed whilst at other pressure is Pi$$es like a me and you after 12 pints.

The other option is that your 1.2 bar restricter ring is in some way not sat right, or filled with sealant/paste and infact is a .80bar restricter ring.

The final option and not very nice one is the turbo's didnt like the overboost and have been overspun and not efficient any longer.

Get that leak test done. A leak can be a turbo killer.

James

Thanks for the info James, I really hope it's not the turbos that are knackered although from what I can tell they still sound the same and there's still a decent kick when No2 comes online.

Can most garages do a leak test for you or does it have to be done at a specialsts (not many up here in Scotland)?

Just out of interest how is a leak test carried out on a Supra?

A leak test on supra can be a little tricky for someone who has not done it before, but the basics are.

Fill with compressed air all pipework between your turbos and the throttle body, you will need correctly sixed bungs - (bean tins ryan calls them) with a airline afixed.

In reality your not gonna find a local garage to do this for you unless they are bored and love beans. We like other specialist will have purchased or adapted special tools for the job.

With the supra there are some areas you should expect to see leakage too, for example through the idle control valve which needs blocking. Also we find the one way breather valves/restricted flow valves on the supra quite useless on most vehicles we see.

Hope that helps a bit.

James

B***ocks there aren't really any garages up here that have much of a clue about Supras. Thanks again for taking time to post up some good info James.

1.2bar = 52mm diameter restrictor ring......might be worth checking the size of it.

My car pulled 0.94 bar with a 1.2bar RR (double decatted), i had to raise the boost via boost controller. Definately check ur RR size as it maybe way to small, where did you get it from?

Si

specialist will have purchased or adapted special tools for the job.

I used the very specialist tool known as an inner tube.

http://i5.photobucket.com/albums/y159/bikervetsteve/PressureTest.jpg

lol loving that, good for checking the intercooler and pipework!!!! although it wont show any leaks around the turbos.

James

I'm in a similar situation... mine was boosting to about 0.9 ish before any mods, and now im BPU its still boosting around the same, with peak recall on the gauge showing just under 1.1 bar. Think a boost controller is called for

I got the RR from Envy. I'll check the width of it although it's in a bloody awkward area to get without a ramp

I was thinking about just getting an EBC to up the boost however I'd like to be sure everything was spot on with the setup before using one.

If your car is decatted with a restrictor ring fitted to reduce boost pressure,it would be a good idea to fit a boost controller to set the correct boost.The boost will be higher in winter than the summer due to air temperature.

Bit of an update on this boosting issue. Went out tonight in the car, 1st run on boost and it got up to 1bar every subsequent run only hit 0.6 bar. It seems like the 2nd turbo isn't kicking in at all!

I took a quick video clip of what was happening and I've uploaded it here:

Boost Gauge Video

Hope no one gets sea sick from watching this!

First run is a straight kickdown, 2nd run is just building up to go past 4,000 rpm. The interesting bit is at the end you can see it hitting 0.6 bar then it dips like it always does just as no. 2 is coming on line then goes back up to 0.6 bar again so i'm not sure if no. 2 turbo is coming online.

Bit of an update on this boosting issue. Went out tonight in the car, 1st run on boost and it got up to 1bar every subsequent run only hit 0.6 bar. It seems like the 2nd turbo isn't kicking in at all!

 

I took a quick video clip of what was happening and I've uploaded it here:

 

Boost Gauge Video

 

Hope no one gets see sick from watching this!

 

First run is a straight kickdown, 2nd run is just building up to go past 4,000 rpm. The interesting bit is at the end you can see it hitting 0.6 bar then it dips like it always does just as no. 2 is coming on line then goes back up to 0.6 bar again so i'm not sure if no. 2 turbo is coming online.

Sounds like the IACV. Try the 5 min TTC mod to see if you get 1 bar.

That'll be one of the VSVs. Sometimes you get boost when you kickdown and sometimes you dont - usually happens over 4k rpm/ 60/70ish mph on the roll.

A new VSV/IACV will sort it.

Just wanted to post the resolution for this incase members come across the same probem in the future.

It was the IACV VSV got a 2nd hand one and after a quick swap, 2nd turbo was back.

Big thanks to ScottM for helping with the diagnosis and jayssupra for the VSV.

Do you have a boost controller johnnyW?

Not yet, just running full decat with RR at the moment. Hitting 0.9 bar at full boost, I'd like to get an EBC to raise it to 1.2 when needed

Think that'd be a good setup to run as 0.9 bar is quite a nice level for driving about "normally".

Think that'd be a good setup to run as 0.9 bar is quite a nice level for driving about "normally".

I planned to do that but I don't think I've ever turned the boost down from 1.2 since I fitted it (about three years ago)!