Over boosting

[BrettMRC]

Ok, so we've now finished the head rebuild on Suggestable's GTE. During the shakedown runs it's pretty obviously running more boost than a stock supra.
(Another boost gauge capable of reading up to 1.5bar is on the way, but currently boost goes off the top of the stock gauge)

I'm suspecting one of two causes:

1) Given the evidence found during the strip and rebuild of general poor maintenance and lack of use, it's possible the WG is seized shut. (Although my own experiences have generally shown most wastegates to fail open)

2) The wastegate spring has been tampered with. (Seen a few references to people shimming the WG on here, but have not yet located an actual write up)

So...

How much boost will the stock turbo produce if the WG is stuck shut? (Car seems to be stock bar an aftermarket induction kit)
What is a safe level of boost for the stock fuel system? (I've been reading and 10psi seems to be mentioned a fair amount)

Assuming it has been shimmed/seized I guess that would go someway to explain the BHG the car was sold with! :kickinthenuts:

 

[suggestable]

Thanks Brett. I'd love to know what was done... Then again, the extra boost is very nice

 

[IJ.]

"Shimmed" is just washers under the WG Actuator mount to preload the spring.

 

[BrettMRC]

LoL! Can't beat the Heath Robinson approach!

I'd like to know what sort of psi increase this is giving over stock though, as although the head has been done properly I've no idea what the stock gasket and ancillaries are capable of coping with.

(And I reckon Suggestable will shit out a kidney if it breaks in less than a week! STAY OFF THE LOUD PEDAL WOMAN!!!! )

 

[ForcedTorque]

Is it possible that you are finally experiencing stock boost? If it wasn't running properly before, you don't really know what stock boost feels like. Any idea what it is boosting now?

Also, pushing it to max boost is not a good idea before a break in.

 

[BrettMRC]

Well it's boosting clear off the stock gauge - which reads to 8psi IIRC?

I've been a passenger in a few MkIII turbo's - this feels quicker on the arse dyno.

Thanks for the help so far

 

[7M4EVR]

I would wait for the boost gauge to come. The factory one is junk...also I wouldn't be driving around WOT until you can monitor boost. Would hate to see u end up right where you started again. What mods are done to the car? How was the head gasket done? And what kind of boost are you wanting to run? Those are all pieces of info we would need to tell you more

 

[BrettMRC]

Sorry - should have said above, now we've seen it's boosting above stock, Suggestable is under instruction not to WOT it

It's a stock HG, skimmed head, shims done - 77ft/lb on the bolts. (Standard job really, new gaskets and seals all round on the top end - new hoses, rad and a decent aftermarket autobox cooler are next on the list)

Only mod is the air filter, and I guess a shimmed WG that's been uncovered...

From what I understand she will be going with stage 1 mods in the spring - so elbow, downpipe/DeCAT... 10psi give or take.

I have an inkling she will go for monster power in the future, as and when that happens we will probably start again with the block and head anyway.

 

[radiod]

You should be able to hear the wastegate opening/closing if you apply air pressure to the line running to the actuator. It should be open ~6 - 7psi if it isn't shimmed from stock.

 

[7M4EVR]

Another thing you can do is somehow open the WG enough that boost levels drop and start to show up on the stock gauge and go from there to get an idea. At least then you know ur safe until the gauge comes. Even with a proper HG job I wouldn't push anything past 12psi and I would daily about 8 until you decide to get into air/fuel management and better cooling upgrades. Do the record anything past about 15psi on the stock CT26 is useless, just hot air.

 

[BrettMRC]

Thanks guys - I've not tried anything yet, but hopefully will escape work in the daylight and get to the actuator this week.

 

[IJ.]

If it's shimmed pull the washers out Brett, it's a time bomb at the moment...

 

[BrettMRC]

Sounds like a plan! After the effort of the last few weeks I could well have a sense of humour failure if it overboosts and shits itself!

 

[IJ.]

Unknown condition bottom end I wouldn't take the risk

 

[BrettMRC]

Exactly!

Looks like there's about 3 washers being used as a shim, was pissing hard with rain last night so haven't shifted them yet. Job for a dry evening.

 

[BrettMRC]

Just a quick update - I removed the shims a couple of weekends back, probably about 8mm in total. Tested the wastegate & actuator both are still working normally. Took it for a run, boosting to dead on 8psi now and still more than fast enough for Suggestable.

Thanks for the info

 

[IJ.]

Very welcome Brett!

 

[BrettMRC]

....sadly now the engine has a few miles on it, a cracked/breached water jacket in the block has made itself known

I think its been caused by the car being sat around unused with a blown head - the acids from the combustion process seem to have had a good time in the water jacket and eaten it away. Suggestable reported rough starting a few days ago, a good look in day light shows it has been pushing water out of the overflow and coating the passenger side (UK) of the engine bay. 99% certain it's not a cracked head or gasket as the head was pressure tested before reassembly and the HG was tested after assembly and after a thousand miles.

To sum up: Bugger.

Going to buy a warrantied engine from a good supplier and just change the whole lot in one go, a long day should see it all swapped over. (Can't see any benefit in chasing faults all over the current engine)

 

[IJ.]

Very rare to crack a 7M to the outside of the engine, more common is between the deck steam holes and the headbolt holes, this can also be caused by either hydraulicing the Hole if it's not cleaned out or crap in the holes that hasn't been chashed and then Studs installed..

Read any warranty very carefully and stick exactly to any stipulations as most suppliers WILL screw you on any claims with the 7M..

 

[realwheeldrive]

JZ swap.