Boost limit(stock cooler and turbo)

[HRthirtyone]

Just wonderin what boost level i should stop at on my HR31 red top rb20det... i am currently running 8.5 - 9 and that is stndard. Also, when does the fuel limit come into play? ive been told 10 and 20psi? which one?

[Roy]

Its only my opinion but id just make sure your exhaust flows well, free up inlet tract to turbo, and be happy with the boost that it runs at this level.

Without wanting to throw on an intercooler and clean up the maps, id say running extra boost will give very little increase in power, whilst increasing wear, possibly damaging engine with high inlet temps and detonation.

Why do i think this, well prior to fitting my IC my RB20DET was no quicker when running 1 bar as opposed to leaving my AVCR off. Now even with an IC i still only run std wategate spring pressure (AVCR off) and i still get 0.85 bar.

Car does have more top end with 1 bar, but pings so i leave boost std for peace of mind until ECU gets the required attention.

As for the fuel cut, i cant help there, my old GTS-X ran an MT8 computer when i bought it, and as for the boost it ran? Well 11psi, but that was with a hybrid T3/4, so my R32 is probably a better example.

[Sydneykid]

There are two problems with the standard turbo, both centred around the ceramic exhaust turbine.

Firstly, being ceramic the turbine is sweated/bonded onto the common shaft and therefore it does not like too much resistance ie; the exhaust is pushing the turbine while the compressor is trying to move air into the engine. Too much resistance (boost) and the turbine and the shaft part company.

The second problem is one of heat, the ceramic turbine will only handle a certain amount of heat coupled with this resistance. The heat builds up over several minutes of very hard driving (say on a circuit) and the turbine shatters or parts company with the shaft. Leaning out the engine to achieve more horsepower also increases the temperature of the exhaust.

So to answer your question, our experience has been that 0.9 bar (13 lbs) maybe OK for a road car as long as it is only in short bursts so that the heat does not build up. If you do any circuit work or long distance high speed stuff, then 0.7 bar (10 lbs) may well be the safe max.

The boost readings above are at the engine inlet. The boost at the turbo will of course be higher than that depending on the airflow of the intercooler and the pipework. By reducing this restriction (better intercooler) you can have more than 0.9 bar at the engine but still have the same resistance (boost) at the turbo.

With a really good intercooler and pipes we have achieved 0.8 bar (12 lbs) on a 200 RWKW road car reliably. But 5 hard laps on the circuit and the smoke escaped.

Sorry that this is a complex answer to your questions but it is a complex scenario.

[Roy]

I am also of the understanding that the NICS turbo isnt exactly a thing of beauty. Not Ball bearing and pretty old design turbine/compressor.

Not knowing whats done to your car or what you have planned i would suggest that you stick with freeing up the engines breathing.

As Sydney kid mentioned without tricking the wastegate actuator with bleeders etc you can get very close to the boost ceiling of the turbos.

Instead of spending $100+ on boost controller (bleeder type) you are better of with spending $350 on an old 7M-GTE (old 3L Supra) intercooler.

Cut and trial fit the piping yourself, (hassle those in the know) then rock up to your local boiler maker/welding shop with a case of beer and you bits to be welded.

Now im getting off topic... sorry

[Sydneykid]

Hi Roy good to see someone else that likes the 7M-GTE intercooler, being non cross flow they fit up nice to a GTST, simple pipework. We have them making 190 rwkw without excessive air temperature. Nice and light as well.

Don't tell too many people though, the price will go up.