Best Maximum boost pressure for a GTA Turbo ?.

Have you got a water cooled turbo on your car?

and have you got a new car Stephen?

The GTA's lag issue is not helped by the long exhaust manifolds and runners to the Turbo.
Using a Manifold wrap, and Turbo wrap, will help keep EGT's up and reduce lag.

Anyone tried this ?.

Paul, yes speak to Clee, and others as well. In terms of turbo response, the transient heat losses through the stainless runners are not significant enough to affect the entropy, in the real scheme of things, you will find there are bigger fish to fry. Don’t forget there is precious little airflow over the headers, and will glow incandescent, something you will only see in the extreme in a front mounted engine arrangement, there is usually significant airflow over the headers to actually cause loss (excluding stationary load conditions obviously). Extracting the heat energy available from the waste gasses in a single stage isn’t that easy, especially over a wide operating rpm range, but the mere fact the waste gate is nearly always operating tells you that most of that energy has been bypass anyway, so I wouldn’t sweat the little stuff too much.

The main reason to wrap them is to keep engine bay temperatures down, and the major benefit here is reducing the heat absorption into the inlet charge – detonation and loss of charge density. The effect on EGT is secondary to the former in the GTA given the rear engine and heat build-up, a real problem to achieving serious power.

The std GTA turbo is already a hair drier, and if going to change then I would go to a newer technology entirely and stay away from the old Garret T3/T4 turbine designs. I worked for Honeywell and had projects with Honeywell Turbine Technologies, formerly Garret before they were absorbed…

I would look up some of David Gentleman’s old posts on here, all lively stuff

Yes ,far bigger fish.
The only real use for wrap in this case is to try and keep the bay cool .I could run more boost on my current setup if not for that .
We got it mapped up to 20 psi last time out but then the det started as soon as the temperatures start to rise
After the turbo money is best spent on intercooling .I'm trying to avoid water/air for weight but that may be the only solution .....
At Rockingham I had to turn the wick down to 16 after a few sessions hard abuse .
One thing with wrap though is it does tend to deteriorate very quickly and falls off Best to seal it as well to try and get some life out of it .

[BIG_MVS]

No, the T3 is not water cooled.

Yours or T3's in general? On the GTA they made them water cooled from 1988 so you may have a later one on yours...

Have you got a water cooled turbo on your car?

Maybe the Turbo off the 21 Turbo would be a worthwhile upgrade (cheap) as it is a cooled turbo and slighty higher spec? Mind you, it would be better going for something modern and cooled for all the work involved.

Si21

Over the weekend i fitted a mechanical Boost gauge to my GTA.
Installed just above the radio position.
I had great fun running the pipework from the engine bay and through the center tunnel. But its all done now...

Anyway, on the way into work today i got a chance to test it once the engine was upto running temp.

My max boost is anywhere between 0.7 and 0.8 Bar.
With 0.8 Bar being 11.6 psi.

So i guess thats about perfect then as is ?.

Cheers,

Paul, sounds good to me. On std setup not worth pushing further for riks to reliability and added heat load. One worth while little upgrade to get a nice torque boost between gears and faster spool on this std setting would be to use a Festo blocking valve and reverse bypass - no electronics and goes inline.
Stops the waste gate creeping open from about 6psi, and setup for an opening pressure of about 8/9 psi. Result waste gate will be kept nice and shut until that point, then crack open and control.

If you want the details drop me a line and I can give you the details of the valve and required spring for the pressure range.

Sounds like you are getting some happy motoring, smile.

Martin

Hi Martin,

Mine already has some sort of a valve installed.
You can see it in this pic, just in front of the Turbo.

Hi, that's the bleed valve, and this sets your over pressure achieved - 11.5 psi, I'm taking about a blocking valve, most people completely over look this little gem.
The waste gate actuator is just a spring as you know, start applying pressure on the diaphragm and it starts to crack open as soon as the pre-load what ever that is gets exceeded. The block valve trick allows you to set that pressure to exactly what you want above the pre-load and below the desired over-pressure set by your bleed valve.
To get fast spool you don't want the waste gate creeping open at all as the turbo spools and builds pressure. The A610 achieves the same with the electronically control Amal valve, and sure you have experienced similar in your Saab past. This solution does exactly that for a few quid and no electronics.
The setting of the block valve also directly sets the boost and (hence torque) surge, from critically damped std to under-damped (read as loads). Just a nice little mod IMO for this sort of generation kit.

That's not strictly a bleed valve ,it's an entry level version of what you describe Martin I think .It has a spring loaded ball bearing that blocks the actuator pipe feed so the actuator doesn't see any pressure until X ..
Better than a normal bleed valve .I've got one on the car ,useful for making on the move alterations when mapping

Ah ok thanks, that will work pretty good too. Do you know what pressure drop is required for it to re-seat i.e. on the way back down pressure wise? May be worth checking. Depending the size of the ball and seat i.e the bleed, if you put a one-way valve passing air from the actuator can back past the valve back to the manifold (around your bleed thingy), you can get it to close the waste gate back up real fast – get back on spool spool spool time, than bleeding back down past the ball bearing slowly, and consequently the WG lazily returning to it’s seat. All air flow init

Just been reading my factory workshop manual.
M.R. 273. Page B-49

It states the D501, should have a maximum boost pressure setting of 850 millibar. 0.85 bar.
Which equals 12.3 psi.

It also states the pressure cut out should kick-in at 1.1bar. (15.9psi)

Mine is maxxing out at 0.7bar, so i think i will give it a tiny tweak at the weekend.

Q..... So if the GTA Turbo runs at 0.85bar standard. Why do people need to remove the cut-out limiter ?. As Lee has already said it is unlikely anyone will ever run over 1bar.

Thanks for this.
Mine is certainly running a little low, then (~9.5 PSI). Didn't realise I should be looking at just over 12 for maximum boost.
I'm going to get one of those Atomic Boost Controllers from GFB. It does what Martin was talking about, holding the wastegate feed closed until the desired pressure is reached to reduce spool-up time etc.

I did think about fitting Saab's APC system to the GTA. See an earlier thread.....

This would do just that. Hold the wastegate shut tight, until a set pressure is reached. The main benefit here is more Torque at lower RPM.

However, in the Saab world, as people often find out.... bring too much pressure in too early. And the Torque shock just shreds the gearbox.
So the art is to get a smooth and gentle Turbo pressure curve. Thus reducing the shock on the gearbox as the turbo kicks in.

Im assuming though, that the UN1 is a tough gearbox ?. I remember reading in magazines in my youth that it was a common gearbox for Rover V8 conversions and alike. Kit cars, and so on.

[mettersl]

Hi Paul,
UN1 is tough, but more boost = more torque. Bigger engines mean the same so A610 is beefed up a little to cope.

A610 is nearly the same gearbox- same ratios, but a different part number.
For Rover V8/Lotus esprit V8 use, there is a kit that ups the max torque of the gearbox by replacing the main shaft with a one piece item. Esprit certainly get through UN1's without this, and Lotus fans claim the Esprit box is already strengthened compared to our boxes.
Venturi 400 is probably the most powerful UN1 car (anyone know what was done to their gearboxes?) I am not aware of anyone needing to do this with the PRV in place- and there are some quite hot alpines around- Tony Smith for one.

Gearbox is one thing but the drive shafts aren't indestructible either . A610 drive shafts have bigger joints but are otherwise interchangeable, but Simon Auto's want a lot for them.
Mr Dell was working on a lower cost solution there...I must get my spare A610 shafts off to his specialist sometime for copying.

Sounds like you have a long way to go before the gearbox will be a problem.
Lee