GT Turbos & Actuator Rates?

[951]

Hi all,

As part of my 3.0 rebuild and upgrade I'm going to go for new ball bearing turbo's, replacing my existing M400 T28's.

Having chatted with Chris & Graham at Universal, either GT25R's or GT28RS's would seem to be the best choices.

To fill in a few blanks, the engine is going together with heavy duty bottom end, forged pistons, flowed & ported heads and uprated valve springs. The 6-speed box is away at the Gearboxman for the usual mods and the clutch will be a helix paddle, although I'm not sure on what lining yet. It already has the Pro Alloy IC and Hard Pipe kit.

Universal would suggest the GT25's if my aim was 500+ and the GT28's if I would be looking for 600+.

Although joining the 600 club would be nice, I think it would probably require more supporting mods to do it properly and safely than I want to look at just yet, and low to mid 500's should be plenty for now anyway!

So, at the moment I'm leaning towards the GT25R's (with a wheel spec'd for, say, 550 max) because I believe they will spool up faster and may be an easier install, although the 28's would give more scope if I change my mind in the future. Any advice here would be great though as I keep flipping from one to other!

I still need to spec the actuators though. I presume that maximum boost will be controlled via the mapping and I need to get appropriate actuators fitted to give me a sensible low boost option? In which case would 0.5bar or 0.7 bar be the usual choice?

Or would it be better to get weaker actuators stil and set a low boost level with a separate boost controller? If so is there a tried and tested path?

Sorry for the presumably basic questions, but I am concious that I'm still on the learning curve with these cars and I want to understand what's involved to make sure I end up with a good overall package.

All advice welcome!

Regards

Graham

[andygtt]

the GT28RS spool up earlier than T28's and have a lot less lag.

The GT25's wil be even earlier but if it was me i'd get the larger ones and have spare capacity as they still spool very well.... you don't have to push them to the very high power.

[GTO600]

Graham,
I think keep it simple & use the GT25'S with 0.50 actuators, should produce you really good useable power.

[Hollowpockets]

I use the standard t28's upgraded by universal and with the same work you list, make 555. I would have liked to go for the better turbos but costs were getting a bit out of control at the time. I use 0.7 bar actuators.

Graham

[Gadgeroonie]

i personally prefer cars that have stronger actuators fitted

you get more power at smaller throttle openings and the car can be driven with very little throttle

I say go for the bigger turbo's and the stronger actuators for maximum turbo spool

can you get a compressor map for the GT28RS, what size AR is the exhaust housing ?

[2.5bluenob]

i dont think it makes alot of difference what actuator you fit. only if you have a high/low boost switch it dictates what your low boost/power will be. But as soon as you switch to high boost it will be over ridden.

Steve

[andygtt]

A .9 actuator is goin to make over 500bhp on low boost with gt28rs not sure what it will do with gt25r.

My car is a very different setup but I run .6 actuator springs and see well over 600bhp.... I could run 2 bar with my little springs!

I went to strong initially and the car made silly power on low boost so we swooped out the little springs lol

Be honest with yourself... With all the mods your doing you will be gunning for 600bhp in the near future :-)

[951]

andygtt said:

Be honest with yourself... With all the mods your doing you will be gunning for 600bhp in the near future :-)

You may well have a point there!

OK, thanks for all the good advice and viewpoints chaps.

Plenty to mull over there.

Just been over to Jetstream to drop off my new Fidanza flywheel and also had a chat with Dave about it. As he points out, it could be that the quicker spool of the GT25R's may be slightly less significant than I was thinking as we will probably need to keep the TQ down in the lower revs to protect the drivetrain anyway.

I'm sure the GT28RS's will still spool up pretty quickly, and if they are not being pushed as hard as the GT25R's at any given level, might that help to keep a bit of heat out of the charge air and therefore the engine?

I gather that GT28RS's with .7 bar actuators could give a low boost level of about 530ish?

Any ideas what .5bar would give?

Out of interest, what boost pressure would you expect to be running at 600 with the GT28's?

Many thanks again guys.

Regards

Graham

[ThatPhilBrettGuy]

T25RS's with good heads will give 400BHP @ 0.5bar. My engine is lower compression than standard however.

[Gadgeroonie]

are the m400 pistons 8.0:1 compression ratio ?

what did you got for Phil ?

[andygtt]

The GT28RS seem to give over 500bhp with 0.9bar with that spring you will get 600bhp and run around 1.2-1.4bar.... I don't know what the effect on high boost power if you went down to the .7bar spring, it would prob make around 450bhp on low boost but may still be able to make 550bhp peak.

My experience is start small in actuators size and work up... I started big and it was a mistake as it was too powerful lol

And what Dave is right, we have all capped our low down torque to protect the drivetrain... its by no accident that we all make between 530-540ftlb... I know mine could have made an absolute mass more than that.

[951]

andygtt said:

The GT28RS seem to give over 500bhp with 0.9bar with that spring you will get 600bhp and run around 1.2-1.4bar.... I don't know what the effect on high boost power if you went down to the .7bar spring, it would prob make around 450bhp on low boost but may still be able to make 550bhp peak.

Errrm, hang on, there is obviously something significant that I have missed about the way these things are mapped !

I'm probably going to sound like a total nob now but it can't be helped.....

I had thought that the actuator would ONLY set the minimum boost pressure that you could get down to - ie the lowest max boost that you could restrict it to. Like the spring in an external wastegate? (Which is what I'm used to.)

Are you saying that, because of the way boost control works on these things, that it also affects the maximum attainable boost pressure? And therefore power??

[andygtt]

the noble runs boost control solonoid (from a vauxhall astra actually)... what it does is electronically bleeds off boost depending upon what the ecu tells it so the wastegate doesnt actually see the true boost the engine is producing and is sort of spoon fed the boost.

For example the std GT03 runs a 0.3 actuator but makes 0.7bar boost... the 'extra' 0.4bar is bled away by the solonoid as instructed by the ecu so only when the engine makes 0.7bar does the wastegate see 0.3bar and opens.

This is what allows us to tailor our boost depending upon revs ... hence my boost is capped down low and allow to increase high up.

[951]

OK, that's how I thought it would work.

I also presume that the amount of pressure diverted away from the actuator is controlled by varying the duty cycle of the solenoid.

In which case is there a restriction on the amount of boost that can be diverted? Is that a limitation within the range of the duty cycle that the ecu can control so that it can't ever divert more than, say, the .4bar in your example?

[andygtt]

ok I get what you mean now....

there does seem to be a limit as to what an actuator can be made to run so for example a std 0.3bar one cant make 1.2bar...

My car is very different as I run dual external wastegates which allow a lot of control so I have been able to run a much softer spring and yet go higher on the boost... apparently mine was going to be able to run 2bar with my 0.6bar springs... god knows what the engine would do if it ran 2 bar but im pretty sure something would break lol

I like running a soft spring as I have a low boost of 408bhp and high boost of over 600bhp with a similar difference in torque

[Hollowpockets]

Not sure if I'm just confused by your example or what but I was under the impression that...

The actuator stayed closed until 0.7 bar is achieved then opens to bleed off excess boost, Which is the low boost setting

Then when on the mapped 'high boost' setting the ecu tells the electronic boost controller to keep the actuator closed until the e.g. 1.3 bar is achieved.

Yes or No?

Thanks

[daddysumo]

Hollowpockets said:

Not sure if I'm just confused by your example or what but I was under the impression that...

The actuator stayed closed until 0.7 bar is achieved then opens to bleed off excess boost, Which is the low boost setting

Then when on the mapped 'high boost' setting the ecu tells the electronic boost controller to keep the actuator closed until the e.g. 1.3 bar is achieved.

Yes or No?

Thanks

Trevor can explain better... Yes you are correct but the actuator is not a switch so it can be used to open and close the wastegate partially throughout the rev range so boost can be altered accordingly.

[Blu3R]

Hollowpockets said:

Not sure if I'm just confused by your example or what but I was under the impression that...

The actuator stayed closed until 0.7 bar is achieved then opens to bleed off excess boost, Which is the low boost setting

Then when on the mapped 'high boost' setting the ecu tells the electronic boost controller to keep the actuator closed until the e.g. 1.3 bar is achieved.

Yes or No?

Thanks

Yes, assuming you have 0.7Bar actuators fitted. The way the boost controller allows you to attain more that 0.7 is as Andy says - by bleeding off pressure so the inlet sees 1.3 (your example) but your actuators see 0.7.

[andygtt]

my understanding is that the the actuator is blown open by the solonoid? 1.3bar goes into the solonoid, 0.7bar comes out which then goes to the actuator and it opens?

we tried changing it round so that the we had the boost trying to blow it open direct from the turbo and the solonoid holding it shut but it didnt work so reverted to std.

for the record, trevor told me right from the start to use 0.6bar springs and I decided to ignore it and start with 0.9bar ones... he was right lol

Asking us is all very well, but it really needs to be a complete package so your best taking Dave's advice... I might be a know it all DIYer but his is the opinion who I hold highest when it comes to nobles and tuning them.

Edited by andygtt on Wednesday 23 November 19:10

[Blu3R]

andygtt said:

my understanding is that the the actuator is blown open by the solonoid? 1.3bar goes into the solonoid, 0.7bar comes out which then goes to the actuator and it opens?

The boost controller is just a restriction in between the inlet and the actuators (technically I think it vents excess pressure to atmosphere). How much restriction is decided by the ECU via the MAP sensor. When the boost controller is disconnected (or switched out) then no restriction exists so wastegates will crack open as soon as the inlet achieves the pressure that the actuator's springs cannot overcome. With wastegates cracked open, turbos cannot build more pressure and an equilibrium is achieved.
With the controller connected, the larger restriction causes the same scenario but at a higher pressure.

Sorry if I'm telling you something you already know there

Edited by Blu3R on Wednesday 23 November 19:41

Edited by Blu3R on Wednesday 23 November 19:43