Bigger Huffer Fitted

[F6 RAPID]

Robin, a few questions for you as this might be good for me when I have the engine out.

1. How does it drive compared with the stocker?

2. I take it bolts to the factory exhaust manifold okay?

3. What is it and rough $$?

4. Has it the same exhaust outlet/size as the stocker I.e. did you have to modify your dump pipe?

Cheers mate!

[xlnt6]

1. How does it drive compared with the stocker?

2. I take it bolts to the factory exhaust manifold okay?

3. What is it and rough $$?

4. Has it the same exhaust outlet/size as the stocker I.e. did you have to modify your dump pipe?

1. At the moment I can't really tell, as the wastegate porting has changed and it no longer boosts like it did before (ie down 6 psi or so). The car is booked in for Friday @ Nizpro for a retune, after that I'll be able to truely compare. Also the diff will be a 3.7 as well to offset the extra lag of the turbo. After the tune I do some back to back comparisons and post the result.

2. Yes, it is the same exhaust housing as stock, single inlet 1.05AR and T3 flange. Next it would be worthwhile looking at a split pulse housing with a custom manifold, like what MrG has done.

3. Turbo is a uprated OEM type with a 66mm wheel and a new backing plate, 0.7AR front cover, ported wastegate with larger flapper and uprated wastegate actuator. Total cost was $900 + $150 for the actuator. Cost is based on a good condition core unit.

4. No. Same as stock.

Cheers

Robin.

[F6 RAPID]

Thanks mate.

[F6 UTE]

Nice work..

If you're going to go a new manifold down the track, will you change to an external gate??

[igsta]

How the hell do you keep your coolant and coolant canister so new looking with all that power.

[xlnt6]

OK, it's about time I put up some data, so here it goes.

After the install of the bigger turbo I had some problems in getting good control of the wastegate actuator. It already had the higher spring rate actuator with the adjustable rod, and the obligitory wastegate flapper enlargement. Initially I had the rod length set too long and the wastegate was partially open all the time. Hence it was very laggy. Then I adjusted the rod length too much the other way and it was basically held shut all the time.

The thing was a missile cause it was overboosting like buggery but it rattled it's head off. To maintain good boost control using the factory solenoid at the kind of boost levels required for a big turbo like this to work properly isn't as simple as it would seem. Never-the-less after reworking of the turbine housing around the wastegate port we managed to get it into a workable state. This is an area that I think can still be improved on, maybe using a seperate electronic boost controller like some of the guys are starting to use.

Following is a dyno graph comparing the original turbo to the uprated turbo. The first is a quick comparison before the car reached it's final tune. Basically it was when I was having the problems with the wastegate control, and a preliminary tune was loaded just so I could get around while I addressed the problem. The new turbo is the red line and the old turbo is the blue line. The blue line is the baseline which I used to base all further tests from and was done on 109. What's interesting is the results for the new turbo were achieved on 98.

The biggest difference in power (in this case down) was at about 4000 rpm. This is explained when you look at the boost profile ie old vs new. Here is the results:

RPM Boost psi (Old turbo) Boost psi (New Turbo)

1790 2.75 2.5

2500 4.25 4.25

3210 10.0 10.0

4280 17.5 14.0

3930 21 17.0

4640 19.0 19.0

5360 19.0 19.0

Max boost RPM

Old Turbo 21.0 psi @ 3850 rpm

New Turbo 19.0 psi @ 4500 rpm

So what is apparent is :

1. The new turbo has additional lag of 650 rpm before maximum boost is achieved.

2. At 3930 RPM (mid range) the new turbo was down by 20 kw or so, but this is because it was making 4 psi less boost.

3. Beyond 4640 RPM the boost was the same, but the new turbo started to come to life and starts making more power on less boost with much less timing (fuel was 98 vs 109). Ignore the fall at the end of the run, like I said this was only an interim tune, and large margins of safety were added at the top end causing the power to drop away. This is what you expect as the larger compressor wheel is more efficient than the original, especially under high flow rates.

Next I'll post up where it all ended up after the wasetgate issue was addressed and post final tune.

Cheers

Robin.

[F6 UTE]

Good thread.

Cheers, and awaiting results

[xlnt6]

Ok, now here's the final result.

Now firstly the aim of the tune was to screw more power out of it at the top of the RPM range. Even though more mid range would have been possible, the fact of the matter is this is basically a "dyno show" come "race tune", so effort was mainly on top end.

As can be seen there is a nice big fat gain from approx 4500 rpm onwards of up to 30 rwkW which is about 40 kw at the engine or so. Given the turbo compressor flows approx 10% more the numbers pretty much add up, ie OEM = 400 rkW, uprated = 440 rwkW. Now some others may be able to get a bit more, if you can get the flow on the turbine side up.

This is what I posted earlier about this issue.

"So far the car makes about 440 rwkW. M6 XR6T is correct, that the existing GT3540 turbo is very well matched (comp wheel vs turbine wheel and housing sizes). Therefore bumping up the flow capability on the comp side only means it pushes the turbine side into the edge of it's performance envelope. ie the turbine side runs out of flow. Given you can't buy a larger turbine AR housing size, the gain is capped by the fact you run out of flow on the turbine side. You can work around some of those issues by reducing backpressure in the manifold (ie like I have already done), and post turbine side (ie. freer flowing exhaust). This is why the next logical setup, like the Nizpro setup addresses these issues. ie. a larger turbine wheel and different manifold, to get the flow capability up on the turbine side as well as the compressor side."

So in summary:

1. The new upgraded turbo does make more power than the OEM turbo by about 10%.

2. The new upgraded turbo has additional lag to get up on full boost of about 600 rpm.

3. The new turbo is more efficient at the higher flow rates, and this is apparent beyond 4500 rpm where it out powers the OEM turbo all the way.

Now for driveability:

Here's what I wrote before "What I have noticed, it that the new wheel is more efficient as the car can support more advance in timing (due to reduction in compressor outlet temp), and it seems to me that there is no appreciable reduction in low down response. The OEM turbo comes on extremely hard in the mid range when you boost it to around 18 PSI. With the upgrade the power is more linear, which means it's much more predictable and streetable. Before the upgrade I made about 400 rwkW but the car use to absolutely fry the tires and wouldn't get any grip. Now, the power comes on like you been run up the ars* by a runaway primemover and the car just hunches down and takes off. So the end result is it's much faster."

So even though it there is more lag, the power is much more deliverable to the road. I think I can still improve the driveability by changing the diff ratio and maybe investigating alternate boost control, and that's where I'll start looking into next.

Cheers

Robin.

[F6 UTE]

Nice gain in peak power, however I'm unsure if I could live with knowing I threw away some low down urge..

If I was given #2 from the get go, I wouldn't know what I was missing, and it would be sensational..

Thanks for the insight..

[Romulus]

Informative result Robin. Well done.

I've seen max power on the stock turbo @ 17-18psi as you mentioned. More boost = less power from excess intake charge temp and exhaust temps, less boost = less power, although you can make up for some of it with more ignition timing.

Looks like the 0.7 housing and comp wheel upgrade are a worthwhile mod.