Wasn't it due to there being a built in oil restrictor?

the new G series definitely comes with restrictors already installed, but I think they always needed to be added to DBB GT series turbos.

As an aside, should we not move these discussions to the Discussion thread

Nearly finished now

Turbo and new downpipe and oil lines fitted.

Full service including new timing belt, water pump, aux belt fitted.

New performance radiator fitted.

Just need to get on the dyno for a mapping tweek, then we will see how it compares with the old turbo

Be interesting to see the power delivery after the dyno session

Cheers Jamie

Sorry I posted on your build thread so can a MOD delete that?

Good numbers, is that dip clutch slippage....?

Yes that is what my guys thought. Maybe too much torque or maybe the clutch plate is due for renewal (after all I think Nigel gave it a good workout over the years!)

That’s a fast car

Yes Nigel wasn't shy when using all the power, lol

I have roughly drawn the new figures onto the old graph to show the difference in spool-up.

Hp generation seems to have improved by 500-700 rpm, but the torque generation is on a different planet

I picked up the car yesterday afternoon and got to test it for about 10 miles of country roads on rhe way home

The car now feels substantially quicker

It doesnt seem to reach boost threshold much quicker (maybe a couple of hundred rpm), but when it does come on it goes from zero to full boost in about 1500 rpm

So previously the power would build progressively as the revs rose, but now it has a massive wave of torque from 3500 rpm that propels the car to warp speed

Sounds awesome, enjoy

I did some road testing today to record the boost response in the real world.

The turbo starts to spool around 2200 rpm
2500 rpm = 0.18 bar
3000 rpm = 0.39 bar
3500 rpm = 0.90 bar
4000rpm = 1.72 bar

What gear Simon?

4th gear from about 30mph.

Impressive

I have plotted the dyno Hp and road test boost results onto the G25-550 compressor map.

The first x is 2500 rpm, the last 6000rpm.

As you can see it runs nicely in the efficiency islands until it is pretty much maxed out at 6000rpm.

I guess with that much torque available there is no real requirement to rev it out to the redline anyway

It will be interesting to hear how it drives - the GT3071 I put on it was still producing full boost at 7,500rpm, which was why it felt so frantic to drive (as well as a bit laggy...) This one looks to be all done well before the redline.

If the torque is as high as you think it might be, I reckon you'll end up needing a clutch, and you risk killing the gearbox, or if you're lucky, just a driveshaft.

Great to see the car is still being pushed to (and beyond) the limits

That's going to feel like a much bigger-engined car to drive - 100ft-lb stronger in the midrange.

Gonna need better tyres (and a lot more often!)

Won't you miss that ridiculous rush that it used to give between 6,500 - 7,500?

The compressor is pretty much maxed out at 6000 rpm because the maximum boost is acheived soo early (4000rpm). However there is no real requirement to rev the engine to redline now because it pulls so hard in the mid range

Joe is currently putting a G25-660 on his car, so he should get a lot more power at the top end where mine is running out of steam.

I'm happy with the choice I made as the purpose of the change was to get the best possible mid range response without loosing too much Hp - it is still making 480Hp which is only 8 less than it was when you had it

I think the clutch was slipping when the car was on the dyno (there is a dip in the torque in the middle of the graph). On the hub dyno there is no wheelspin so the full amount of torque would have gone through the clutch, however on the road there will likely be some wheelspin thereby reducing the load on the clutch and gearbox.

It probably needs a new clutch plate soon anyway as it has about 50k miles on it now. Any idea how much torque the Helix organic clutches are designed to hold on a Coupe?

The rediculous rush is now from 3000 - 6000

I seem to remember something like 330lb-ft. I was slightly over the limit, but you’re in a different postcode….

The clutch would occasionally slip if I left my foot resting on the pedal as it hit max boost, so it was clearly at the limit with the old turbo.

Have you thought about using the Blitz boost controller to limit the rate of boost gain? Going from no boost to full boost in 1500rpm will be entertaining for a while but could soon get tiresome. You have four different channels - they don’t have to use different boost rates - you could have different channels for different gain rates.

I specifically used channel 1 for when I had non-petrolhead passengers. 1.0 bar boost and a really gentle boost gain. It still made about 400bhp, but the gain was very gradual, so it was less frantic.

TBH I'm never really driving it with my foot flat to the floor like you were on your track days and runway top speed runs So the power should come on slightly more progressively when I'm feeding in the throttle on the twisty roads
I'll see how it goes, but if it does turn out to be too crazy I can turn down the boost a little .