469 BHP

Fingers crossed for a good day tomorrow - it looks like Leighton will be able to get the mapping done before the snow arrives, although the drive home to the Midlands looks like it may need some self-restraint....

I've driven the car briefly tonight and I have to say, even at less than half a bar, it feels very different - perhaps the old turbo was rather more shagged than I thought

Well, im sure you know the cold weather will definitely help with the feel of it and even the power figure.

Good luck, look forward to hearing the difference/result.

Good luck - 485 is my guess.

Hmmm, interesting turbo this... I shall let Nigel give his own feedback first as he has yet to drive it in anger.

What did it make???

Only checked the tuning section around 100 times today.... I'm peeeeeeing my pants with excitement here! Hope nigels got home allright!!

Nick

No news in this case seems like bad news!

I was overtaken by Nigel on the M6 today around 5pm ish so I'm guessing he got home fine.

And we have a winner...


Drum roll.....





Technics

Fuller story later, but as usual for me, it didn't go entirely to plan. Max power was 452, but this time at 1.5 bar, rather than the 1.7 bar used previously.

The problem is that the injectors couldn't keep up with the turbo - they were at 100% duty by 6000rpm at 1.5 bar. I also suffered a lot of misfiring, so Leighton had to put some spare plugs in

However, it is definitely faster, just not where we expected it to be. I reckon it's spooling roughly the same or ever so slightly later than my 2871 - it's hardly noticeable though - I can easily live with it.

It's also reaching full boost slightly later, but only just. Again, it's not so bad that I'm bothered.

However, the way it keeps on pulling is amazing - the bigger turbine wheel has freed the previous restriction and it just flies . MUCH stronger now after 5000rpm, all the way to the new 7500rpm redline. Leighton says the power is still rising at the redline, which is encouraging for future mapping sessions when the issues are sorted.

Even on the 2871, the boost used to tail off towards the redline, but now the boost trace is impressively flat - a perfect 1.5 bar all the way to the rev limiter

Can't wait to find some 630cc injectors and get it back to Bristol, but sadly, I'm going to have to wait - two to three months probably. Right, where's the kids' piggy banks....

Awful drive home though - nearly four hours - seems they forgot to grit much of the M5.....

Ahem...

Not a bad prediction




Sounds like a good result so far, well done.

Yes - not bad at all!

I guess I was hoping for mid-range gains, and if I'd had a billet wheel on a GT2871, I reckon I'd have got them.

As it is, what I appear to have done is gone up a size on the turbo, and then removed the extra lag by speccing the billet compressor wheel.

I was difficult to test the car yesterday - I only got a handful of full-throttle squirts on the M5 before the snow got too bad and meant that ANY throttle was an issue.

However, do you remember the first time you drove a Coupe with a big turbo? That feeling of the world going into reverse just when a small turbo starts to run out of puff? Well, this feels similar. The GT2871 definitely dropped boost as the revs rose - probably as much to do with the hot side strangling it, rather then the turbo being unable to produce the boost. I ran it to the redline twice and while it feels no better OR worse below 5,000, it really takes off above this point.

The interesting point is one of traction - Leighton made a point of remarking that despite the weather, he didn't suffer any traction issues - rather than a thump in the back of a small turbo, it's more akin to that feeling you get from a plane when taking off - just a constant, relentless surge. TBH, it's nicer (and easier) to drive, although it probably doesn't feel quite as quick as some, simply because you don't get the big thump

Off to change the plugs now that it's above freezing outside....

Well done!

In your first post you said the car produced:

1.5bar
451bhp @ 6826rpm
368lbs/ft @ 6036rpm
402wheel power @ 6678rpm

1.7bar
457bhp @ 6575rpm
389lbs/ft @ 5702rpm
410wheel power @ 6482rpm

So I am a little surprised that the injectors couldn't provide enough fuel for more than 452BHP with the new turbo. I guess it indicates that the BSFC is more at higher RPM, which makes sense.

Having said that, wasn't it predictable before you got on the dyno that the 440cc injectors were going to be the limiting factor?

I normally size injectors for turbo engines based in a BSFC of 0.5 lbs/BHP/hr and 80% duty cycle - though some may think this is over-cautious. This makes the 440cc injectors good for 430BHP @ 100% duty cycle and just 345 BHP @ 80% duty cycle.

The 660cc injectors, on the same basis, should be good for 495 BHP @ 80% duty cycle - 617 BHP @ 100% so plenty of headroom.

What was torque figure nigel??
You posting the graph or is Leighton gonna do it in his section?

Nick

good point about my old 1.5 bar figure - I'd forgotten about that

Don't forget I'm also running a 3.8bar FPR, which effectively increases my existing injectors to something around the 550 mark

I've had a suggestion that I ought to check my fuel pressure - the walbro is six or seven years old now and could be starting to lose its efficiency - has anyone else had falling fuel pressure?

I guess Leighton will post the graphs, as he has them in electronic format

Will be interesting to see in the near future with bigger injectors.

I know what you mean about the extra pull from 5k onwards, it just doesnt give up, its a really nice strong pull all the way.

Do I win a prize then?

I had forgotten you had a 3.8 bar FPR.

I'd say that checking fuel pressure would be a good idea; at 3.8 bar the 440cc injectors should be working at < 80% @ 452 BHP.

I'll let Leighton comment, as I have no way of checking the fuel pressure, but I don't want to replace the fuel pump just to test the theory

You/someone could check with a fuel pressure gauge before changing the pump? Perhaps it can be checked with a suitable reader via the OBD socket? I don't know.

I have a feeling the fuel pressure isn't "seen" by the ECU - it's a simple pressure relief valve that sets the pressure, so the ECU will simply assume that's it's correct and fuel accordingly.

This would explain the issues experienced with the voltage drop if the pump hasn't been directly-wired - if the ECU was watching the pressure, it would alter the fuelling maps to suit

I thought the ECU used maps as opposed to looking at fuelling and only looked at the fuelling when it's idling?

1.5bar
Power: 453bhp @ 7107rpm
Torque: 342lbs/ft @ 6545rpm
Wheel power: 399whp @ 7074rpm



The injectors were pretty much 100% on the old turbo, but the problem we have with the new turbo is that the power is still climbing beyond where the 2871 had run out of puff.

Nigel's injectors are 440-450cc, so at 3.8bar fuel pressure they will flow circa 490-500cc. This of course assumes the pressure remains constant, especially at high loads/rpms, which the Walbro 255 should be able to achieve up to around 500bhp.

Using RC Engineering's injector calculator a BSFC of 0.55, we can see that 450 flywheel power would require a 460cc injector @ 3.8bar pressure running at 100% duty. On most 20vt engines, I do find 450bhp to be the flow limit of this particular fueling setup.

In terms of max power from Nigel's turbo, well you can see on the graph that power is still climbing. I think we may see 460bhp @ 1.5bar, and perhaps closer to 470-480bhp @ 1.7bar if we can extend the limiter to around 7800rpm with the fuel delivery to match.

It's a very smooth drive, more like a supercharger than a turbo. Very tractable with a frentic pace that only grows as you keep the throttle planted. It should be very kind to the transmission, and certainly driveable in many more conditions like yesterday.

is it possible to plot nigels old turbo result at 1.5 bar on the new graph.... ??

Nick

It is, but I haven't finished tuning it yet, so it's not really a valid comparison. There is a trade off between less mid-range and more top end, but I am hoping to narrow this gap once it is fully optimised. For now, Nigel can just enjoy

Leighton - I'm at Motormech on Saturday - I reckon Paul will have a fuel pressure test kit - I assume I'm expecting to see 3.8 bar at tickover, but how can I test the pressure on boost?

If the pump is struggling, I guess it will be because it's struggling at the top end

I wouldn't bother Nigel, you would have to test it at full throttle at high rpms to get any real result. I have a fuel pressure kit which I do use for diagnosis, but as I said above, your horsepower correlates with 100% injector duty on your current setup so there is no suggestion at all that you have a fuel pressure issue, just need bigger injectors!

Angelo's car which pushed out 518bhp on a GTX, well even with the 630cc injectors it was struggling for fuel at the top end, so we installed a second inline pump. The Walbro 255 pumps are rated to approx 500bhp, so it was no surprise that a second pump was needed. We use twin pumps (and if required a larger external swirl pot) on all cars above 500bhp, especially in the race cars.

well - I'm not expecting to reach 500bhp, so I'll stick with the single Walbro for now

I still think I'll get the static fuel pressure checked though - just in case

Hi Nigel,
Wow – a good result! I assumed a maximum output of 450HP with your small hotside…
It is clear for me, that the cold side (with new comp. wheel) is able to do much more boost – therefore the power graph is still climbing and probably this compressor could do now >500HP.
But your small hot side won’t go much further…
First evidence is this:

1.5bar
451bhp @ 6826rpm
368lbs/ft @ 6036rpm
402wheel power @ 6678rpm

1.7bar
457bhp @ 6575rpm
389lbs/ft @ 5702rpm
410wheel power @ 6482rpm

Between 1,5Bar und 1,7Bar 6HP difference, only…
I don’t think, that you will gain much more with a bigger fuel pump – maybe another 10HP, but not more.
Your results show, what has been proven by GTX series with new billet wheels already. In most cases a little bit more lag, but much more top end. But exactly this “more top end” you cannot use because of your 0,64 T25…

To your 3,8bar fuel regulator… unfortunately this regulator will effect in nothing in combination with your weak Walbro 255lph.
Please have a look to these graphs regarding Walbro 255lph:
http://www.autoperformanceengineering.com/html/fpspecs.html
At higher pressures the performance of this fuel pump will break down. Therefore it is senseless to heighten fuel pressure… this you can do with a Bosch 044 (which is still really strong at high pressures), but not with a weak Walbro…

Sorry for my words – I wish you much luck in still getting a few HP…
Juergen