- In a word where most RB26 owners are ditching the stock twin turbos in favour
of a big single, the Integrated Motorsports R34 GTR is bucking that trend and they've
actually gone back from a big single to low mounted twins.
We're here with Peter from PMC Race Engines to find out why they've made that switch.
So Peter for a start this car has been developed over a number of years.
Last year when we were at World Time Attack Challenge it was running a BorgWarner EFR 9180.
Let's go back to last year, what sort of power were you making on that turbo and what sort
of boost were you running?
- Well the big problem with the EFR is we maxed it out and it just didn't have any
air left at about 950 horsepower and we really needed to step it up because cars
were just getting out of control.
We really wanted 1200 horsepower and there just wasn't any single turbo that we could
pull off a corner and just have no lag and still have that 1200 horsepower.
- So basically when you're in that BorgWarner EFR range, the 9180, that's the big boy,
that's the biggest turbo that BorgWarner produce and it is rated essentially around
that 1000 horsepower mark.
It's not that surprising that you were basically on the limit at that power level.
Now as you've sort of alluded to there, there are definitely a lot of turbos in the
single turbo variety that are capable of much more than 1000 horsepower but
you had a problem in that the area you wanted to be in, you kind of fell into a
grey area in terms of turbo selection?
- Yeah it's so important to have a snappy throttle response and you need that throttle
to be like a really big NA car as you come off a corner and the big single just won't do that.
Yes it'll have that 1200, 1300 horsepower no problem with the big Precision or a Garrett
but it just doesn't work on the track so we had to go to twins and when Garrett brought
these 660s out, it just changed the game.
- Alright so the turbo you've just alluded to there you're now running a pair of the
G25-660s.
Now they're probably 18 months, maybe two years into the sort of public release of that
G series turbo but they are still relatively new and particularly at the point in time
where you guys made the call to go twin G25-660s, there wasn't much data if any
data out there.
So that's a ballsy move, how do you sort of, talk us through how you make that call
that this is the turbo that's going to work for you.
- Well knowing turbochargers and reading the maps and really searching for what you,
these products, we're just so much R&D that we took a gamble because we didn't
know for sure if they were going to be as good as Garrett said they were going to be.
Lucky for us they were.
They really do snap on and when you push them they just carry so much top end.
At 35 pounds we're seeing you know over 1200 horsepower at the engine and yeah
it's just changed the game, there's just absolutely no lag and it's just like a really
big engine.
- Alright so you've got 2.8 litres as well feeding these turbos so that's not a small
capacity engine but still you've only got half of that feeding each turbocharger so
what sort of rev range are you getting out of the G25-660s, or essentially I guess the
other way of looking at that is, what's your boost threshold, where are you seeing
full boost?
- Look it depends on where we put our inlet camshaft but we can have 30 pounds of
boost at 6000 and over 1000 horsepower.
That's a little bit too riling and we have to actually back that out a bit to give
it drivability off a corner otherwise we have four tyres exploding you know.
But we try to blend the boost in and we try to make about 1100 from 7000 to 10,000.
We try to roll that through that period which is a really strong flat torque curve and it makes
it very fast.
- Now I think that's an area that a lot of people overlook.
We talk a lot about lag and the downsides of lag but we're talking there maybe about
an engine that's only producing 400, 500, 600 horsepower where you can put all of that
to the ground the second it can make it but when you're starting to talk about 1000 plus
horsepower, there's that fine line between the turbos hitting so hard that it overcomes
the traction available and causes wheel spin.
So that's just the area you are sort of talking about there, getting that fine balance?
- Yeah I mean without the management systems we have today, we're running the MoTeC M150
and we're using traction and boost strategies and it's imperative too because we're running
a small tyre in these cars and we'd just blow the tyres clean off them.
So we bleed that boost in and each gear we're putting a little bit more in with
wheel speed and that's the only way we can get it done.
- Now a comparison that I'm personally really interested in, if you overlaid the
boost and the power graphs between the 9180 and the twin G25-660s, who wins,
where's the winner there?
- The twins kick ass.
- So the twins are better everywhere?
- Yeah they're absolutely fantastic.
I was surprised myself with them, they just really work, they really come on and they're
on easily 500 earlier than the 9180 and they just draw a line straight over the top of them.
250 extra kilowatts with the same boost.
- OK so there's been a lot of debate out there in the general GTR community about this
twin versus single debate and the general consensus is at least in the street to
relatively highly modified GTRs, the single turbo is the way to go.
So do you put that down to packaging constraints around the way people are
using twin turbos?
A lot of them obviously are designed as generally basically replacements for the
stock twin turbos, or is it just these G25-660s are that much better than what's
previously been available?
- Yeah definitely the technology's improved, wheel technology's come so far.
You know when you talk about a dash five or dash seven from the past,
they're 30 years old but that's not the whole story.
Big singles have just got so much better and the 35s, the 87, 6870s, the 9180s are just
fantastic turbos and they're very hard to beat but there's that one spot where we
need to be able to go a little bit further and still have that drivability and the twins
do that but the only downside to these big twins is that you really need to run a higher
pressure ratio and that means that you have to drive that wheel very hard.
Now that doesn't work so well for a road car because it's so savage.
You really have to have your tune just so good, otherwise it really ends badly.
- I will argue that there's potentially one other downside with twins and that is the
packaging, there is a lot going on in that engine bay and I certainly wouldn't want
to have to do any servicing work on that rear turbo.
But of course that is a price you pay, you know you're going to be facing that
sort of problem so it's kind of a given with the twin turbo package.
Now look it's always nice when a plan comes together, you've gone and made what at
the time was a bold move going to a relatively untried turbo and it has worked out for you.
Now there's still a couple of sessions left this afternoon at World Time Attack and we
really wish you guys all the best and hopefully the car can put down a representative time
with that new package.
Thanks for the chat there Peter.
- Thank you very much and we are going to turn it up now so hopefully it all goes
well and Matt can do a really good time.
- Best of luck.
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