- In the world of drag racing, the aim is always to get to the end of the strip
as quickly as you can.
Obviously this requires power and it requires traction so it might seem a little bit strange
bringing about a class which is, in this case the X275 class where the cars are forced
to run on a 275 mm wide radial tyre.
But that's exactly what this Supra behind me is built to run on.
We're here with Varun from 101 Motorsport to find out a little bit more about what goes
into building a competitive X275 class racecar.
So for a start Varun, as a tuner and obviously here as a driver and builder of this car,
you kind of seem like you might be putting yourself on the back foot running in that
X275 class, what's the appeal of running in that class, and I do know that it is a very
competitive class with a lot of people racing in it.
- Obviously a lot of restrictions, keeps the class very tight and just being able to,
it's all about power management in this class.
It's an amazing tyre, the amount of power you can actually put down in these tyres.
Once you make the tyre hook, you can just feed it all in and it's amazing around the
whole world what people are doing with these tyres, taking over, it's a new class,
and as I said it's controlled, it keeps everyone honest I guess.
And yeah it's the new fun, exciting class and I think it's a lot more affordable because
of, as I said to you earlier, a lot of the events are 1/8th mile racing so you're
only going half track, half time, your engine lasts twice as long.
- You're not actually beating up on the components quite as bad?
- Yeah and it's good like it's really opened it up for a lot of people.
Not only the 275 but the smaller tyre classes, radial things it's really kicking off.
And it's really good.
- I just want to talk a little bit more about that tyre 'cause I sort of made out that it's
a real deficit in terms of traction but the reality is as you've sort of addressed there,
it is actually amazing, the amount of traction you can get out of that 275 radial tyre.
What sort of ETs are these cars running, in fact what's the best ET you've run in
this Supra?
- Well going back to how much the tyre can actually cop, it's all about the start line.
That's the big trick here.
Controlling the power on the start line.
A lot of people, you go out, 'cause this tyre once it lets go of traction, that's it,
you're finished, the run's over.
So you need to plan it and then go, that's the whole tricky part of it.
But back to your other question so our personal best is a 6.79 at 212.
- Could you give us some perspective here in terms of the Australian record,
where are you sitting?
- Australian record, so obviously we're a Supra, 2JZ, straight six, there's a lot of
people, big block hemis, twin turbo, 500 plus cubed running in our class.
So obviously they're making a bucketload more power.
The record I think on this tyre in Australia is, I think it's in the 6.50s.
There's a lot of people in the 6.60s.
But I think as far as the sports compact people go such as ourselves, I think we're
number one at the moment.
- So you just mentioned that there is a wide variety of different engine combinations
and chassis in the class but the 275 tyre basically is the leveller of the entire field?
- Yes that's correct so all makes, all models, all engines, you name it.
There's obviously weight restrictions, restrictions to what you can do with the
chassis, suspension, depending on the power adders like if you have two power adders
then it also, it limits your weight as well so you can't keep going down down down and
add more power, if you add turbo plus nitrous then I think it has to go 100 pounds
over the minimum weight.
Things like that, so it does keep the field very level.
- Now a lot of the cars we're seeing here at Sydney Jamboree 2020, we've got full
tube chassis cars and obviously it gives a lot of flexibility in the design of the car.
It's pretty apparent straight away looking in the engine bay of your Supra here that all of
the factory strut towers are still in place.
There are pieces of the bodywork that have been cut away but essentially it's still a
full factory chassis, can you talk to us about why you've gone that path,
is that a requirement of the rules?
- As far as the rules go for the 275 class, you can't modify the chassis as such,
you have to keep the factory rails.
So we've built this whole car full stock chassis, stock body.
As far as body goes, you see there's a lot of people that run in 275 class,
actually in this particular class, there are full chassis cars running in the 275.
So rules wise, I'll have to sort of touch up on that but from when we built the car,
the rules have sort of changed.
So when we built the car, we weren't allowed to do a rear half so a lot of people cut the
chassis halfway and they'll do a rear clip, so like a full aftermarket chassis from the
half back so then they'll put a four link and all that sort of stuff.
But when we built the car, we went according to the rules that we weren't allowed to
touch the rear chassis so we've just kept the whole car as standard as we possibly could.
So it just looks like the Supra.
- Now seeing as you've just been talking about the rear of the car, one obvious and fairly
dramatic change that you have made, factory Supra, obviously an independent
rear suspension design and you've gone with a live rear end which is obviously
common place in drag racing circles.
Can you talk to us about the advantages over an independent rear suspension
for those who maybe aren't quite up to speed with drag racing technology?
- Yeah so the main, obviously the biggest advantage is strength and being able
to control the tyre, the footprint of the tyre on the drag strip, obviously independent
rear end suspension when the suspension travels, the camber changes, the toe changes,
it's a lot harder to keep that tyre planted because the camber's going in or out
or the toe's going in or out so it's a lot more difficult.
So for the guys that are still doing the IRS thing, it's really cool to see what they're
doing and obviously, with an IRS car the way they transfer weight, the way they need to
transfer weight to make the car get out of the hole is a lot different to the way a live
axle rear car transfers weight.
You'll often see the IRS cars, they'll hook and they'll bog and you'll see the back
of the cars almost touching the ground but with a live axle car, as the tyre hooks,
you see the diff sort of twist forward and the body actually lifts away from the diff
so the car, as the diff is pushing into the ground, the body actually separates.
So it's kind of opposite.
So you'll see in the back of this thing, the shocks are actually upside down.
So it works different, it's a lot to get your head around to set these things up.
This is a live axle, because we didn't want to cut too much away, we stuck with the ladder
bar so obviously just single bar, top and bottom linkages.
So you can adjust the angle...
- Little bit simpler than a four link?
- Yeah a lot simpler than a four link but obviously doesn't need the upper and lower
arms, just one arm that does the adjustment.
- Alright let's come back to the engine bay, obviously, 2JZ, we're no stranger to those
engines, they've been well proven time and time again and a number of competitors now
in the five second zone with the 2JZ engine.
So can you start by telling us how much power you're making with that engine
and what sort of boost pressure you're running?
- Currently on the hub dyno, 2100 horsepower, 75 pounds of boost.
And that's where we're at at the moment, that's what we'll be racing with this weekend.
- Methanol fuel to do that?
- Methanol yeah of course, methanol fuel, 12 2400 cc injectors, big Waterman fuel pump,
we have water to air, like an ice box intercooler.
- Now I wanted to talk about that water to air intercooler 'cause that's pretty apparent
there in the front of the car and you've got the icebox sitting there on the passenger side
and a lot of competitors when they're running on methanol fuel, we almost see a 50/50
divide between competitors who run no intercooler and those who do.
Obviously the methanol fuel runs very cool and the ability for it to absorb heat out
of the combustion charge as it goes through a phase change means that we can get
away with no intercooler so why have you made the decision to stick with an
intercooler when it's a potential weight disadvantage?
- As you know, the cooler the air the more power so we've gone with that just so we
have a bit more consistency when we're tuning, when we're running.
And just have that little bit of a chance for it to make more power.
There's a fine line, there's a bit of a, you have to make a choice like do you
want power or do you want, if you have more power, you can put more weight in.
So yeah it's a fine line there, you have to sort of compromise with that.
We went with the water to air just because of that reason.
We start the run, we start our run, our intake temps are sub 20 degrees, at the end of the
run at 75 pounds we're seeing 80 plus now so around 80 degrees but you'll see that.
And also it makes tuning a lot easier so obviously with hotter air temps then as
you know we have to pull ignition timing and whatnot.
So monitoring the exhaust gas temps and all that's very important here also.
But yeah we run that, just a bit more consistency and we think it's got an
advantage, even though I think we're putting another probably 50 kilos
in the car because of it but I believe that running that would make another
150 horsepower.
- So it's paying for itself.
- Yeah so I think that that decision that we've gone to do that, water to air,
is definitely paying off for us.
- Now another thing that's obvious is that you have chosen the billet block.
And I feel like at 2100 hub horsepower you're probably kind of in that region
where it's been well proven that the 2JZ cast block can handle that power,
probably on that line where you may want to go one way or the other and there's a lot
of people out there who will argue, if you go billet is it still a 2JZ, I don't want to
get into that argument but can you talk us through your own decision process
with why you went billet over cast?
- So previously the cast engine was doing a good job.
We realised that when I was driving and looking through the data I realised that
the car's going to perform a lot better with more RPM so when we looked into building the
engine for more RPM, the stroke, the previous engine we had was a 3.4 so obviously
revving the 3.4 wasn't very...
- With the longer stroke, the piston speed starts to get pretty scary plus your rod
to stroke ratio?
- So it wasn't ideal so we wanted to go a 3.2 but what we ended up doing was a
3.3 and trying to bring the rotating mass down, we wanted to bring the
rotating mass down as much as possible, the only way to do that and keep strength,
aluminium rods.
So with the cast iron block, we couldn't physically fit that rod in there without taking
too much of the block away, the bottom of the bore obviously has to be cut
out and all that sort of stuff.
- The aluminium rods for those watching who maybe aren't familiar, they're a lot
lighter than a conventional steel rod but the problem is that they are also a much larger
rod so that's where you're talking about the clearance to the bottom of the bores?
- Literally double the size so if you see like an aluminium rod next to a conventional
steel rod, it's double the size.
So when that crank is swinging that around, it needs a lot more room so yeah to do that
and to keep that strength in the block, we had to go the billet route.
- So at this point, would it be reasonable to assume that going from the cast block to
the billet block, if we take out for example here the alloy rods, making a necessity,
you're not necessarily seeing any additional power or performance advantage from the
billet block over cast right here where you are now?
- No just literally, just for strength.
That's all we've done it for and I think, we were going very good with the cast block
and realistically I think, and we were only grout filled so if we went full grout,
I think we would have been close to still running the same times that we are now
but it was just peace of mind for us that we have that strength and the engine can
handle this power without having to worry that it's going to let go.
So yeah it was more of a thing where we just did it for insurance.
Obviously crashing it, failures at this speed can be very critical.
- Definitely, you've got to take that safety pretty seriously.
Now the other thing I want to talk about here is the drivetrain.
We've talked about the rear end but you've made a point a couple of times
already about making sure that that tyre stays hooked up and this is where the
transmission really becomes so key.
And we've seen a lot of competitors with manual base transmissions or maybe
Lencos or Liberty, G-Force, whatever.
And particularly getting out of the hole might be alright but then on the gear shift
the power is interrupted and this can disrupt the car and basically lose traction
so can you talk us through your direction with the drivetrain?
Or transmission I should say.
- So we've gone for a TH turbo 400, it's a three speed transmission,
trans brake, it has a lot of transmission pressure control valves in there.
The torque converter itself, we've just recently added a lock up clutch in the
converter.
And yeah it's a big job, we're controlling the transmission in three different ways
on the start line.
It's really tricky so obviously with a torque converter you have that degree of slip
all the time and as you said with the gear changes and disrupting the load in the tyre,
you'll see that a lot of people in this class run an automatic transmission because
that gear change is a lot smoother than a manual transmission or a clutchless
transmission so it does keep the load on the drivetrain.
Now I just want to come back and just talk about this torque converter and the slip.
So the torque converter really in an automatic transmission takes the place of the clutch
and particularly it does seem to make here with drag racing, the car a lot more
consistent run to run, there's no maintenance in terms of adjusting a slider style clutch.
But the downside is that in most instances with a torque converter, there's always some amount
of slip which means that you're essentially giving away a little bit of power, it's just like a
very marginally slipping clutch.
So you mentioned a lock up converter, can you talk us through how that works
and where the advantage is?
- OK so a lock up converter, so at this, once we reach this power level, 70 plus
pounds, we started to find that no matter what we did with our converter,
we were always getting more and more slip, as we turned it up, the slip through
the converter, as you said just like a slipping clutch, it was just slipping more and more.
So what the lock up converter does is there is a clutch, there's clutch packs in the centre
of the torque converter and it's controlled by a solenoid, oil pressure controlled,
so the way we control that is we haven't even turned it on yet but we've used it
on the dyno and it's definitely taken the slip away and it carries the power through
the whole rev range instead of it used to fall over because of that converter slip.
So what it does is it's opening the solenoid, we control a solenoid through the ECU.
When it opens, it'll open the solenoid, through the input shaft of the transmission,
that solenoid will allow oil to go in and fill the drum, the clutch packs in the
middle of the converter, when those clutch packs grab, it makes the engine to
transmission a 1:1 drive.
- So the idea there are you using that sort of basically once the car's past the 60 foot,
once you no longer want or need the converter to slip?
- Yeah so what we're sort of aiming for is we're turning it on, so we're turning it on
under three conditions and that's race time, throttle position obviously, 'cause you need
to make sure that you're into it.
And driveshaft RPM 'cause obviously once the converter locks up and goes 1:1 you need
to make sure the engine's obviously going to come down to whatever the driveshaft
RPM is so it's kind of like a fine line that we have to sort of pick where to turn that
on because as soon as that lock up converter, as soon as that lock up clutch comes on,
the engine will be dragged down.
So at the moment we have it set at 7500 RPM but I think we're going to
erase that because I think it's a little bit low but it's just to see, obviously today's
testing, we'll see what happens so yeah but we did check on the dyno, we checked
its operation and yeah definitely when you overlay engine RPM and driveshaft RPM,
when that lockup converter comes on, then you see the engine RPM come
down to what the driveshaft RPM is and then they'll come up together.
So we're hoping that we can really utilise this torque converter and turn
it on at the correct time.
- Look it's been interesting getting some insight into what makes a competitive X275
class car, obviously here at testing today for Jamboree we wish you all the best and look
forward to seeing how you go tomorrow, best of luck.
- Thank you Andre, always a pleasure.
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