- Engine swaps are pretty commonplace in today's motorsport world but one of the engine
swaps I haven't seen before is swapping a 13b rotary into a GCA Subaru WRX.
We're here with Scott from Mofab to talk a little bit through the process that he's gone
through with this car behind me.
So Scott, for a start, the swap from the EJ20, the EJ20's a pretty well proven platform.
Yes it's got it's weaknesses but some could argue that the 13b's got plenty of its own.
So what was the impetus behind ditching the EJ20 and going rotary?
- Something that sounded cool, was different, potentially lighter with the
billet plates, not there yet but when we can.
And the dry sump.
So didn't really want to have to put a dry sump on the car yet.
As you can see I've spent more money on getting this in here now but at the time
I thought it was going to be easy to do and things have changed.
- Yeah hindsight's always a really easy thing to look back and when you've poured
so much money at some point you've just got to keep on going.
So understandable maybe looking back that dry sump system for the EJ might have
been a cheaper option.
So obviously no dry sump on the 13b, is it not a requirement with the rotaries,
do they not have oil control problems like a boxer engine does in a motorsport
environment?
- Yeah the windage issues associated with this engine compared to something with
a crankcase and the crankshaft and all the stuff spinning around, not an issue here.
They are making dry sump systems now for this application but at this point still with
some of the design work that I've done, unnecessary.
Now one of the aspects of the Subaru platform of course is the four wheel drive
system and interestingly you have managed to retain that with the rotary engine.
Is it a challenge to do so, is the rotary one of the few engines you could transplant
into this and still maintain the four wheel drive platform?
- Yeah so I needed a package that was going to be fairly short, the rotary was about
the only one that fit that.
With the adapter plate it moved the motor about 1.75 inch forward.
So to combat that I moved the whole engine and trans package back three inches to get
a little bit behind where we were and that's about as far as I could go to keep the axles
from binding in the front.
- And for those who aren't aware with the Subaru transmission the front drive comes
out of the front of the transmission so it's not like a prop shaft that runs forward to
a separate differential.
Now in terms of the transmission as well, this is something that the early GC8 five
speed gearboxes were renowned for being made out of glass, they break
pretty easily so what have you actually done there in terms of gearbox strength?
- Unfortunately right now zero, it's still a stock '04 STi six speed.
We got plans to put a trans cooler in it, six speed sequential is probably the next,
where we need to go probably from here moving forward.
- So what's the process of adapting, in this case the 13b up to that Subaru
six speed transmission, how difficult is that?
Are there off the shelf parts of is this something you had to actually design
from scratch?
- Off the shelf parts, we tried to talk to Kennedy Adapters out of the U.S.,
they said that they were out about eight weeks on getting the parts so we started
looking in your neck of the woods and contacted a company actually based out
of Australia that had used this application for flipping the motor around and putting
it in the back of a beetle.
There's a lot of rotaries down in Australia, Subaru trannies are stronger than the
Beetle transmission so that's why they'd made the part.
- Alright so the engine you've got there now sitting maybe a little bit higher than a
horizontally opposed boxer four cylinder, have you got any numbers on what the
weight difference is and whether you've moved the centre of gravity higher in the
car going to the 13b?
- Corner balance weights, front corners are about 750 ish, rears are about 350 ish for
the rear stuff.
- So have you got data like how much different that was to the EJ?
- Not that I can remember off hand but with the additional weight of the other
turbo it's probably about the same as what it was before.
- Alright seeing as you've just mentioned the turbo system, that's probably the next
place to move onto.
And you've gone with a fairly unique setup here running a twin system instead
of what most people would be going these days to a large single.
So what was the driving force behind that decision?
- So trying to keep the I guess the snap throttle response on right.
So smaller shafts, less weight, little more complexity with packaging but based off
the fact of how we built the car anyway, I wanted something that was going to stand
out like the rest of the build to begin with.
Little louder.
Transient response is great with the twins, little wheels, they light up really quick.
It's really simple with the rotary setup because you've got a tube for every turbo
so you just pop 'em up, set 'em on.
We're running a single TiAL wastegate 60 mm to keep the boost in check.
That seems to be working great with wastegate priority and stuff like that.
- Now in terms of those turbochargers, what is the specific model you're
running there?
- So I have two G25-660s with a 0.72 outside.
- OK so this is one of the newer or relatively new releases from Garrett with the
G series and obviously the design there was to try and reduce the weight of the
components and again get that boost response up so obviously all of that
working in parallel with what you're trying to achieve there.
Now at the moment you are running from what I understand, a stock engine,
is that correct?
- That's correct yep, stock port as well.
- So what's that engine producing in the way of power with those two G25s?
- Currently right now at a bar of boost we're making 450.
- Is that 450 at the wheels?
- That's at the wheels yes.
- What sort of dyno's that on?
- That's on a Dynojet.
- Are you looking at increasing the boost pressure or is that the limit for the stock
motor as far as you're concerned or are you looking at building a motor that's
going to be able to support more power?
- So with the weight of the car, it weighs 2700 pounds,
we're trying to get the power up.
This car, really to be competitive needs about 650 to 700 but we also want to work with
reliability as well so I think 650's probably going to be the magic number for now
until we can prove the rest of the package and make sure everything else works.
- Just to be clear though, the 650, you're not going to try doing that on the
stock engine?
- No no no we'll pull it apart and, billet plate potentially, stud it, port.
- Now in terms of rotary engines, they do unfortunately have a bit of a reputation
for being unreliable and a lot of that, in my opinion is maybe not entirely
justified, we see a lot of poorly built engines and we see a lot of poorly tuned rotary
engines and of course they do need to be treated with kid gloves in order to get
them reliable.
In terms of the tuning on this, what are you using in terms of electronics to make sure
it's going to be reliable?
- So electronics package is am AEM Infinity ECU, Ecumaster PMU.
- For those who aren't aware, PMU that's their power management unit or power
distribution module so basically solid state control instead of relays?
- Correct yeah.
- And the fuel system on the engine?
- So FIC 2150s, we got six of those.
Dual Bosch 044 pumps and a Radium surge tank.
- So six injectors for two rotors, so how are you staging those and how are they
controlled?
- So primaries, secondaries, the secondaries come on after, you'd have talk to the
tuner when he has those dialled in.
- So safe to assume they're a single primary and two secondaries per rotor,
is that how you've got it set up?
- Correct.
- And again the rotaries do have a fair appetite for fuel so the staging there
is quite critical in getting a nice smooth powerband without any big steps.
Now in terms of the boost control, are you running that through the ECU
as well?
- Yep three port with the AEM.
- And are you using anything in terms of speed or gear based boost control to
make the power delivery a bit more usable?
- So we do have the option to log turbo speeds, we don't have that set up yet
but we have it there along with e map as well.
- Now what is the car actually being raced in, what sort of classes are you competing in?
- So I built the car for time trials, started to get into the time attack stuff with
Gridlife and then would like to try to do some global time attack stuff as well.
Maybe COTA with Super Lap Battle, things like that.
And then eventually make another stab at the hill climb.
- Now you're talking there Pike's Peak?
- Correct.
- Now in terms of the car, the class you're running in, it looks like you've gone
some way torwards an aero package on it, is that limited by the rules for the classes
you're racing?
- Yeah according to the rules I can't have a complete flat bottom so currently
the car's got a front splitter, rear diffuser, but we're going to try to find some ways
around the rules to be able to kind of make those things come together.
- Have you got any ideas on how much downforce that's all producing right now?
- With this wizardry, no, no not at all, we're looking at designs of different cars,
putting 'em together and talking to some people that have a pretty good handle on
what works and what doesn't work and trying to apply it as best we can.
- Alright look Scott it is a work of art, particularly if you look into the engine bay,
you can see the attention to detail that has gone into it.
It's already an impressive package even on that stock engine so looking forward to
seeing what you can get out of it with a built engine that can take a little bit
more boost and seeing what it makes once you get to push those G25-660s to the limit
so best of luck for next year's racing, thanks for the chat.
- Appreciate it, thank you.
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