- With the release of any new performance car, there's obviously some level of
delay before aftermarket components are released out into the market.
And with the A90 Toyota Supra becoming a fan favourite, obviously a lot of engine
builders and tuners have been looking for more power out of the engine.
Now we're here with Barry from Mahle Motorsports to talk about their just
released forged piston.
So Barry, when you are dealing with what is a relatively new engine and you're looking
at developing components such as pistons, what are your first design considerations
when you're deciding on the new piston design?
- Well for any kind of application, first thing to start with is what does the customer need?
What are they asking us for?
When it's something brand new like this it's a little bit harder but we know that with
a Supra, these customers are going to go fast with this engine and they're going to build it as
hard as they can.
So we started with looking at the OE data because Mahle makes the OE pistons for
these BMW engines which gives us a little bit of an advantage.
From there we worked into OK what kind of boost do we expect these pistons to see?
Which turns into crown thickness measurements and what material we need to use.
From there we just kind of work our way up and we end up with a great product
at the end most of the time.
- Now there's a lot that goes into that, I'm going to dig in deep on a few of those
components, the first of them is the compression ratio.
So with the stock BMW inline six engine being a direct injected turbocharged engine,
as with a lot of these engines, direct injection and forced induction, we are seeing quite
high compression ratios, that seems to work quite well with direct injection even on a
relatively low octane pump fuel.
But of course a lot of these tuners are removing the direct injection system,
reverting to port injection because there's a lot more flexibility and also increasing the
boost level so what did you decide to do there with the compression ratio?
- For our piston we actually dropped the compression by half a point,
based on that fact.
Customers need, if they're going to turn the boost up, they like a lower
compression ratio, they're going to run pump gas and also we decided to keep
our direct injected bowl in the centre of the piston, that way we know it's all in the right
space and it's in the right location.
If they want to keep direct injected, it'd be just fine but if they want to
go port injected, it's still in a localised spot on the piston to where we can
feel comfortable that the fuel and air coming into the cylinder is not going
to have any kind of weird turbulence or anything like that.
- Now I want to come back to that bulb, before we do that, is there still flexibility
in compression ratio or is that a fixed part with just that 10.5:1 compression?
- Right now in our catalog it's just a 10.5, we've already had a couple of people today
ask for a lower compression, they're going to run a lot more boost than normal
and that's something they can definitely call us up and we can do that.
- I assume that once you've got that base design, it's relatively easy to make
modifications to aspects like that?
- Yeah absolutely and it has a dome in the centre so normally less compression is the
easier version, going higher compression's where it gets a little tricky.
- Alright so you talked about that bowl and again for those who aren't really
aware of what you're talking about there, a common aspect with direct injected engines,
can you tell us why that bowl's important, what function does it serve?
- So the bowl is fixed right underneath where the direct injector comes into the
chamber, the bowl pattern is meant to distribute the fuel evenly throughout
the cylinder and make sure that the fuel is spread out in a manner to which it
can burn most efficiently.
That is something that we, our bowl design shape etc comes from the factory BMW spec
and then dimensions so it's something that we're really confident in and it also allows
us the chance to have a really solid dome design that's unique and that we know works.
- So it would be possible for a piston manufacturer to actually create some
major problems if the person tuning or building the engine retained the direct
injection and it didn't have that bowl because you weren't getting the
distribution of the fuel through the combustion chamber?
- Correct yes you could have some kind of localised hotspots or some kind of
detonation issue, if you're not distributing that fuel correctly it could definitely
cause issues.
- Alright so the BMW engine is an aluminium engine block and we're seeing a lot of
modern alloy engines now for weight reasons use a Nikasil coatings but this still runs
a cast iron, ductile iron sleeve?
- Correct yes.
- Does this mean that you can overbore the engine and are these pistons available in
oversize?
- The pistons are not available for oversize right now.
I believe they're running a 3.5 mm wall thickness around the cylinders,
I'm not 100% sure on that.
But we can definitely do an oversize if the customer wants it, we just do not
have it on the shelf right now.
- Now obviously at this point in 2019 these engines are essentially all brand new so
you're not dealing with something that's got 100,000 plus miles with a lot of bore
wear so are your pistons designed to be a drop in or do they still require some
machining to the bores?
- They are drop in, ready to go.
They are going to be lighter than the factory pistons based on some of the
features that we changed, the crown is actually thicker which is a good feature we can come
back to but with it being lighter, yes you'll have to look at weight balancing your
crankshaft but we figure if somebody's putting these pistons in, they're going to
the racetrack, then they're going to balance it anyway.
- Now you just mentioned the crown thickness so can you just talk us through
the importance of crown thickness in a high performance, high boost application?
- So crown thickness is important for a couple of reasons, one is the pressure that the
crown's going to see from just the combustion levels.
So you need thickness there just for support and two it's going to work as a heat sink to
get crown heat down through to the oil.
We've seen cases where if you have too thick of a crown, the heat stays in the alloy and
it doesn't actually ever get cooled off.
So there's a threshold there that you need to stay within and with our different
alloys I think we've kind of dialled that in over the years and with this part,
it's on the thicker side just because we know that that is what, these are going to see
high boost.
- Normally with an aftermarket forged piston, we tend to see the weight increase and given
the fact that you've just said the crown's thicker, again it would stand to reason that
you would be expecting an increase in weight so where has that weight saving come from,
where has the reduction in material come from?
- On this piston it's going to be from, one we're running a shorter pin.
That's going to eliminate some pin bending, we're also, when you say a shorter pin we
also have a thicker wall so you're going to eliminate bending but you're also going
to still have support.
When you shorten that pin, your pin bosses are going to come in which is going
to save you weight an it's also the undercrown, the way the skirts and everything are designed,
we put weight wherever we think it's going to be the most helpful for
a motorsport application.
- So at this point in time, and obviously it's a constantly moving target,
I think we've seen power figures hovering around that 1000 horsepower flywheel mark
from the A90 Supra.
Given your engineering design of this piston, where would you see the limits being
in terms of power potential?
- For the engine or for the pistons?
- For the piston.
- Well over 1000, well over 1000.
We have a design that's pretty similar for another BMW that it's around 1100 to 1200
right now and honestly I think that the Supra's a little more robust because I think people are
going to try and set more records with it.
- Yeah it's definitely a popular platform and we look forward to seeing where people get
to once more and more people get their hands on the engine.
Thanks for the chat there Barry and if people want to find out more about that
piston, where can they go to?
- mahlemotorsports.com is the first place I would go, that has the product listing,
it also has links to all of our tech videos.
Mahle Motorsports Instagram is very up to date as far as what's going on in the
office and all of our offerings, everything like that.
And also our YouTube channel is a great spot to check out any kind of feature videos
or customers having a problem putting something together, we've probably talked
about it on there and tried to help you out.
- Perfect, thanks for the chat.
- Yeah no problem, thank you.
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