- When it's time to modify an engine and make a lot more power, one of the common
modifications that is made is to go to an aftermarket inlet manifold or plenum
chamber as we also refer to them as and these days we are often spoilt for
choice with a lot of aftermarket manufacturers with offerings for a variety of popular cars.
Now we're here with Shannon from Plazmaman to talk a little bit about what goes into the
design and development of an aftermarket plenum.
And Shannon you've got products for a range of cars and we're a little bit bias here,
we are running one of your plenums on our SR20VE turbo engine so I've got first hand
experience with them.
I'm interested to talk to you a little bit about the development process you go
through and I know here at World Time Attack you are just debuting a prototype
for the Mitsubishi Evo 10.
So when you're starting with a blank sheet of paper and looking at an upgraded
inlet manifold that's going to actually give some performance benefit, what are
the first elements that you need to consider before you ever start actually
manufacturing?
- So first of all we have to look at obviously space constraints.
That's probably the biggest thing is what we can package in there.
Secondly will be the customer's requirements or the target audience.
So what sort of power they're looking to make or are they out of injector for example.
Also sometimes it's mostly about improving efficiency as well but really it's just about
what the customer needs.
- OK so I just want to start with, there's a few reasons why we may want to upgrade
a plenum chamber and obviously one of those elements is power and that sort of also comes
into its own when we're stating to chase really big power levels, very high boost levels
and that's not going to be for everyone.
At that stage the factory inlet manifold may start to become a restriction.
The other element though is that let's be honest, they are a great looking item
so they do a great job of sort of tidying up an engine bay as well so the aesthetic
element still a consideration when you're designing these?
- Yeah so we do try and make them as aesthetically pleasing as possible.
I mean you are spending a lot of money on something like this so you do want it
to look good as well as perform.
- Now one of the questions that our audience probably are wondering is let's say I've got a
lightly modified turbocharged engine, maybe it's a 4G63, maybe it's an RB26,
something relatively common in the JDM tuning world and maybe we've got an
aftermarket turbo fitted to that and it's still a street car, it's not an all out race car,
by fitting just the plenum chamber and no other changes over and above what
we've already got with that aftermarket turbo, can we expect an improvement in
performance or is it really once we start fitting massive turbos, massive boost,
massive RPM that these plenums come into their own?
- Well it does really depend on the engine, some do respond better than others.
But as a general overview, majority of them won't really respond until you've
got a lot of boost into them where they start to, either their airflow distribution
will become an issue or even throttle body sizing can become an issue and
generally you'll start to see the power gains just aren't there as they rise and
that's sort of when something like ours will come into its own.
- So we've seen this ourselves with a variety of cars where with the factory
inlet manifold, once we get higher in the RPM range, higher in the boost, you start
to see the power curve roll away and then you can go to something like one of
your plenum chambers and the RPM, at higher RPM it tends to just hold that
power further into that rev range which is what we're sort of saying there?
- Yeah so sometimes you'll just find that the engine simply can't consume, it's
wanting to consume more air and the factory inlet or throttle body is the
restriction and it just can't provide it.
- Now in terms of the actual design and validation before you start making the
product, there's a lot that goes into the airflow path and trying to optimise that,
is this something that you're doing from experience and by eye or are
you using a flow bench or CFD to kind of design the part to be the best it can be?
- So it probably is a combination of both.
So the main founders of Plazmaman have got many many years of experience so
they do know as a rough guide what's required.
From there, from that concept of what they say we'll then take it to an electronic
platform and do things like CFD where we can work out what's the best balance between
them because sometimes having an inlet that can make the most amount of power
overall will actually not be as good as something that has a broader mid range
and is much more drivable and you can actually put down more power sometimes
in that sort of application just doing that, having a better window.
- Yeah I think it's something that's easy to lose track of.
Obviously everyone likes a big dyno power number but what is really easy
to overlook is it's not always just the peak power value, it's the area under
the power curve that actually becomes more important and this comes back to another
element with the inlet runner length.
Now in a naturally aspirated individual throttle body world, it's very common to
test on the dyno with a variety of different length trumpets and find the
best compromise of where that gives you the best power curve.
That's a little bit harder to do when you're talking about an aftermarket plenum chamber.
Do you do any validation around that with making different length runners?
- So we do but again engine bay constraints can control that as well.
I mean anyone who makes an inlet manifold has to come up with the same
thing, unless you've got a complete race car where you can remove material,
that is sort of what's going to dictate the overall ability to make the most
efficient inlet but yeah we certainly do test and develop these things and try
and work out what's going to be, like again you are catering for so many different people
when you make one of these and you're just going to have to try and bring the best
overall package so yeah it is a bit R&D involved but at the end of the day it's the
greater overall balance that you're looking for.
- OK so another thing that I wanted to ask you about was just the volume of the plenum
chamber in general vs engine capacity, is there general rules of thumb around this?
Is it a case of big is better or is it not quite that straightforward?
- No not quite straightforward, you will lose air speed and throttle response
if you go too large.
Yes again, wide open throttle, not really going to make a difference but yeah on a
street car you'll certainly notice it, that's for sure.
I have spent a lot of time talking people out of going bigger is better, especially on
things like RBs.
They all seem to think you need a 100 mm throttle body and the biggest plenum
you can fit but it's not the case.
- That's a nice segue into the throttle body itself and another reason that someone
might be wanting to fit an aftermarket plenum chamber is the freedom to then
add a motorsport drive by wire throttle body to a car that was conventionally
cable throttle.
Now I know there's probably some people listening who have their own views about
the pros and cons of drive by wire, we're not here to debate that, it's a
technology that a lot of people are embracing so yeah talk to us about that
throttle body sizing vs power requirements and why a lot of people are going too big
and what the downsides I guess of going too big with your throttle body are.
So by going too large in your throttle body, there's a few things.
Air speed is the most important one so yes you basically, pedal ratio is another
thing which people don't really talk about but I mean you think about it, if you've gone
from a 60 mm throttle body to a 100 mm throttle body, you've gone, well basically
doubled the size of it.
So whey you put your foot down, what used to be half throttle is now full throttle.
- The throttle modulation as far as the driver's concerned, which affects the
torque that the engine's producing at part throttle, that whole feel is completely
changed, what you're getting for a certain throttle opening is now completely
different?
- Yeah and we get a lot of tuners who bring us, a lot of Skylines and things like that
and they'll say this car has an 85 mm throttle body and it's a 2.5 litre engine, I can't tune
this car, it's simply like a light switch and this is half the reason, because it's all
or nothing.
- So I mean there are some tricks to a degree, we can get around some of that
with the mapping of the pedal position vs the drive by wire but it's not a magic
bullet that's going to fix a combination where the throttle body is just physically
way too large for the application?
- That's right it's definitely not the way to do it.
Just getting the right size throttle body and the best packaged inlet and the most
efficient combination is always the best way to do it.
- OK so just to give our listeners, our viewers some sort of actionable numbers, if we were
to talk about let's say for example, well a couple of examples, maybe a
2 litre, 4 cylinder engine in maybe the 400 to 600 horsepower, a solid street
modified engine, what sort of throttle body size would you see being suitable
for that application?
- Somewhere between the 60 and 70 mm would be fine.
I use a really good example with a lot of people, I know you're sort of talking
4G63 here but a Barra for example, it has a 70 mm butterfly so it's 80 mm
outside, 70 mm inside.
That'll support 1000 horsepower so we kind of have a general rule, so for around
60 mm, it'll support around 800 horsepower, after that, yeah 72, 74 drive by wire for example,
they're good for about 1000.
Then you can go 85s, 85s are usually good for about 1500.
After that, yeah you know, I mean I've seen a 90 mm LS throttle body make
2200 at the tyres.
- So those people who think that they need a 90 mm throttle body on their
street driven 4G63, they're not in the ballpark.
- Yeah exactly and we basically say what you should do is try not to over throttle
body things.
Try and measure your pressure drop, so measure in the inlet and before in the
intercooler pipe, see how much of a differentiation you've got, sorry bad word.
- Differential pressure across it.
- See how much of a difference you've got there.
If it's more than about 4 psi then it's probably worthwhile changing.
- Yeah I think it's a common misconception where people see people fit larger throttle
bodies and think that that's a must have without actually testing to see if that
restriction actually exists in the first place and obviously there's no point throwing
money away for no reason and as you've just said you've got a lot of downsides that come
with that throttle body that's too large as well.
Now the other element you talked about was fuel system restrictions, can you
elaborate on what you mean by that and how you can fix that with your plenum chambers?
- Yeah so sometimes it's very very hard to get a large enough injector when you're at that
power level in a single injector and it means that your cold start, your cruise, and just
general drivability is going to be affected because of it so by going to two injectors
you can either run one small injector and run one large injector so you can do your
small one for cold start cruise and the large one for wide open throttle.
Or you can run two injectors the same size and again just make the car much more
drivable and be able to have a higher power output.
- Now an interesting element, I'm sure it's not just Plazmaman that are doing this but
again we're running your product on our SR20 and what I quite like from a plumbing
standpoint is the fact that your duel injectors are side by side so you don't
need two fuel rails and the complexity that goes along with then plumbing lines
to those.
Now I posted something up about this quite a long time ago on our Instagram and I had a
few people raise a concern about fuel distribution if you're only running one
injector at a point given that it's essentially flowing the fuel primarily down one inlet valve.
Have you got any thoughts around that, is that a concern, is there any real merit
to that or do we get enough of a homogenous mixture formation anyway by the time it's in
the cylinder that it just makes no difference?
- Yeah so it is a valid point.
What we find is when people do do this, they might run only one turned on, they'll
usually only do it for very light boost and for cruising and then they'll progress
or stage into the second one.
In reality though, it is pretty much well atomised by the time it gets there.
I mean we haven't had any failures from it at all but I mean I wouldn't personally
run it that way.
But yeah it's just that's what most people, that's sort of the general rule
is just to run the one injector just for cruise and very very low boost.
- Which is exactly what we're doing.
It's really more about getting the idle quality to be really really nice with a
small injector which you just can't do if you were to run a single and certainly,
at least in our application by the time we're into positive boost and higher
in the RPM, we're running both injectors at the same sort of duty cycle so it's
kind of a moot point.
- ...be important so yeah.
- Last point I wanted to talk about here, sort of to circle back a little bit to the
validation and it's easy to assume that a factory inlet manifold, even aftermarket
inlet manifolds are providing equal flow distribution of air to every cylinder.
And sadly that's not always the case particularly where you've got individual
cylinder lambda to actually monitor the air/fuel ratio it can be quite surprising how
much variation you're seeing.
One of our test vehicles we're seeing about a 5-6% variation between the leanest and
the richest cylinder with a factory inlet manifold which I think a lot of people
will overlook.
Now what do you do there, is there validation around trying to improve that
situation with the flow distribution with a factory manifold vs your ones?
- Yeah so all of the billet ones, because we do the CFD we can get them very very close.
They're usually within 1%.
But things like the big block one that we do, you are stuck by the cylinder heads.
So you're only going to get them so far but we certainly do improve them
wherever possible.
The factory FG manifold is another one that's really good.
Everyone goes oh you can make 1200, 1300, 1400 horsepower on them.
You can but them you ask any of the tuners how much they are trimming
number 5 and number 6 and they will say it is very very bad.
And also we find with cars like that if you ever get a chance to hardness test the
pistons afterwards, you'll find number 6 is being very very hot.
- Now I think it's one of those aspects where if you don't have the data, which most people
don't, it's easy to assume but unfortunately that's not always going to be the case and
certainly as the power levels and the boost climb, those small inconsistencies that
were OK in a factory power level, they start to become more of an issue.
Alright now if people want to find out more about your product and see what you've got
available, where can they do that Shannon?
- So they can visit us on our plazmaman.com, our website, or they're welcome to have a look
at our Facebook page, Instagram, Tik Tok, any of those places.
- Perfect, thanks a lot for your time there.
- No problem, thank you very much.
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