- Over the course of our SR86 build episodes, we've received a huge number of questions.
And we tend to see some of the same questions crop up over and over again.
So instead of me replying with the same reply time and time again in the comments section,
we're going to address some of those more common questions here so that everyone's
got a better understanding of why we're doing some of the things we're doing and the thought
processes behind it.
So let's get stuck in.
Alright our first question comes from Dirtydougimpand, he has asked,
would you ever put a Honda K Series in an 86?
Now we've been asked this exact this question in a few different forms probably
I dunno, about 10,000 times so it's a good one to get started with.
Usually that question goes, should have put a K20 in it, should have put a K24 in it,
put a K series in it, you'd never have any problems and so it goes on, so let's dive
into that.
First of all, really important for me to state here at the start that I have nothing against
the Honda K series engine in fact in my opinion the K20, probably one of the best
naturally aspirated four cylinders ever made.
Cylinder head flow is exceptional, between the VTech system that switches between high and
low cam lobes and also the continuously variable intake cam with Honda's iVTEC,
it is an exceptional engine that provides great power as well as a really wide powerband.
So why didn't we go that route?
Simply put, we didn't have one.
Now I know that not everyone has watched every episode and we did explain this right
back at the start so let me just reiterate because we do get this question every single
time we release a new episode.
At the start we had about a 4.5 week timeframe when we realised that our stroker 3UZ-FE
was not going to be ready.
That gave us 4.5 weeks to do a full engine swap on the car and get it ready for the first
round of racing.
Now even as it was, as you've found out probably watching these episodes, that didn't
actually quite go to plan.
But what we did have in the workshop was a built SR20VE turbocharged engine that
we'd built for our 350z, that was sitting there gathering dust ready to go.
There is no way that we would have had the time available to first of all source a Honda K20
then build it to suit a turbocharged application, physically mount it in the engine bay,
adapt our TTi six speed sequential gearbox to it, wire it, plumb it etc, there is no way we
had enough time available.
So that is the main reason why we didn't go down that path.
However a lot of people have also in the same vain, asked us why on earth we chose the
SR20 engine, basically a fair few people kind of claiming that the SR20 is old
technology and to paraphase, dog shit.
Well, in one way, fair enough.
If we're talking about the SR20DET that we'd conventionally find in an S chassis car,
I personally have tuned 100s of those over the years and I also don't really have a lot of
love for them.
They don't tend to make exceptional power for the sum of the parts.
They'd have a problematic cylinder head that doesn't flow well and also the rocker assembly
doesn't really like high RPM.
So in my opinion probably not the best choice and I really do apologise to those
SR20 lovers out there.
However when we switched to the P11 or P12 Primera VVL cylinder head,
this is a game changer and it's really almost difficult to compare a VE cylinder to the earlier
SR20DET.
So what's different with this head?
Well first of all the port flow is so much better than a DET head.
So all other things being equal, it's simply got the potential to make more power.
The game changer though really is in the valve train actuation.
First of all, the VVL cylinder head fixes the main problem with the DET rocker assembly
was prone to making its way out of the cylinder head and causing all sorts of
expensive damage.
The rockers in the VVL cylinder head are shaft mounted, they cannot get away,
this is why these heads, particularly in drag applications, continuously or
regularly I should say rev to 10,000,
10,500 even 11,000 RPM with reliability.
Other aspect with the head which is useful for us is that it actually has Nissan's take
on Honda's VTEC mechanism.
So it has three cam lobes per cylinder, it has two smaller lobes that are optimised
for low RPM performance and a larger lobe that's optimised for high RPM peformance
and it's switched via the ECU via oil pressure.
So Honda's VTEC system in Nissan's form.
So the idea behind this is that it gives us the best of both worlds and particularly
with a turbocharged application, gives us a wider powerband.
That's exactly what we saw, we've got a powerband that starts at 4500 RPM where
we reach full boost and we're actually making full power up at 8800, 8900 RPM.
So it does exactly what we had hoped for there.
On this basis, I can't do a direct comparison between the VVL cylinder head and the K20,
just with my own experience on the dyno it's probably a pretty close second to the K20
engine so not a bad option for us.
For the Honda lovers out there though, you'll be pleased to know that we are
actually going to be building a turbocharged K24 for an upcoming circuit racing project.
It's a little way off, probably not going to see much of that for the next 12 to 18 months
but it is going to be there.
Now the other question in the same vain that we got here is why don't we go with
the K24 because of course capacity is king?
Fair enough.
Now there is again a reason behind our decisions here.
Obviously the primary one I've just gone over, we didn't have time to source a K24
and build that, just the same as we didn't have time to build a K20.
But the K24 for this particular car would have been problematic.
We run in different classes in the endurance racing championship here and the class we
run in is called class B, it runs up to 3.5 litres of engine capacity.
Now we're only running a two litre but with turbocharged engines there is a 1.7 times
multiplication factor.
What this means is if you don't want to drag out your calculator, two litres times
1.7 brings us near to the top of that 3.5 litre capacity class.
If we go 2.4, that's going to bump us up into the top class where we would realistically
be needing somewhere around 650 to 700 wheel horsepower to be class competitive.
Now with a 2.4 K24 for example, there's no real problem with making that sort of power,
however the issue is that to get the power to the ground we would have needed wider
wheels and tyres, this would have required a wide bodykit, basically re engineering the
entire car and we just didn't want to do that with this particular 86.
So the next project we will be working on, we will be looking at running in that
unlimited class, that top capacity class, we will be engineering a chassis with wider
wheels and tyres that can make use of the power that the K24 can produce so you can
stay tuned for that.
Another question again, sort of along the same lines that I've seen pop up numerous times is,
should have gone K series, you'd have had no reliability problems.
I'm sorry but that is unrealistic.
Yep the K series engine is a great engine, it's been well proven however I've been in
motorsport for long enough to know that if you've got an engine in a car, it's got the
potential for reliability issues.
We'd probably have had different reliability issues to work through than what we've seen
with the SR20VE but I can guarantee we would have had some issues that cropped up that
we'd have needed to work through.
Our next question comes from Brandon Taylor and Brandon's asked, what are your biggest
concerns moving forward with reliability for endurance racing regarding this set up,
how do you prioritise what needs the most attention when setting up this vehicle
for these races?
OK Brandon that's actually proven to be a pretty big question and we've obviously seen
our fair share of hurdles to jump over with this particular build which is why we took
stock and decided to slow down the development and sort everything out.
So let's talk about the reliability issues.
So obviously we've had problems with the cooling system and we've had problems
most recently with a shim in the cylinder head.
So the direction we're going to address these, first of all, moving to the smaller cams which
we talked about in a previous episode, so moving to the P12 cams should move our
powerband lower in the RPM range.
So the aim here is to reduce the maximum RPM that we're running to.
We never really envisaged running this engine to 9000 plus RPM, it was just a case of when
we got on the dyno, that's where it wanted to make power.
So moving it to a point where our maximum RPM is around 8000, hopefully with the
P12 cams this should also aid our low RPM boost response so bring the turbo on boost a
little bit earlier.
I think all things considered, the lower we can keep the RPM limit, it's sensible that's
going to put less stress and strain on the engine, so that's our number one priority.
The shim, that honestly is a really simple thing though, don't use an ignition cut
and you're not going to have that problem.
So basically this, as I explained in a previous episode, was a hangover from the rev
limiter setup on our 1UZ-FE which used a bucket and shim valve actuation instead
of a rocker arm.
So getting rid of that, going to back to fuel cut, that's going to eliminate the problem of
the shims getting out and should not be an issue for us.
Then we've got our cooling system and this is really where we still need to do some testing.
Obviously we moved from the mechanical waterpump to the electric waterpump.
That proved to be a really good thing.
However even in the testing that we did, it looked like while we were on top of
control of our water temperature, our engine coolant temperture,
if I had to place a bet, I think at this stage we probably needed to still do a little bit
more work around our oil temperature.
Our oil temperature moves a lot slower than our engine coolant temperature but
over the course of a track session we were seeing a general trend where the oil temperature
was still starting to climb, hadn't really plateau'd which is what we need to see.
And that's something we just need more testing.
At the point we did test the car though, we still didn't have a finalised cooling package
and particularly the exit from the oil cooler as well as the transmission cooler,
that wasn't optimised and it was sort of exiting straight towards what was left
of the front bar so bit of work to do there and this is something we really want to test
before we actually end up going to our next endurance race event.
Our next question comes from Killsteeldevon and this is another really common question.
Other than cost or availability, is there any reason you didn't go with an EFR or G series
Garrett turbocharger?
And basically this questions' cropped up continuously and you can insert your favourite
brand of turbocharger in here.
And again, we have a little bit of method to our madness here.
And it might seem that in today's age that choosing an older Garrett GTX 3076 Gen 2
turbo might not be that sensible.
There are clearly superior turbos available from Borgwarner with their EFR series as
well as Garrett's new G series with the G25660, even maybe the G30.
So here's what we were thinking with this choice.
Now remembering again, this particular engine was built for our 350z, it was built about
18 months ago and the project kind of got put on hold just due to the workload we had
around the shop here.
The original intention, we were working in conjunction with Garrett and what we wanted
to do was get some solid data on the differences between their older GTX turbos and the new
G series so at the time we put that turbocharger on the engine, the G30 turbocharger hadn't
actually been released and the intention was to do some back to back testing.
Now that's something we still want to do.
While the G series turbochargers have been around now for quite a while, we've seen precious
little in the way of really solid back to back data.
The reason for this is most times when people change turbochargers, they've probably changed
four or five other things at the same time so it's really hard to get a gauge on exactly
what of the difference we see on the dyno sheet was attributed to just the
turbo change, compared to maybe a cam change, intake change, intercooler,
you name it, all of the other changes that go hand in hand with our build.
So that's what we wanted to do, that's why the engine is so heavily instrumented as
well in terms of exhaust manifold back pressure as well as turbocharger speed,
also got inlet and outlet pressure on the compressor and inlet and outlet temperature
on the compressor.
Along with EGT as well so this allows us to really validate exactly what the turbocharger's
doing.
That is also still something that's still totally on the cards but clearly we've had our hands
full just getting the engine up and running so that'll be something for the off season.
Our next question comes from a couple of episodes back and we had a couple of
questions along the same vain, this one comes from Brett Walker.
And to give you some context around this, this was after we put the engine back together
with some slight modifications, the electric waterpump, a new cylinder head that had
some slight modifications to the combustion chamber, we also went to the Supertech
aftermarket valve springs and we ended up moving to exactly the same Garrett
GTX3076R Gen 2 turbo but we moved from 1.01 exhaust housing down to a 0.83.
And when we hit the dyno, we pleasantly found that we were up around about
40 to 45 wheel horsepower at exactly the same boost.
Not something that we were unhappy about.
However given the changes made, the increase in power seemed a little disproportionate
to the sum of the parts changes.
And we sort of had a bit of a tongue in cheek title for this, why are we making
more power?
Now the reality is we've got a pretty good idea of where the power improvement came
from but we had a couple of people basically cite that the smaller exhaust housing is the
likely source of that additional 45 wheel horsepower.
Now Brett Walker's question here is, at higher boost, or statement really,
at higher boost levels or higher mass flow you probably will reduce max power with
the smaller exhaust housing, but since you're not at max capacity of the turbo, the smaller
exhaust housing has moved to a combined compressor turbo to a higher efficiency,
thus more power for that much mass airflow.
Now the chances of this being the total result, total reason for our 45 wheel
horsepower gain are unfortunately probably a little bit unlikely and it really comes down
to how the turbocharger system works.
So for a given amount of power, essentially we need a specific mass flow from our turbocharger.
We also know that we were comparing the two turbochargers at exactly the same pressure
ratio and in order to achieve that pressure ratio at a given mass flow, we need a
specific turbo speed.
What I'm saying here is that essentially our operating specifics for our turbocharger
in terms of compressor flow and speed, or speed specifically are going to be identical
because our pressure ratio has remained the same.
On the other hand though we now need to get the mass flow through the engine,
so the air goes into the engine, it's mixed with fuel, it's combusted and then it needs
to make its way out the exhaust system.
The problem here is that the smaller exhaust housing, what that does is it creates more
exhaust back pressure.
This is a good thing in one way because it provides more drive energy to the turbocharger
so this is why when we move from a large AR housing to a smaller one, we tend to pick
up lower RPM performance, it reduces the boost threshold, the turbocharger comes
on boost at lower RPM.
This is one of the things we wanted to achieve.
It did exactly that, we brought the turbocharger in around 300 RPM earlier.
All other things being equal though, a the same pressure ratio, we can rightly
expect the exhaust back pressure is going to be higher.
Now when that exhaust back pressure increases, it's essentially choking the flow through the
engine.
Basically it makes it harder for the engine to expel the burnt combustion gases out into the
exhaust system and if our exhaust back pressure becomes too high, we get into a situation
where the exhaust, the spent exhaust gases can actually go back into the cylinder and
basically dilute the fresh intake charge.
So moving to a smaller housing almost certainly is going to be not an explanation
for a 45 wheel horsepower gain.
Granted at lower boost pressure, the exhaust back pressure probably isn't going to be
skyrocketing and as Brett as rightly stated, once we start pushing this particular
combination harder, it's likely that the high RPM high boost power will start to drop
away compared to what we would have seen on the 1.01 but claiming that as the reason for
our power gain is probably also a little bit optimistic.
When we're looking at this, what we want to look at is the, sum of the parts changed.
So we've got a change to the exhaust housing AR, all other things being equal, the turbocharger
is identical.
So we know that that smaller housing should in theory create more exhaust back pressure
hurting our high RPM performance but bring the turbocharger on earlier, it's certainly
brought the turbocharger on earlier.
That shouldn't aid our power though at high RPM, it should hinder.
So let's look at the other things that I mentioned.
We've had some light modifications done to the combustion chamber shape.
That should aid mixture formation.
We've also moved to a different piston that's raised the compression ratio marginally.
Again on E85 that should be an improvement in our efficiency and our engine power.
We've also moved to a aftermarket valve on the inlet and the exhaust.
These aftermarket valves should improve our flow, our airflow in and out of the
cylinder head.
There's also been a little bit more time put into the valve seat geometry and again,
getting the valve seat geometry correct can aid flow.
So when we're looking at on one hand, all of these things, oh I should also mention
the electric waterpump which will give us a small but measurable gain in power,
so when we're looking at all these things on one hand which are proven to improve our
performance and we've got this other option here, the exhaust housing which the physics
simply says is going to reduce our power, if it looks like a duck, quacks like a duck,
then probably it's a duck so I'm going to go with the things that should have improved
power being the reason why we picked up that 45 wheel horsepower.
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