- When it comes to high boost turbocharged engines, we can essentially make as much
power as we want provided that we can seal the cylinder head to the engine block
and this is something that's really easy to overlook.
With my own background in turbocharged 4G63 drag engines, I'm no stranger to these
sorts of problems.
Now we're here with Julian from Julian Godfrey Motorsport to talk a little bit
about some of the technology that goes into sealing the cylinder head to the block.
Now Julian off camera we were just talking a little bit before about your experience with
the 4G63 and in particular you've built some engines that have been used in,
is it rallycross?
- Rallycross yes with the 45 mil restrictor so then with obviously running a lot of
boost low down and the problem is trying to seal the head to the block.
- Now with a 45 mil restrictor, ultimately that is still going to hold back the maximum
amount of power you can make, that restrictor goes pre turbocharger,
restricting the airflow in so just before we get too far into the engine details,
what sort of peak power are you seeing with that 45 millimetre restrictor?
- Around about the 580 horsepower but then we work close to 700 pounds of torque,
down at 4000 RPM so that's what really does the damage.
- Yeah I think that's the part that most people would overlook so that's why
I want to focus on it.
I mean, 500, 600 horsepower these days is the street car level for a lot of people.
So it's not unheard of but the problem is as you say that torque down low.
What sort of boost pressure are you running down at 4000 RPM?
- We are actually hitting three bar of boost so it's a lot of cylinder pressure.
We're running 9.5:1 compression ratio so it's a very high compression ratio
at three bar of boost.
- OK so explain to us there the mechanics of why this causes a problem with head
gasket integrity.
- 'Cause the cylinder piston speed's very low at 4000 RPM, it doesn't release the
pressure very quickly so it's a lot of cylinder pressure for a long time.
And that's why the head gaskets struggle at low RPM.
- I think for most people they sort of look at an engine block or a cylinder
head when it's sitting on a workbench and it all looks nice and rigid and pretty
solid but when you're talking about those sort of cylinder pressures for a long
period of time, what's easier to overlook is that those components are actually
flexing a lot so you actually see the cylinder head and the block essentially flex apart.
How much movement would you expect you are getting in there?
- Well especially with the 4G63 there was actually a lot of flex in the block.
The block is a very early design, I think it's from the early 70s.
The actual stud bosses underneath the deck are not going into anything
they're just sitting in the fresh air underneath.
So all it is is just a thin deck to hold them down.
I did a little test when we couldn't keep a head on it, gasket on a 4G63.
I just put some little oil control rings on top of each bore, put the head on
there and just torqued it up to just 15 pounds feet and straight away the block
was distorting.
You go up to sort of 35, 40 and you've distorted 20 thou.
So there's no point putting big studs in there because it's the block that's the problem.
- I think that's easy to overlook there, the general trend is when you're taking
a stock 4G63 and you want to make more power and run more boost,
the general off the shelf components most people will go for would be a multi layer
steel head gasket and a set of perhaps ARP studs which provide a little bit more
clamping so you're saying that the studs really aren't the issue there because
as you clamp the head to the block it's actually distorting due to the thickness
of the deck surface?
- Yeah that's right and the more your torque the stud up the more it distorts
it before you even put any cylinder pressure in there.
- So you could think that you're actually making things better but the reality is
you're making your life harder right from the get go even before you add boost?
- That's right you're probably almost maybe better off on standard bolts.
Bit softer bolts and it would last longer.
So eventually we actually went to a 12 mil steel plate on top of the block to try
and stiffen up the deck face.
- Alright so just talk us through that process, how does that work?
'Cause that's not something that we see a lot of people doing and there's probably
a fair bit of work involved in doing that.
- Yeah there's a lot of work in doing it 'cause obviously changing all the
cambelt length and so yes to sort that side of things out.
Exhaust manifold's sitting higher in the engine bay so it's a lot of work to change
it but in the end that was the only way we could keep one together on
a rallycross car.
It's a 12 mil steel plate with a flange liner going into the steel plate.
- So that steel plate, first of all the thickness of it, 12 millimetres plus the material strength,
that gives you that rigidity that you need in the deck surface to stop it from
moving around?
- That's right it keeps it nice and flat there and then you can, once we'd done this 12
mil steel plate, we did the same test with these oil control rings on top of the bores,
torqued the head down and then it wouldn't move at all.
Obviously once you got up to about 75, 80 it started to distort a little bit but it was
so much better than the standard setup.
- Now there's a couple of technical aspects that you're going to need to deal with there.
First of all, that steel plate being placed on top of the cast iron block.
Obviously you've got water jackets, you've got oil galleries, you've got oil
returns so how are you sealing those on the underside of that steel plate?
- So on the underside we've got o rings machined in the steel plate for the oil
feeds, returns and the waterways.
And then on top we still just use, we actually found the best on top was
two standard gaskets on top of each other.
The two half mil gaskets and that gives us our best result.
- So no requirements for anything too flash like o rings et cetera?
- No just the two standard gaskets on top of each other and that cured the
problem and we've never had a problem since.
- Now the other aspect there, you've obviously now got this plate on top
so you've talked about the flanged liner so can you talk us through what that
is and how that works?
- We used the steel Nikasil liner, flanged liner which was counter bored
into the top of the steel plate and then the gasket actually sat on top of the,
or the firing ring sat on top of the flanged liner.
So that was pushing on the top of the liner which was pushing on the steel plate.
And then the bolts were pulling from underneath the steel plate from the
block and it just kept it much squarer when you've got high cylinder pressures.
- With the steel material that you've used for that sleeve, stronger than a cast iron
material so do you get away with quite a thin sleeve when you're using steel?
- Yeah we're down just I think one millimetre thickness of steel liner.
'Cause you've got very small bore centres with the 4G63, you can't go too big on
the allowances anyway 'cause they'd be into each other.
- And you mentioned that Nikasil coating as well so can you just talk us through why
that's required on a steel liner?
- You can't run a steel ring onto steel so you have to change them to a Nikasil surface.
So we get them Nikasil coated and get the piston ring Ti nitrided
It's like a gold coat on the ring to stop the rings from picking up on the Nikasil.
- Now the other aspect there with adding a 12 mil deck plate to the top of the block,
that's going to allow you to run a longer connecting rod in order to get your
deck height for your piston correct or back to where it should be.
So are you taking advantage of that in terms of rod to stroke ratio or are you
using a stroker crankshaft and still retaining a reasonable rod to stroke ratio?
- No we just made a longer rod 'cause we go on the cc of the engine for the
regulation with two litre so we'd still use a standard throw but just a longer
rod which helped the rod ratio.
- Is that a real advantage though when with that 45 millimetre restrictor you're
obviously limited in terms of maximum RPM, we'd generally see the longer rod to stroke
ratio really come into its own as the RPM range increases?
- Yeah I don't think there's a great advantage of actual power performance but it may be
slightly less stress on the components again 'cause you've got less angle as it's
pushing the piston down.
All that angle with high cylinder pressure, it's always going to help if you've
got a longer rod.
- Alright look, great to get some insight from a completely different form of motorsport
than I'm used to and how to deal with the 4G63 problems.
Certainly something that potentially we could have looked into ourselves.
If people want to find out more about you and your company,
how can they reach out Julian?
- racetuners.com so quite an easy one to remember.
- Alright thanks a lot for the chat Julian.
- Thanks very much, no problem.
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