- With the power levels that the current crop of forced induction engines are producing,
the ability to make more power really comes down to being able to seal the combustion
pressure inside of the cylinder and this is where head gasket sealing and head gasket
integrity comes in and I'm no stranger to problems with this with our own drag
program from years back.
So we're here with Ryan from SCE Gaskets to find out a little bit about the different
options that are available and where the pros and cons of these different options
come in.
So Ryan while we don't see too many of them on the modern crop of performance vehicles,
back in the early days it was common to see manufacturers using a composite style gasket.
So relatively cheap I'm assuming to produce but some downsides when we start adding
power adders, turbochargers, superchargers, can you talk us through what the limitations
of a composite gasket are?
- True, all true, the things that were nice about a composite gasket is that it
allowed us to seal oil and coolant quite easily.
And those gasket construction style, that composite style was good for
compression ratios of 8:1, maybe up to 10.5, 11:1 and then around 12:1 they
begin to fail.
Because there's just no backing to the combustion seal there.
- So essentially nothing to stop that combustion pressure trying to push out
through that composite gasket when the combustion pressure gets high enough?
- Precisely, when you begin to lift the head a little bit or unload the clamp load
on the gasket, then the web strength of the gasket wasn't there to prevent it from
just pushing out.
- Now you've just mentioned something which I'm sure we're going to touch on again but
something that's often overlooked is it's not just that combustion pressure we're trying
to seal, particularly in a production engine we've got oil galleries, we've got oil drains
going between the cylinder head and the block, we've also of course got water jackets there
so sealing that is key so you've mentioned there the composite gasket is very good at that.
Now the the next sort of gasket that most people in the street performance market
will probably move up to and a lot of the modern crop of performance engines
come equipped with these from the manufacturer is a multi layer steel or
MLS style gasket, can you talk us through the construction of one of these gaskets
and where their advantages lie?
- Well like the composite gasket, the multi layer steel by way of the embossments
in the various plates that make up the gasket, attempt to retain clamp load by basically
spring pressure and that retains the coolant seal out in the outer areas of the deck.
Around the combustion chamber we have a much more aggressive embossment that
accomplishes the combustion seal.
Then there's a next step, in our case we call it the gas stopper, the GS where an inner plate
is folded back upon itself to provide even more clamp load in the combustion seal area
so the MLS gasket provides that web strength that the composite gasket did not have
while providing a dependable coolant sealing by way of the various embossments and
sealants out there and then a much more aggressive combustion seal by way of
aggressive embossments and the additional gas stopper in the centre.
So all without serious distortion of the upper cylinder wall which adds to ring sealing.
Now you've kind of also touched on another subject there that I think a lot of people
might not consider is that even when we've got a head gasket that is sealing properly,
under high combustion pressure we will tend to see the cylinder head tend to lift
very marginally off the block.
So you're talking about that spring effect there, so that's allowing essentially that
gasket to move and take up that gap or what would become a gap as the cylinder
head lifts very very minutely off the block, is that reasonable to say?
- That is true and in the industry we call that memory, the gasket remembers that it needs
to stay sealed by way of that spring tension that's now trapped within it by way of the
embossment.
- Now you mentioned the embossing around the water and oil jackets, we also often see
a coating placed on these MLS gaskets on the sealing surface, on the head and the block
so what is that coating and what does that do?
- The coating is actually Viton, a very very thin layer of Viton.
Now most MLS style gaskets are coated, the entire gasket, this is an area of research
currently in gasket engineering where we're now beginning to move those coatings around where
we can locate the coating where we need to essentially trip the clamp load where we
want it to go, if there is a particular problem area in the cylinder head where it's leaking
coolant or where the deck might be weaker, we can begin to steer clamp load where
we need it.
So there's a lot of research going on in that area, very interesting.
- Now with the MLS gaskets, one question we quite often get asked is can we reuse an
MLS gasket.
Obviously with a composite gasket, once the head's removed, if the engine's been run
and heat cycled, it's basically destroyed, you've got to scrape it off and replace it
but MLS gaskets will generally come off pretty well intact as they went on so
what's the situation there?
- That's a definite maybe.
What you'll have to do is inspect the gasket when it's pulled off and if there is good
sealant around the combustion seal area, it can be reused.
If the sealant has been scrubbed off of that area, which is fairly common, we would not
recommend it because actually the clamp load would be a little bit lighter in that area,
simply because it's physically thinner.
- Alright so once we get to a point where the MLS style of gasket is no longer up to the task,
where we're starting to push into very high boost pressures, very high specific power
outputs, we quite often see, at least some of the highest powered engines in the world,
the likes of Top Alcohol and Top Fuel, will run a copper gasket with a o ring in a receiver
groove, can you talk us through that technology and how that helps to seal
combustion pressure?
- Yes well actually there's a step that's now been introduced in between, kind of a middle
step for engines with extremely high boost that are still liquid cooled, we have an
innovation that we call the Vulcan cut ring style head gasket where we have actually
a composite outer gasket with a solid stainless combustion seal.
Provides a very very dependable seal for very high boost, liquid cooled, OEM style engines.
After that, as you referred to the cooper gasket, after that we get into the solid
billet blocks with exotic fuels and extremely high boost pressures either from a turbo
or a centrifugal blower, that's where we go to the end results which is the copper gasket
with an o ring and a receiver groove.
Which again, in that configuration, when we provide an o ring and a receiver groove,
we've given that engine the ability to actually lift or unload the clamp load just a slight bit
and still retain a combustion seal by way of the o ring and receiver groove.
- So for those who aren't aware of that o ring and receiver groove technology,
essentially we've got an o ring, most often seems to be located in the cylinder head
and then a matching receiver groove which sits in the block directly under that
o ring so essentially the copper head gasket is quite soft, it's annealed and then
when the head is clamped in place, that deforms the o ring down into
the receiver groove so kind of will we say essentially creating a combustion lock?
- Precisely, that is precisely the idea and you said something very important,
that the o ring should go into the cylinder head because in every case where we're
using a copper gasket the cylinder head is constructed of alumnium.
So if we were to cut the receiver groove into the aluminium it becomes dull
essentially and the seal is less crisp.
So we place the o ring in the cylinder head and the receiver groove in the iron
sleeve, that way everything retains its sharpness, the seal is reusable,
the head gasket's reusable and as you say the copper, while it is malleable,
it's not compressible so we actually force it by way of the o ring into the combustion
seal, the receiver groove sorry into the outer edges of the receiver groove and it makes
a very square, in essence like an upside down top hat shape that allows a very very robust
combustion seal.
- So on that basis, essentially the head would have to lift beyond the point where the
copper comes out of that receiver groove at this point before we would have problems
potentially with the head gasket leaking?
- True and those usually only happen in some kind of a catastrophic failure where the
head gasket then becomes a fuse, the alternative would be that we
break a rod or throw the crankshaft out of it.
- Now on this basis, you might be thinking or viewers might be thinking well this sounds
like the ideal solution so why isn't everyone running a copper head gasket?
But of course copper head gaskets come with some downsides, can you tell us
about those?
- Sure yeah as I said the copper head gaskets really now are suited for those
engines that are billet style blocks, don't have coolant because the copper
is really not well suited for coolant and oil sealing, they tend to weep.
When the block and heads are cold, let's imagine that we had the copper
head gaskets on a street car, and that car is cold at room temperature sitting
in your garage or wherever, you may see coolant dripping on the floor because
the cold sealing is not good.
The copper, unlike the MLS or the composites or the other styles has no memory to it.
So when things are cold and kind of shrunken up a bit, the cold sealing is not there.
They're perfectly suited for high combustion pressure, extreme combustion pressures
and in a Top Fuel engine we develop in the order of 15,000 psi.
Whereas a street car, even a high performance street car will be in the 1200 to 1800
pound range.
- It's a different world for sure.
OK so definitely not suited to our street car application because of the water and
oil sealing.
So coming back to your other option which was the stainless steel cut ring.
So can you talk us through how the cut ring works and how that seals
combustion pressure?
- Yeah that's a very interesting hybrid style gasket.
We use completely different materials like we reach back to the old composite for the
gasket sealing around the exterior in the coolant and oil passages because it's
so well suited for that.
Essentially it's a pillow, just compresses down, seals that area, like I say inside the
combustion chamber we've got these huge pressures while out in the coolant area,
we've got 22, 24 pounds.
Now in some cases we've got oil pressure up, oil drains back still the relative pressure
is quite low.
So then you switch to the other material that's sealing the combustion chamber and that's
a solid steel ring.
On top of that ring we've got very fine micro ridges that bite actually slightly into
the cylinder head and form an extremely durable robust combustion seal.
So we've got kind of the best of both worlds.
- So basically like a little knife or a series of knives cutting up into the cylinder head.
- Somewhat yes, somewhat.
- Now obviously the next thing people will be thinking is well that sounds like it's going to be
damaging my cylinder head.
So where does the situation lie with that, so if we want to maybe pull the engine
down and freshen it up, what's the situation going to be like for the deck surface
of the cylinder head?
- Great question.
And a logical one.
In our experience, in all of these applications where we've pulled the cylinder head off
to service it, it is really, there's no more damage to the cylinder head than you
would find with a composite gasket that has a solid wire combustion seal in it.
In essence, it's a friction brinelling of about two thousandths of an inch.
So a two thousandths clean up pass as you would normally have done, ready to run again.
- And two thousandths of an inch is really not going to make any measurable,
have any measurable effect on the cylinder head.
So interesting that you're using the composite gasket around the outside there so where is the
reasoning behind that versus using maybe an MLS gasket for the remainder for
sealing oil and water?
- Another great question, I love the technical side of this.
If we were to use a non compressible material for the combustion seal and a non
compressible material for the coolant seal, then we have a very very difficult balancing
act to perform.
In our case, what we can do is have a very compressible outer gasket that then
allows us significant clamp load on the combustion seal which is where we
want it.
- So allowing you to get the clamp load only on those rings versus maybe having
it offset if you're using an MLS style gasket around the outside, not getting the clamp
load then on those rings?
- Well truely there still is some remaining clamp load because we've compressed
that composite body.
But the majority has been tripped to the combustion seal where we want it.
- Alright it sounds like an interesting technology, certainly something I'd be
interested in playing with myself but thanks for giving us some insight into the
various options there and if people want to find out more about SCE Gaskets,
where can they go to?
- They can visit us at scegaskets.com.
- Perfect, thanks for your time.
- Thank you.
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