Copper Head Gaskets

[petert 554]

Here's two screen shots of what happens to the CR and squish height when you install a thinner head gasket. DrSarty used the 0.7mm on his XU9J4 which pushed the CR up to 11:1. I recommend a 0.5mm on the XU9J4Z which will give 10.4:1. Most important however, is the decrease in squish height. I try to optimise this on every engine I build and XU engines never fail to impress with this attention to detail.

 

0.7mm on XU9J4

 

0.5mm on XU9J4Z

 

Copper head gaskets are a great idea on wet sleeve engines as the liner protusion really pushes into the soft copper, negating the need for O-ringing normally necessary on iron blocks.

 

Naturally there are downsides with this modification. First, you have to watch valve to piston clearances, but that's normal with any performance cam/compression increase. Second, the life of a Cu gasket on an aluminium head/block should not exceed 3 years without maintenance and quality coolant must be used.

[Rik 0]

So what, if any material was taken of DrSarty's XU9J4 head?

 

Was it a Cometic gasket used?

 

Rik

[petert 554]

So what, if any material was taken of DrSarty's XU9J4 head?

 

Was it a Cometic gasket used?

 

only just the smallest skim to clean it up. It was a copper gasket from me.

[VisaGTi16v 1]

Are these gaskets expensive? Available seperately? CR is a bit beyond me. Would you see any extra power from purely increasing it or do you need to adjust the timing, fueling etc and so on as well?

[petert 554]

Are these gaskets expensive? Available seperately? CR is a bit beyond me. Would you see any extra power from purely increasing it or do you need to adjust the timing, fueling etc and so on as well?

 

PM sent.

Available in 0.5, 0.7, 1.0, 1.6 and 2.0mm thicknesses. Any bore size.

 

Yes, the engine will respond to the increase in CR and decrease in squish height. Particularly if you have aftermarket cam(s). The standard 3 row '161' ECU can handle up to 11:1.

[smckeown 1]

thanks to peter's input i'm also going this route for me new engine.

 

I must say, even after researching, I don't understand the difference in relationship between reducing CR and reducing squish height, I don't see the difference.

[Rippthrough 98]

thanks to peter's input i'm also going this route for me new engine.

 

I must say, even after researching, I don't understand the difference in relationship between reducing CR and reducing squish height, I don't see the difference.

 

Squish is the distance between the piston and the cylinder head quench areas.

[Anthony 1,000]

Yes, the engine will respond to the increase in CR and decrease in squish height. Particularly if you have aftermarket cam(s). The standard 3 row '161' ECU can handle up to 11:1.

Sadly, we don't really get that ECU over here - we get the 354/355 3-row ECU's (non-Lambda)

[smckeown 1]

Squish is the distance between the piston and the cylinder head quench areas.

 

yep understand that. So don't you get the same when you incraese the CR by skimming the head. What's the inter-relationship between CR and squish height is my real question?

[Rik 0]

Whoever answers seans question above - please can you also add a little explanation on hwat a quench area is lol!

 

Rik

[cybernck 400 1 Cars]

would the copper gaskets run ok on a turbo'd engine and how much

would a 2.0 mm one lower the c/r, compared to a standard gasket?

[smckeown 1]

Whoever answers seans question above - please can you also add a little explanation on hwat a quench area is lol!

 

Rik

 

this is useful

http://www.rbracing-rsr.com/squishcalc1.html

[Rippthrough 98]

yep understand that. So don't you get the same when you incraese the CR by skimming the head. What's the inter-relationship between CR and squish height is my real question?

 

No as the quench area's don't move any closer, just the chamber volume decreases. I'll let petert go through it as I have to go out!

[smckeown 1]

No as the quench area's don't move any closer, just the chamber volume decreases. I'll let petert go through it as I have to go out!

 

Yeah that's ok still understand that, but there is less volume for the air/fuel to mix therefore hasn't squish increased ?

 

looking more at the diagram, it seems if you skim yes the area under the inlet would be more squished, but the area in the pic to the left is still the same, so am coming round to understanding ir more. The pic helps a lot, I didn't realise there is an area to the left that isnt open like the chamber volume. I thought it was one big chamber.

Edited February 6, 2007 by smckeown

[Anthony 1,000]

As far as I'm aware, squish height is the distance from the top of the headgasket (ie the face that meets the head) to the top of the piston - ie the part of the combustion chamber that is not in the head itself.

 

Clearly skimming the head doesn't affect this height, but decking the block, moving the piston further up the bore, or a thinner head gasket will reduce the squish height.

 

Does that make sense Sean?

[petert 554]

Sadly, we don't really get that ECU over here - we get the 354/355 3-row ECU's (non-Lambda)

 

I'd imagine they have the same headroom in the fuel mapping at full noise. ie they'd run around 12:1. The extra fuel used to power produced in a mildly modified engine leans this out to around 12.5-13:1.

[petert 554]

would the copper gaskets run ok on a turbo'd engine and how much

would a 2.0 mm one lower the c/r, compared to a standard gasket?

 

I think you'd need to o-ring turbo, just to be safe. A 2mm gasket would lower an XU9J4 to 9.77:1. May as well use XU9J4Z pistons.

 

Sean, notice how the Quench Distance is changing in the examples.

[cybernck 400 1 Cars]

the engine is already a Z , but i want the c/r just a little bit lower .

[midnight motorsport 0]

Here's two screen shots of what happens to the CR and squish height when you install a thinner head gasket. DrSarty used the 0.7mm on his XU9J4 which pushed the CR up to 11:1. I recommend a 0.5mm on the XU9J4Z which will give 10.4:1. Most important however, is the decrease in squish height. I try to optimise this on every engine I build and XU engines never fail to impress with this attention to detail.

 

0.7mm on XU9J4

 

0.5mm on XU9J4Z

 

Copper head gaskets are a great idea on wet sleeve engines as the liner protusion really pushes into the soft copper, negating the need for O-ringing normally necessary on iron blocks.

 

Naturally there are downsides with this modification. First, you have to watch valve to piston clearances, but that's normal with any performance cam/compression increase. Second, the life of a Cu gasket on an aluminium head/block should not exceed 3 years without maintenance and quality coolant must be used.

 

hi peter, me again, was asking about cams yesterday!! was just wondering how accurate your cc measurements are in these calculations, and whether these are standard bore and pistons, dont mean to sound funny, the reason i ask is that i only did a rough cc check on my engine and made the piston cut outs to be 1.2 cc, and made the piston to deck height slightly more at 16 thou, the engine is standard apart from the head and cams, and bottom end will be sorted once back together, balanced etc... new pistons and liners, anyway, i used a 1.6mm old head gasket to check piston to valve clearance, and have 120 thou inlet 116 on ex.. so have a bit to play with, anyway iv done a cr check using my cc calcs, and a 1.5mm gasket, combustion chamber= 38.2cc, cr is coming out at about 10.5-1

i want to use a thinner head gasket and can prob get away with a 1.1mm which will get cr up, and squish as well, but what i am thinking is that if you have done your calcs on a dry build they will prob be more accurate than mine? and will prob use them to calc my cr, hope this sort of makes sense? lol many thanks for your help and advise, cheers, jay

[petert 554]

Standard piston to deck clearance is approx. 0.015", and 1.2cc is about right for the pockets.

[PumaRacing 1]

hi peter, me again, was asking about cams yesterday!! was just wondering how accurate your cc measurements are in these calculations, and whether these are standard bore and pistons, dont mean to sound funny, the reason i ask is that i only did a rough cc check on my engine and made the piston cut outs to be 1.2 cc, and made the piston to deck height slightly more at 16 thou, the engine is standard apart from the head and cams, and bottom end will be sorted once back together, balanced etc... new pistons and liners, anyway, i used a 1.6mm old head gasket to check piston to valve clearance, and have 120 thou inlet 116 on ex.. so have a bit to play with, anyway iv done a cr check using my cc calcs, and a 1.5mm gasket, combustion chamber= 38.2cc, cr is coming out at about 10.5-1

i want to use a thinner head gasket and can prob get away with a 1.1mm which will get cr up, and squish as well, but what i am thinking is that if you have done your calcs on a dry build they will prob be more accurate than mine? and will prob use them to calc my cr, hope this sort of makes sense? lol many thanks for your help and advise, cheers, jay

 

Every engine will have production tolerances but FWIW I make the standard deck clearance to be 0.5mm and chamber volume 39cc on an unskimmed head. With a std 1.6mm gasket that gives 10.2:1 CR on the XU9J4 allowing 1cc for valve cutouts.

 

Liner length and rod length can vary quite a bit. A few thou on each anyway so the deck height will always be a variable.

 

What you really need to consider is what happens when the engine gets up to temperature. The aluminium block will expand by a massive 20 thou (0.5mm) at 100 degrees C. The cast iron liner will expand less and the 4 to 5 thou protusion at room temp will all but disappear. The steel crank and rod will expand by about 9 thou at the same temperature. The piston will be a big variable depending on how hot it gets but at an average 250C from the crown to the pin centreline it will expand by 7 thou. That means your deck height and squish is now 4 thou larger and the CR correspondingly less.

 

On a cast iron block the reverse happens. The block will expand less than the rod and piston, the CR goes up and the squish height goes down by about the same 4 thou. That's an 8 thou (0.20mm) swing in what happens between an iron block and an alloy one, all caused by the difference in coefficient of expansion of the two materials. 12 ppm per degree C for iron and 22 for LM25 aluminium.

 

So you can run the squish height a lot closer with an alloy block at room temperature to end up with the same running clearance when it's hot as an iron one.

 

The big question is what that squish can be set to and still not cause piston to head contact at peak rpm. I once built a 4 pot 8V race engine (iron block, 7.5k rpm limit) and pushed the envelope to the bitter limit. At stripdown after a season there was no contact but you could see particles of carbon on the piston crowns that had just been squashed a tad so running clearance was no more than a thou or two. In fact the piston crowns were basically clean in the squish area because there was no opportunity for carbon to build up. The burn was so fast that the engine dyno guy had to rethink his ignition timing settings for that engine which he dealt with a lot because his normal ones were far too high. I think we ended up with 28 degrees which is closer to what 16V engines normally run.

 

Of course that doesn't mean such a tight squish clearance was optimal and without testing progressively larger ones at the same CR (by skimming the head) I'll never know. The engine did win everything it went in for but that still doesn't prove anything. It might have done anyway with different settings. I think the most it gave me was data about just how much rods stretch when the engine is running at high rpm and how much I could alter things with an alloy block.

 

One thing I've read more than once is that there's a danger area in setting squish. You either go to basically zero, as I did above, or you go to at least 30 thou running clearance. In between you can actually exacerbate detonation. But what room temperature static clearance equates to 30 thou running clearance and how does that vary with crank and rod stiffness, rpm limit, block expansion and a host of other things?

[Mandic 0]

Thanks for that!

 

Haven't actually thought about CR change, makes sense now...

 

Cheers

 

Ziga