[Mk2] [Turbo] head gasket replacement problem. 3sgte

[chrishewett]

I seem to be having a problem buying the head gasket I need.
I am fitting a replacement head to my rev 3 turbo. The block is standard ( just honed) and the head has not been skimmed. With the je pistons this should give a compression ratio of about 9-1 with a 1.00mm gasket. I wanted to buy a 86mm 1.2mm metal gasket but the only one I can find is an athena at £140. I was hoping to buy one cheaper than that. I am told that the cometic, at £89, is 87mm and suits all bores. I am not very happy with reducing the gasket between the bores when I don't have to. Also, I can only find a cometic in 1.3mm.
Can anyone with more knowledge than me advise?
Chris

[Nic]

You could try contacting this UK head gasket manufacturer.

http://www.ferriday.co.uk/copper/gasket_list.shtml

[chrishewett]

Looks like they only make them in .6 or 1.0 mm.

[bobhatton]

I seem to be having a problem buying the head gasket I need.
I am fitting a replacement head to my rev 3 turbo. The block is standard ( just honed) and the head has not been skimmed. With the je pistons this should give a compression ratio of about 9-1 with a 1.00mm gasket. I wanted to buy a 86mm 1.2mm metal gasket but the only one I can find is an athena at £140. I was hoping to buy one cheaper than that. I am told that the cometic, at £89, is 87mm and suits all bores. I am not very happy with reducing the gasket between the bores when I don't have to. Also, I can only find a cometic in 1.3mm.
Can anyone with more knowledge than me advise?
Chris

What piston to head clearance have you designed the engine for?

[chrishewett]

What piston to head clearance have you designed the engine for?

The engine is as I bought it. All this is guess work. I will attempt to measure the clearance when the head is off.
Meanwhile I am trying to get an idea of what gasket will be safe. I havn't been able to find a single supplier who seems to know much about what they are selling. TCB dont even know the thickness of the gasket they supply, simply saying that " everyone uses them". My local toyota suppliers don't know the thickness of the standard toyota gasket. I'm not even sure whether the thicknesses quoted are before or after being crushed.
JE state that the cr with a 1.00 mm gasket on a standard block and head is 9-1 so I am wanting to lower that slightly as I will be boosting at 1.1 bar or maybe a bit more.
As you can tell I am not very knowledgeable on this subject so any guidance would be gratefully received.

[bobhatton]

What piston to head clearance have you designed the engine for?

The engine is as I bought it. All this is guess work. I will attempt to measure the clearance when the head is off.
Meanwhile I am trying to get an idea of what gasket will be safe. I havn't been able to find a single supplier who seems to know much about what they are selling. TCB dont even know the thickness of the gasket they supply, simply saying that " everyone uses them". My local toyota suppliers don't know the thickness of the standard toyota gasket. I'm not even sure whether the thicknesses quoted are before or after being crushed.
JE state that the cr with a 1.00 mm gasket on a standard block and head is 9-1 so I am wanting to lower that slightly as I will be boosting at 1.1 bar or maybe a bit more.
As you can tell I am not very knowledgeable on this subject so any guidance would be gratefully received.

The correct piston to head clearance should be 1.0mm on most setups. For 1 bar boost on road fuel you should be at 8.0: 1 compression ratio unless you are going to 10000 rpm or so then it can be a bit higher.

Design the engine for the use and power you need before buying parts or you are just going to have problems

[gavinda]

If you are unsure of the history of head and block you should cc and that will take away some of this guess work.

It's all very well saying drop your CR to 8:1 and on a fairly stock setup intending on running more boost I am in agreement.
However this 8:1 is not all it seems and one of the questions you need to ask is what camshafts are in the head? This and the type of fuel are important when choosing you CR

[chrishewett]

Thanks for the input guys.
I assume that to get the cr down to 8-1 would require a thick gasket and from reading other threads it seems that can cause other problems.
I will take measurements when the head is off but the guy who is doing the head change wants to turn it around quickly once he starts which is why I wanted to source the parts before then. I am only changing the head because of a tapping noise which I suspect is a bucket. Clearances are fine.
The cams are standard rev 3. I just use optimax or similar fuel.
I wish it was a bit simpler!

[gavinda]

If the 9:1 as calculated by piston manufacturer is with a 1mm gasket, then yes you would need to more than double that to bring it anywhere near 8:1 which means your squish is over 2mm = awful . I don't think the je is calculated with 1mm tho is it? CHECKED and you are correct it is.

[chrishewett]

Why ever would JE produce pistons for this engine which gave a 9-1 cr ?

[gavinda]

Couple of reasons. It has been suggested that it's for competition engines running high octane race gas so able to run the higher CR. secondly a fully built engine with late inlet valve closing , tied in with longer duration cams can have the intake valve still open as the piston rises, this results in different characteristics resulting from the static compression ratio depending on where in the rpm we are looking, for example at low rpm cranking pressure is reduced, in laymans terms effective compression ratio is altered

[chrishewett]

I see. Basically it means I have the wrong pistons.
Any suggestions as to what I should do If I can't face replacing them at this point? Could the setup I have be the cause of the last two engine failures? I suspect a cracked block. It now has a good rev2 block.

[gavinda]

Some 'experts' are very keen on dynamic compression ratio which takes the intake valve closing into consideration, unfortunately other factors can be missed out using this approach and basing everything on dynamic compression ratio as things get quite complicated.
I suspect JE produced a piston for engine builders who had late IVC and rightly or wrongly required a higher static CR to raise there ECR.
Wishing you hadn't asked?

[gavinda]

You could have some work done on the combustion chamber, plenty do this anyway to improve it, this could gain a few cc's to drop your CR, or have work done on piston tops. Both are quite common.
Combustion chamber work is looking best option with regards to your setup, at least get you closer. Other suggestion is water meth kit to raise octane to run higher CR

[bobhatton]

Why ever would JE produce pistons for this engine which gave a 9-1 cr ?

Because in the USA racing fuel is cheap and there is also E85 fuel, so 9:1 is a good compression ratio.
You will find in Europe the piston manufactures list 8:1 pistons

[chrishewett]

Uk websites are selling pistons for the 3sgte at 9:1

[bobhatton]

Uk websites are selling pistons for the 3sgte at 9:1

They may do, but websites are not the engine builder.
The engine designer/builder has to pick all the right parts to work together, its not as easy as just getting a box of bits and putting them all together.

Every engine I have build has had custom pistons.

If you have had problems with engine damage in the past then you have been using the wrong parts, everything has to work together.

[chrishewett]

I have now been told that the pistons have been machined to give the original compression ratio. Maybe I should use a standard toyota head gasket. Or would it be advisable to go for a thicker one?
I will take measurements when the head is off anyway.