what size head gasket

[simpson_eh]

just recently had a problem with my engine blowing smoke on cold start traced it to the stupidly expensive 1.2 mm hks headgasket, so my question is what size gasket do i need

just had the head and block skimmed running wiseco pistons 9.0.1 comp
looking to run over 400bhp just not sure what size i actually need have some looking into the size but thought id ask here as the like of bob etc are always very helpful

cheers

Tony

[badgerbob]

http://www.imoc.co.uk/forums/viewtopic. ... highlight=

Have a read of that mate, its similar to what your asking

[badgerbob]

How did you get on with this bud?

[Peter Gidden]

just recently had a problem with my engine blowing smoke on cold start

traced it to the 1.2 mm hks headgasket

Tell us more.

[simpson_eh]

Down to the block not being skimmed first time around my own fault teach me won't it.


Went for a cometic 1.65mm gasket to bring it down a lot. After having a chat with someone

[Peter Gidden]

Down to the block not being skimmed first time

Ahhh, OK. So not the head gasket then.

[bobhatton]

Down to the block not being skimmed first time around my own fault teach me won't it.


Went for a cometic 1.65mm gasket to bring it down a lot. After having a chat with someone

To get the right piston to head clearance at 6500 rpm I would use a 0.8mm gasket, if you are going to rev to 9000rpm I would use 1mm gasket.
Any thicker and you are going to have an amount of charge between the piston and head that is going to give bad detonation.

The compression ratio of your pistons are too high for anything over 0.8 bar boost on road fuel.

[moscoworbust]

High Compression Low Boost -- VS -- Low Compression High Boost

Big debate.

[simpson_eh]

now i really am confused, the head and block was skimmed so i was told this gasket would bring the comp back down with those pistons not cause me more probs

i had full blown chat with someone who said that was the way to do it due to the pistons, he was told what turbo and all the work that had gone into it and what power i was after,

was originally running a 1.2mm gasket with these pistons running 340bhp at 1.4bar with 335ftib mapped by ryan so was that gasket wrong?

[badgerbob]

Any thicker and you are going to have an amount of charge between the piston and head that is going to give bad detonation.

Is this due to the quench of the pistons bud? wiseco state a maximum piston head to clearance of 30 thou (0.75mm)

[bobhatton]

Any thicker and you are going to have an amount of charge between the piston and head that is going to give bad detonation.

Is this due to the quench of the pistons bud? wiseco state a maximum piston head to clearance of 30 thou (0.75mm)

Yes that is right, so a 0.8mm gasket would be the right one to use.

Head gaskets should never to used to change compression ratio, the pistons are changed to do that

[bobhatton]

now i really am confused, the head and block was skimmed so i was told this gasket would bring the comp back down with those pistons not cause me more probs

i had full blown chat with someone who said that was the way to do it due to the pistons, he was told what turbo and all the work that had gone into it and what power i was after,

was originally running a 1.2mm gasket with these pistons running 340bhp at 1.4bar with 335ftib mapped by ryan so was that gasket wrong?

The stock head gasket is 1.2mm but that leaves an amount of charge between the piston and head, that is why you read so much about blown head gaskets and broken ring lands with the 3sgte engines.

You should never fit a thicker head gasket to try and change compression ratio. Machine the pistons or get new ones to lower the compression.

[simpson_eh]

The rev 1 and 3 gaskets are interchangable anyway, nether have full coolant passeges and both are semi blocked.

So i just carry one set of gaskets for the 3sgte period

If your 9.0:1 and you were saying about the power you wanted to run i would lower the CR to keep some longetivty in the block. the pistons are very high already but the thickest i sell is a 1.65mm for £100.00 CR is based on a 1.4mm gasket anyway from JE and wiseco pistons. So 1.65mm depending on your skimming amount would estimate into the 8.6-8.8:1 so back down to similar to standard

Let me know if that is anygood to you

this i s the reply i had
hence i purchased 1.65mm

[badgerbob]

now i really am confused, the head and block was skimmed so i was told this gasket would bring the comp back down with those pistons not cause me more probs

i had full blown chat with someone who said that was the way to do it due to the pistons, he was told what turbo and all the work that had gone into it and what power i was after,

was originally running a 1.2mm gasket with these pistons running 340bhp at 1.4bar with 335ftib mapped by ryan so was that gasket wrong?

The stock head gasket is 1.2mm but that leaves an amount of charge between the piston and head, that is why you read so much about blown head gaskets and broken ring lands with the 3sgte engines.

You should never fit a thicker head gasket to try and change compression ratio. Machine the pistons or get new ones to lower the compression.

Dont mean to hijack your thread bud but hopefully the questions im asking will also help yourself, basically I'm currently in the same boat as you at the moment, I bought a set of wiseco 9.0:1 pistons and had initially planned to run these similar to what you have.

I have been studying for weeks now on different engine builds and the best ideal set-up. As Bob has stated the gasket must not be used to set the desired Compression ratio (I did not realize this until just a few weeks back).

So far I have come to make the call my pistons will have to be sold and swapped for lower cr units.

The power I originally aimed for with my 9.0:1cr wiseco's was approx 450bhp and to be achieved using local garage available fuel (99 octane). with a decent map and supporting mods it could be achieved.

But...

The chance of det and fatal engine damage is far greater than if you were to start off with lower cr pistons

I'm at the point where I have found the crucial tolerances to abide to in an engine build. Firstly the Piston to head clearance, this is important due to the quench effect and ensures healthy combustion occurs at the centre of the piston. To much gap that explosion occurs across the whole piston (exaggerated) and causes det between the faces,

Like Bob has said the stock clearance is quite great and can be reduced considerably (thinner than stock gasket)

By doing so on a stock engine this would increase the compression ration on standard pistons and most common forged aftermarket ones. (8.5:1) marginally.

For that reason Im at the point now where im looking to sell my 9.0:1 pistons in exchange for some low compression wossner ones (8.0:1)

Im yet to check the piston to valve clearance but Im currently checking that as we speak to confirm they will be ok.

The end result would be me having to run higher boost to achieve the level of power im after but as a positive I can do so safely in comparrison to higher CR pistons. Aiming to run a gt3076r those figures should seem possible...so far lol

[bobhatton]

If you drop your compression from say 9:1 to 8:1 you will lose 3% in power, and for any given boost you will have a larger charge in the cylinder, as there is more room, so that will give more power.

One of the most important settings in the engine and comes about by the head and piston design is the ignition timing advance.
Toyota will have spent a large amount of time getting this right and it should never be changed by much when setting up an engine. Unfortunately most ECU tuners do not understand this and just retard the advance to get an engine to run with whatever fuel and boost they are presented with.
By retarding the timing the engine will lose up to 30% of its power, but as stated above lowering the compression will only lose 3%.
If an engine is detonating then the fuel octane needs to be higher or the compression lowered, not the ignition timing retarded.

Look what Toyota did when it changed to Rev 3, the boost went up and the compression ratio went down, 8.8:1 down to 8.5:1, does that not tell everyone something?

Now with pistons, you will find them in the USA at 8.5:1 and 9.0:1 off the shelve, that is because most people over there will run race fuel, its very cheap, but over here you will find pistons at 8.0:1 or even lower for some engine and that is because for racing we have to use road fuel and not race fuel.

[badgerbob]

If you drop your compression from say 9:1 to 8:1 you will lose 3% in power, and for any given boost you will have a larger charge in the cylinder, as there is more room, so that will give more power.

One of the most important settings in the engine and comes about by the head and piston design is the ignition timing advance.
Toyota will have spent a large amount of time getting this right and it should never be changed by much when setting up an engine. Unfortunately most ECU tuners do not understand this and just retard the advance to get an engine to run with whatever fuel and boost they are presented with.
By retarding the timing the engine will lose up to 30% of its power, but as stated above lowering the compression will only lose 3%.
If an engine is detonating then the fuel octane needs to be higher or the compression lowered, not the ignition timing retarded.

Look what Toyota did when it changed to Rev 3, the boost went up and the compression ratio went down, 8.8:1 down to 8.5:1, does that not tell everyone something?

Now with pistons, you will find them in the USA at 8.5:1 and 9.0:1 off the shelve, that is because most people over there will run race fuel, its very cheap, but over here you will find pistons at 8.0:1 or even lower for some engine and that is because for racing we have to use road fuel and not race fuel.

If only all information I have read up on was as easy to understand as this. cheers

[bobhatton]

The rev 1 and 3 gaskets are interchangable anyway, nether have full coolant passeges and both are semi blocked.

So i just carry one set of gaskets for the 3sgte period

If your 9.0:1 and you were saying about the power you wanted to run i would lower the CR to keep some longetivty in the block. the pistons are very high already but the thickest i sell is a 1.65mm for £100.00 CR is based on a 1.4mm gasket anyway from JE and wiseco pistons. So 1.65mm depending on your skimming amount would estimate into the 8.6-8.8:1 so back down to similar to standard

Let me know if that is anygood to you

this i s the reply i had
hence i purchased 1.65mm

Unfortunately the advice you were given is right in as much as that will lower your compression ratio but will make detonation worse as it will leave a larger amount of charge between the head and piston where detonation takes place.

For a turbo engine it is very important to do everything you can to keep away from detonation when designing and building the engine, it is not something that can just be dialled out during tuning, but I know a lot of people think it can.