Engine question

[j80leo]

Has anybody on here had a HKS headgasket which is 2mm or above or any different size over standard toyota gasket as my mate at work as got a sierra cosworth and he has told me that you can not increase the size of your headgasket to lower your compression or the engine will blow, your thoughts on this welcome:d

[jim_supra]

That's a good one I doubt HKS would make a 2mm metal head gasket for a Supra if they caused engines to blow:D

 

Also, a lot of the Na boys who are doing NA-T conversions fit thicker head gaskets to lower compression so they must be in trouble.

[j80leo]

i told him that HKS do a 3mm headgasket he said its just a cheats way of lowering the compression?

[rob wild]

HKS 2mm HG have been used many times on here and on SF and in 6 years of being on both i've not heard of any blowing. TBH Its not often you hear of supra engine blowing HG. Your mate is right in the sense that your 'cheating' but its the low cost option apposed to using pistons with a larger dish i.e. 17cc to 20cc etc. However by using a thicker HG you are removing the 'squish' factor from the engine.

[j80leo]

HKS 2mm HG have been used many times on here and on SF and in 6 years of being on both i've not heard of any blowing. TBH Its not often you hear of supra engine blowing HG. Your mate is right in the sense that your 'cheating' but its the low cost option apposed to using pistons with a larger dish i.e. 17cc to 20cc etc. However by using a thicker HG you are removing the 'squish' factor from the engine.

 

Thanks for the info rob;)

[ADL Mark]

A thicker headgasket will attract more detonation if this is to happen inside the cylinder, that's why it's a frowned upon practice in engine tuning generally.

[Digsy]

Why's that then?

[ADL Mark]

When detonation occurs, it will attack the weakest place in the cylinder, that being the head gasket. The thicker the head gasket, the larger the weaker place is.

[Chris Wilson]

Using a thicker than stock head gasket reduces the squish Toyota designed in, which is to help stop det by moving the bulk of the charge from det prone areas, it's a far from ideal way to drop CR. That said modern thinking errs on a high compression ratio, very little turbine size induced back pressure, and good mapping at modest boost levels. WRC cars now run high N/A levels of CR and a lot of squish to give stunning off and on boost performance. It is tricky to get the balance right, but gives the best on road performance on pump fuel when you do achieve this.

[ADL Mark]

I thought I was right, but you explain it much better Chris

[Digsy]

Ah, so when you said "will attract more det" you meant "will be more prone to damage from det" rather than actually causing it, or making the engine more prone to it.

 

I can't say I've ever seen a head gasket damaged from detonation. That's usually piston crown and combustion chamber surfaces, and they can usually let go pretty damn quicky. If you had bad det I'd be surprised if the first thing to fail was the head gasket.

 

I concur with Chris that squish lands are definataly making a comeback and geometric CR is going up. 12:1 on an NA isn't uncommon these days.