Headgasket

[n0v0s]

I understand that normally, headgasket thickeness is chosen according to piston protusion/ amount skimmed off the head..

I am taking off 1mm from my piston crowns..

Is there an advantage with using a 1 notch, 'thin' gasket - does it give a better 'seal' ? Compared to a 3 notch? Or is there no difference.

I've bought a 1 notch, but am thinking about buying a 'thicker' gasket instead if there is no difference in the sealing properties, and a thicker gasket would further lower my compression so is preffered.

Also, has anyone had an FAI mls gasket fail on them? Cost me £30ish from eurocarparts, reasonable?

Cheers

[mark_airey]

obviously a thinner gasket will be less likely to blow in theory as there is less area of gasket for it to pressure against, and yes a thicker one would further add to your decomp.

I have had issues with FAI and was asked by my engine man if the gasket was in black red and white packaging, if so that would be my problem, buy a decent gasket!

Also, I'm concerned here, are you fitting a supercharger?? as if you skim 1mm off your pistons it will be shit without............

[n0v0s]

obviously a thinner gasket will be less likely to blow in theory as there is less area of gasket for it to pressure against, and yes a thicker one would further add to your decomp.

I have had issues with FAI and was asked by my engine man if the gasket was in black red and white packaging, if so that would be my problem, buy a decent gasket!

Also, I'm concerned here, are you fitting a supercharger?? as if you skim 1mm off your pistons it will be shit without............

Hey Mark,

aah shit, will have to go back to them and see if they have anything better! Got a bit too spend happy with new gaskets.. The concept you mention above - is that something which is known? I probs being dim at the minute, heavy night an' all.. but I can't help but feel that as the actual SA of the gasket is the same (meeting the block/head), regardless of the thickness - the chances of the different gaskets blowing would be negligible? Infact, wouldn't a thicker gasket have greater tensile strength?

No supercharger, just a big fk off snail to go on. I am also concerned that 1mm would be too much, but as it will be a DIY effort with a grinder i'll have to hope for the best! ..?? hah

[mark_airey]

Hey Mark,

aah shit, will have to go back to them and see if they have anything better! Got a bit too spend happy with new gaskets.. The concept you mention above - is that something which is known? I probs being dim at the minute, heavy night an' all.. but I can't help but feel that as the actual SA of the gasket is the same (meeting the block/head), regardless of the thickness - the chances of the different gaskets blowing would be negligible? Infact, wouldn't a thicker gasket have greater tensile strength?

No supercharger, just a big fk off snail to go on. I am also concerned that 1mm would be too much, but as it will be a DIY effort with a grinder i'll have to hope for the best! ..?? hah

Yes the mating face area would be the same but the but area that sees the cylinder pressure, as in the edges of the gasket around the bores would be larger due to the thickness of the gasket if you follow me, mines fine at 40 PSI on a 5 notch though so I wouldn't worry too much and the difference in gaskets is so small though that I can't see it making a massive difference TBH!

As far as gaskets go I tend to look for Payene or Elring stuff and Ruan swears by Victor Reinz

TBH I wouldn't bother with decomping, just fit some HDi rods, but really don't take 1mm off the pistons...........its too much, especially after talking to Dave and James this weekend. if you want to do still it then maybe try it with 0.5mm..........

[n0v0s]

Ahh, i see. Yeeah, i got all excited when the bloke brought out all my shizz and i saw a victor reinz .. but it was the cam gasket

I'm due to go back to eurocarparts today to pick up my exhaust/inlet gasket anyway (they have a nice recessed gasket which looks to provide a much nicer seal - well the om606s use that style so i'm assuming so anywye!) Will probs just get the elring / cheapest mls that isnt FAI then. Probs be better i get something like a 3notch and AIM to grind off 0.5mm to be safe lol.

Hopefully get the head back today from skimming, it's all comming together WOOOP!

[n0v0s]

I've now come back with a 5 notch elring mls oh well

[Dave]

I can only attribute my power loss issues down to my severe decomp I've tried different turbos, different pumps and pump parts and generally can only source the issue back to the CR. Its just the power/reliability play off...

[n0v0s]

No way man, gutted for you! But at least you have moaar pistons lying about?! It was 1mm you lopped off right Dave?

[Dave]

yeh plenty more blocks to strip, bout 1.1 i thought i'de go that bit more for reliability but now seems to be unable to produce enough exhaust flow to get good boost.

[n0v0s]

Well it was a worthy effort either way Probs best to keep skimming to under 0.5mm then, if that... And just get a thicker gasket (not that they produce much noticeable drop in cr..) I think I'll try aim for 0.3mm, should be interesting lol

[Dave]

I'm just going back to stock CR, I dropped for the piece of mind that it would make it reliable, but (I think) it has caused so many issues with exhaust flow and generally not burning the fuel well enough... James did some math and generally for a drop of 23:1 to approx 17.8:1, think thats the drop in CR anyway, then it needs 20% more air per stroke to make the same power as stock. I didnt think it would cause this many issues, and with HDi rods I will risk stock CR, f*ck it if it spews its guts again then I will probably go forged.

[n0v0s]

A drop from 23.1 to 17.8:1 from just 1.1mm removed?! Wow. I didn't expect such a sensitive drop. I don't think i'm going to do it then, power>reliability!

Do you know how much it dropped to cylinder pressures by though? Do you know if its a linear relationship, or exponential/some sort of complicated non-linear relationship between the 3 variables?
If the expo. It would be interesting to see if theres a sweet spot, to find an acceptable compromise between reduced exh/airflow and decreasec cyl. Pressures and CR drops/reliability..

[con67]

Try deepening the grove on the cloverleaf or even the cloverleaf itself, skimming the whole piston is a bad idea as is thicker hgs for lowering cr. You want all the air to move into the chambers not sit around just outside them. Theres some saes on combustion chambers knocking around the 'net.