Head Gasket thickness...

[tte]

I just got my head machined...and I lapped the block.

1/. What thickness head gasket should I use to retain stock compression.?
2/. If i decide to use the HKs 1.2mm gasket how much will my compression raise by and how will this affect my ability for more boost?

Cheers,
Roy

 

[SupraDread]

I just got my head machined...and I lapped the block.

1/. What thickness head gasket should I use to retain stock compression.?
2/. If i decide to use the HKs 1.2mm gasket how much will my compression raise by and how will this affect my ability for more boost?

Cheers,
Roy

do a search there is ton of info regarding HG thickness and proper install techniques:icon_bigg

 

[suprarich]

The 1.2 is nearly the stock size, you would just need to add the amount of material removed from the head and block, to that size. i.e. if you removed .8mm of material, you would need a 2mm headgasket to retain stock compression.

 

[noah89t]

^^^^^^
exactly what he said, stock is close to 1.2mm
i had 20 thousandths total removed from head and block and went with a 2mm greddy gasket.
and greddy does make an 83mm bore to keep it closer to stock unlike the 86mm bore that everyone advertises
here are some conversion charts
http://www.shoppingsense.ca/convert_mm_to_inches.htm
http://www.convertunits.com/from/inches/to/mm

 

[Doward]

1st question needs to be, how much was cut off the head?
BTW, you did get the timing cover cut as well, yes?

Approx how much was removed from the block?

 

[Halsupramk3]

you also need to know if the head or block were ever cut before. if so that would also need to be added in. to get my CR i had my shop calc the stroke length (length of rod/crank travel), piston dish volume, head chamber volume, height of piston in relation to block deck (is it even or is piston higher). all these measurements will tell the CR. because so much was shaved off the head/block that even with a 2mm hg i have 9:1 CR. i have not run it over 10psi on 93octane much but it has hit my boost cut of 14 a few times.

 

[tte]

10 thou of the head and I lapped the block...
Guess I could use a 2mm head gasket.

I wonder how it will be like running a 1.2mm HKS gasket...it would increase the compression but then I would have more chances of detonation.
Maybe adding water injection would solve that problem right?

Cheers,
Roy

 

[Stu_22]

Can You measure a second hand head to see if its already been skimmed

 

[starscream5000]

You need to steer clear of the 1.2 MLS if your boosting after the removal of that material . Especially since you don't know how much you removed when lapping.

 

[jdub]

Can You measure a second hand head to see if its already been skimmed

Doesn't have to...stock head thickness is 116mm from the valve cover deck to the HG deck. The best way to go would be to use a MHG thickness that makes up for the difference for the material removed from the block & head.

Since you lapped the head and didn't deck it, did you have the machinist check the head for flatness? For a MHG, both the head and block must be perfectly flat.

 

[MRSUPRA]

"10 thou of the head and I lapped the block...
Guess I could use a 2mm head gasket."

With .010 removed from the head= .25MM removed.
So a 1.4mm headgasket should be fine.

BTW a little extra compression has its benifits too.

 

[loki2043]

so what do you do if the damn machinist didn't stamp on the block how much he took off and didn't remember?

 

[starscream5000]

I forget how tall the stock block is... You'll have to measure both the head and the block, the head is IIRC 116mm from valve cover seats to the deck?

 

[bwest]

so what do you do if the damn machinist didn't stamp on the block how much he took off and didn't remember?

measure the pop-up of the pistons (how far above deck the crown is at TDC).

plug that into one of the many comp ratio calcs (it is a measured value). In one of the threads here, IJ measured .020" on a stock block and piston set-up.

I measured .005 on my block with JE's and .006 off the top of the block. I suggest double checking and not guessing this measurement.

 

[Doward]

What kind of machinist doesn't document how much material he removes? Measuring the pistons in the bore will give you a good idea how much was removed, but it won't be exact.

You'd have to measure from the crank centerline to the deck, and that won't be easy if it's in the car. You could also measure from the saddle to the deck, but I believe most manufacturers measure from the crank centerline.

Odd that the TSRM doesn't mention a spec for the block height. I'm planning on zero-decking my own block

 

[bwest]

Doward-

I understand why you would want to measure from the crank centerline, but why wouldn't measuring the pistons at the deck be an accurate measurement? I'm not disagreeing, but unsure how an 'actual' deck measurement is less than accurate? I've done it this way for the last 10+years when setting up port timing , squish and comp on 2cyl engines, how would this be any different (from a measurement perspective)?

 

[suprarich]

If I remember correctly, the deck height is 198.5, and yes on the 116mm head

Just put on a 2mm headgasket and call it a day!

 

[tte]

Doesn't have to...stock head thickness is 116mm from the valve cover deck to the HG deck. The best way to go would be to use a MHG thickness that makes up for the difference for the material removed from the block & head.

Since you lapped the head and didn't deck it, did you have the machinist check the head for flatness? For a MHG, both the head and block must be perfectly flat.

The head was machined and 0.010" was taken off.
I only lapped the block and checked with a straight edge.
I checked the straight edge at work on our granite surface plate and it was flat..
I checked the block from side to side n diagonally a few times and its flat after lapping.

Now I cannot use a 1.2mm gasket so it will increase the compression alot.
I could use a 2mm gasket but it would lower my compression.
I wanted to keep it at stock.

I will measure the block tonite n see how much I took off by lapping.


Cheers,
Roy

 

[suprarich]

You can buy a 1.4mm headgasket also. Tha twill put you back to right around stock compression. It seams to me that you have removed approx .25 to .30 of a mm

 

[jdub]

Measure the head thickness as well...like I said, 116mm is stock.

According to the figures you've posted it looks like a 1.6mm MHG is what you need. Stock HG = 1.37mm (according to IJ), add to that .25mm for decking the head. This assumes this is the 1st time the head was decked.

A 1.4mm MHG will work...it will raise your compression only a small amount like suprarich said and it is more readily available iirc.