Minimum Head thickness

[TheNewRed]

Hey guys, whats the absolute minimum headthickness allowed on the 7M. Mine is measuring 4.516, and my problem is that it has already been surfaced for a composite gasket and needs just a light pass before its useable with a MHG. I've already had .015 taken off the block surface, and the mains have been realigned. can a 3mm HKs compensate?

Thanks

 

[ma71supraturbo]

The TSRM make no mention (as far as I'm aware) of machining the head at all. But you should be fine having made 2 passes on it.

As far as MHG thickness -- 1.2mm is stock (.047in) If you've machined a total of .032 from the block and head, you'd want a 2.0mm HG to return things back to stock. If you've machined .071 from block and head, then you'd want a 3.0mm HG (to return to stock)

 

[TheNewRed]

Thats what i figured MA71. I just got off the phone with cometic, and they said they could make me a 2.5MM thick, with 84.0155mm bore head gasket for $220.I just need to know the very maximum i can take off of the head before i run into piston/valve interferance. On paper, this 2.5mm custom gasket looks like it'll work fine i just want to be sure b/c the minimum spec that i pulled from Prosis(AERA program) says that minimum thickness is 4.5600"(115.824mm) once again im sitting at 4.516 right now so i dk. i want the CR to be in the 8.5-9.0:1 range so i dont want to put the 3MM on.

 

[hvyman]

stock is 1.38mm. you can find the stock specs for head thickness is the tsrm and then add what was removed from the block and head to 1.38 and you will get the right size that you need.

 

[ma71supraturbo]

stock is 1.38mm. you can find the stock specs for head thickness is the tsrm and then add what was removed from the block and head to 1.38 and you will get the right size that you need.

Where in the TSRM is it? I looked through the cylinder head section and didn't see anything. And I've been out of the supra game for the last few years, but I thought the stock hg was 1.2mm when compressed?

 

[hvyman]

nope 1.38 compressed. let me see if i can find it...

 

[hvyman]

http://www.supramania.com/forums/showthread.php?t=97552&highlight=stock+head+thickness

i was off .01 mm its 1.37.

 

[ma71supraturbo]

right in the stickies lol ::hang::

That's so weird that Greddy, HKS and Titan would have 1.2mm's as the default...

 

[TheNewRed]

Im aware of correcting the problem with a different head gasket but my question was: How much can i take off of the cylider head surface before i run into "Squish" problems. i presume CCing the combustion chambers would let me know something? Or any other learking problems this would cause.

 

[Velocityfreak]

So if you went for the 1.2mm head gasket, you are increasing your compression ratio, what effect would that have on our compression numbers? Obviously it will go up, but how much, and is that going to increase detonation?

I believe the engine efficiency goes up with increased comp., but the increase in compression will have what effect on turbo spool?

 

[TheNewRed]

Really? Nobody?

 

[hvyman]

you will have better low end with faster spool but detonation will become a big factor.

 

[Velocityfreak]

The new red - As long as the top of your block is still straight, then i think you are on the right track with the wider thicker gasket.

However, you have to realize that if the head was already overheated and warped and then milled then the top of your block is still warped. You are looking at cams that are going to have to bend each revolution placing unwanted stress on the cams and journals. Theres a good post floating around about trying to fix a head that was warped by annealing (a heat treatment process)

So the question you have to ask yourself is what was the condition of the head before all the machine work. Did you blow a gasket and then decide to have it machined? If not, then you still should have checked the straightness before the machining.

If the block was fine before machining then sure...no problem drop a thicker gasket on there and torque it down.