Dyno day with the 260Z

[LeonV]

3 hours ago, HuD 91gt said:

I ran 0.021" over deck, with my pistons, and a 1mm mls gasket and the car ran, never hard though (has having guide issues). Eventually switched to .050 mls after reading Bryan Blake's post. Curious how yours works out.

Doing ok so far, I have about 2000 miles and 12 dyno pulls on it. Hopefully it stays together!

[madkaw]

Thanks Leon,

doing the data mining on this stuff I've also stumbled across some of Bryan Blakes posts . He squeaked out the .022 number , but reluctantly . It's not a number you want to get wrong putting these engines together and could lead to some crashing. A 1mm gasket is a special order in most cases and 1.25mm is about the norm.

.017 sounds about right for STOCK piston height and so the shave got you just where you want with a .049 gasket. 

[LeonV]

No worries Steve! If (when) I pull the head off again, I'll try to get a measurement of compressed gasket thickness so I could give you an accurate, true-to-life number using the OEM HG. I'm assuming when you say 1.25mm gasket you mean uncompressed?

Let me know if you need any help with your build!  

[Zed Head]

Could you stick a piece of plastigauge in the spark plug hole and squish ti to determine the distance?  Something like a piece of weed wacker cord might work also, depending on how elastic it is.  Just thinking...

I measured my factory stock fire rings on my used HG and they came out to 1.25 mm.  I don't think the fire rings are very elastic.

[madkaw]

1.25mm compressed

[jonathanrussell]

When you guys measure a compressed head gasket, do you measure at the fire ring?

[Zed Head]

The fire ring is the hardest part of the head gasket and would determine how far the head is from the block and pistons.  So that's where you'd want to measure, for clearance calculations.

[LeonV]

I'm not sure plastigage would work considering it tends to stick to whatever crushes it but it's an interesting thought. I could try using something like lead solder which will keep its shape after deformation and hopefully not remain in the combustion chamber.

My strategy would be to set a dial indicator to the block and zero it to a plate mounted to the head. Without messing with the indicator, pull the head off, remove the gasket, and reinstall the head flat to the block. The indicator will say what the compressed gasket thickness is. Knowing that deck height is 0.021", piston-to-head clearance can be accurately calculated. Of course, this involves pulling the head...

[sweatybetty]

i measured a fel-pro head gasket tonight. the compressed was 1.12 mm average at the fire ring

[LeonV]

17 hours ago, sweatybetty said:

i measured a fel-pro head gasket tonight. the compressed was 1.12 mm average at the fire ring

Interesting, thanks for the data.