Head Gasket & Bore Size

[JeffersonC]

I punched my block out to 87mm. Will the stock head gasket work or are they specifically made for 86mm bores only?

[nimblestix]

Gaskets are made for larger bore sizes like 87mm so I'll assume the correct sizing matters.

sent from a galaxy far, far away

[Dragon Humper]

Well, that is debateable. Of all the other engines that I have built there was never a larger bore head gasket avail. You just used a stock bore gasket. As long as the fire ring on the stocker isnt hanging way out into the bore I would think that would be fine.

The main reason, I think anyway, to use the larger gasket is to lower the compression ration. You never find selections of head gaskets in any other circle of engine tweeking that has THICKER and larger gaskets. I believe that it's all to keep the compression ratio from climbing after a block and head skim combined with bore increase. That's old school thinking though, you are much better off keeping the quench areas as tight as possible with a slight increase in compression. Makes for a much snappier motor with LESS chance of detenation. Happier off boost too, especially at idle without an IAC valve as per your other thread.




Jon.

[Skym]

I punched my block out to 87mm. Will the stock head gasket work or are they specifically made for 86mm bores only?

Stock 86mm and 0.5 oversize (86.5mm) pistons use 87mm or 88mm bore gaskets -

http://www.tomeiusa.com/_2003web-catalogue/e103-104_RB26_gasket.html

Also mentions the compression ratio vs thickness of gasket.

More info on how the compression ratio is worked out and the different types of headgaskets -

http://www.tomeiusa.com/_2003web-catalogue/e102_gasket.html

I would think 88mm bore gasket for 87mm bore on block. That's going by if a 87mm bore gasket works with 86mm bore on block.

[gezed]

i used stock head gasket for 86.5mm bore and it still looked like the head gasket bore was larger than the block bore