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Head Gasket vs Quench
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Hello,
Trying to get ducks in a row for purchase of engine components, I gather the consensus view favours the composite HG over the earlier laminated metal. Has anyone given thought to what the added .020" compressed thickness does to squish/quench characteristics of the chamber? Perhaps pertinently, why did Lotus need HG's of varying laminations with the introduction of the 912? Steve?? |
¿ªÔÆÌåÓýThere¡¯s a related discussion on the forums below, has had some recent updates. May help some. Good luck with the build.Eric CEH From the iPhoneOn Feb 12, 2022, at 14:16, wigl@... wrote:
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¿ªÔÆÌåÓýUnless you can find some new old stock the old Laminated metal haven¡¯t been available for ages so the new composite is the only option thats available most places. Taken by itself the .020 thicker gasket lowers compression by about half a point. So 10:1 becomes 9.5:1 etc. If your putting a new head gasket on are you doing any machining to the head? Any decking of the head will cut into the .020¡± gain of the gasket and reduce the compression hit. Basically if the head is decked .010 then the gasket only adds .010.?When Lotus changed gaskets in the 90¡¯s they didn't do it for the thickness difference, presumably they did it because its a better gasket. They compensated for it by machining the block .020¡± lower. That¡¯s easy to do in manufacturing, they have to cut it anyway so adjusting for a different gasket is a piece of cake. ?if your super serious you could do the same thing but that means machining the block and re setting all of the liner heights. If your liners are low or if the block deck is rough then thats something to consider but I wouldn¡¯t do I it for the compression unless it was needed for something else. Rather than decking the block the better fix would be higher compression pistons. Again its a lot of expense just for .5 compression but if your doing pistons anyway then add .5 to what you were going to get. ? The original Goetze gasket as supplied by Lotus was .supposed to be 020¡± thicker but I think the aftermarket composite that JAE sells ends up being a little thinner. Not the full .020¡± but a little bit. That¡¯s based on measuring some used JAE gaskets and Used Lotus composite gaskets. I don't remember the actual difference but it was on the order of .005 or something after crushing.? Dave C On Feb 12, 2022, at 2:16 PM, wigl@... wrote:
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Appreciate the thoughts, gents. It's a bit of topic drift to focus on CR, my fuss on this primarily concerns the quench characteristics and those would have been central to Lotus' going at the block as described by DC. I've got a NOS HG in hand, so that's an easy option. Pistons are in the picture as well, Kemp offering either his usual 2.2 set at 11.5, or jobbing out to a pal ( as he puts it ) for a set at 10.5. FWIW, my engine Sims specify 96+ octane (R+M) /2 for the build I'm targeting, more like 98+ at 11-1 CR. That's with optimal spark timing, otherwise to be retarded at points in the range if compensating for lesser grade. Further on CR, Sims modeling 11 vs 10.5 generate minimal difference in power outcome, unsurprisingly. Seems wise to opt for the 10.5's, therefore.
So on deck I've got HG, head-block studs, at the forefront, cam and head work looming before long. Been futzing around in emails long enough on this, trying to move it forward. Cheers |
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