deck question height

[keone71]

my question is if it is ok to be less than .040 on deck height,and does it depend on what cam you use so piston wont strike the valves?say a fk-43 with 1.4 rockers?my deck height measures .034

[jfats808]

Check piston to valve clearance with playdoh. .034 is cutting close for me. I wont go less than .040, but that's just a personal opinion. Others have gone down to where youre at. Better ensure your stuff is balanced.
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2276 IDA's 86C 11-1 DD !
2017 48 Trijet DRLA's W125

[Danwvw]

It's starts to get close below .030" the main thing is to check it with the dough, modeling clay or whatever. Check the valves too but they won't even be close unless your running a lot of lift.
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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[Quokka42]

It's not usually piston-valve clearance that is a problem with too little deck, as the engine ages wear and carbon buildup conspire to bring the head and piston into contact. Tighter decks are more common with racers who rebuild their engines a lot more often than most of us, in fact in top fuel the engines actually run a negative number! The ridiculously high compression and combustion pressure compresses and stretches things enough that they don't hit.

If your parts and engine building precision are high enough .034 is probably just enough - What compression are you chasing that needs it that tight?
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There has only ever been one man who was perfect, and they nailed Him to a cross.

[vwracerdave]

.040" is considered the safe minimum. You can hold your breath and take your chances with less. There is also nothing wrong with having .060-.070" deck height. It is just pure Internet bullshit that you have to run exactly .040" deck height. I've seen engines with over .0100" decks run and last many years.
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2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[keone71]

[keone71]

[Quokka42]

Stick 10 thou spacers under the cylinders and sleep soundly at night.

While 40 thou' isn't complete bullshit it's a guideline, not a rule or maximum. It comes from a study where around 1mm was found to be a point where no engine gained any further benefit from squish or quench, tempered with the fact that I mentioned earlier, where wear, stretch and carbon can combine to cause a situation that will actually cause detonation.

Actually, I've been around a bit longer and I'd fit 20 thou' spacers for a bit of a buffer against needing to find extra-high octane fuel. You'd be surprised how little difference those couple of points make in real-world performance, or how easily you can damage things if you are forced to fill with a lower octane fuel.
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There has only ever been one man who was perfect, and they nailed Him to a cross.

[Northof49]

Some of those cnc ported heads come with such big chambers it tempts one to skimp on the deck height to get compression up. CIP1 sells its cnc heads with 69 cc chambers. Obviously not a good idea for getting acceptable compression.
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1958 Karmann Ghia owner

[[email protected]]

you need to check the chamber volume in the heads.

Most guys will tell you that you need to match the CR to the cam, and unless you know the chamber volume you don't know the CR. You have a little flexibility of DH and chamber volume. Once you know your chamber volume, we can help you with the best solution to finally buttoning the engine up.

It may include some cylinder shims.
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[Northof49]

I plan to first check and set deck height, then order heads with appropriate cc's.
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1958 Karmann Ghia owner

[[email protected]]

I try to do my calculations with .055" deck, that way I can adjust a little either way if I need to.
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It's just advice, do whatever you want with it!

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[mark tucker]

mine is .034"

[raul arrese]

[jfats808]

[keone71]

[Quokka42]

Looks like they know the difference between sashimi and sushi in Hawaii - I hope you have wasabi with that?
_________________
There has only ever been one man who was perfect, and they nailed Him to a cross.

[jfats808]

Yea, some like wasabi. I like chili pepper water myself. I gotta eat raw fish in some form at least once a week....
_________________
2276 IDA's 86C 11-1 DD !
2017 48 Trijet DRLA's W125