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Discussion Starter #1
Does anyone have experience running a thinner than stock (0.85mm) head gasket on pump gas with a Gen5?


I'm curious as to how low I can go without race fuel, as I'm not racing - just lots of track days, and I don't want the hassle/cost.


I've measured my squish dimension, and it's 0.99mm. Race kit manual says optimal is 0.65mm. So, to get close I'd go to the 0.55mm gasket, but I don't want detonation problems.


Any feedback would be appreciated. Thanks.
 

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just inquiring, u sure that stk head gasket .85mm, all previous gens were .65mm. so deck height on ur motor only .005-.006? dont have experience with gen 5 but lots with previous gens. my std street 10 builds are .45mm hg and .015 head mill. run on pump gas no problems. my 07 has .45hg and head milled .028, does fine as long as ur moving but not a red light/stop and go traffic bike anymore. ur not gonna detonate or overheat at that suggested minimium squish on pump gas doing what u do. just surprised at those numbers. if correct going from close to .040 squish to less than .030, bike gonna really wake up everywhere in powerband. btw, tightening the squish helps prevent detonation.
 

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Discussion Starter #3
just inquiring, u sure that stk head gasket .85mm, all previous gens were .65mm. so deck height on ur motor only .005-.006? dont have experience with gen 5 but lots with previous gens. my std street 10 builds are .45mm hg and .015 head mill. run on pump gas no problems. my 07 has .45hg and head milled .028, does fine as long as ur moving but not a red light/stop and go traffic bike anymore. ur not gonna detonate or overheat at that suggested minimium squish on pump gas doing what u do. just surprised at those numbers. if correct going from close to .040 squish to less than .030, bike gonna really wake up everywhere in powerband. btw, tightening the squish helps prevent detonation.
You are correct, sir. The Gen4 race kit manual shows .65mm as the stock head gasket dimension. However, for whatever reason, the Gen5 manual shows that .85mm is stock (see image).

Thanks for the feedback, gents. Still hoping to hear from someone who's done the mod on a Gen5, but if I don't I'll just take the plunge and go with the .55mm gasket. If it doesn't work out, I'll just have to swap back. PITA, but not the worst thing ever. Cheers.
 

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Does anyone have experience running a thinner than stock (0.85mm) head gasket on pump gas with a Gen5?


I'm curious as to how low I can go without race fuel, as I'm not racing - just lots of track days, and I don't want the hassle/cost.


I've measured my squish dimension, and it's 0.99mm. Race kit manual says optimal is 0.65mm. So, to get close I'd go to the 0.55mm gasket, but I don't want detonation problems.


Any feedback would be appreciated. Thanks.
I'm getting ready to build a super stock spec engine on my 2018. Is your bike the R or RR?

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Does anyone have experience running a thinner than stock (0.85mm) head gasket on pump gas with a Gen5?


I'm curious as to how low I can go without race fuel, as I'm not racing - just lots of track days, and I don't want the hassle/cost.


I've measured my squish dimension, and it's 0.99mm. Race kit manual says optimal is 0.65mm. So, to get close I'd go to the 0.55mm gasket, but I don't want detonation problems.


Any feedback would be appreciated. Thanks.

The Thai Kawasaki racing team mechanics used the 0.65mm head gasket when they built my Superstock engine and it’s ran good on 95RON pump. You might be going a little to thin with a 0.55mm head gasket and risking PTV clearance.


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The Thai Kawasaki racing team mechanics used the 0.65mm head gasket when they built my Superstock engine and it’s ran good on 95RON pump. You might be going a little to thin with a 0.55mm head gasket and risking PTV clearance.


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Going thin on the head gasket will reduce P to V clearance, however this shouldn't be the primary concern. Narrowing the gasket is general used to reduce the squish area ( Piston to head ) to control the available space in which the burn can spread before pushing the piston. Anyway if it's to tight the piston will tap the head and unload the ring reducing power and possible damage. If it's loose then the flame will travel to these areas before pushing the piston and cause a loss of power. Get it just right and make the best power.

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Going thin on the head gasket will reduce P to V clearance, however this shouldn't be the primary concern. Narrowing the gasket is general used to reduce the squish area ( Piston to head ) to control the available space in which the burn can spread before pushing the piston. Anyway if it's to tight the piston will tap the head and unload the ring reducing power and possible damage. If it's loose then the flame will travel to these areas before pushing the piston and cause a loss of power. Get it just right and make the best power.

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Thanks for the explanation..lol

Stock Cam timing works with 0.65mm headgasket if you go thinner you’ll probably have to adjust timing to have the proper PTV clearance. As already posted and from the manual, the squish should be fine with 0.55mm.


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I can confirm, 0.55mm squish is safe. The reason squish can be tighter 2011 onwards is the connecting rods are better designed resulting in less rod stretch. I have built 4 motors with 2011 rods onwards with exactly 0.55 squish, all were built to rev up to 14.0000 and I can confirm without doubt there has been no piston to head contact.
 

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agree with michael, yet to see any piston/head contact with minimium squish listed as safe. been down to .024 thousands with piston and head deck surfaces clean of carbon buildup but no contact present. agree also ptv no concern when determining squish, set it tight as possible, then work out ptv with cam timing if necessary. even stock cam timing usually way more than adequate with squish minimium or sightley less as far as ptv. i've decked stk piston 10 heads as much as .032 with .45mm hg race only motors, only slight cam timing changes needed as far as safe ptv. tight engines always make the most hp/torque and are safe doing so if everything measured as already stated.
 

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Discussion Starter #12 (Edited)
I'm getting ready to build a super stock spec engine on my 2018. Is your bike the R or RR?

It's a 2016 R.


Thanks for all the feedback, guys. The Gen5 racekit manual sets 0.65mm as the ideal target for squish. The 0.55mm gasket leaves me at about 0.69mm of squish, so I expect to be fine. Already planned to check PtV clearance, just to be sure, although I don't expect any difficulties. Will fiddle with cam timing, if necessary.

Excerpts from the manual re: squish and PtV clearance attached.
 

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Well the only thing are you need to put probably a manual switch for the radiator fan, because when you put up the compression the motor develop more heat so in trafic in hot day the motor will have a tendency to overheat, so with the manual switch you just put it when you are in heavy trafic and heat. Unless youflash the ecu and you put a lower kick on temp for the radiator fan.

But yea it's wake up the motor and if you put the right cam degree number even more.
 

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Well the only thing are you need to put probably a manual switch for the radiator fan, because when you put up the compression the motor develop more heat so in trafic in hot day the motor will have a tendency to overheat, so with the manual switch you just put it when you are in heavy trafic and heat. Unless youflash the ecu and you put a lower kick on temp for the radiator fan.

But yea it's wake up the motor and if you put the right cam degree number even more.
I lowered my fan temp trigger to 195 in the flash on the stock engine. It made a big difference

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Discussion Starter #16
Thanks for the good points on the fan trigger temp adjustments. Fortunately, that's something I've already dealt with, as the kit ECU doesn't have a fan circuit. I've been using a variable temp controller with a temp probe in the radiator to trigger the fan circuit for several years, and it works really well.
 

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Tell you what though i just got done tearing the head off my 4th gen last night... A lot more of a job than i was expecting it to be.
 

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So you guys are able to run 0.0215" without piston contact? And still be able to run mill let say 0.020" and run a low LC on the intake?
 

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Brother I would suspect you will be far to the safe side as long as you haven't decked the piss out of the thing as well which I'm certain you haven't just because I know how you do things. On my Gen 1 motor with thin gasket ( No decking ) I ran 87 regularly without issue. I never ran 93 as the motor simply didn't require it. Some common sense applies to these situations naturally, like don't lug the motor in high gears at low revs. That's begging for a problem.

Also as mentioned here already the Gen 4 up rods seem to be a bit heavier made. I suppose Kawasaki decided the extra rotating mass is a good trade off for the tighter deck height it allows. Only reason I can think for adding weight to the rotating assembly of any engine. In ten more years all this won't matter much since my guess is everything will be battery powered. LOL
 

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So you guys are able to run 0.0215" without piston contact? And still be able to run mill let say 0.020" and run a low LC on the intake?
.021 PTH is pretty tight. The race manual will call for about no tighter than .026, and that is across the board (ZX 6/ZX 10, every year I've seen). I believe my last motor was a little tighter than .025, and I had the shadow of contact on a couple pistons... it had worn away the ceramic coating on a couple of the exhaust pockets. It was more likely a sort of quench wear than actual contact (valves were still sealing), but that's pretty damn close!

What you measure for static clearance kinda goes out the window at 13,000 rpm. Piston rock by itself can soak up a lot of clearance, and can throw your static measurements off by a bit too. That .026 number kawi calls out is pretty tight... they give a .65mm-.80mm range for acceptable, right in the middle of that makes for good performing, safe set-up.
 
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