Piston to head clearance

Piston to head clearance, or squish.
There seems to be different opinions on what this clearance should be.
My local builder says i can get away with .040" .
Paul Gast says i should go for .048" to .053".
What I'm getting out of this is i can get away with .040" but if i get pre ignition i may have to adjust cam timing .(= larger lobe centers= less torque.)
It seems to me that the tighter the squish, the more turbulence u have to get a better burn and prevent pre ignition. And at the same time it will raise cyl temp and promote pre ignition.
I ran about .050" successfully, on my last 1135cc build. That will be my target for my currant 1200cc build unless you wise men change my mind.

If i go with more clearance i will not have timing issues. Less clearance = less than 1 HP gain.
Does anyone have a Minimum number that they can back up with experience?

What is your opinion and why.

.040 is pretty tight, also what about valve to piston, sems that would be very close also,

The valve to piston clearance should be fine with my little .425" lift cams. It was before.
I will be sure to recheck all clearances when my new pistons and block arive. Thanks for the heads up though.

Speedomotive (long time hot rod motor builder) has a lot to say on the subject.

www.speedomotive.com/t-showbymodel.aspx

.035 to .040 on something thats not going to be over revved .045 if you think you may miss the odd shift
forged pistons run loose in the bore untill they are up to temp compared to cast pistons. so allow a complete warm up before thrashing on it or your pistons can tag the head if they rock in the bore if they are cold and you are running really tight clearance
make sure the rods are ok (good idea to have them resized if they are showing an egg shape in the big end) and make sure the rod bearings are correct. too loose and you may get pistons touching the head

I read the speed article and understand now what I wanted to know, thanks steel. Ill measure quench from the top and the sides of the piston and find a medium for my motor. Mark your engine has diff. measurements so I can't answer your question but> The pre ignition part of the article tells me alot about how to set your timing, with me it's built in from memory and markings but mostly by the way the motor revv's. I try to make the motor run as strong as poss. without having a handful of timing thrown in there. It needs to be able to breath through the power band. That being said I think it's best to combine the two adjustable areas for a mighty fine ride. I'm working with 170-180psi so thermally my engines burn charactoristics are not adjusted by the same parameters as yours would be. But knowing how this fuel behaves is just bitchen. Bartender, hand me another one...:blink:

If Paul Gast said it you can take it to the bank. Hes been building motors longer then most people on here have been alive

id stick with the .050,i pushed the limits years ago and it cost me a brandnew motor with less than 50 miles on it,i did manage to save the 73 z1 engine cases but crank ,pistons and head were destroyed in the process!:S :blink: :ohmy: :huh: :dry: the motor was built for a hot streetbike but i somehow got talked into putting it into a dwarfcar that needed a motor.it would of been fine in a motorcycle but sitting sideways in that dwarf car with little airflow to #s 1 2&3 brought out expansion issues and took it out hard!but it was smoking every car on the track for like 9 laps before it let go!:woohoo:remember dragbikes that only run a 1/4 mile at a time and get cooled off can get away with a lot more than a streetbike ridden all day in traffic

steell wrote:

Speedomotive (long time hot rod motor builder) has a lot to say on the subject.

www.speedomotive.com/t-showbymodel.aspx

Excellent article! Thanks.

steell wrote:

Speedomotive (long time hot rod motor builder) has a lot to say on the subject.

www.speedomotive.com/t-showbymodel.aspx

Thanks Steel. That was a good read.
Thanks for all the input guy's. It seems i can run .040" but i will likely go with .050".
My block and pistons should go in the mail to me, mon or tues from Fast BY Gast.

What is the piston to head clearance on a stock KZ?

I read the article of speedmotive but it did not give actual answers on cam timing and measured compression. I did not understand in the article about knocking 10 degrees after TDC while ignition is 30-40 degrees before TDC.. even retarding will not go beyond the TDC.
Did I miss something??