Head to piston clearance.

What is recommended as a minimum clearance piston to head on a 9000+ rpm Blown Hemi ?
( Winberg crank, Brooks rods, venolia 4.310 pistons with HD 257 gram pins.)

Thanks in advance
Shoebox

 

I have run as low as .060 piston to head, but at 9000 rpm, you will get shiny spots on the head where the piston touches. With a fat head, we run between .080 and .100 clearance.

 

The general rule of thumb is .080 on the intake and .100 on the exhaust. If you want to go tighter, you better make sure you have good valve springs setup at the right seat pressures. Also, when you check, make sure to use the head gasket and put in the appropriate lash if it's a mechanical cam. That will make a big difference in terms of giving you more clearance.

 

Nothing quite like getting the combustion chamber polished while it runs!!

 

Some people would pay good money for that.

Brandon Booher
NHRA TAD #35

 

Head to piston ..

Hi Ken .
I had .060 but for some reason the chambers got more than a polish ( polish with a profile..in all chambers )
Valve clearance is not a problem.
I run Veney heads on a std deck with 7.074" Brooks -4.5" Winberg

Thanks a lot for quick replys.
Geir

 

Hi Mopar!
I have good clearance piston to valve with 550lbs int.and 420lbs exh. ( thats seat press)and roller cam with .477 / .485 on the lobes 1.7 / 1.52 ratios.

Thanks for your advice .
Shoebox

 

if there hitting on the outside of the dome just relieve the head little i used to run a veney head motor got it back from a race tore it down and like to passed out when i seen where the piston had been toughing the head called engine builder and machinist he told me to relieve the head where they were touching a little and put it back together after doing that a couple of times no more rubbing 9200rpms and it ran very very good

 

Head to piston ..

Hi Jim !
I had some rubbing last year with 7.04 rods and .040 gaskets and did some work on the outside of the piston dome as you mention and also changed to a .060 gasket with zero trouble after that ( other than pitcing a rod the last race of the year that scrapped the crank, rods ,pistons and block , cam etc)

After a rebuild with an other block crank etc. and 7.07 rods this year to bump the compression i measured clearance to the head without gasket and then assumed there was enough with an .060 gasket but nope i had to learn the hard way again

 

has that block been resurfaced are decked put and 80* gasket on one way to check this put it at tdc using a dial indicator then un bolt the rod push it up till it touches the head and check again then see what you have for clearance

 

Head to piston..

The block has not been decked at any time only had a line bore.this spring prior to assembly.
Good tip Jim i will try that further on .
Thanks a lot
Geir

 

This is basic engine blueprinting.

The easy way to do this is with Play-Dough.
Get it at any toy store.
Spray the chamber lightly with Pam cooking spray so it will not stick.
Spread a thin layer of Play-Dough on the piston dome.
Put the gasket and head on (without O-rings is better) and snug it up.
With spark plugs out turn engine over by hand.
Pull the head and you can measure the clearance in every direction by the thickness of the Play-Dough on the piston.
You can do the whole process again with the valves adjusted and measure the actual piston to valve clearance.

In the days before Play-Dough it was called claying up the engine.
You can also measure the CC's of your chamber with clay by pushing the clay into the chamber cutting it smooth on the deck and dropping it into a measuring container marked in CC's and see how much fluid it displaced = raised the fluid level. Viola your chamber size. So much faster and more accurate than messing with fluid and a Burrett.

A dab of Play-Dough on the tip of the spark plug turn the motor over and presto an accurate way to check piston to spark plug clearance.

If you want to get carried away you can rock the piston in the bore with a hard wood dowel from the bottom.

This system works on rod to cam clearance. Piston to crank clearance. How thick your thrust shims for cam end play need to be. Pan to pick up distance. Transmission input shaft end play. You get the idea.

Play-Dough = Good stuff and can be reused over and over.

 

Head to piston ..

Thanks T.A.D. 776
I have been playing with similar clay-like stuff on former engines i have built and yes its a good tip.
The way to detect combustion chamber volum without burret was smart.
Thanks a lot, you guys are so full of knowledge.