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Minimum head to piston clearance?
Posted: December 7th, 2008, 6:37 pm
by SilverXJ
Just curious as what the minimum piston to head clearance is on our engine.. would it change if one went with a forger slug such as I am dong here: viewtopic.php?f=8&t=444
Re: Minimum head to piston clearance?
Posted: December 7th, 2008, 7:50 pm
by Mgardiner1
I think the listed in the FAQ section, there is mention of keeping it .040 or above. How much do forged pistons expand? I know the hypereutectic pistons expand the least, not sure how much of an impact that would have on engine running quench figures.
Re: Minimum head to piston clearance?
Posted: December 7th, 2008, 8:28 pm
by SilverXJ
Found it
.However with piston expansion and rod stretch(AT HIGH RPM) the minimum clearance is .045"(absolute minimum is .040")
What exactly is considered high RPM though.
I sent an email to KB about what they recommend......
wasn't there a piston FAQ or am I having some sort of memory problems?
Re: Minimum head to piston clearance?
Posted: December 8th, 2008, 3:35 am
by Mgardiner1
Piston FAQ found here: viewtopic.php?f=27&t=67
Quench FAQ found here: viewtopic.php?f=27&t=73
Re: Minimum head to piston clearance?
Posted: December 8th, 2008, 5:46 am
by Flash
I real have been thinking of changing this..... However with piston expansion and rod stretch(AT HIGH RPM) the minimum clearance is .045"(absolute minimum is .040")
I truly believe that most of us(those staying with in the stock rev limit) could tighten the quench to .035" with out a problem..............But I'm only guessing so,.........I have left it as .040"
Flash
Re: Minimum head to piston clearance?
Posted: December 8th, 2008, 7:43 am
by SilverXJ
Got a reply from Keith Black
Hi Chris .060 or greater. Thanks Tech dept.
That seems huge to me.
Re: Minimum head to piston clearance?
Posted: December 8th, 2008, 9:23 am
by seanyb505
Maybe they didnt think it only revs to 5250?
Re: Minimum head to piston clearance?
Posted: December 8th, 2008, 9:36 am
by Flash
SilverXJ wrote:Got a reply from Keith Black
Hi Chris .060 or greater. Thanks Tech dept.
That seems huge to me.
There has been several that have set the quench between .040-.045 But if your going this low or close, your not building a simple stroker and you should be checking all aspects of it......like valve to piston as well as piston to head
.060" is just a c.y.a. number.
Flash
Re: Minimum head to piston clearance?
Posted: December 8th, 2008, 10:19 am
by SilverXJ
Ok.. so I follow up with Keith Black and ask how much the clearances would change once the piston is warmed up.
Hi Chris the wall clearance will grow some the height won't grow much as long as your rods are steel. You should be alright. Tech Dept.
So, then where did they get the .060" number from? I can understand accommodating for piston rock, but it shouldn't be that great to make the clearance so high.