[Fot] Piston to head clearance

[fubog1]

 I'm still burning up (precious) brain cells on this, yes interesting, but that's one of my questions also, exactly how was the reported gain established?I've always gone with the theory that more is better when it comes to turbulence, which requires minimal squish clearance.I would imagine that chamber & piston top configuration, ie flat-tops or a lump on top, may be part of the equation as well...Yes compelling discussion!
Glen Efinger

    On Friday, January 12, 2024 at 10:57:08 AM EST, Ken Knight <kknight at klaenv.com> wrote:  
 
 
Interesting discussion and I would agree on point.  What would interesting to know is how the HP change was measured; chassis dyno or engine dyno?

  

Ken 

  

Sent from Mail for Windows

  

From: Lorne Fritz via Fot
Sent: Friday, January 12, 2024 7:13 AM
To: tr4racing at googlemail.com
Cc: fot at autox.team.net; fubog1
Subject: Re: [Fot] Piston to head clearance

  

Good point. 

  

On Thu, Jan 11, 2024 at 6:45 PM <tr4racing at googlemail.com> wrote:


That is one thing to consider.

When is turbulence supporting and when is turbulence overdone and disturbing.

 

I could imagine to force too much turbulence with a very small squish gap the flame front expansion is compromised, thus slows down, and lowers the hp output.

That’s why we had the best power with 0.047” gap.

 

Cheers

Chris

 

 

From: Fot <fot-bounces at autox.team.net> On Behalf Of fubog1 via Fot
Sent: Thursday, January 11, 2024 8:01 PM
To: Lorne Fritz <lorne.fritz at gmail.com>; Steven Belfer <steve at artwithcars.com>
Cc: fot at autox.team.net
Subject: Re: [Fot] Piston to head clearance

 

Steve nailed it, both on the ##s, & the importance of it.

It depends on what rods & crank, piston to wall clearance & what RPM, but for most applications that's right in the ballpark.

I've run as little as oops not enough ie .025 or less, .028 minimum (you won't get any carbon deposit on the squish area), but to play it safe nowadays I use .030-.032

Also on these engines it's not only a CR related issue, the squish is very critical, you want to minimize the clearance between piston top & head to maximize the squish effect, which creates turbulence, which assists in good combustion...

 

Glen Efinger.

 

 

On Thursday, January 11, 2024 at 01:00:50 PM EST, Steven Belfer via Fot <fot at autox.team.net> wrote: 

 

 

You want as little as necessary because this is where your high CR comes from.  The thickness of the head gasket is the major part of P to H clearance.  I ran .026 P to H clearance at Cal Speedway and the piston kissed the head and I spun a bearing.  My machine shop guy likes .040 for safety but I’ve been running .032 and it’s working out great
~Steve


> On Jan 11, 2024, at 9:13 AM, Lorne Fritz via Fot <fot at autox.team.net> wrote:
> 
> 
> Hi.  In the past I have had pistons hit the head and leave a mark(TR3/4).  What piston to head clearance are most of you running? Thanks in advance,  Lorne
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