[Fot] Piston to head clearance

[Ken Knight]

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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