[Supras] stock piston boost

[Jim Jobe]

Tough call.

I've seen 15 psi on very hard runs in the 150 range and
the pistons looked great.  This was on a stock turbo, 550's,
lexus, old school afc, stock base ign timing, and nothing more
than an EGT to tune.  This same set of pistons was
reinstalled after a light hone and pushed to 2 bar of boost
resulting in 520rwhp.  This time 550's, VPC, old school afc,
stock base ign timing, EGT and WBO2 to tune, generally around 11.5
richening up to 10.8:1 by the end.

Basically, if you have fueling or ign timing issues you can
kill a piston with minimal boost on a few easy pulls (actually
just one pull if detonation is bad enough).

Therefore:
Do you have enough fuel octane to support 15psi?  93-94 pump is required
What is the base ignition timing?
  What changes have you made that could modify ignition timing (such
  as a lexus afm, afc, afr, vpc)?
What is the air fuel ratio, say per 100 rpm, when load is above
 10psi?
What do pre-turbo EGT's read and where is the probe located?

For plugs - I've disagreed with the blanket statement that
a colder plug is needed.  That started about 10 years ago
when a well known member/drag racer had to switch to a colder
plug.  What most do not realize is he had a custom ignition
timing map in a remapped ECU and the car was built for the
1/4mi (with an automatic tranny, btw).

6 is the stock heat range.  I've run 7's and they fouled
out too easily for my tastes, and I have not seen any indication
(plugs read under scope) on my car or the other locals I tune
that 6's are too hot.  For reference, that's back when my
car had a stock ECU, VPC/AFC tweaked back for 720's (meaning
lots of ign timing advance), and a 63mm T4 turbo.

I do prefer the copper plug, bcpr6es-11.  The electrodes
are larger thus less chance for overheating and copper
is the better conductor.

On Thu, Nov 15, 2007 at 12:27:06AM -0500, berniek at technicaldevelop.com wrote:
> I'm beginning to regret the fact that I did not install Weisco or other 
> forged pistons in my JDM when freshening it.  I know this has been 
> discussed before with answers spread over quite a range, but I'd like to 
> get a consensus if possible:  What safe boost is OK with stock pistons 
> assuming 11.5:1 or richer mixture?  What about top speed runs?  I'd like 
> to touch 150 just once.  Present boost is 15 PSI on a 57 trim CT26. 
> 
>