[Supras] stock piston boost

[Dave Henry]

The stock pistons can take a lot as long as you have enough octane and a/f 
is safe (as Jim said).  I ran 22-24 psi for quite some time with a mix of 
110 and 91 in the car, this was with a mid size T04 turbo (a PT52 if you 
want to look up the specs). If I recall I think the car made around 440hp at 
the wheels. I drove the car hard and it held up fine, until I made the 
mistake of racing a guy on a 10F nite, when I accidentally set the MBC wrong 
and I got around 34 psi.  LOL  needless to say all the ringlands were 
crushed after just an instant of WOT.  I let off as soon as I heard 
detonation but it was too late.

DaveH

----- Original Message ----- 
From: "Jim Jobe" <jjobe2 at supratech.org>
To: <berniek at technicaldevelop.com>
Cc: <Supras at supras.com>
Sent: Thursday, November 15, 2007 9:01 AM
Subject: Re: [Supras] stock piston boost


>
> 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.
>>
>>
>
> _______________________________________________
> Supras mailing list
> Supras at supras.com
> http://supras.com/mailman/listinfo/supras_supras.com
>