[Supras] losing performance

[Hacker J]

Bernie,

The ECU apparently is sensitive to coolant temperature.  I am working (slowly) on a way to quantify the affect, but others have reported that with the coolant above a certain value (220F I think) adjustments are made to timing and fuel. I would suggest you monitor coolant temp and see if it correlates with your performance loss.

I am wondering if you have quantified the impact of switching from the stock filter to an aftermarket air filter.  I have not found any data on the flow of the stock filter with cold air duct. The factory design certainly seems better from the standpoint of avoiding hot underhood air.

Jon
90T


----- Original Message ----
Tonight I thought I would have some fun with the rejuvenated toy
 (550cc, 
Lex, Walbro, 57 trim, 3" turbo back exhaust, etc.).  Rt 80 was almost 
empty and relatively free of cops.  So I did a couple of runs through 
second third and fourth gears (first run:  5900 RPM in fourth, 120 MPH,
 
beautiful before shifting to fifth and coasting down).    Each time,
 the 
performance got worse, with some light bucking in high gear.  I know 
that fuel starvation is not the cause for several reasons, including 
fast responding A/F ratio between 9.5:1 and 11:1.  It seems as if the 
performance is best when just warmed up, and then decreases as full 
boost runs are made.  And then again, at 15 PSI boost, I'm starting to 
consider if spark plug heat range it too hot. 


Right now I still have the stock platinum spark plugs, abrasive cleaned
 
and gapped a little tighter due to 15 PSI boost.  I'm beginning to 
wonder if the heat range is too hot, leading to detonation and
 retarding 
of the spark by the knock sensors.  No ECU codes have ever been set 
since first startup after the engine swap.  There has been quite a bit 
written about use of copper core plugs due to heat dissipation 
considerations, but a plug made of any metal can be configured to be 
cold or hot.  So why should copper or other metal of construction be 
different from a standpoint of heat range, assuming the heat range is 
correct to begin with?


Suggestions would be appreciated.  Thanks.


    Bernie







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