Good morning all, I have been having an issue with my ITA 240SX for about 1.5 years now that I just can't seem to pin down. It made for a very discouraging race weekend...
The car runs ok for the first few laps of a session, but then it's almost like a switch (or a bad sensor that doesn't like heat). The car looses power, and the sound of the exhaust changes to a flat (almost splatty) tone.
I have a new (last september) stock radiator, summit oil cooler, stock water temp gauge (which never shows above normal) and oil pressure gauge (about 50psi when I'm above 2500rpm). I don't have an oil temp gauge (will install one before next race weekend)
I have both a stock auto trans ECU, and a chipped manual trans ECU (problem happens with both ECU's)
I have installed a crude heat shield to keep exhaust heat away from air filter (and have a heat-tape wrapped Injen cold air intake), and monitor incoming air temp, which only went above 75F when I was right on someone's bumper.
Things I know:
fuel pressure is good all the way through the rpm range
air/fuel is 11.5 - 12.5 all through the rpm range
(both of the above from a dyno session last october, which showed VERY dissapointing numbers)
water doesn't seem to be getting too hot (unless sensor or gauge is bad, but sensor was replaced last september when I did the radiator) also using a 160F thermostat
using stock heat-range plugs, with an MSD coil
I took the distributor dust cover off at the track and the disc and sensor underneath were clean (I'm thinking about replacing the sensor just because)

Things I don't know:
EVERY other 240 I've seen in person or online ALWAYS has an oversized aluminum radiator... do I need one? If so, who/where do I get it from?
Is this a spark or heat issue? Anyone ever run into a similar problem?

As you guys know, this car is FAST when running right... I got down to 1:20.7 at Nelson Ledges in my rookie year (driving like crap). I know that I'm cornering much faster now, but I just watch everyone pass me by on both straights and this past weekend, couldn't get below 1:22.

Hopefully no Mazda guys are reading, but on the back straight this past weekend, my uncle passed me like I was standing still (in an ITA RX7!!!)

Any ideas???
Thanks,
Mike