CrispyRX7

iTrader: (139)

A simple observation...higher engine temps can contribute to detonation/preignition from hotspots in the combustion chamber
(and regardless of the AIT's)
Additionally running higher coolng temps on fresh motors is probably
not as detrimetnatl as running the same temps on a 60k motor for example.
As over time engines do loosen up. Each time an engine is thermally cycled the engine bolts may stretch (and why we check the torque whenever the flywheel is off). Over time the engine gets looser and the possibility of cooking a water seal gets higher when the aluminum and iron engine parts expand at differring rates.
Run a hot motor and you takes your chances.
...IMO
Crispy

rceron

Manny, good to hear you didn't sell your RX-7 (like everyone else). Now that it is purely a fun car, strip it down and run 10 lbs boost.

Going to Mid Ohio (first time) on 23 of Oct. See if you can make it.

Ramon

Wargasm

At Summit Point in the summer time I was running 10 PSI (street is 15 PSI) and I was hitting about 104 C at the maximum. Every few laps, I would "coast" on the straightaway and that would bring the temps back to around 100 or so. I don't know what my air temps were.

SleepR1

I read you, Chris. I'm going to try the NPG+. If it's not sufficient, I may try the NPG-R (despite the need to change the NPG-R every other year). NPG-R has a higher BP (400 F), higher thermal conductivity, and lower viscosity @ 7 to 10 psi cooling system pressure.

Yeah, I couldn't bare to sell, and take such a huge hit. Yeah, 10 psi will be my limit. In retrospect, 12 psi may have been a bit high. The new motor will have much larger ports than KDR's so, 10 psi should be plenty of boost for maximum CFM flow.

Send me the info on the Allegheny Region PCA DE. Perhaps I can sign up as an instructor with them? I have LOTs of time @ Mid Ohio. Going there Sept 6/7 as an instructor with TracQuest.

SleepR1

104 C's really not that hot. I wouldn't worry until 110 C to 115 C (with conventional coolant). Evans NPG+, 130-ish C, 265 F (according to RTS3GEN) with FMIC is par for the course on a hot day running full-bore!

rynberg

Wow, I ALWAYS run at least half a tank of 100 octane when tracking the car. As Crispy pointed out, a hot motor is much more likely to detonate, making high octane gas even more of a priority.

FWIW, I had my hottest track day this weekend. 103F in very dry desert air at 2500 ft elevation. Pretty much the worst combination for driving a car hard there is. By afternoon, I could only do about 3-4 laps before water temps were pegged out at 230F/110C. I've REALLY got to get back under the car and seal that radiator airtight.

SleepR1

Didn't think I'd need race gas, since I was tuned to 10.9 AFR with 93 octane pump gas. Lesson learned the expensive way...

rynberg

It's too bad about your motor, Manny. There's no way to say if running at least a partial tank of racing gas would have helped or not. It may have been something else entirely that blew your motor. Race gas certainly is expensive ($5/gallon) but I do it for insurance.

SleepR1

My guess as to how/why the motor failed is a localized hotspot on the rotor housing making conditions right for detonation.

The way the apex seal chipped at the corner leads to this guess. My conventional coolant was 85% water, so at 115 C, 239 F was definitely running at the high end of water's cooling capacity. FMIC makes matters worse, as the water doesn't have much chance to condense back down to liquid, so things were definitely boiling in the rotor housing.

Switching to Evans NPG+ will prevent the hotspotting on the rotor chamber. The motor will be bathed in liquid coolant despite the hotter operating temps with the Evans NPG+ (I've read 130 C, 265 F).

Running larger ports, with less boost will put less heat stress on the motor. Boost pressure is a restriction in air flow; intake and exhaust port size become limiting factors in CFM air flow through the motor. Larger ports mean less boost and better power production.