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FWIW, I spoke with Reg Reimer at the Glen when he and Andi were doing the One Lap. I was concerned about tracking with an AFR being a flat ~13.0:1 and we looked at my '94 and 18psi BPU dyno together. Andi and I had been concerned it was too lean, but Reg said it's fine and didn't see any problem. He explained the engine management will lean it out as much as it safely can, and the dyno indicated that all appeared to be working fine.

It runs great on the track at up to ~16 psi with '94, and knock response has only been experienced at 16-17 when I'm really pushing it coming out of a corner and WOT...only T7 at RA and Oak Tree at VIR for some reason. Just a studder as timing is being pulled. I have no cooling mods other than for the brakes. My ps fluid usually does overflow a bit, and I have used race gas when it's really hot.

So I'm not sure what the engine management is doing to AFR on the track, but it's reasonable to assume it may be richening it up somewhat compared to 18 psi on the dyno. Just thought I'd share his views as I was a bit surprised. I usually just keep it down to 15 psi.

Bruce
 

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mav7 said:
While I didn't have a wideband when I road raced in the past, I can say that on hotter days my A/F would be richer than on cooler nights. So I would assume the car would get richer as it gets warmer.
Isn't the richening AFR when running hotter the result of the ECU's efforts to control detonation as determined from sensor inputs?

As far as me adding a fuel controller to richen mine up a bit for more power, I think I'm running pretty close to various limits at 406/408 @ 18 already. I can't usually run more than 16-17 without clutch slip anyways and the knock response tells me the engine's had enough too :-( I'd want to go beyond basic BPU to support more power. I'll be trying out a water injection system on my MR2 track car this summer. It's tuned to 12.0:1 and 300 whp. I think WI would be great on the Supra as well as it might eliminate the need to run a FMIC and upgraded rad for BPU's on the track by reducing intake and combustion temps. I'll know it's working if it resists heat soak.

Bruce
 

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mav7 said:
I didn't realize the ECU would add fuel if it detected knock, I only thought it would pull timing? Anyway as a result of this, the car could get richer (and EGT temps get hotter).

Bruce: Water injection isn't such a bad idea although it adds complexity to things... one more thing to fill, one more thing to go wrong, etc. I'd rather get the stock cooling system as efficient as possible, and go from there if it isn't enough. People have been doing some interesthing things lately for cooling. A NSX that was in my area for a national NSX meet had the AEM with a single turbo setup (running 15psi) and water injection. It was a very neat setup and seemed to perform well (that car at 15psi destroyed my supra at 16psi). It also partticipated in a racing event at WGI and from what I've heard the car performed well with the water injection. I actually might look into that as a cooling mod... but after I get an upgraded radiator and an oil cooler. BTW.. that mr2 track car sounds mighty fun :)
I don't know where I got that from, but for some reason I thought the ECU did dump fuel under knock conditions...does anyone know for sure?

I know what you mean about complexity. I've purposely kept mine stock under the hood so all the work-around mods won't work for me. I'll be chronically knock limited. Race gas, when available at the track, can handle the knock concerns, but isn't practical or convenient for the street or autoX. The Aquamist system, if you're interested, should work the same as on the MR2, and just tee into the stock washer bottle 6mm windscreen supply line. When fluid gets low your OEM warning light would even come on. Windscreen washer operation is unaffected. Activation of WI would be via the adj. pressure sensor teed into any boost line. I have mine trigger the spray at 11+ psi. The water nozzle would located just ahead of the throttle body.

If I ran out of water, which for me would be never, it would be no different than if I didn't have WI...other than the return of heat soak, and the ECU's reaction to pull timing and reduce power. Btw, my AFR tuning on the dyno was done using regular washer fluid, although I will mostly refill with distilled water at the track, and AF ratios actually became richer on runs where the WI was tested. I just think it's great way to add additional intercooling, and reduce in-cylinder combustion temps. I figure my knock sensor (blown twice last year), pistons, and ringlands will thank me. And with a predicted consumption rate of 1 gallon (99 cents!) per tank (or 30 min. run session), I figure it will pay for itself pretty quickly. This is a popular mod on MR2's partly because of it's limited size intercooler intake duct and the engine's sensitivity to knock.

I have friends that track NSX's and they are very capable competitors with just tires, suspension, test pipes, and a measly 270 or so bhp! There was a yellow supercharged NSX at VIR that we had our way with it in the TT. We had arranged to come around the Oak Tree turn together and then nail it. I came around first with him right on my tail and nailed it. A moment later I looked in my mirror and he was way back there! I got off the gas, thinking he had mechanical problems, and then he blew by me! My buddy was riding with him, and at the end of the session I asked "what happened?". The only problem was no grunt! Sounds like the turbo you saw worked a lot better!

The MR2 is a lot of fun, but just doesn't handle as well as the TT. You need big brass ones on every corner you try to go fast through. The rear just wants to pass the front, and will if you pick the wrong line and have to correct mid corner. It defines "commited" and I always feel a great sense of accomplishment when the checkered flag comes out and I'm still shiny side up :)

Bruce
 
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