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Old 04-19-2021, 02:18 AM   #26 (permalink)
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spyder2 - '00 Toyota MR2 Spyder
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Originally Posted by Ecky View Post
I imagine you could get a fair bit of mileage with running as little lean as 1.04-1.07 lambda, even without adjustments to ignition timing.

Heat isn't an issue at low load (which it would be during cruise), and temperature actually starts to drop off past ~1.04-1.05.
Yes, but the gains are bigger if you can go leaner. Lean burn is like high volume cooled EGR but with faster flame velocity. To get the best effect, you can bias everything lean and run open loop idle richer, or run open loop lean while cruising. Running open loop in commonly used operating conditions has its own drawbacks, and not forcing open loop limits the gains. Biasing the sensors means a few hundred bucks in narrowband emulators, a bunch of custom wiring, and a lot of custom tuning to reset the ignition timing.

For a car that doesn't have emissions restrictions and for which you have complete control over the ECU's programming, you definitely want to run very lean, maybe with warmed intake air or a hint of EGR to help with ignition.

This engine isn't short on EGR thanks to the MASSIVE cams, so pumping losses aren't actually that big of a deal. The intake vacuum is pretty modest near minimum load (i.e. pressing on the pedal enough to actually move the car), around 0.6 bar.

@cRiPpLe_rOoStEr I wouldn't call it particularly sophisticated, it's very similar to a Ford V8 in design. This car adds a 2 scavenge pump dry sump system, DLC coated shimless bucket lifters and a forged crank. Everything else is pretty ordinary, and thankfully it seems to all hold together unlike Porsches of the same vintage.

The coolant temperature goes up FAST, though it's a 1.5 bar system so it can run a little hotter than most cars I've seen. I do have some concerns that the radiator is near its limit and my grille tape might not be a good idea. Of course, this isn't relevant to the discussion as lean burn decreases peak combustion temperature and only increases EGT at high load and high speed where the slower combustion speed is a problem.

Last edited by serialk11r; 04-19-2021 at 02:32 AM..
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