i wouldn’t say it’s without a tune. Rather, it’s with a tune for the old exhaust.

It won’t go to 850 rwhp on pump gas. Not enough octane. And the 90-degree exhaust blowdown interference kills cylinders 1 and 6 above 6000 rpm. It’ll probably go to 730 on pump gas but almost certainly not over 750.

Itll do more on high octane race fuel.

...some of the clamping arrangements need to be beefed up further. This clamp, for example, is a little too wide to maximize the force it can take. The clamp is the width of the groove, but the rubber boot requires a little more side clearance to allow the clamp to really anchor the rubber in the groove:

The LH is huffing and puffing at these load scales, so John is repeating the tests with two LH units, one original and another JDS rebuilt. The original LH is about as exhausted as Joel Embiid was last night:






(Hard to talk trash when one is totally out of breath.)

Kuhn lab is still in the shakedown and debugging mode. Still only running these about 16 psi boost runs that put out 700 rwhp to get everything thoroughly tested before the blue engine gets "turnt up":



My TE WBO2 controller is flaking out, so that needs to be replaced. John is going temporarily run his controller to record the AFRs.

The second pump activation logic needs to be tested and verified. A single Bosch 044 handles 700 hp rich against a lot of manifold pressure. 0.6 bsfc in lb/(hp*h). Gasoline 1.65 lb/liter. Bosch 044 pumps 255 liters/hour against maximum relevant pressure. 700 hp at the crank or 600 hp at the wheels with these conservative assumptions. Since one needs at least 13 psi in my car to produce 600 hp at any rpm, any switching logic be that eboost2 or Hobbs switch with 10 psi switch point with say 1 psi hysteresis will work.

The fuel return system works as the fuel pressure is rock solid at about 75 psig in these test dyno runs with two pumps hard wired on. That’s with injectors seeing a 4 bar pressure differential between the fuel rail and the intake runner.

It’s Mother’s Day so John’s dyno facility is a no-go zone for him. Not a no-go zone in the sense that you need a two-car police escort to go there but an absolute no-way-no-go zone.

So I’m at a swim meet watching my oldest and decided to write up a little post about lean spool. Lean spool is an idea that we’ve copied from Mitsubishi and want to test with the twin turbo 928.

Let’s think about air-fuel ratios for the rpm ranges in which the turbo is running at low speed and the wastage is closed. One of the high priority goals in those rpms is to get the turbo to spin faster. The idea is to run the engine pretty lean in the spool-up region.

I think that one way to think about this is as a trade off between torque to the wheels and energy to the turbine. If im right, then the optimal AFR has to be between lean best torque AFR and the maximum exhaust gas temperature AFR. For a typical car, the LBT AFR is probably 13.2 or something and maximum EGT AFR is around 14.7. For 928 S4 that seems to burn pretty efficiently, the LBT AFR (without the knock constraint binding) is probably around there or even higher. So the best guess optimal spool AFT would be around 14.0 or so. But I will have to think thru the whole issue of excess vaporize fuel “steam” also influencing the turbine spool, so it’s back to the thermodynamics text book for me.

EDIT: More I think about it, the more complicated it becomes. Now I’m thinking that the unburned fuel will cause the turbine to run like a steam turbine. In other words, a Brayton cycle with stoichiometric AFR and full combustion and then adding a phase-change Rankine cycle aspect to it by vaporizing and not burning the excess fuel. I’ll work a little more on that theory and then we can compare it to results.