Incessant ping-like sound

[X64v]

...you mentioned that the quench area seemed somewhat negligible...The thinking is to provide a pad where a flat top piston pushes nearly everything out of one section, and that movement inside the dynamically combusting chamber assists proper ignition and helps prevent detonation.

 

When I say quench area, I mean the effective quench area between this specific head and these specific pistons. Yes, this head has a large quench pad, but the area of that pad used by my pistons is what I'm deeming 'negligible'. (Although, looking back at my pictures, it's a little larger than I thought)

 

In actuality, the stock turbo pistons, with their dish, pretty much by definition kill the quench effect of this head (almost?) entirely. TRUE utilization of quench pads only occurs with well matched flat top pistons that nearly impact the head at TDC, and if a relief is needed for compression then the piston relief mirrors the CC in the head as much as possible.

 

This was exactly my point in my posts with Six_Shooter. Not only does the turbo piston not have much area to make use of the quench effect, it does not come close enough to the head to quench at all (or so I've read, correct me if that's wrong).

 

That's also why I'm a little stumped as to why this head works better than the other one. They're both more or less open with the dished pistons, why does the P79 work so much better? Or another way of looking at it, why did the E88 work well with flat tops, but not dished pistons?

[WizardBlack]

Might ye be troubled to update the appropriate Megasquirt Map Sticky with your latest maps? Particularly timing...

[X64v]

Yeah, I might as well. I'll post them here, too.

 

Full Set-Up:

 

Stock turbo bottom end

Stock T3 and exhaust manifold

P79, unshrouded valves, minor exhaust port work

Stock N/A "A" cam

400cc injectors

Unintercooled

Stock FPR

3" mandrel downpipe and exhaust, no muffler

N42 intake, stock 50mm TB

BPR7ES plugs, gapped at .030"

 

Fuel Map:

 

Spark Map:

 

The fuel map puts me at 12.5:1 to 13.0:1 at idle, 14.7:1 to 15.5:1 at cruise in all situations, and ~11.5:1 under all boost levels.

 

The y-axis graduations above 100kpa on the spark map are approx. 2 psi increments.

 

Both maps tuned up to 172kpa (12psi in Tucson, AZ) (~2400' ASL, ambient pressure usually 90kpa indicated)

[Hyuri]

According to my reading of Six_Shooter's explanation: the P79/dish combo would be forcing the charge towards the plug/valves, and the shape of the chamber would stir that up in such a way as to cause a more thorough mixture and prevent any area from stagnating. Still needs the quench area, doesn't need flat tops. Possibly even works better with dished pistons.

 

Make sense to anyone? It's illustrated!