Overbore has been calculated into specific torque output already. Still at ~75. Exhaust may be better but I'm at 5 psi backpressure and a 3 psi reduction won't get you from 68 to 75, especially since I'm operating the GT2560 closer to its max efficiency island (200 kPa, vs. 230). I have headwork too, and oversized valves. Note that my buddy Ian got almost exactly the same torque curve as me, even tho I have VVT and a shorty tubey manifold, and he doesn't.

244 tq @ 16.5 lbs @ 3700 rpm on mustang dyno
220 tq @ 16.8 lbs @ 6400 rpm

84 mm 9:1 NB1, NB2 VVT, square top, 3", 2860, stock tub

so the incremental cost of the 2860 over the 2560 produces the same result of all that fancy head work?

:)
When I try to sell the turbo, I get smart guys saying it is run of the mill turbo which is valued at $100-200 in great condition. When I dyno or race it I get different smart guys telling it cannot produce the results it does.

Piping has effect and this one could not fit into Miata as Ben told, unless you move front suspension 2' forward and firewall 1' back.

Turbo is still for sale so I can get that EFR or GTX there like designed. I want to have throttle steer on fifth gear as well :)

I agree that piping is more critical than ppl realize

why I have fins on the twin charge pipe between the turbo and the dual inlet intercooler

larger volume, lower velocity, longer residence in heat rejection area BEFORE I/C
grab as much charge cooling as possible without sacrificing flow

sorry I missed the hill climb, would have loved to have seen your car perform, sure looks nice on facebook

instead I got to do solo laps at Bristol

but planning to be there for the next event

Pressure drops can be measured.
It would be interesting to see what TIPs are in hrk's setup.

A 2860 vs a 2560 will make more power, but spool up at a higher RPM. That matches with what this dyno chart shows.

Fancy head work and a really efficient exhaust with a 2560 ought to make more power up top, but also let the turbo spool up at an even lower RPM. That's why I don't understand why hrk's dyno chart doesn't show 200 kpa until 3700 RPM, while my car (2560 with vanilla FM2 parts) does it at 3300. I would have expected to see it around 3100 RPM on hrk's plot.

This is why I asked if the '2560' had been a typo for '2860'. It's not though, the part #s off the compressor and pictures do indeed point to a 2560.

Are there any boost leaks that would be delaying spoolup?

--Ian

Sometimes headwork will delay spool because it hurts low velocity/low flow conditions.

I think that would have to be one big assed pipe between the head and the turbine to get the kind of volume to affect velocity that much

I think it has more to do with the dyno not presenting enough load at the beginning of the pull. It releases the axle and allows the engine to rev up at a fixed rate, set up as a user configurable option in delta RPM / second. I have noticed that turbo car tend to spool faster with their wheels on the ground compared to the dyno. Heikki may have a log saved from last weekend that we could use to compare spool on the track vs spool on the dyno.

Ben you can change this on the dynapac. Set the start rpm to something lower than when you think the turbo should spool, set it to hold for a couple seconds there, and then set it up like normal.

I'm quite familiar with how to use the F11 Settings Menu. :brain:
Holding the car back for a few seconds is very hard on the car, quickly creating very high temps. Part of tuning is keeping conditions stable so you can correctly value the effectiveness of the changes made between pulls. Another part of tuning is not putting the engine in danger, IE lugging the engine at massive load for an extended time.

I think a better option would be if a knee point were added in software, allowing to change the slope of the pull rate at after a configurable RPM.

LOLOL@Leafy teaching Ben how to operate a dyno.

Next you should tell him about Megasquirt:laugh:

is that as in less load, lower KPa, less combustion gas, less spin?

What was the sweep time setting on the dynapack?

If he had absolutely no clue about that feature it would not surprise me. The first dynapac I went on it took me 20 minutes of arguing the guy and then finally showing him that you could make it hold the car at a specific rpm.

That would be nice to know. The shop I had the miata at, knew exactly what to run for an s2000 or a stock miata but I kind of just pulled a number out of my ass for my car because they had no idea.

The chart shows the MAP starting at 140 kpa and at 1500 RPM, so I'd think there'd be plenty of time to get the turbo spooled up. Sweep time would be of interest, yes.

The car has a 6-speed and 3.9?

--Ian

5 speed and 3.9
log manifold for turbo as well

/\ I was just about to comment on that: its a super basic log manifold, not some tubular high flowing goodness, which makes this even more surprising.

log manifolds spool better in most cases.

it's also making a lot more boost at redline than 4K, but it still takes a dump in tq after 6K.

I thought that only applied to high flowing tubular manifolds where the runners didn't crash into one another. apparently I was wrong