Ever think of picking up a cheap 2554 from the Nissan world? You can generally find them for $100-200 and would swap right over. Might offer you the better response that you want.

My plan would be to have 2 maps, switchable. I plan to have a race map where, at minimum TPS, the ignition timing is normal. At the point above minimum TPS where power delivery equals engine braking, between 2500 and 4500 rpm or so (I'll tune all this once it is up and running) I'll run maximum retard and a throttle bypass solenoid. I plan to run the retard and bypass flow as high as possible without the engine putting out enough power to accelerate. Once I've found that point, I'll tune backwards to make it so that the retard drops off slowly, the bypass solenoid cuts out, and power delivery increases somewhat smoothly as TPS further increases.

The bottom line is I'll decrease the retard to normal advance values long, long before WOT. The effect should be that I can get pre-spooling on demand in the rpm range where it is needed by pre-positioning the throttle into the low power output spool region before I want power. Then as I roll on the throttle past the apex, the timing advances to increase power, the bypass closes, and boost rises rapidly if I get on it hard.

why not focus on things that actually improve spool/low-end?

Look at the VE graph here:
CAPA : Eaton Superchargers

My powerband would run from ~4700 to 13000 rpm on the MP62. I calculate that based on 90% VE at 13000, and overdriving the SC to get 10 psi even though the mechanical displacement times drive ratio implies 11 psi. Then, at 4700 rpm, the VE is about 60%. 0.6x11=6.6 --> less than 7 psi at less than 3000 engine rpm. All this normalized for temperature.

As stated in OP, because he's already underwhelmed by the topend on the 2560 and doesn't wanna give up any more.

Otherwise that would make perfect sense.



oh and OP: if you're gonna stick fancy billet wheels onto the 2560 just get the efr now and don't waste money/time.

Can you explain your thoughts? Here are mine:

The center of the island for the GT2560r is basically at 10 psig at sea level and about 200 hp.

The bottom of the island for the EFR6258 is at about 15 psi at sea level and about 260 hp or so. The middle of the island is at about 22 psig.


The EFR may well spool better, but it seems far from ideal, given it will have lower compressor efficiency pretty much everywhere.

Why do you care so much about compressor efficiency? Yeah its nice to wave your dick around but if you only want to make 200 hp, your turbo is too big. For an AX car you should be aiming to have turbo that you ride right along the surge line, then the top, the the choke line of the compressor map. So what if thats in the 65% efficiency range. You'll still make the power you want to make, without blowing up the engine and the smaller turbo will spool faster and have a lower boost threshold. And 200hp is not enough for a SSM car to be competitive never mine an XP car. You should be shooting for at least 400 in XP just to keep up.

Okay, are we talking about lag, or are we talking about spool. These are different things.

The dual throttle setup is a very cool idea, that will do wonders to minimize lag (which is why it was used in F1 way back when), but it wont make the turbo spool any faster.
Of course I question how much true lag you would even be experiencing, since that turbo shouldn't have any trouble getting going at high rpm when you suddenly give it the throttle.

Do you have something to contribute here, or just showing off your people skills? :D

Better exhaust manifold.
Smaller IC.
Larger TB.
Better IM.
Better Head.
VVT.
Better exhaust.
EBC.


When you can easily build a 2560 to make 250rwtq at 3500RPM at 14psi with simple bolt ons...


If you went to a 2554, you might gain 20-30rwtq below 3K, but above that, youll still peak at 3500 but much less overall torque than the 2560 will provide in that range, then it will run out of steam at 5.5K.

compare the two here:

https://www.miataturbo.net/attachmen...ine=1351171600
140tq @ 2.5K
190tq @ 3K
225tq @ 3.5K


https://www.miataturbo.net/attachmen...ine=1351171600
140tq @ 2.5K
180tq @ 3K
225tq @ 3.5K


You can see the output below 3.5K is very similar, but you can see by the rounded curve of the 2554 that it spools faster and more linear, the problem is, the actual output is on par with the 2560 spooling slightly slower and then increasing expotentially.

The gain in spool is outweighed by the nil extra output. and then youre left with a turbo with less top-end, where your 2560 can potentially hit ~300rwhp.

Below 2800 or so doesn't exist for purposes of my build, because if I get down that low, I'll always shift.

2800-3500 having a large chunk of the extra power of forced induction is important. 6500+, having a large chunk of the extra power of forced induction is important.

Goal: As much power as possible between 3500 and 6000 rpm, without sacrificing having a chunk of power on tap within 200 ms of going WOT between 2800 and 3500.

Those graphs pretty much match my impression of the gt2560 vs gt2554 in terms of power on tap. The gt2560 wins at every single point in the critical region of 3500-6000 rpm. On top of that, my old gt2560 setup was still pretty close in terms of responsiveness. It was still the fastest car at our biggest event last year. If a turbine upgrade on the GT2560r will give it faster spool, and less exhaust side pressure ratio above the wastegate cracking pressure, that plus the rest of this might just be enough. I'm not completely convinced that the EFR6258 will put down more power in the 3500-6000 rpm range than a worked over 2560 at 10 psi on a 1.8l engine. Can I get a probably from someone with some experience running an efr6258 at low boost? :)

why do you love to stroke off 10psi so much? if youre goal is: As much power as possible between 3500 and 6000 rpm, then why are you limiting yourself from being able to make as much power as possible between 3500 and 6000 rpm by keeping the boost at low donkey dick level?

18psi on is super amazing. I mean the GT2560R would love being run at 18psi, heck it would take 20 like a champ.

Thanks
I know.

:brain:

lololol

Better exhaust manifold - I think I've got a decent compromise between cost, flow, and volume right now. I'm doing some minor porting on it, and it seems the runner are slightly smaller than the exhaust ports, with semi tangent convergence to the t25 flange.


Smaller intercooler - well, I'm starting from no intercooler, and working up. It will probably be a small inline water to air. No FM retardedness on this build.

Larger TB - Stock is 2.125 ID. I think I have a ~2.75" bore throttle body around somewhere... With ~2" OD charge piping I don't think going any bigger will help....?

Better IM, check.

Better head..... I'm leaving that alone

VVT, check.

Better exhaust - I'm making huge improvements here, with 3" piping coming off of the transition from the turbo exit flange, 5" 100 cpi cat, and straight through muffler. I haven't decided on the wastegate plumbing, but thinking I'll do a 9.4" circumference bellmouth with a slow transition to 3" round. The other option (presuming I stick with a garret turbo) is a 2.25" to 3" tapered 90 bend off the turbine exit with a divorced DP rejoining the flow about 10" downstream.

EBC - I'll do something that holds the wastegate completely closed until just before the boost target is achieved.

I'd like the stock internals to stay internal, and I'm not opening the engine up this year.

you can push more than 10psi. i like the exhaust plans.

If he runs a non-fail intercooler, Brainy? :giggle:

What's with the FM hate? They make a solid proven product that a lot of users here have had great success and reliability with for years.

I don't have a horse in this race, I'm just curious.

Generally speaking, people skills are not required in totalitarian regime ;)

They dont make anything superior in terms of turbo parts.