Built 1.9L with GT2560
 

Engine built over the winter by McCully Racing Motors (McCully Racing Motors- There's no Replacement for Displacement.) 2002 VVT engine with the following parts:
Manley Rods
Supertech 84mm pistons
BE oil pump
SuperMiata damper
Supertech OE size valves
Supertech springs, titanium retainers
Combustion chambers and area behind the valves cleaned and smoothed
Tumble generators removed from intake manifold
Oil squirters retained
9.5:1 effective CR

Turbo kit:
FMII, current manifold and 2.5" downpipe
GT2560
Old style steel intercooler pipes with vertical flow intercooler designed by BEGi circa 2002
Boost pressure set to 15psi with Hallman Pro RX
Hydra 2.7 ECU

Exhaust, FM 2.5" duals with Vibrant 2.5" 200 cell cat

Torque is about where I expected, 268ft-lb, but horsepower is a little disappointing at 265hp. I have tuned similar cars to the 275hp to 290hp range. Above 5300RPM the boost dropped off from 15psi to 12psi at redline. I'm happy to make 265hp with 12psi, but would like to know why the boost dropped off. I have made more power on other cars with 2.5" exhausts. I have never tried to push more than 12psi through one of these old intercoolers. I am sourcing the wastegate actuator from the turbo outlet. I will move this source over to the intake manifold to see if that makes a difference. Comments welcome

Boostleak?
Turbo pressue beyond efficiency? (Think the GT2560 should be well capable of 15psi though)
Heat soaked intercooler/ intake gets too hot? (think you should be able to see a difference in boost drop on the Dyno vs Road use, Or Hot vs cold day)
Boostcontroller not set correctly?(doubtfull)
Exhaust restriction? (not enough flow on the turbine side) Personaly have a 3" Never tested with a 2.5"

Regards,

Jarno

More preload.

My 2560 makes 20 psi tapering to 17. I use 3" d.p. & exhaust , and a 2.25 intercooler.

Personally I think that's a really good power curve.

Have you measured compressor outlet pressure? The curve looks like it's flow-limiting to me (constant power above 5800 RPM or so) and if MAP is dropping off then increasing pressure drop through the intercooler would make sense.

--Ian

Thanks for the feed back guys. Make no mistake, I'm not complaining. The curves are good, I was just surprised by the boost drop off. On this car I have always sourced the boost signal for the wastegate from the compressor outlet. Running between 10psi and 12psi the boost was always steady. After I got home from the dyno it occurred to me to move the boost signal to the intake manifold. Now the boost holds steady at 15psi to redline. The intercooler is restricting the flow. I'm running an old BEGi design from the late '90s. The car feels stronger. When I get the time, I'll get it back on the dyno for new numbers.

An intercooler upgrade is in my future. I'm in no hurry, the car feels great now.

Ken Hill
2002 HZ Yellow LS
FM II

You mean the cold side of the intercooler plumbing right before the throttle body, right? Putting it on the intake manifold will needlessly overspool the turbo on part throttle stuff, and it might not be the best thing for the wastegate can to see vac.

No, I'm sourced from the intake manifold. I do not agree with the theory that this configuration will "overspool" the turbo at part throttle. The speed of the turbine is a function of the flow of exhaust gasses from the manifold which is a function of the load on the engine. When operating the engine at part throttle, and below the boost target, the wastegate is closed. This condition produces the same turbine speed regardless of where the MBC signal is sourced. I have already determined my intercooler is only a restriction at boost pressures above 12psi and engine speeds above 5500RPM. Therefore, with this signal source location, I'm only spinning the turbo faster then the previous configuration when there is sufficient flow through the engine to make more than 12psi and the engine speed is above 5500RPM. Granted, I am getting about 1psi of overshoot because of the length of the air column from the intake manifold to the MBC, but that is acceptable to me. Also, vacuum on the wastegate actuator is not a problem at all. The diaphragm is plenty strong to take vacuum as well as boost pressure. Everyone using EBC through their ECU is doing the same thing as I am. The ECU controls when the wastegate opens and the ECU makes that decision based on manifold pressure.

You have it backwards. Couple things:
1) most, if not all, OEM's source from the compressor or right after and don't care much for boost drop off cause they can compensate with the bcs if need be. this makes life easier for the turbocharger and prevents potential overboost situations.
2) most (all?) ebc solenoids are by default open, and the signal closes them. not vice versa like you stated
3) when you are at partial throttle and upper rpm (boost threshold), it is very easy to create a situation where your IM is in vacuum or low boost, but turbo and charge pipes are shooting through the roof, because throttle body is causing a major restriction which is causing a major decrease in flow and increase in pressure.

What he's saying is completely correct, and you are wrong I'm afraid.

for the record: I also agree it's not as big a deal as most here make it out to be, but they are right and sourcing from the IM is not desirable

1) Agreed. When using EBC the best location for the boost source for the EBC is the compressor outlet. The ECU is going to manipulate this signal to achieve the desired boost pressure as referenced from the intake manifold.

2) Agreed. In the rest state when the engine operates in vacuum, the EBC valve is open, air flows from the inlet to the outlet unobstructed. However, when 0psi or a small amount of boost is generated, the boost control algorithms I'm familiar with, will close the ECB valve to spool up the turbo as quickly as possible. If the boost target is 15psi, at 10psi the EBC valve will be closed, trying to get the boost up to 15psi. At this point the system is acting no different than my arrangement. The wastegate actuator sees no signal, the wastegate is closed, and the flow of exhaust gasses are sufficient to support 10psi of boost.

3) Where is the energy coming from to make the boost pressure "shoot through the roof"? When the throttle plate is in a position to make something less than the boost target in the manifold, the resulting exhaust gasses are sufficient to spin the turbo to make less than the boost target, or whatever this value is plus the pressure drop through the intercooler. Yes the throttle plate is a restriction to flow into the intake manifold, but it is also a restriction to the flow out the exhaust and this controls speed of the turbo.

I believe the misconception here is that the turbo always makes significantly more boost that the boost target and that is simply not true. The speed of the turbine and the resulting boost pressure are controlled by the flow of exhaust gases from the engine which by a large amount is controlled by throttle position, not the location of the boost signal for the EBC or MBC.

Yes, I will agree I am spinning my turbo at 18psi to make 15psi in the intake manifold above 5500RPM. But I do not agree that the turbo is making significantly more boost at part throttle because of the restriction of the throttle plate.

I'm not claiming my solution is the best solution. Certainly a better intercooler with lower pressure drop is the better solution and I will get there someday. But for the time being, my solution is not the warp in the space-time continuum some make it out to be.

Oh and I almost forgot. The reason plumbed my MBC this way was to prove to myself the restriction was coming from my intercooler and not my exhaust. I know 3" is better, but I have made 15psi to redline in other cars with 2.5" exhaust. Before this exercise, I was not sure if I was buying an intercooler, exhaust or both.

at around 3500+ at part throttle (let's say below 50%) your car will easily generate enough exhaust to make the turbo hit it's MBC commanded 15psi before the IM while the IM will see much less than that.

You can easily test this and see for yourself, you don't have to take my word for it. Like I said, I honestly don't think its a huge deal, but it's not a theory, it is fact. There's really no need to keep your turbo on full-boil when you're only asking for 20-30% throttle.

Still chasing this bugger huh? I'm learning some stuff here too. Maybe I'll move my line from back of the maifold to pre-TB also

:facepalm: