Turbo Choking???

Possibly found an answer to the F2T's mysterious mid RPM stumble... Possibly the exhaust not exiting fast enough??? I've changed ECU's, BOV's, Fuelpump, Injectors, Dizzy, Plugs, Wires all with no change... Lowered the boost to 10psi and it'll pull to the redline without a hiccup. Matt Cramer says its no an interference/noise issue, so does this sound plausible? Sucks to think I might have to sell my GT2871R to go to a T3/T4... I must have at least 300whp out of this thing! Here is a pic of the turbo mounted on the engine.

.... is that a stock o2 housing?

I still don't think the turbo is what's causing your issue, but I guess I didnt look at it real close last year, because I seriously doubt that will make 300whp.

If it makes you feel better, the turbo on the black car looks ever more bizarre than that. Compressor housing is easily twice the size of the exhaust housing.

It's certainly a theory though. What I don't get is two things: how dudes are hitting 18psi on tbird hybrids easily, and that your car made 15psi well past where you're having problems now on the street last year on drag day. But ate E36 M3 afterward. So it DID do 15psi without issue. And 14psi. And 12psi.

The other thing to consider is that maybe that turbo is trashed. If it has a bunch of flow, that o2 housing is going to kill it. Poiny blank. The old Highball Racing cars ran bigass o2 housings and exhaust on stock turbos. For reliability/longevity reasons. Either way, you're leaving a bunch of power on the table with that.

Did we ever verify for sure that it's not overboost settings in Megasquirt?

Is this issue already described in depth in some other thread?

http://grassrootsmotorsports.com/forum/grm/ms-savy-people-please-help-whats-happening/63962/page1/

Yeah a few of them.

This is the most recent with the best info.

No one has ever been able to ID it Ben... I never looked at the one on the Probe when I had it. I really don't know what that thing is 100%, but the numbers on the Garrett tag say its a GT2871R. The boost control settings are confirmed and not the culprit... Though I do wish that were the issue!

I'm 99% sure that's a stock o2 housing. The whole turbo looks really small to be a 2871.

Have you verified that this is a ball bearing turbo? As in... taken a look inside?

446179-32 Ind. Exd. Trim A/R (Compressor) 53.1mm 71.0mm 56 0.60

Wh Dia Trim A/R Type (Turbine) 53.8mm 76 0.86 Wastegated

Posted in the other thread. For the purposes of this thread i will say that a 2871 could make 400hp in a perfect world but there's no way you're getting close to it with that discharge housing thing. That's amazingly bad.

The one on my Lancer is pretty damn bad too. I think it is most of the reason why my turbo does not spool very quickly. The highest ive ever heard of anyone trapping through the part that is on my car (at a similar weight) was 108mph. That's not even 300hp.

A 2871 is the smallest turbo I think could make 300whp on this motor. It would struggle to hit 300whp on this motor in a perfect world.

This isn't a 2871 in the truest sense of the word because that IS a stock exhaust housing and a stock o2 housing.

I still don't think the turbo is causing the problem, but the setup is very far from ideal at this point.

UNLESS.

Dan... can you get a video of what it's doing? If you turn the boost up, the higher the boost, the earlier it goes all bad? The rpm number doesn't make sense, but I wouldn't be surprised to see compressor surge on this turbo/motor. Backpressure can also kill turbos, and this o2 housing is creating backpressure. A lot of it.

There is a pretty good video buried in the other thread. Unless the issue has changed?

I'll crank it up tomorrow and make a video.... I'm betting this is a Thomas Knight Turbos Hybrid or very similar... They machined out a stock IHI Housing and put a GT2871R CHRA in it, but the Compressor Housing is supposedly an RX-7 Turbo II with a T-3 Wheel (all unconfirmed)

That is the weirdest damn thing i've ever heard. It's better than stock but i wouldn't have paid someone to create it!

I didn't read the other thread, but if you have good power a 10 psi, and it starts to run badly over that, and your fuel pressure isn't dropping off, then you don't have enough fire at the spark plugs. Tighten up the plug gap, or try a more powerful coil/coils.

Streetwiseguy wrote: I didn't read the other thread, but if you have good power a 10 psi, and it starts to run badly over that, and your fuel pressure isn't dropping off, then you don't have enough fire at the spark plugs. Tighten up the plug gap, or try a more powerful coil/coils.

I'd be looking here. Not sure what you mean by "stumble" but I'd confirm your A/F numbers, is your fuel map causing it to go lean there? What's your injector setup like? Primary to secondary transition?

dansxr2 wrote: I'll crank it up tomorrow and make a video.... I'm betting this is a Thomas Knight Turbos Hybrid or very similar... They machined out a stock IHI Housing and put a GT2871R CHRA in it, but the Compressor Housing is supposedly an RX-7 Turbo II with a T-3 Wheel (all unconfirmed)

It COULD be, but i had a full TKT setup a couple years ago that i stupidly sold, and it looked nothing like this. But i suppose there were 2-3 different ones, then you get the JGS Tools hybrids in the mix, and who knows.

Streetwiseguy wrote: I didn't read the other thread, but if you have good power a 10 psi, and it starts to run badly over that, and your fuel pressure isn't dropping off, then you don't have enough fire at the spark plugs. Tighten up the plug gap, or try a more powerful coil/coils.

He runs a tighter gap than i do, same plugs, currently has a Pertronix Flamethrower coil, NGK Plug wires.

I have the same setup, with more gap, and an MSD Blaster 2 instead of the Pertronix, and have no issues at well over 20psi. If he's having ignition issues, it could be the coil, but he's had 2-3 in there at this point and they all did the same thing. I think that if there IS an ignition issue, it's going to be Megasquirt related.

When we ramped this up to 15psi last year, it was on a stock ECU. Dan says something happened after that because it was doing the same sort of thing on stock ECU after i rode in it, but it DID run correctly at one point.

1988RedT2 wrote:

Streetwiseguy wrote: I didn't read the other thread, but if you have good power a 10 psi, and it starts to run badly over that, and your fuel pressure isn't dropping off, then you don't have enough fire at the spark plugs. Tighten up the plug gap, or try a more powerful coil/coils.

I'd be looking here. Not sure what you mean by "stumble" but I'd confirm your A/F numbers, is your fuel map causing it to go lean there? What's your injector setup like? Primary to secondary transition?

It's got RX7 460cc injectors and a 255lph pump. Plenty of fuel, but i still don't really like the VE tables he has.

I'm really wondering now if the turbo is just trashed due to the less-than-ideal setup.

Streetwiseguy wrote: I didn't read the other thread, but if you have good power a 10 psi, and it starts to run badly over that, and your fuel pressure isn't dropping off, then you don't have enough fire at the spark plugs. Tighten up the plug gap, or try a more powerful coil/coils.

That would've been my first guess.

In reply to Swank Force One:

I still think it looks like a stock hotside with a slightly larger cold side housing on it(TC tbird) maybe?

Yeah i'm almost thinking this is just a run of the mill t-bird hybrid.

Well, it's got what looks like a t25 to t3 compressor housing backplate adapter on it. I dont know the t25 center section on sight but i do know it uses a compressor backplate that is cast onto the center section and holds the cover with a big snapring and when you put a t3 compressor section on it (which im 95% sure is where the term t28 refers to because it's not a 'real' turbo family) you use an adapter like that. The t3-style cover is held to the backplate by 6 bolts.

I have something similar to adapt a t04b-sized compressor section onto my VNT-25 center section for a project i've never started. It is supposedly a chinese 2871 knockoff i got the compressor stuff from.

Found pics in my photobucket:

dansxr2 wrote: Here is a pic of the turbo mounted on the engine.

If that was the stock O2 housing, then we'd be looking directly at the O2 sensor in this pic (it sticks out to the front).

Turbo going out ? Have you looked at it with light ? Turbos usually go out with a bang and rarely give a warning. If it spins free and there's no sign of rubbing then keep looking elsewhere. If its running fine at 10 psi then goes to crap when you raise the boost I'd look at the clamps and hoses. Valve springs shot ? Bad ground ?

pic of compressor housing