VJ-20/Tbird hybrid spikes 17 then settles at 13

[atomicEGT]

Curious how you were maxing out 460s with a VJ17 hybrid and 15psi... Is the Mazda FPR not 1:1?

[Iantboyd]

When I spoke with a gentleman at IHI years ago he gave me the turbo specs for all of the IHI / 323 related turbos and including the Tbird. The compressor specs were the same between the VJ17 and the tbird. Yes the turbines were different though as the 17 was externally gated iirc.

Thats good info, any chance the maps for this exist?

[92dx]

Curious how you were maxing out 460s with a VJ17 hybrid and 15psi... Is the Mazda FPR not 1:1?

I always ran solid low 11 AFRs on 15 psi for ages with no problems. It was when I upped the boost to 17-18 psi. Thats where I noticed it was leaning up. The wideband would start creeping up into 13s at around 5000 and thats as far as I went with it, back to 15. Everything normal again. As I said tho, I assumed injectors, but maybe it was not. I have been wrong before lol. I decided just to leave well enough alone.

I had a walbro 255 and a GTX FPR. The mazda FPRs are 1:1

[atomicEGT]

weird- it's not that I don't believe you or anything, I'm just sort of confused how the same ECU/injectors (I have an A-code, but I don't think that would make a difference?) would be leaning out at 18 psi on a VJ17, when they give me AFRs in the 10s at 35 psi on the Holset...

[cis2711]

92dx- The b code vaf may be leaning you out as it is from a naturally aspirated car. My 425cc injectors can flow up to 550cc if I increase fuel pressure but at normal fuel pressure they haven't leaned out yet and I'm spiking as high as 18psi in fourth gear pulls. I will be alleviating the boost spike soon when I change my boost source from the compressor housing to the charge pipe after the IC.

[cis2711]

atomicEGT- how in the world are you running that much boost without harming the GTR bottom end? That holset has to be putting out some serious cfm at low boost levels...I can't imagine what it is at 35psi! I want...

[92dx]

Beats me. I cant imagine 460s at 43.5 psi rail pressure supporting a holset pushing 35psi and not be well above 85% duty cycle. Im no tuning wizard, Im just going by injector size calculator and formulas I've seen.

cis2711- What is your injector duty cycle at 18 psi in MS?

[cis2711]

I'll have to check idk.

[cis2711]

The 425cc injectors should be good for 300hp so I've heard.. I MIGHT see 240hp at 18psi.

[bomdoutscort]

The GTR bottom end is forged im pretty sure.

[atomicEGT]

atomicEGT- how in the world are you running that much boost without harming the GTR bottom end? That holset has to be putting out some serious cfm at low boost levels...I can't imagine what it is at 35psi! I want...

sorcery. seriously, I have no idea, the internals are all stock with the exception of some used ARP head studs. it moves a lot of air, that's for sure. it also goes from a few pounds of boost at 3k to all of it by 4k, so the power curve is pretty wild.

Beats me. I cant imagine 460s at 43.5 psi rail pressure supporting a holset pushing 35psi and not be well above 85% duty cycle. Im no tuning wizard, Im just going by injector size calculator and formulas I've seen.

at 35psi, it's not at 43.5psi at the rail or whatever the Escort FPR is- the FPR sees boost and adds a pound of fuel pressure for every pound of boost. I did the math a while back, at full boost they're the equivalent of like 700cc injectors.

The GTR bottom end is forged im pretty sure.

rods are, pistons aren't.

[cis2711]

Are you saying that my factory FPR sees boost and adds fuel pressure as boost increases? Or do you have an aftermarket FPR?

[atomicEGT]

That's the theory, anyway. I've got a stock EGT FPR on one of Mike's fuel rails, with a vac signal direct from the nipple on the TB side of the GTR manifold.

This motor has also seen 9000ish rpm when I mis-shifted it and somehow managed to not scatter itself all over the highway, so there might be some other wizardry going on, I dunno.

[cis2711]

Where did you get your holset from? I'm building a 1980 Mustang drift car with a 5.0 that I'd like to turbo.

[atomicEGT]

bought it from someone on the forum. they turn up on Craigslist a fair amount too.

you should make a thread for the Mustang in the general automotive section, I'd like to see it.