I would have thought a bit more fuel in the ramp up section would cause it to still be burning when the exhaust valve opens and therefore expanding in the exhaust manifold. But that's just a preliminary thought since you brought it up. I'll have a cup of coffee and think about it.

 

I'm actually a little surprised at the top end, 15psi on a turbo that big with a 1.8L and makes the same torque as my 2554R/stock 1.6L/Begi mani/2.5" exh/13psi from 6000 to redline? I am on E85 but I figured the GTX with a 3" exhaust would be flowing a lot more efficiently than a 2554 in the high revs.

 

Yep, that too. It falls off really hard up top, so it's lose/lose

 

Log begi mani or tubular?

 

I dont think begi made the s4/s6 for the 1.6

 

That rich does slow the burn a bit, but it also drops your EGTs which is bad for spoolage. Leaner drives up EGTs and helps spool the turbo.

 

Example, assuming the dyno wideband is accurate: https://www.miataturbo.net/dynos-tim...5/#post1280722

 

The "direct pulses" or whatever it's called, cast mani.

 

which (imo) is still better than the FM in terms of flow, but still lightyears behind proper tubulars

 

A year later....did this ever get figured out? Im trying to pick my next turbo but these results aren't helping. It took codrus 24 psi and 100 octane to make 340 on the 63mm billet wheel. I still think the bigger gt2871 may be superior to the billet stuff

 

Yeah, threadsurrection, but..

These numbers are far from impressive, Im about to run a Premium Gasoline NB8a setup with a GTX2871 and if it doesnt destroy this setup ill be so mad.

Dann

 

Even a standard gt2871 should destroy this. A gtx2863 did destroy this. Thats why i asked if it got figured out because something is up

 

I haven't changed anything since that dyno run except some reliability mods. The possible restrictions are the FM log mani, the 70 degree bend in the 3in downpipe about 10 inches from the turbine outlet, the 2" hotside intercooler piping, the intercooler, etc. Everyone so far says my timing is good, but pointers are welcome. Is base timing off or maybe a tooth off on a camshaft? I'm not sure.

It's been parked mostly and I've been busy selling a house. But I'd love some ideas.

 

Cant be the manifold. Miatamike did 400 on a begi cast mani. FM has built 400whp+ stroker motors on their mani. I dont think it flows as good as a proper tubular, but it should be fine for 300-350+

2 inch hotside IC piping shouldn't be a big deal either. Again, FM runs 2 inch and its fine. And the standard size for the turbo outlet is 2 inch

Whats your air filter setup? Maybe choking the big azz turbo?

Still puzzling tho. Im still thinking this is the turbo for my goals but if i struggle to hit even 300whp ill be mad asf

 

Air filter is of adequate size but is in a poor location. Using NA8 intake manifold and Skunk2 throttle body. 3 inch downpipe is covered in heat shields but I have an old picture from a prior disassembly depicting the sharp turn. It is still many times larger than the turbine outlet so even though it's not ideal I don't know if it could cause a tremendous amount of restriction.

This is the downpipe and manifold (with a different turbo).


This is a good depiction of the difference between the turbine outlet size and the 3in pipe:


Again, the bend in the downpipe (very old pic, many of the surrounding components have been changed or rerouted):


As she sits this morning. Note air filter location far less than ideal.

 

Its not the downpipe. the hotside, and I use some silly small intercoolers on dumb builds, its unlikely that.

 

the cheated radius on the downpipe right at the turbine exit doesnt look like it would promote flow very well but who knows. thats not the gtx2867 is it? looks like a small chinese thing

 

This is the GTX2867R:



This was Chinese 2870:

 

YUP.

 

not even talking about spool tho. there is no reason the HP should be this low

if i had a turbo that big and shiny and was making as much power as ppl with stock engine and gt2560 id lose sleep at night. not even trying to sound like an ***, just trying to pick my next turbo and i cant have this happen to me...