Hybrid Turbo - T04B Compressor, 0.70 A/R

[Ineptitude01]

I'm nearing the end of my 280ZX build, and the engine and trans are back in the car.

 

Go figure it's only now that I start worrying my compressor may be too big.

 

I had the stock turbo rebuilt as a hybrid, which is common enough in these parts, but I'm wondering if maybe I overdid it a little bit for what's essentially nothing more than a freshly rebuilt stock engine.

 

Here are the turbo specs:

 

Nissan T3/T4 Turbo

T04B Compressor Housing .70AR

"H" trim Compressor Wheel

Nissan .63 Turbine Housing with wastegate assembly

Stage 1 turbine wheel

Water cooled center section

 

I've looked around, and I can't seem to find anyone with a super similar turbo. Does anyone know how this is going to perform for me? I'm planning on a 2.5" crush bent exhaust, from the turbo back. (MSA style downpipe, no cat)

 

I was looking on the AZCC site, at the turbo tips, and Goldilocks says "too demanding". Not sure how similar my turbo is to the one the map is based off for the T04B on there, though.

http://atlanticz.ca/zclub/techtips/turbo/turbomaps/index.htm

[Bernardd]

Most likely you'll have some surge issues. And you didn't size the compressor too large, you sized the turbine side too small. Your engine should be fine because of the small turbine housing wheel. You won't be making much more power than stock and if you up the boost too much the back pressure could cause detonation issues.

[Ineptitude01]

So what should I expect to be safe until? 15psi like the AZCC page suggests? I was intending to run stock boost until the engine is broken in, and then raise to 10 or maybe 12 later on. This is my first engine build, so I wasn't trying to go real over the top.

[SleeperZ]

Your turbo is similar to mine, I think I have a higher trim on my compressor, it's the V1/V2. At least at altitude in Colorado it kicks butt.

[Pyro]

I use that compressor. t04b-h3.

 

but use a Stage 5 t3 turbine.

 

that compressor will surge on a L28 if you make boost too soon in the rpms. And a stock turbine will do that. (make low rpm boost).

 

So either swap the h3 for a v1/v2 or s trims, or open up the turbine to a stage 5 to delay the boost.

 

But, a stock cam will only make power to 5000 rpms and the stage 5 t3 turbine makes full boost around 3500 so this will make a short power band. The stage 5 turbine really requires a bigger cam to extend the power band out to 6500.

 

I use the msa turbo stage 1 cam (260 intake/250 exhaust 114 lsa) and it seems my engine makes peak power around 6000 - 6200 rpm and pulls hard to 6500. boost starts a 3000 and hits full boost (12-14 psi) by 3500.

 

The H3 compressor is better for a 3.0 liter engine that is set up for high rpm power.

 

if you plan to use a stock cam then change the compressor to a v1/v2 or s trim. you will be happier.

[Ineptitude01]

Sorry to bring this back from the dead. Been busy with first startup.

 

I just drew up a compressor map, can someone verify that it looks okay?

 

My math is according to the Atlantic Z turbo page, and I think this should be right.

 

Looks like I really did need a different compressor.

 

Since the money is spent, and it's on the engine, what should I do? Tear it off and start over? Is there any chance that I'll somehow have a slow enough spool to be safe?

 

Maybe I should just get an intercooler with huge pressure drop...

[SleeperZ]

^^^ Looks like it will work as well as a factory T3 (not great.) The V-trim compressor and stock T3 turbine will do 12 psi much better. Pyro nailed this one, and your compressor map verified it.

Edited March 10, 2010 by SleeperZ

[Ineptitude01]

Rats. I thought I had done my homework before I sent the turbo off to the shop, but I guess I needed to do a little more. Well, I was going to keep boost stock until break in's over anyways, so I guess I'll just have to see how I like it. Is there any chance that having a 0.70 A/R is going to make it play a little nicer with the L28, or am I totally screwed? I mean, this compressor is ENORMOUS, compared to stock. I have a hard time believing that I'll ever see 12psi at 3500rpm. 7psi I can believe, since the stocker tends to be in the 2800 range, but it just seems crazy that it would be able to spool up so quick, for being such a big ol' thing.

 

Just found my pics of it on the bench. The shop did a really good job with this thing, I just wish I'd given them a little less creative license. They maintained to the end that this thing would be able to do 18psi for me some day, if I really needed that. I'm starting to think not. Anyways, pics:

[Ineptitude01]

Ahoy, naysayers!

 

I return with news of first startup and delicious turbo spool. The T04B is doing great for me. Still running stock boost for break in, but I've got my homebrew MBC waiting in the wings. Comparing it to my dad's 83 Turbo with the stock T3... there is no comparison. I hit full boost at 3000RPM instead of 2800RPM, but my spool starts earlier, and I have far more lowend. It definitely doesn't have the sudden onset of boost that you expect... But I promise, I'm still getting the whole 'OH GOD I'M FLYING' sensation coming through first gear, and I hit full boost in first, which I haven't seen on the stock 83 yet.

 

No surge so far. Still at 7psi, but maybe we'll see some more coming up on 12. I'll definitely keep you guys posted, but right now, I'm real pleased. It's very drivable, and the helical LSD is maybe my favorite thing ever.

 

I wish I knew a place in the Bay Area that would let me do dyno runs 'for science'. I'd love to see how my power curve compares to stock. Just using my gut feeling, stock feels exponential, and my turbo feels logarithmic. And I'm loving this potential convexity.

[letitsnow]

Looking at the math, 7psi should be fine, and it is. The problem will start creeping up around 10psi and be noticeable at 12-15psi depending on how well your engine actually breathes compared to what you thought when you drew the lines on the compressor map.

[Ineptitude01]

This past weekend I installed an eBay MBC and raised the boost to 10psi.

 

Still seeing no problems. It runs better than ever, actually. I haven't seen (or heardany surge.

 

The other thing I'm now considering is that when I was calculating the numbers for my map, I assumed a very low volumetric efficiency for the L6. I'm pretty sure that I used 80%, since I have pretty low expectations of the L28ET's flow potential. Now that the shock of first startup has worn off, I'm discovering that I'm really hitting full boost more between 3200 and 3700 than by 3000. This is obviously 10psi now, but I feel like it was the same story with 7.

 

What should I have assumed for the volumetric efficiency? 85%? Certainly not 90%, right?

 

Maybe I'll just build my spare shortblock out as a forged piston stroker. Rebello's not that far from me, after all. Displacement seems like it would fix my problem.

[Ineptitude01]

Okay, I had my most boring class today, so instead of paying attention, I revisited my compressor map. Turns out, I did a few things wrong. Today, I followed to the letter the guide on this site:

 

http://www.lovehorsepower.com/MR2_Docs/compressor_flow_maps.htm

 

This matched up with what I've learned from Maximum Boost, and more google searches. I tried again with a volumetric efficiency of 85%, which is what was suggested for a stock 2 valve engine. It still seems a little bit optimistic to me for the L28, but maybe with a reconditioned P90 head, the ol' L6 thinks about it.

 

In any case, I screwed up the 20% redline flow bit, since I had failed to understand that it's supposed to be at a pressure ratio of 1.0, which makes a lot more sense.

 

So I redid the map, and the whole thing looks much closer to what I've been observing actually driving the car. I always like to have an explanation that fits my symptoms.

 

So here's the map done over again for 7, 10, 12, 14, and 16psi.

 

The knee on each PSI rating is at 3500rpm. If it were at 4000rpm instead, the knee on 16psi would be right on the surge line (24.61lb/min). Clearly any more boost than 16psi would do a whole lot of nothing, even were it inside the surge line.

 

 

The more I drive this turbo, the more I like it, but I'm having trouble fully enjoying the thing right now. I'm having significant trouble with my ECU connectors at the moment. The slightest wiggle on the connectors can kill the motor, or cause it to have a rich, lopey idle that turns into an inability to rev over 2000rpm. The poor car is dying mid intersection, coming back to life, flying to 3000rpm, dying, and then idling at 650 thereafter. Wiggling and swearing can get it to have a proper idle with no richness, but for the moment, it's a pretty unreliable mechanism. I'm going to go out and get some Caig DeOxit tonight, and see if I can get the pins cleaner, but I'm not optimistic.

 

When my spring break comes up, week after next, I'm planning on installing a compressor bypass valve, doing the 300ZX ECU/MAF swap, and converting the popoff valve to a pipe plug.

 

I'll keep this thread updated until I have a final report on this turbo application. Lemme know if the new map makes more sense.

[Ineptitude01]

Okay, perfection! (Or thereabouts)

 

Most of the odd running issues were solved by Caig DeOxit Gold. I sprayed it all over the critical connectors, especially the ones on the ECU. Worlds of difference. It got through the corrosion like it wasn't there. I highly highly highly recommend it.

 

This past weekend, I did a valve adjustment and retorqued the manifold bolts. Boom. That right there was the rest of it.

 

I've got neutral manifold pressure by 1800rpm, positive pressure by 2500rpm, 7psi by 3000, and 10psi by 3200.

 

I think that should be the most of it. If I ever get this car to a dyno, I'll post up some results.

 

Thanks for your help, everyone.

[Xnke]

Hmmmm, this would imply that we could work backwards, and get a better effeciency number for a stock L28ET. Am I correct in that now i could take your graph, rework the knee for the 10PSI line to be at 3200RPM, assuming that you have no compressor surge, and solve for the new set of lines?