RMDZidane

Here is what a VNT25 turbo does when it's maxed out, through a 2.5 in. exhaust, catalytic converter and Magnaflow



I went to have my Miata run on a dyno to see where it stood before I took it to a day at Thunderhill. I had gone for a baseline dyno about a month before when I'd first gotten the car running with some semblance of quality after getting it together. I hadn't been able to adjust the variable vanes on the turbine side yet so that accounts for the difference in the two graphs represented. The AFR's were low 11's and timing moved from 9 to 13 deg. at full boost during the runs. VNT's have no wastegate so I was concerned about boost getting out of control. Fortunately it settled at 16-17psi. Knowing that, I tuned a bleed valve to reach that boost level as soon as possible. That is what I got with the second graph.
The car is responsive and fun to drive. I had a blast on the track with it. I'm concerned about the VNT25's reliability so I'm going to install a t3/t04 that I can get to try out sooner rather than later. Thanks

messiahx

iTrader: (2)

I think you are the first to use a turbo like that on this forum. I just read up on it and that's some pretty cool technology. I remember reading about variable vane/nozzle turbos when Porsche put them on a 911 not too long ago and it turns out Garrett had it down in the 80s! Very cool!

I guess I'm a little confused on the boost control with a turbo like that. From what I gathered here: http://www.thedodgegarage.com/turbo_vnt.html, I take it that you use the method described for boost control there and your bleed valve is more or a less a ball & spring type boost controller that vents/bleeds to atmosphere upon reaching target pressure? Any pics of the setup?

BoostedTrixx

This is cool, I like the unique qualities of the VNTs...

any real ignition tuning done or just a simple 9 to 13 deg change at WOT?

Braineack

iTrader: (62)

you're going to hate a t3/t4 after having that. I'd look for a better compromise.

RMDZidane

Yes. You are right. I used the same site as a reference when I hooked up and made adjustments to the bleed valve. I used a bleed valve because it only slows down the actuator rather than hold back all boost signal until the target boost is reached.

I use a TEC II which is an ancient ecu made by Electromotive. I tuned the ignition maps using chassis ears while doing full throttle runs on the freeway As a result timing settles at about 9 degrees when I hit full boost somewhere around 2500rpm and slowly climbs with revs until it reaches 13 or so at 6100-6200 which is where I shift.

I see what you're saying, but the t3/t04 is free, so I'll try it first I've had a great time with bigger turbos in the past on other cars.

Braineack

iTrader: (62)

that's a lot of timing retard to keep it safe...might as well bleed off boost after 5K and keep timing higher. Less heat (therefore less prone to detonate) and same power output.

RMDZidane

I thought about that. With the way the variable vane boost diaphragm works, I can do it in the other direction: keep boost low until higher rpms, then the exhaust energy forces them wide open and boost climbs to 16-17psi. The only way I can lower peak boost is by making the diameter of the exhaust smaller.

Out of curiousity, I unscrewed my WB sensor from the downpipe today to see what effect it would have, and boost shot up to 19-20psi and it was good with no detonation. I re-installed the sensor and decided that it would be dangerous to work in a test pipe for track days.

Full_Tilt_Boogie

iTrader: (1)

Thats a pretty neat dyno.
What you need is two of those turbos used sequentially like a super or RX7 so itll hold that torque to redline.
That would be fun.

18psi

iTrader: (76)

holy quick spool batman.

lol I'll bet that thing feels like a vw 1.8t

webby459

iTrader: (8)

THAT would make for a rad autocross turbo.

Faeflora

iTrader: (2)

Damn, there's not many miata turbo dynos where the torque is higher than hp. 190ftlbs tq at 3k rpm? That's pretty ******* cool.

RMDZidane

Thanks guys. 18psi. funny you say that because I bought a 1.8t GTI for an old girlfriend in 2000 and it had a similar powerband after the, seemingly standard, GIAC, TBE, and CAI stuff was done to it. It was just a lttle bit slower

Unfortunately with this turbo, longevity is not very good. Chrysler went back to a standard turbo after a year of using this one. I've noticed in the three months that I've been using it the transitional spool after shifts is beginning to suffer a bit. I suspect the vanes may be getting a lot of carbon build up. I'm going to have a look at it this weekend. I'm also getting curious about the units that Porsche and BMW have been using that have VGT technology

Dust

water injection? there are a few threads about cleaning of vnt turbos on tdiclub if you are interested in cleaning. What are you using to control the VNT?

RMDZidane

Hey Dust thanks for the tip. I'd forgotten about TDIclub. Yesterday I took the VNT apart and looked at it. I realized that it was nonsense for me to keep f'ing around with it. I decided to use an ancient Turbonetics t3/t04b that suits my style a little better. I'll do some tuning with it and go back to the same dyno facility to get some new figures.

RMDZidane

Bringing this thread back from the dead because I'm taking my Miata to get dyno'd at FFTEC here in the Bay Area. Same setup but with a t3/t04b from Turbonetics that I've had on for a while. I'll post up how it goes....

18psi

iTrader: (76)

Should be interesting. Those guys put out some seriously fast evos/dsms

RMDZidane

I got baseline numbers yesterday. 182rwhp and 180lb/ft tq. on their Mustang dyno. I had 14lbs. boost and the timing went from 11 degrees at peak tq.(4000rpm) to 14 degrees at 6500rpm. I will post up the graph tomorrow sometime. To the guys who PM'ed me, I can't respond until I have a few more posts.

miatamike203

Cool numbers and fun turbo to play around with but even better to see engine bay pics with some other pics....

RMDZidane

Sorry Mr. Mike. The area underhood is far too ugly to photograph. Lots of heat wrap, zipties, and electrical tape so no pics are gonna be forthcoming

Like an a$$ho!e, I didn't bother checking my tune before getting the baseline numbers. I checked after and found that my MAP was not connected properly (the TEC II is notorious for having bad connectors) so I was getting detonation whenever in boost....probably been going on since late February or so since that's the last time I checked with my 'det cans'. It has dropped my compression by at least 15 points to 150, 145, 130, 120. So that's kind of weak. I believe that may be one reason my power figures were a bit low even for a stingy dyno like Full Functions. So I'm figuring I'll go dyno again to get more accurate numbers this week. And post up the sheets so that this gets back on topic