Premium Dude

After a lot of reading, and calculating, and checking compressor maps, I am still very confused as to what T3 to go with on my d16y8. When I looked at the compressor map for a 50 trim, it looked almost perfect for a d16 @ 10psi. (unless I did the calculations wrong). According to my compressor plots, at 2000rpm I would be just past the surge limit, and entering the least efficient ring. Does that mean the turbo will begin to spool then?
The 45 trim compressor map looked pretty good too, but my redline was a bit farther away, past the most efficint ring. Does that mean my boost would start to drop around redline?
And then after further research I found that the stock saab turbo's are 45 trim, right? Are those ball bearing? What are some other stock turbo's that are 45 trim?
And finally, what stock turbo is a 50 trim? I couldn't find any info regarding that.
Oh, one more thing. What are the specs on the skyline t3?

Thanks a ton guys.

RJwaggs

Once you pass the surge line, you will begin to make boost other than atmo. Boost will not drop if you are feeding the turbine enough gas. If you're in it, then it will continue to produce. While a comp map is not everything to picking a turbo, it does tell you a lot. You want to try and stay in the most efficient range possible. You also want to be in a very efficient operating level when you want max power. No point in aiming for max power when your compressor is most efficient at 3000rpm, ya know?

Post up what you found/calculated for the 50trim @ 10psi.

Premium Dude

Sure, here are my calculations for both the 50 trim, and the 45 trim @10 psi on a d16y8:

Pressure Ratio: 1.782312925

RPM Corrected Mass Flow
2000 5.45826212
3000 8.187393181
4000 10.91652424
5000 13.6456553
6000 16.37478636
7000 19.10391742

And here are the compressor maps for the 50 trim, and the 45trim with the above points plotted on them:

RJwaggs

Well, from what I see, I would say the 50 trim is what you would want to go with. You efficiency would be higher for a greater period of time and you would not be so close to choke flow at redline. You would spool just a wee bit later with the 50, but I don't think it wold be too big of a difference.

I'm not sure if you know, but the larger the trim, then the better off up high it will be. The larger fan allows for more air to be induced, therefor supporting the upper RPM/power lvl's where more air is needed. The smaller provides for power lower in the band and spools quicker as well (when dealing with the same A/R and in reproducable condition). Again, not sure if you knew this, but a good aspect to think about none the less.

Premium Dude

So according to those compressor maps a 50 trim should start spooling around 2500rpm? Is there any way to tell when the turbo would reach full boost?
But it does look like the 50 trim is a great turbo with max efficiency from 4000-6000rpm. My only concern now is, what turbo's have a 50 trim? I have heard great things about the .42/.48, and the .48/.60, but I have no clue what trim those are.
Thanks.

RJwaggs

Many turbos have a 50trim wheel. You will have to do some research to see which vehicles came with 50trim T3's.

Premium Dude

After a lot of research this is all I could find regarding 50 trim t3's:
First, I looked at the t3's off the saab's that had the .42/.48 housings, but they only came in 40 and 45 trim.
Then I looked into the .60/.48 housings that came on mustang svo's and turbocoupes, they were 60 trim though.
In fact the only thing I could find that was remotly 50 trim was the 1990-1996 300zx turbo. It has a .42 t3 housing with a 50 trim wheel. However the exhaust side uses a t25 housing that is .53 (manual) or .48 (auto), and has a 62 trim wheel.
I hope I am wrong and there are some t3 50 trims out there, because it seems to suit my exact needs.

RJwaggs

There is bound to be something other than a .42/.48 50trim T3 that suits your needs. Someone will know.

Premium Dude

A .42/.48 would be ok though wouldn't it? Or do you think that would be too small? Because I was hoping to find something like a t3 .42/.48 with a 50 trim, but I cant even find that. Closest thing I found was that 300zx turbo, but it uses a t25 exhaust housing. I would prefer a straight t3. Thats why I started looking at the .60/.48, but those are 60 trim, and looking at the 60 trim compressor map tells me that it might be a bit too big for my d16. Although I read that a lot of guys like their .60/.48's on d16's so who knows.
I'm so confused :P

RJwaggs

Well i think this is where my road of help ends as I have no turbo experience, only book knowledge. Sorry.