Fabulous post. If even half of what you asked gets answered it will really help some of us lurkers. Also, have you considered super charging vs. turbo?

From: Chris Barber <cbarber@texasattorney.net>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Wed, March 17, 2010 7:34:51 AM
Subject: [FlyRotary] Turbo Considerations....careful, its long

I have been surfing the net 'til my eyes blur. I have read the archives, which tend to topic shift just a bit <g>. I am all but ready to pull the trigger on my turbo and wastegate purchase as, hopefully, my welder will have my manifold ready soon. I have been using an Asian knock-off turbo to this point for planning/spacing etc, but it should be about time to get the actual flight stuff. I have learned a whole lot about turbo operations and theory, however, The problem is, the more I tend to get informed the more overwhelmed/confused I get.

I could just punch in the info from John Slades set up. A Turbonetics T04E-50 big shaft tangential with P trim and a Tail 46 wastegate. This is also very close to the turbo the Grrrls are using (different Aspect ratio, 9.6 v 1.15) Current pricing for the T04E is about $1100.00. It is about $400 more with ceramic bearings....heck, point of confusion...do I need ceramic bearings.....it cost more....it must be better, right?;-) Also, there are widely varying prices on what seem to be very similar, but not exact turbos. Drives me crazy not completely understanding if the differences matter in my usage.

The TiAL wastegate is around $500.00...ah, but a "Performance" brand wastegate is "only" about $350 (I must have spent about ten hours reading various forums on the glory of TiAl verses Performace...yeah, at home recovering from surgery gives you this type of net time). Heck, for that matter an ebay Asian knock off is only about $80...tempting, but NO! (but hell, for all I really know, the Asians may be making one hell of a solid wastegate...just figure this is the wrong place to put blind faith...but for that matter, the Performance wastegate may be made in China anyway <heavy sigh>

When "they say" wastegate is 46...is that 46mm and if so, where exactly is that measured? I do know now, sortat, that a larger wastegate is better for controlling lower boost and even kinda understand why so the MUCH cheaper TiAl 38 is not in the picture here.

The problem with just punching in John's info and running with it is I don't have the understanding to be an informed buyer. While price is NOT the controlling factor, it pains me to just throw money at something in a blind manner IF there may be viable options. When it is all said and done, it may be punching in John's numbers. I know he and the Grrls did their homework. I do NOT want to reinvent the wheel but I would like to know why the spokes are made out of wood, so to speak.

I was reading about a 20b using a Garrett GT4088 Journal Bearing Turbo 1.19 A/R - which is selling for $899. Then there is Dave Leonard who makes reference to a, IIRC, BNR turbo. Don't know anything about that brand....I have at least heard of Garrett but do not know if the GT4088 would do for a 13b that it would do for a 20b.

When I look up the Turbonetics, while the part number I list is the T04E, the returns include the T3/T4 combination designated in the profile. Uh, I was thinking that meant is was a hybrid, which, as I understood it, we do not want. Or, does that have some other meaning that I am unaware? Is there a secret handshake that I do not know about? I have read the info on choosing a turbo on the various websites, but there is much information presented that presumes a base I obviously do not have <sigh> and also geared to auto needs. As a rule, I really do not care or need fast spool up.

It is my understanding that turbo selection is both art and science. Nice if it is your passion and you live for learning every nuance, however, I am just trying to understand the "standards". Great thing about "standards", there are so many of them...and in this case I am beside myself trying to figure out how the standards to one manufacture transfer to another.

I am not looking for huge power gains...yeah, we all seem to say that. But a bit more power, esp on take off (gee, have I heard that before?????) and of course, normalizing, would be sweeeet. Especially in my heavier Velocity. Al G did it with a 20b in the same kit airframe. However, that ship has sailed for me.

Actually, that brings up another issue I have been curious about. Why so much preference to a relatively hard to find and expensive 20b over a turbo??????? I noticed it routinely in the achieves. I understand the 20b is more powerful out of the box and the conventional wisdom seems to say the 20b is simpler...tubo's add complexity. Well, the 20b does have an extra moving part <g>....but, unlike the turbo option the 20b does not do much for you in thin air, the turbo does. Also, a 13b turbo install would still seem to be lighter than a 20b N/A install. What am I missing or do we just really like the cool factor of the 20b (no disagreement there from me).

I once again throw myself at the mercy of the collective wisdom for edification. While y'all pine away on it all, I will be confusing myself further doing some more surfing and remind myself of the other questions I meant to ask.

As always, thanks.

All the best,

Chris Barber

Houston, GSOT