REFLECTOR: To Turbo or Not

[Chuck Harbert]

Scott, I'm late in responding, but it wouldn't seem to make sense to take 
off the turbo on the possibility that there won't be 100LL or an alternative 
additive. I think there are just too many airplanes dependent on 100LL to 
eliminate it without an alternative available. When they got rid of 100 
octane auto fuel, custom cars with high compression engines ended up adding 
octane boosters to prevent detonation, or they buy racing fuel (100-108 
octane) which cost about the same as avgas. You're right that you can keep 
the boost down under 30" (turbonormalizing) if they go to lower octane fuel.

The whole advantage of a turbo is that you carry sea level power to higher 
altitudes which allows you to significantly increase (200 kt cruise) your 
ground speed in the thin air. You've spent a lot of money to get this 
engine, so before you dismantle it on a unlikely possibility, I'd go forward 
with your original plan.

That's just my opinion.

Chuck H


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After reading another article about  100LL  going away  sooner than we
think I started thinking about the  tsio520 I'm installing...  Wise for
the long term?

One solution to running TCM's new 97 no-lead(or some other low octane
alternative) would be to limit the boost to 30 inches, which would allow
running a lower octane fuel.  A reasonable solution except for that fact
that then I would be carrying all that weight of the turbo system, not
to mention the extra maintenance costs and not getting all the
benefits.  Most of the lost benefit would be take off, initial climb and
emergency power since cruise MAP's would be in the 25-30 range.

So I decided to add up the benefits of no turbo, assuming my 520 could
be made to run sans turbo with  minimal cost.

1.)  I think the turbo system with, large heavy turbo, support brackets,
wastegate, wastegate controller, extra exhaust pipe, 4 long oil lines,
intercooler, extra induction tubing, oil reservoir, upper deck pressure
lines, large external scoop for intercooler & turbo,  all weigh up to 80
lbs.  Maybe more. Thats a lot of weight.

2.) Less maintenance just because there is less there of high
maintenance items plus not running the engine at such high MAPs.

3.) The compression ratio on this engine is 7.5 to 1 which would allow
the use of auto gas.

4.)  No large scoop and large bulge that would have increased drag quite
a bit.


Possible down sides..

1.)  I have put quite a bit of $$ into getting the turbo system to
work,  I could recoup some of this by selling the parts.

2.)  I'm not sure how much horse power I could expect.  Typically about
285 at sea level, but with the 7.5 to 1 pistons instead of 8.5 to 1 that
would be reduced.  Anybody know by how much?

3.) Getting the current injection system to work  without  the turbo
charger.  I'm not sure  if thats possible , which means  the added cost
and  work of getting  a  standard TCM injection system for a  io520.
Its possible I would need just a different  controller.

4.) Loosing the benefit of high altitude turbo charging which can be a
huge speed  increase.

5.) Odd ball engine install..

I'd appreciate any comments one way or the other...

Scott

--------------------------------------------------
From: "Scott Derrick" <scott at tnstaafl.net>
Sent: Friday, April 17, 2009 6:20 PM
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Subject: REFLECTOR: To Turbo or Not

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