REFLECTOR: To Turbo or Not

[Chuck Jensen]

Scott,

Most times, our first instincts are our best instincts, and you are probably in a good spot.  100L may go away eventually, but it's demise has been predicted for a long time, and we are still pumping.  Of course, that's not reason to turn a blind eye to that eventuality, but also not a reason to change your plans because something 'might' happen in the future.

The advantage of a turbo would seem to depend greatly on your mission profile.  If you fly from higher elevation airports or fly long distances, the speed at altitude is a wonderful thing indeed.  On the other hand, if you hopping around Florida at sea level to get hamburgers and go to some fly-ins, the turbo likely has little, or negative, value.

Review your original thought process for selecting the turbo.  Was your check list faulty then, or are you needlessly doubting yourself because it's still valid.

My favorite arrogant expression, 'the last time I was wrongs, was when I doubted myself.'

Chuck Jensen


-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Scott Derrick
Sent: Friday, April 17, 2009 9:21 PM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: To Turbo or Not


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