REFLECTOR: To Turbo or Not

[nmflyer1 at aol.com]

Scott, 

If it was me, I wouldn't be too hasty about changing my plans at this point. You are awfull close right now, and there is no way that they are going to get rid of 100LL very soon without some way to address higher compression engines. 

If they go with the 94UL that they have been working with, you are still pretty close to a reasonable octane for your setup. They might keep 100LL around as they try and address higher performance engines, or they might come up with an additive that gets the octane to the point where turbo'd engines can be happy. 

Regardless, I think that you have time to finish and enjoy your project, then try and hedge against the future. Blending your own fuel (Like I do), ising additives, or knowing they won't render a large chunk of the GA fleet worthless gives you piece of mind & time.

Of course, if you are just looking to change weight, heat, complexity, fuel concerns, etc.. that is a different matter. 

I would press on. Then start covering your bases with research. You might purchase a stand alone Knock sensor like I did just for insurance & piece of mind. 

Kurt. 


-----Original Message-----
From: Scott Derrick <scott at tnstaafl.net>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Fri, 17 Apr 2009 7:20 pm
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 altit
ude 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



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