REFLECTOR: Need for speed

Tue May 21 11:58:34 CDT 2013

I have a turbo on my Franklin, and expect someday to reduce my 
compression ratio from the current 10.5 down to about 8.

What others have said about the differences between turbos and 
superchargers is true.

I designed and built my entire system, and that is not a simple thing.  
The plumbing required is difficult to figure out, but if you can go off 
the shelf, then go that way.  The complexity I had to deal with was the 
exhaust plumbing, scavenge pump and cowl temps.  My wastegate is manual, 
and it looks like a simple throttle body except built to withstand the 
high temps.  It's pretty simple, but does add another knob to the panel 
that must be managed.  I received all of the parts from a Piper Seneca, 
which included the controller and all of the other bits to make it 
automatic.  There's a LOT of parts to make it automatic.

If I were to do it all over again, and I'm not sure I would, I would 
choose a solid off the shelf automotive turbo.  Learn how to read a 
compressor map.  That goes for superchargers too.  There's no need to go 
aviation here, and you can get ceramic, ball bearing, or even water 
cooled technology.  The bonus is that you should be able to get what you 
need for about $2,000.

Supercharger vs turbocharger:

The turbo will be more efficient.  It is heat driven to a large degree, 
with temperature drops across the turbine of around 300F. There is a 
penalty in back pressure, so it's not a free lunch. Compressing air is 
compressing air.  It doesn't matter how its done, it takes power to do 
it.  To get 8PSI of boost can require in the neighborhood of 20 HP.  
It's either coming off the supercharger belt, or out of the exhaust.

There will be heat transmitted from the turbine wheel to the compressor 
wheel.  I'm not sure how much heat is transmitted this way into the 
intake air, which should be as cool as possible.  All compressed air 
will heat up.  First due to compression.  PV=nRT here.  The air will 
also heat up due to the inefficiency of the compression process.  A 50% 
efficient compression cycle will put that extra 50% of energy into the 
compressed air.

With the supercharger, it's direct drive, unless there's some new tech 
I'm not aware of.  At higher RPM's the blow off valve may be releasing 
pressure in order to maintain a limit on the MAP. However, there's no 
exhaust tubing to contend with, and the cowl temperatures will be lower.

On 5/21/2013 6:46 AM, Geoff Gerhardt wrote:
> Guys,
>
> Ok, in my pursuit for more speed, I have narrowed down on two mods. 
>  Definitely will be changing my exhaust - I'm working with Clinton at 
> Custom Aircraft on this.  He is quoting some pretty big numbers 
> (+18HP) for switching from the standard Velo exhaust (2x2-1) where 
> each cylinder is battling the other to a 4-4, we'll see.  I am looking 
> forward to better cooling as I won't be adding pressure to the lower 
> cowl with the exhaust hole cutouts (pretty big on mine), and 
> exhausting out the cowl will create a lower cowl pressure to draw 
> cooling air out.
>
> Now, for the big speed increase, turbo or supercharging 
> (normalization).  I'm exploring a couple options there.  There's a guy 
> close by who has a complete RaJay turbo normalization system for an 
> IO-360 off a Mooney.  Its been rebuilt.  He says its a very simple 
> system, manual wastegate. I still haven't got a price from him, tho, 
> and I expect it will be $20K+, tho.  The other option is 
> supercharging.  I talked to the guy from Forced Aeromotive 
> <http://www.forcedaeromotive.com/homebuilt.htm> yesterday.  Their 
> system sounds pretty bulletproof and simple and provides 8000' of TN. 
>  That is, at 8000', you still have 30", flying at 10,000' would be 
> like flying at 2000' without it - you get the idea.  It has no 
> wastegate, the manifold pressure has a redline of 30" that you're not 
> supposed to exceed, so at a low elevation field, you would not take 
> off with full throttle, just advance it to 30".  As you climb, just 
> keep nudging it up to maintain 30".  It is a nice, simple install and 
> costs ~$10K.  Apparently, you can climb like a bastard with it, and 
> can expect >15kts increase at cruise.  I'm leaning more towards it 
> than the turbo.  The one big advantage to the supercharger is that it 
> has a pretty cool air charge (unlike the turbo that, even with an 
> intercooler, the air produced is hot).
>
> Any thoughts?  Anyone had experience with turbo/supercharging an IO-360?
>
> Geoff
>
>
>
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