"Parlow, Eric (Turbos-Asheville)" wrote:

I'm building a RV-8A.

I would like to use a turbocharged 20B with 2.85:1 and CS prop.

Planning for 350 bhp climb & 200 bhp cruise to 12k ft.

What challenges am I facing?

Eric Parlow
RV-8A

In regard to the engine not many. You need a motor mount and cooling
system. As I recall Tracy Crook is building a similar but NA
combination. Feel free to ask any questions on here. The big thing
before you start is build a full size mock up or get 3D software
to make sure everything fits where you think it is going to fit.
You will have to build a 20B turbo manifold because as far as
I know there is nothing off the shelf. There are signs that
there will be a low profile intake manifold available.

Paul Lamar

That's going to be a real performer Eric!
Just wondered about your choice of the 2.85 ratio.  Some people want the
additional engine rpm that a 2.85 ratio will allow (for more HP) but

since

you are turbocharging, you can easily meet your HP goals without reving

the

engine past 6000.

Also, ask a few prop makers what they have available that would work
efficiently at 74" long , 2100 rpm and 350 HP.  You may be surprised at

the

answer.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

Why are 2100 RPM and 74 inch props magic numbers Tracy?
You have my mystified.

Paul Lamar

Just the usual operational reasons.
6000 / 2.85 = 2105 rpm
 74 inches is the largest prop diameter recommended for the RV for ground
clearance reasons.

Sure, you can run the engine faster but if you can easily meet or exceed the
HP targets at a lower rpm, why do it?

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

I am not arguing the turbo charger bit. You can always taylor
the turbo charger to give you all the boost you want at almost
any RPM you want. What I am saying is you can always get more 
power with a NA rotary, P-port or street port, by running it faster.
Up to the limits of the rotor bearing which seems to be around
9200 for the current rotors. The RX 8 rotors are lighter
and the limit there may be over 10,000 RPM.
 
Make the prop smaller in diameter and use wider blades 
if necessary to absorb the additional HP.

Klause runs his prop at over 3500 RPM at 250 MPH.

Paul Lamar
 
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