snips...

I still have not decided where to put the oil rad but Mike's Will's idea
sounds pretty good. On the other hand perhaps on the plug side of the engine
the long way using the stock RX7 oil cooler and under the intake
plenum. Neat thing about the RV4 is the alternator will fit
in the stock position.

This water rad core volume is about 24 X 19 X 2 or about 900 cubic inches.
The intake air for the water rad should be about 30 to 40 square inches or
about 6.5 or 7  inches in diameter as a first guess.

This cowling is enough different from an RV6 and the slope is such that
I think NACA ducts will work for oil cooler and intake air. If they don't
the holes can be converted to snorkels like tracy is using for his intake air.

I estimate the intake area for the oil cooler should be about
15 square inches. That is about a 3.5  inch diameter hole.
A 3.5 inch flex pipe ought to work with a bell shaped diffuser
where it transitions to a square oil cooler of about 400 cubic
inches as a rough first guess. Perhaps 12 X 12 X 2.5 inch thick.

I know the stock RX 7 cooler is 25 inches long. How wide is it
and how thick is it? Ken?

All rad exit air goes out the side where the three inch exhaust pipe
is. There should be a flap there. BTW I forgot to streamline the exit
area on the fire wall. Very important for low cooling drag.

If you decide to use this scheme make sure you shield the exhaust
pipes so the rads do not "see" them.

snips....

Paul Lamar

Ken Powell wrote:

Paul, the stock RX7 oil cooler is 19.5" x 4.5" x 1.5" (not including the
tanks) for a total volume of only ~ 131.625 cubic in. It is 22.75" with the
end tanks and ~ 25" if you had the hose fitting (a banjo) attached.

I am considering a muffler like you show in this drawing.  It does not
appear to be a tangential; do you need the perforated pipe in this
design?  Is there any way to make it tangetial?

Not tangential. No room. I would leave it hollow as internal perforated
pipes run white hot and soon destroy themselves. You could try 
Inconel however to confirm. Even my C182 muffler spit out its guts 
one time :-)

Thanks to Paul, Bill, and Militch and everyone else for helping with
this issue.  BTW, if you look at page 26 of the RV-4 plans you will
notice that the cowling is deeper than the fuslage to allow for the
exhaust pipes.  This will give you an extra couple of inches for the
radiator.  Wish I had the plans in front of me so I could give you the
dimensions.

Thanks,
Ken Powell

That is an amazingly small volume to cool (dissipate) 33 HP worth of waste
heat.  Roughly 600 total fuel HP potential. 200 net HP out of the engine shaft
(33% efficient). 300 HP waste heat out of the exhaust. (When are we going to 
get turbo compounds?) 100 HP waste heat out of the cooling system. 33 HP 
waste heat out of the oil cooler. One HP is 2545 BTUs/hour. 

The RX7 oil cooler is obviously very well designed indeed.
Tracy lives in a flat area. I wonder if it would cool adequately if you had
to climb over some of these 12,000 foot mountains we have out
here in the West.

Paul Lamar
 
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