clare at snyder.on.ca wrote in message
...
On Wed, 25 Jan 2006 19:47:08 -0500, "Morgans"
wrote:


"Peter Dohm" wrote

Interesting. I had assumed they were originally flying with 80HP or
less,
but had no idea it was that much less. Thanks.

You could find many people that would argue that low of a HP figure. I
think your 80 is closer, and in might be a few more than that.


Original flying corvairs were the little engine - 145 cu inch, IIRC,
producing 128 ft lb gross torque at 2300 RPM. So, at 2300, 56 hp.
If run at 2700 rpm, torque approx 125 ft lb, and 64 hp.

The 164 inch engines produced up to 160 ft lb torque at 2600 or 2800
rpm depending on the engine, for 80 hp at 2600, or 85 at 2800. Mine
produces 90 at 3000.

With a fancy cam and a bit of rework they will put out closer to 170
ft lb - and at 3200 RPM with a small prop, that is 103 hp almost 115
at 3500 rpm. The factory 140 hp engine supposedly produced 140hp at
5200 rpm and 160 max torque at 3600. That means the torque dropped off
to 140 at 5200. The 110 does not breathe nearly as well at speed, so
the 14% torqe drop of the 140 would be more like 20% on a 110 - or 122
ft lbs at 5200 for 120 hp if you ran a 2:1 PSRU for a 2600rpm prop.
And that's being optimistic.

Assuming 170 peak torque at 3000 RPM (likely pretty close with OT10
cam and properly prepared for aircraft use) it is pretty close to a
100 hp engine .For the extra 10 HP there is a couple hundred dollars
worth of Camshaft etc required over and above what I've got -so I'm
satisfied, so far, with what I've got. We'll see what 90 HP does in a
Pegazair when we get it together.

My engine has 180 degree equal length headers and a short smooth equal
length intake with a 50mm carb, and it's a 140 based engine, so it
breaths a bit better than a "stock" 110 at 3000 RPM

Thanks, Clare, for a lot of excellent specifics and history.

It seems that those original engines were smaller than I remembered, and
produced less maximum torque even for their size. That shouldn't surprise
me, considering the power levels of the compact cars the Corvair was
designed to compete with and the people it was designed to serve.

I always tend to think of these little engines in terms of installing them
in go-fast machines, for their power. To me, that means turning a 52 inch
propeller about 3500 to 3600 rpm. So 95 to 100 hp may not be all that
crazy--especially with a rear drive installation such as offered by Great
Plains for their VW based engines. That is similar to Steve Whittman's V8
canversion, and presumably to his Formula-Vee racing installation as well.
Thanks to Richard Lamb for the link to Great Plains earlier in this thread.

OTOH, before someone else posts yet another recitation that more propeller
disk area equals more thrust and therefore more performance...

I took a quick look at a set of posted specs for the Pegazair, on
UltralightNews.com, and suspect that you are just about at the top of the
horsepower and rpm range for that installation. It would not surprise me at
all, using your numbers above, it the 80 hp version gave identical
performance to the 90 hp version in the Pegazair's speed range.
(Discalimer: I am not qualified to make this observation.)

Peter