Corvair conversion engines

On Wed, 18 Jan 2006 21:26:23 GMT, "Don Lewis n FTW"
wrote:


See: http://www.flycorvair.com/crankissues.html


"Ron Webb" wrote in message ...
Do you have a link for the broken cranks? I cannot find anything about broken cranks on the "Corvair authority" site.

http://www.flycorvair.com/

I did find the following statement:

"I have never seen a cracked head, cylinder, case, crank or rod in the hundreds of Corvair engines I have inspected. It is a very
strong engine."

The Corvair engine has been flying since the early 1960's. Seems odd that ANY flaw would only now be being discovered.



They are only recently flying at 115HP in 200MPH planes - which is a
totally new world. Previous engines were flying at 60HP and 90MPH
without any issues.




Everything seemed OK until yesterday when I read the most recent updates on their website. Seems that the "untreated" automotive
cranks have been cracking in a very short time. Nitriding seems like the only solution. But with standard cranks cracking at
under 100 hours, what would be the expected life of a nitrided crank. Twice as long, four times as long, eight times as long?
This would still fall short of the 1500 hour TBO stated by the Corvair Authority.

Does anyone have any first hand experience with Corvair conversion engines? Any info on their realistic life and reliability?

TIA,

CV

clare at snyder.on.ca wrote in message
news
On Wed, 18 Jan 2006 21:26:23 GMT, "Don Lewis n FTW"
wrote:


See: http://www.flycorvair.com/crankissues.html


"Ron Webb" wrote in message
...
Do you have a link for the broken cranks? I cannot find anything about
broken cranks on the "Corvair authority" site.

http://www.flycorvair.com/

I did find the following statement:

"I have never seen a cracked head, cylinder, case, crank or rod in the
hundreds of Corvair engines I have inspected. It is a very
strong engine."

The Corvair engine has been flying since the early 1960's. Seems odd
that ANY flaw would only now be being discovered.



They are only recently flying at 115HP in 200MPH planes - which is a
totally new world. Previous engines were flying at 60HP and 90MPH
without any issues.

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





Everything seemed OK until yesterday when I read the most recent
updates on their website. Seems that the "untreated" automotive
cranks have been cracking in a very short time. Nitriding seems like
the only solution. But with standard cranks cracking at
under 100 hours, what would be the expected life of a nitrided crank.
Twice as long, four times as long, eight times as long?
This would still fall short of the 1500 hour TBO stated by the Corvair
Authority.

Does anyone have any first hand experience with Corvair conversion
engines? Any info on their realistic life and reliability?

TIA,

CV

"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.
--
Jim in NC

Here's a formula that is helpful in determining an engine's horsepower.
It is based on an MEP of 150 psi., sort of typical of an 8.5:1 CR. CDI
X RPM / 5280. An O-320 at rated 2700 rpm, using this, gives 163.6 hp.
Of course, this 5280 constant only works for normally aspirated
engines. The 60 hp 800cc/49ci Hexadyne, featured in the just-out
Contact! issue #81, calcs to 53 hp at 5750 rpm, but it's 9:1 CR, so the
published 60 hp seems reasonable.

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

clare at snyder.on.ca wrote:



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 the specifics, nice post!
John

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

"Peter Dohm" wrote

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.

Willim Wynne does not reccomend turning the Corvair engine at more than 3000
RPM, and pretty much says right out, that doing so has been shown to break
the crank, in all of the cases he has studied.

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.

Some pretty experienced people (in VW engines) have said that the valves are
the weak link, and that much more that 45 HP will melt the valves down, if
run at that level for more than a few minutes.
--
Jim in NC

"Morgans" wrote in message
...

"Peter Dohm" wrote

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.

Willim Wynne does not reccomend turning the Corvair engine at more than
3000
RPM, and pretty much says right out, that doing so has been shown to break
the crank, in all of the cases he has studied.

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.

Some pretty experienced people (in VW engines) have said that the valves
are
the weak link, and that much more that 45 HP will melt the valves down, if
run at that level for more than a few minutes.
--
Jim in NC

That is an interesting assertion. I really don't know. The number would
conform quite nicely to a 1600cc/96cid engine producing around 60hp; as well
as most older normally aspirated aircraft engines, which seem to have
maximum continuous power figures in the 0.5 hp/cid range. There is even a
rather famous dissertation, supposedly published in Contact!, which suggests
failure due to heat dissipation problems in the valves and/or heads of
automotive engines operated above continuously that power level.

As it happens, I am really on both sides of this issue--and may not be
technically qualified on either. (Required disclaimer as I am neither a
mechanical engineer nor a mechanic)

On the "this is unadulterated manure" side: there is a dissertation
attributed to an engineer at one of the big three auto makers and posted
here a couple of times, possibly by Corky, asserting that manufacturer
testing includes a 100 hour run at full rated power--and that the failure
about which they are concerned is the harmonic dampener. That is in keeping
with articles I read more than 30 years ago in my school days, which stated
that the exhaust manifolds glow incandescent during this proceedure.
However, the colant and oil are maintained within their normal temperature
range during that portion of the testing proceedures. On modern automotive
engines, this equates to more than 1.0 hp/cid; and 100 hours is clearly much
more than a few minutes.

However, my real problem with the valve assertion is that I really don't
know anyone who managed to run one of these little air cooled engines long
enough and hard enough to burn a valve. I do know of two broker cranks on
Corvair conversions (same person) and at least one, and possibly two, broken
cranks on VW conversions (same other person). Both are mentioned on the
FlyCorvair site, so I am really not adding much that is new. I am convinced
that all of the failures were torsional damping issues. The only burned
valve that I know of on an automotive conversion was on a liquid cooled
Geo/Suzuki engine and was traced to a carburetion problem--which was run at
a much higher power level. I was told that the carburetion problem was
corrected and has not recurred.

On the other hand, I strongly suspect that very high power levels equate to
accelerated wear; and I really dislike very short TBOs. So all of my own
scratch pad doodles are based on continuous power levels of less than 0.5
hp/cid, and usually significantly less.

Peter