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Hi Ken:
So, you are considering putting an IO-520 into a IV. Here's the details. When
I was ready to buy an engine (non-turbo) for my IV, in 1995, I had two
choices: a new, new-design IO-550, no cores on the market for rebuilds, OR
build-up an IO-520, for which there were/are good cores available.
TODAY, I would use an IO-550, new from Lancair, certificated engine/prop,
engine has proven to be a good one. I am not addressing the TSIO-550, or
Lycoming TIO-540 installations.
I love to fuss with engines, so I applied myself to fitting in an IO-520 in
1995. Using a good shop, Victor Aviation in Palo Alto was crucial, they were
great to work with. They found me a good IO-520BB core, fitted 6 new
cylinders, heavy crank, con. rods, all the mods, ported and balanced. All big
Continentals share basic dimensions. The IV installation requires a shallow
oil pan, dynafocal case-mounted feet, making it a drop-in fit to the stock
engine mount, stock Barry isolators. Lots of room above the engine as intake
and exhaust are below. Intake crossover tube is switched to the rear of the
engine, custom fitting needed below cyl. #2, close to mount riser. Throttle
body is from a -NB engine, mounted below front lip of oil pan and feeding the
intake manifolds from the front. Welded-up tubing to make connections. Custom
intake fitting with alternate-air door. Controls from Spruce readily fitted
for Throttle, Prop and Mixture. All hoses from Sacramento Skyranch, lifetime,
integral firesleeve design. Great service from the hose shop guys. (re-read
the measuring guide twice in your Spruce catalog, angled fitting at one end,
keep the other end straight, if you must have an angled end).
Since you do not have turbos, you do not need the two blisters on the IV cowl
bottom. I used an ES cowl!! No mods to the top, added a chin bump-out to
accomodate the throttle body and a NACA scoop on the bottom right.
Prop is the same, no bad RPM ranges per Hartzell. Use stock IO-550 exhaust
from Lancair, made up 1" taller, to clear intakes. Since they make them long
anyway to bend and cut them down to size, this is easy for them to supply.
Heat muff same.
Few teething problems, only real added mod was to install a richer injector
on #5 cylinder, which was leaning too early.
Lots of work for an IO-520. You would have a simpler time of it with the 550.
Insurance and resale considerations push you to the 550 too (certificated
engine/prop). I am quite happy with my IO-520, cruise 200Kts true at 12,500,
burning 12gph.
I'll be at Oshkosh, if you want to see my bird, look for N295P in the camping
area south of row #60, check the registry.
Good luck,
Robert
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LML homepage: http://www.olsusa.com/Users/Mkaye/maillist.html
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