CHT
 

What is the truth with CHT on a Lyc.O320 / 160 HP in a RV9? Is 460 F really too much in a long climb up to the flightlevels? Is 360 - 390 good in the cruise ? :confused:

Thanks for your advice!

Pit

Good question...
 

Most of the current mechanic writers out there now are espousing anything under 400 all phases of flight. Above 400 it's time to do something right now to lower the temps. Lycoming's number has remained unchanged throughout the years at 500.
In my Mooney I try to stay below 400 except in initial climb - I don't pull back until 1000-1500' and usually see about 435 max - under 400 in cruise. In the RV, same motor as yours, I don't have instrumentation but I usually climb pretty slowly, using the speed to cool the motor.
Not an official answer - don't think there is one, except 500. Research the difference in strength of the materials at between 400 and 500 degrees and decide your technique based on that research. For me, minor excursions over 400 are acceptable until an altitude when I feel better giving up power for temps.
Patrick

400 F
 

Patrick, thanks. I experienced the same temps in my M20J as you did. And that is what makes me scratching my head. The RV9 is significantly higher in the initial climbout. Later or higher when pulling back the throttle and in the cruise I saw 390 and a bit lower. Are these temps usually and regularly normal for an O320 in a RV9?
Pit

Your temps look high to me, but I also do not subscribe to the "do something immediately if over 400" theory. I've never heard it said by anyone I considered smarter than a Lycoming engineer. 460 would worry me though

Look into baffle sealing around the engine. If that's not it, check timing.

CHT
 

Mahlon Russell was at Mattituck in LI for many years. He has stated that he has never seen any evidence that 425 hurts a cylinder. My 0 320 with 10-1 pistons runs 375 in cruise. During break in in ambient temps ranging from 90-110 F. I had to pull the power back at 500' on takeoff and level off to keep the temps at 400. I have a very tight cowling with small inlets and outlet. At present I have a fixed cowl flap which is 75% open all the time. I believe the cowl flap is very effective. Not an RV. I do have a plenum and absolutely believe in the plenum. All CHT measurements taken on cylinder #3 with the cooler mounted aft of 3.

I don't think you'll find anyone who is comfortable with 460 F, even during a climb. Unless you're climbing at a really low airspeed, there is no reason your temperatures should be that high.

So, what speeds do you climb at? Can you post some pictures of your baffles and seals? Is your engine's mixture properly set (at a 1,000 rpm idle, if you slowly lean it, do the RPM's increase by at least 25 before it dies?).

Selma:
Numbers seem high to me. My 9A o-320 160hp runs 375 F (highest cyl) on a 90 knt climb on a 80 F day. Cruise (same cly) runs 325 F in cruise. I'll show 13-15 gal/hr on climb and I lean to 7 gph in cruise which gives me around 1200-1300 EGT.

What do you have for instruments? I have the cheap vans steam gauges and had to change my CHT gauge out the other day when it was getting up to 450-500F. It was also showing 250F with just the master switch on before even starting the engine. The gauge change out cured all ill's.

doug
9A
kit #625
650 hrs

I've done everything in the book and I still see up to 430 on hot lower alt climbouts but I still have to reduce mp big time. I am still unhappy about this. When it's 80-90 degrees I am very unhappy with my setup. I've heard you can get the wrong carb with an Rv... That's all I have left to try. I'm always under 400 in cruise but that's up high. If I lived at sea level I would have to make a change

Have you had an experienced (successful) builder take a look under your cowl? I've known a few bright folks who missed fairly obvious things on the baffling and seals.

The truth ....
 

The truth is in the operations manual you got with your engine from Lycoming. Pretty much anything else is educated opinion.... and probably good opinion but Lycoming built it !

Can't speak for the O-320 but the O-360s run hotter than most think and the manual calls for under anything under 400 in cruise. I think peak is 450. I found this in a generic O320 Lyc Manual. My O 360 manual has something similar and I frequently see 425 F on a hot day in slow climbs.

SECTION 3 0-320 10-320 SERIES

Manual leaning may be monitored by exhaust gas temperature
indication, fuel flow indication, and by observation of engine speed
and/or airspeed. However, whatever instruments are used in monitoring
the mixture, the following general rules should be observed by the
operator of Avco Lycoming aircraft engines.

GENERAL RULES

Never exceed the maximum red line cylinder head temperature limit.

For maximum service life, cylinder head temperatures should be
maintained below 435 F. (224 C.) during high~perfornzance cruise
operation and below 400 F. (205 C.) for economy cruise powers.


Again, read the manual for your engine. Also note that A models just tend to run a little hotter in climb due to congested air flow around the engine/nose gear mount.

Hope this helps.