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How Much Power to Use with IO-540's

logansc

Well Known Member
To all the fast guys with IO-540's:

I'm looking to fly my first race this weekend in my F1 (125 nm, roughly 35-37 minutes). I understand there is typically little problem with running at or near 2,700 rpm, but the real question is how much MP? Mine will pull (according to the engine monitor) just over 30 inches on T/O, but that kind of horsepower for that long seems inadvisable to me.

If it's not wise to run wide open, what power settings would you guys with 540's recommend? My Rocket has a K1G5 running ECi parallel valve cylinders, running slightly pumped up pistons at 9.5:1, if that makes any difference.

Any helpful information would be appreciated.

Thanks,


Lee...
 
I advise all my competitors to use modest power settings

None of them seem to pay any attention. I do not have a 540 but I would be very surprised if those that do anything less than max power all the way, There has been a shortage of Rockets this year except for Bill Beaton and Wayne Hadath from Canada. Maybe they or Tom Martin will add something.
I run WOT, max rpm (2700-2720 RPM for now), leaned for max power with my O-360-A1A whether it is 100 or 500 miles. Last year I flew in 21 races and 14 so far this year. Still trying to go faster. Hope you have a great event.

Bob Axsom
 
I worried about the same thing my first race. I was told, shove everything forward and put your feet against the panel to brace for turbulence. :eek:

I knew the engine is supposed to be ok with WOT as long as you pour enough fuel in there. So I ran what felt comfortable, which was 2500rpm and WOT (27" all I could get that race).

The next race I did 2550 WOT. I run 2600 now as that is a prop limit. At the Hill Country 150 Race (2012) I tried to descend at 500fpm between turns 2 & 3, but this put me well over Vne. I backed off a bit to 205KTAS. After the race, Bob A and others said there is no Vne in Racing. :D

Run it as hard as you want, the motor will be fine. just keep the CHT & EGTs in check.
 
Lee,

Bob is right...full blast. Brian's right too...mind the temps (I'd add Oil T to the mix too). And no...as Ax said, no one listens when we tell them to run at 2500 or less...dagnabit!

For me, the short answer is:
- Black knob forward till the panel flexes, then hold it there. ;)
- Blue knob to 2780-2800 (my RPM for fastest speed with my Hartzell BA).
- Red knob depends on altitude.

Your RPM selection will depend on your engine/prop combo limits (mfgr and personal).

I lean to 390-400 on the hottest cylinder at Reno, perhaps 380-390 on a SARL/X-C race. That is not much leaning at SL, and a fair bit at higher DAs. After a while you get a feel for ballpark fuel flow for various DAs that give you good temps. In a SARL/X-C race, you can tweak it as you go. 370, lean a quarter turn and wait/watch. 400, richen a quarter turn and wait/watch. Specific race-day conditions will make things vary a bit, and we (the Rocket boyz and I) have had many discussions on how to find max power EGT at full blast at SL, and have yet to hear of a fail-safe way not to overshoot and stay clear of detonation, other than keeping the CHTs under control, and leaning very cautiously at low DAs.

Safest answer is "whatever you're comfortable with, as long as the temps stay in your personal limits". Starting off leaned (or richened, depending on how you look at it) for slightly cooler CHTs (mid 300's) to watch how your Oil T and EGTs look is a safe approach too. You'll get to see how your engine cools at race speed over a period of time. A conservative approach to power management (leaning) also has the benefit of being able to focus on flying the course for your first race too.

Hope that helps! Have fun and let us know how much you enjoyed your first race!! :D

Cheers,
Bob
 
WOT

Lee, I asked Alan Barrett about WOT for 45 minutes during the first of your races in my -10 while down at Sun 'n Fun.

He said that we can run those IO-540's wide open for their entire life and we wouldn't hurt them! Maybe somewhat reduced service life, so that's what I did at R2R, both times, winning both years as well.

Alan did add, though, that a little more 'bite' in the prop, may well be faster than 2700 RPM's, so I experimented on the way over there...WOW! at 2620, I gained 6 MPH, from 211 MPH to 217 mph, according to the Dynon's TAS readout. Oil crept up to 210 deg near the end and CHT's went to 405...no problem.

See ya Saturday, as an observer,
 
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Lee run the be jesus out of it. Your Lycoming will thank you for it.
Have a great race.
 
Well---its going to fun---what ever he decides to do!! I'm going to watch------and NOT from the back seat this time!!!LOL
Tom
 
Lee
I would run it at 2700rpm if it is real smooth there. If it runs better at 2650 then run it there. The BA prop will give you more speed as you increase rpm, I am not sure where the runs out as I only took mine to 2700. If you are using a three blade MT then there will not be much difference between 2600 and 2700 rpm.
As Bob stated run it full rich and watch CHT and Oil Temp. My personal goal was 400cht and no more then 215 OT. The engine is safe for higher temps but those were my goals. More power will be had by running a bit lean but watch the temperatures closely. Personally at 30" I would likely just leave it full rich, it is one less thing to worry about. For the most part you are using more power but the extra speed gives you quite a bit more cooling air as well.
There have been remarkably few engine problems in the SARL races over the years, but there have been a few. They may not have been related to the extra power but just normal wear and tear. I had a distributer cap crack in my only race last year and the added roughness at higher power settings got my attention! In that case it was just time to rebuild my mag, 600 hours. As the mag is a back up to the more efficient EI I tend to ignore it; lesson learned.
I may be wrong but I do not think there has been a total engine failure in a SARL race so far???
Try to have enough fuel to safely run the whole race on one tank, leaving 5 gallons or so of reserve in the other tank. Again it is one less thing to worry about.
Going low gives you more power but moderate turbulence can cost you 4 knots so keep that in mind.
These planes climb fast and so it is wise to climb for a wind if one is there, even on short legs. I need at least one knot of tail wind per thousand feet to justify a climb.
Make a mini course with similar turns and practice full speed turns before the actual race. It is amazing how much faster they come at you at 220 knots then they do at 176 knots.
 
This is all terrific information guys. Thanks to everyone for all the great advice!

Unfortunately, since I'm kind of in charge, I have a lot to do over the next couple of days (even taking the day off tomorrow) so I won't get a chance to practice. I'm really just running for fun. Not much chance to win on handicapped time (Cessna 150's will run amazingly close to their "book" max speeds), but I do have a chance at "Fastest Around the Course". There's a Mustang II that I guess I should be a bit worried about and a Mooney 20K "Rocket" also.

Anybody in the southeast who's interested. Jump in!


Lee...
 
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