Cruise speed/fuel burn at high altitudes in RV 4?

Please forgive if there (likely) are other threads discussing this subject, but for those of you who have flown high-altitude x/c’s in a 4, what kind of true airspeeds and fuel burn did you have? I’m wondering what kind of performance to expect around 10-12k feet; not high enough to require oxygen, but still high enough for reduced drag and to lean the engine. And also how it performs at 13k-16k feet if you’re willing to use oxygen?

A higher horsepower engine combined with c/s prop can really make the difference performance-wise, and having a fuel-injected engine allows leaning more for improved efficiency. The max ceiling for the 4 is 23k feet, though performance is probably mediocre at that point. Besides, I’m non-IFR, so I won’t be ascending to the flight levels. From reading older posts, I've got an idea of how the 6 thru 9 models perform, and am wondering how the 4’s compare (and the 3’s if anyone with experience in those want to chim in). I also know what the Vans website states, which is for 8k feet. But what have you personally experienced?

I did a search for older threads but didn’t have results. If anyone wants to provide a link to a thread(s) where high-altitude performance for the RV 4 has been discussed, please do.

I fly an RV-4, IO-360 Hartzell CS normally between 8 and 12k. Above 9k you are full throttle adjusting power according to RPM. Full throttle at 9k gives me around 21", 2,100 rpm give me around 65% at around 160 mph indicated 7.5 gph, around 185 - 190 mph true.

-4 O360 C/S at 7500ft TAS 168 KTS 11.5GPH 23/24RPM CHT375 EGT1440. I just purchased this and that’s all the data I have so far.

Duncannon said:

Please forgive if there (likely) are other threads discussing this subject, but for those of you who have flown high-altitude x/c’s in a 4, what kind of true airspeeds and fuel burn did you have? I’m wondering what kind of performance to expect around 10-12k feet; not high enough to require oxygen, but still high enough for reduced drag and to lean the engine. And also how it performs at 13k-16k feet if you’re willing to use oxygen?

A higher horsepower engine combined with c/s prop can really make the difference performance-wise, and having a fuel-injected engine allows leaning more for improved efficiency. The max ceiling for the 4 is 23k feet, though performance is probably mediocre at that point. Besides, I’m non-IFR, so I won’t be ascending to the flight levels. From reading older posts, I've got an idea of how the 6 thru 9 models perform, and am wondering how the 4’s compare (and the 3’s if anyone with experience in those want to chim in). I also know what the Vans website states, which is for 8k feet. But what have you personally experienced?

I did a search for older threads but didn’t have results. If anyone wants to provide a link to a thread(s) where high-altitude performance for the RV 4 has been discussed, please do.

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I had a discussion about this the other day with Dave Anders (RV-4 guru), and he told me on long x-c's he flies at 17.5K on oxygen and sees 200 MPH @ a fuel burn of 5.5 GPH ...
But you have to remember (or even know) what he has done over the last 35 years with his highly decorated & modified airframe.
If you don't know who Dave is - go find out.

HFS

Carbureted Superior XP-360 Plus running the Vans Sensenich fixed pitch prop. Original cowling, pants, etc. Climbs well enough to 17.5 but I've only been there once to say I did it. At more reasonable high altitudes for cruise between 8000 and 11000 I really couldn't tell you what IAS reads. More interested in GS and, more importantly, TAS. More than once I've had to back off the power to stay at or below 180 kts TAS. This is close enough to red line that it's close enough. Under the right conditions a 4 will quite happily blast right past redline without even breathing hard.

This usually happens a couple of times a year between 9,500 and 10,500 feet but most of my trips are shorter nowadays and I will regularly see 160-165 kts TAS at 5000 feet or so. As to fuel burn, it seems to make very little difference what my altitude is. I can almost set my watch to 8 gph running 2450 to 2500 be it at 3,000 feet or 10,000 feet. It's so predictable that I never bothered with fuel flow. Power begins to fall off quickly above 10,000 and unless there's a good reason (like Texas Summer Turbulence) to go higher I'll save the O2 for another day. With CS and FI you might find your sweet spot and fuel burn a bit higher.

Sounds like you have a mission. Let us know what you find out!

Flying back and forth from Bend to Aurora over the Cascades I’d usually be at 10.5, 11.5 or 12.5. (Still climbing 1,000 ft/min when it gets there)

Typical numbers I’d see at WOT at 11.5K
-162kts TAS
-2450 rpm
-8.5 gph

That’s with an 0-320 and MT constant speed. My O-320’s never been real fond of leaning out… though I have some experimenting I want to do with that.

HFS said:

I had a discussion about this the other day with Dave Anders (RV-4 guru), and he told me on long x-c's he flies at 17.5K on oxygen and sees 200 MPH @ a fuel burn of 5.5 GPH ...
But you have to remember (or even know) what he has done over the last 35 years with his highly decorated & modified airframe.
If you don't know who Dave is - go find out.

HFS

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Looked him up, and his 4 is capable of 227 kts (261 mph), whereas the average 4 on barnstormers will not. Therefore, it’s safe to assume the average 4 won’t perform like his will at 17.5k feet.

My 4 @8.5K ft, WOT/2400 rpm O320 carby FP prop ROP (I’m not a fan of LOP, fuel is the cheap part of flying) 30LPH all equals 157 kts TAS

I recently bought my RV4 and flew it approximately 1200 miles home. 160hp 0-320, fixed pitch Catto Prop. Fuel burn below 8000 averaged around 7.5-8.0 gph over a 2-3 hour leg, around 165-168 kts.
Out west over mountains I had it up to 12.5. Leaned out, speed around 160 knots, fuel burn was 18 gallons for 3 hour leg (around 6gph). Amazingly efficient planes!

I think i figured out that i can cover about 32mpg
0320 carb sensenich GA, magnetos.
9500 2500 rpm tas 165kts 6.7 gph
Old school lean until rpm drop then richen until it runs smooth.

A few more data points:

O-320-D1A - 160hp - carburetor - dual magnetos - MT 3-blade C/S Prop
Took these numbers from recent photos of my panels during cruise.

X/C I like to cruise wherever the winds are most favorable. ROP down low. Up high and below 70% power I will run at peak EGT.

MPH make me feel faster.

Rbb469 said:

-4 O360 C/S at 7500ft TAS 168 KTS 11.5GPH 23/24RPM CHT375 EGT1440. I just purchased this and that’s all the data I have so far.

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Those are similar to my -7 numbers, your FF seems high, I'm at 8.8 gph.