B

BlakeB

Well Known Member
I currently own a RV8 with a 0-360 A1A. The guy I bought it from had 7.3. to 1 pistons in it. Not sure how much horse power it produces and I'm thinking about changing them to 8.5 to 1 or 9.1 pistons. I have a 3 blade catto prop. The plane perfoms great, it just seems to be a little sluggish on take off. I'm not an engine guy, but my understanding is my engine is derated right now and is very capable of producing 200hp. Any advise would be greatly appreciated!

Thanks,

Blake
 
Same Engine 180 HP

I have the 8.5:1 pistons and I am interested in more HP. Contacted Barrett Precision Engines, Inc. in the Tulsa area and was told he could put in slightly higher compression pistons while keeping it carburetor fed and increase the horsepower by 7 or 8 but that is still far below 200 hp. He said to go higher would require fuel injection. The company advertises on this website and they will answer this type of question candidly.

Bob Axsom
 
More power

When I rebuilt my O-360 I went with 9.2 range pistons and notice improved take-off performance. Fuel burn is also higher.

I may be wrong but it seems the 200 HP O-360s are often the angle valve version.
 
Low Compression O-360

Lycoming used to have an O-360 low compression engine that was rated at 170 HP. It was built for 80/87 octane avgas, similar to the 150/160 HP difference with the O-320 engine. The lower compression pistons would allow for the use of regular unleaded auto gas if you desired.

Jim
 
Blake,

You mentioned that your -8 "seems to be a little sluggish on take off."

This could be more your prop or empty weight.

What kind of 75% power cruise numbers are you seeing at 8500' DA?

I ask because my 135 HP O-290 powered RV-9 goes up at over 1400 FPM w/ two on board and full fuel. Solo I'm off the ground in around 250 feet.

That's why I think your prop might be biased towards cruise and/or your -8 is overweight.
 
I'm using a 3 blade catto prop. The plane came with the prop. Once you get over 100mph it perfoms awesome. Maybe your right, you can only do so much with a fixed pitch prop. The extra HP sure sounds attractive.

Blake
 
BlakeB said:
I'm using a 3 blade catto prop. The plane came with the prop. Once you get over 100mph it perfoms awesome. Maybe your right, you can only do so much with a fixed pitch prop. The extra HP sure sounds attractive.

Blake
Click to expand...

I'm not saying that part of what you are seeing as far as performance goes, isn't related to slightly lower power output, it is probably the result of you having a fixed pitch prop set up for good lower altitude cruise.

This is a compromise of using a fixed pitch prop.

As already mentioned, only the angle valve IO-360 is rated at 200 HP. The O-360A1A is only rated at 180 HP with 8.5:1 compression. Even if you change the pistons you still will not ever produce 180 HP with the fixed pitch prop. You need to be able to turn up to full rated RPM to get full power. This can only be done with a constant speed prop.
 
Superior claims that it develop 168-172hp

When we ordered our Superior O-360 kit, we specified 7.5 pistons so that we can run auto gas. Superior claims that it will develop 168-172hp.

Other folks have told me their Superior with 8.5 pistons burns auto gas just fine but detonation is sometimes difficult to detect outside of a controlled environment without appropriate instrumentation.

I'm in no hurry (I'm used to a C150) but prefer to send Chevron as few $$ as possible.
 
Agreed with the previous two posters - get a C/S prop and keep the low compression (or, at least don't go over 8.5). The T/O performance will be hugely improved with just the prop, and you won't see appreciable extra improvement from the extra 10hp that higher compression pistons would bring. Meanwhile, you are future-proofed against any new legislation limiting 100LL. Comparing the costs of the two changes, your bang-for-the-buck is good for the prop and not so good for the pistons (and that not even counting the increased wear on the engine).

For those worried about detonation in very high compression engines (over 8.5:1), short of the much anticipated anti-knock system from a not-to-be-named vendor you can also simply switch to electronic ignition and retard the timing a touch. For reference, my 10:1 IO-320 uses 20BTDC instead of 25BTDC. The hotter spark of these systems will prevent excessive power loss from the retarded base setting, while the timing advance features of these ignitions will assure you are still getting better-than-MAG performance at altitude / reduced power settings. My limited understanding is that anything over 10:1 is a racing configuration, and may need even higher octane than 100 to prevent detonation.
 
Thanks

Thanks for all the information. How much am I looking at converting my engine and prop to CS? Just Curious.

Thanks,

Blake
RV8
 
It depends on your engine.

If your prop flange already supports a C/S prop, you can just add a prop and a governor. Vans has great deals on props, so you could probably do it under $10k. If your engine is not designed for a C/S prop, you have two options:
a) Swap engines
b) Get an MT or Sensenich Electric prop.

The MTs are not typically as fast in cruise as a hydraulic Hartzell, although the difference is noticed more in something like a Lancair than an RV.
On the plus side, the MT is typically much lighter than the hydraulic solution, perhaps even as light as your fixed prop (which would eliminate recalculating all of your CG stuff). I don't have much information on the Sensenich, but you can get them through Eggenfellner.

Anyway, assuming an MT you will probably be in the $12-13 range for prop and controller, depending on the difference between the dollar and Euro. The Eggenfellner is $9 or $10k (3 or 4 blade) for the prop and another $1k for the controller.
 
FP prop

I had a Aymar - Demuth then switched to a 3 blade Catto on a O-360 (8.5:1 pistons) RV-6A. I got fine climb performance out of my airport at 6700' MSL and even out of Leadville at 12000' Density Altitude.

When I rebuilt my engine I went to 9.5:1 pistons and have noticed a shorter take-off roll.

RPM at liftoff is in the 2200-2300 range. That does result in lower climb performance compared to a CS prop but I have never justified the cost to convert to CS since most of my time is in cruise (yes CS helps there too).
 
Not Necessarily!

breister said:
It depends on your engine.

If your prop flange already supports a C/S prop, you can just add a prop and a governor.
Click to expand...
The crankcase and front bearing must also be compatible. There are a lot of engines with hollow cranks that still cannot run a hydraulic prop.
 
slugish climb in a 180hp -8 FP?

I would suggest a cheap fix to this problem would be for you to go rent a Cherokee 140, load it to full gross weight, then take a trip on a hot day. Then when you jump back in to your -8 you should no longer have that sluggish feeling. Of course just do not go out and fly a Rocket, or the sluggish feeling will return to the -8.
 
Last edited:
Mel said:
The crankcase and front bearing must also be compatible. There are a lot of engines with hollow cranks that still cannot run a hydraulic prop.
Click to expand...

Good point - I was not fully specific.

You can mount an electric on virtually any hub - all caveats apply. Also, the electric props are not nearly as responsive as the hydraulic, so you can potentially over-rev your engine if you push in the juice too fast.
 
Ours..

....is 76", Blake but we asked for max cruise speed. Craig told us that it would turn around 2200 on initial takeoff and it does exactly that. If you'll try climbs at 140-150 MPH, you'll be surprised at the climb rate since you'll be generating more RPM, more power and so on. Even as high as 160 MPH will climb near 1000 FPM.

Regards,
 
You must log in or register to reply here.