H

Hack

Active Member
Just joined the site after a long think about what I want to buy. Pretty much there on the 4.
A question, as I look around and start getting serious about getting a fix on the market price, is I am not seeing a lot of performance (read speed) delta's on a 160 hp vs. 180 hp engine. Can you guys give me a little gouge on what I should be considering. I think I will be using my bird for commuting (200 mi. trip) about 50% of the gime. Maybe 40% just flying locally, and 10% acro.
Would love to hear what you guys think, and look forward to meeting many of you in the years to come. Also would like to hear what you think about the avionics suite I should be looking for. Don't think I am wanting IFR, but I am wanting night VFR.
Thanks

hack
 
Hack said:
Just joined the site after a long think about what I want to buy. Pretty much there on the 4.
A question, as I look around and start getting serious about getting a fix on the market price, is I am not seeing a lot of performance (read speed) delta's on a 160 hp vs. 180 hp engine. Can you guys give me a little gouge on what I should be considering. I think I will be using my bird for commuting (200 mi. trip) about 50% of the gime. Maybe 40% just flying locally, and 10% acro.
Would love to hear what you guys think, and look forward to meeting many of you in the years to come. Also would like to hear what you think about the avionics suite I should be looking for. Don't think I am wanting IFR, but I am wanting night VFR.
Thanks

hack
Click to expand...

Others have more experience here, but here's my take:

either engine is more than adequate for an RV-4, although as a rule more horsepower is always better. (you can throttle back if you want less)

The weight difference O-320 to o-360 is negligible, depending on the exact engine model. (parallel valves--the angle valve 200hp o-360 is a different animal and not well suited to the -4)

The price difference can be significant, which means you might be able to afford a better 320 equipped airplane compared to a 360. This is offset by the fact that the nicest airplanes tend to have 360s.

Biggest performance difference is in the climb. The O-360 will climb noticeably better, all things being equal. If you based at or near KABQ this is likely important. Even an O-320 equipped RV-4 with a fixed-pitch cruise prop will run away and hide from most GA airplanes in climb though.

The climb differences between the engines are completely overwhelmed by the difference between a constant-speed and fixed-pitch prop. If I had to choose between O-360 FP, and an O-320 CS it is IMHO a no brainer. The constant speed prop wins hands down.

Hope this helps.
 
Tally Ho RV4 1200 level

Thanks James.
I should also add that I weigh in around 220lb. After doing a little perusing I find that I have to take in CG here, and as the CS adds some weight on the engine I think your suggestion makes even more sense.
How about speeds? What can I expect at cruise settings?
 
Hack,
Welcome. James is giving you accurate gouge. The speed of a recip machine only increases with the cube root of the power increase. Thus a 180HP engine has 1.125 more power than a 160HP one. The cube root of 1.125 is 1.04. So in theory you will only see a 4% increase in speed. However, you will get the full 12.5% increase in rate of climb assuming the weight is equal. A constant speed prop will out perform a cruise prop by 10 to 15% at climb speeds, so James is right on with his assessment that the prop can make up the difference between the 0-320 and 0-360. You also get a 1 for 1 increase in rate of climb for weight difference. ...so
Look for:
-Light empty weight
-0-360 C/S as top performer
-0-320 FP as bottom performer

I fly an 8 with 0-360 FP and have no complaints, but I don't live in Albuquerque.
And... your 200 statute mile commute? It'll take ya about an hour to get there.
Get enough avionics to get your butt out of trouble in case the wx closes in on you, and perhaps a Garmin that has terrain mode for all of those big rocks you live near.
Good luck Pard, and welcome to the party.
 
No substitute

Yep, all above is accurate, for the RV8. The numbers for the RV4 are closer and the RV4 performs much better than the 8 on 160HP.
Here is some comparison for you: My 300HP Rocket trues at 195 knots at 11.5 gph and will almost make 3000 fpm on a cool day. My 150HP Wood prop RV4 trued 155 knots at 7.5 gph and climbed out of Leadville CO (9927')at 1000 FPM. Fly both airplanes 400 nm and the Rocket gets there 20 minutes earlier on slightly more fuel. The 180 C/S RV4, less than 10 minutes. My bottom line has always been not how fast they are, but how slow. I need to land on a 1500' strip with trees. Not many airplanes can boast both.
Dogfights, aerobatics, hands down the RV4 rules, (the Rocket dominates). I finished my -4 in 97' for less than 20K. I also liked the light nose and simplicity. Is the 180 C/S RV4 a great airplane? Absolutely. More expensive, sure. Is the 160HP great? Absolutely. Is 10 minutes and 500 fpm worth 10K more? Do you need it? Weapons school answer for what's best for you? It depends.

After 2500 RV4/Rocket hours you see what I fly...:)

Smokey
HR2
 
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Hack,
I have a 160 HP wood prop RV-4 also. You and I weigh about the same. I land at some 1300 ft grass strips pretty regularly. No issues either way. Climb is pretty amazing for so little horsepower. It will do about 2500 fpm initially and taper off from there (solo) I opt for speed though. I tend to nail 1000 fpm and do 160 mph over the ground.
I can also putt around at 155 mph at about 5.5 gph.
You'll love the plane.

Dennis
 
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