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160hp rv4 vs 180hp rv8

dave_091

Active Member
Hi guys, quick question.

I have a 160hp RV4 with a fixed pitch metal sensenich cruise prop. I am thinking of building a 180hp RV8 with a fixed pitch sensenich cruise prop as well. Should I expect about the same performance from the RV8 as I am getting now with the RV4?

Thanks for your input.
 
Nah, get a constant speed -- it's worth another 30 HP or so on takeoff because the engine can turn 2700 RPM, static, instead of 2100 or 2200. That extra power gives you acceleration and climb that are really fun! And at cruise, at least some fixed pitch metal props are limited to 2600 RPM, and that will trim a bit of your cruise performance.
 
Nah, get a constant speed -- it's worth another 30 HP or so on takeoff because the engine can turn 2700 RPM, static, instead of 2100 or 2200. That extra power gives you acceleration and climb that are really fun! And at cruise, at least some fixed pitch metal props are limited to 2600 RPM, and that will trim a bit of your cruise performance.

CS isn’t in the budget :rolleyes:
 
-8 vs -4

Hi guys, quick question.

I have a 160hp RV4 with a fixed pitch metal sensenich cruise prop. I am thinking of building a 180hp RV8 with a fixed pitch sensenich cruise prop as well. Should I expect about the same performance from the RV8 as I am getting now with the RV4?

Thanks for your input.

I think you will see slightly better performance from the -8 if it’s built well. I have talked to a number of -4 owners who say that equal horsepower -8’s seem to be a bit faster than their -4’s.

The -8 will be slightly heavier on the controls.

Skylor
RV-8
 
Short answer: yes

Long answer:

I fly an 8 with a FP and XIO-360.
My brother built a 4, and even that i like the cowling “cheeks” better, i did not fit in to my comfort. I am 6’4”. So it was the 8 for me.

My 8 compared with the 4 (O-320, FP) from my brother and the 4 (O-320, FP) of a friend who i fly formation with, we are all in the same ballpark.

Performance wise, as you live in a region without very high temps in summer and pretty close to sea-level! I don’t see the point for the gain in performance on takeoff and climb that a CS will bring. I rather see the weight-saving from a FP over the CS.
The 8 easily becomes a bit nose heavy, so the lighter you go up front, the more docile the handling will be…

Just to have the option, for later or resale value, i opted for a hollow crankshaft.

I would recommend a ground adjustable prop though.
The Sensenich i have is light, runs smooth, delivers advertised performance and is easy to adjust.
You will most probably end up with your “sweet spot” setting and just leave it there, but at least you could adjust if you go e.g. tour the rockies for less pitch.

Try to keep the 8 nose light for a 4-comparable handling.
With 180hp FP -8, you will not “pull away like a rocket” from a 4, you are in the same ballpark with more room, a fullsize passenger seat and more cargo compartment.
A fast -4 will creep away from you. A standard 4 will not, you will.
 
Last edited:
RV-4 vs RV-8

I bumped into Van several years back and discussed this very question with him. At the time my Hangar-mate was building an 8 and it looked so much fatter than my 4; I wondered about drag/speed compared to the 4. According to Van they will be within 1 or 2 mph on equal horsepower. This has proven to be the case in my flying my 360 powered 4 against an 8. I’m typically faster only because I have a hotroded motor. I haven’t flown with an IO-390 powered 8 and I’m sure they would outpace me.
So the answer to your question, according to Van would be the 180 hp 8 would cruise faster than the 160 hp 4. When riding in the back of a buddies 8 I couldn’t believe how roomy the passenger compartment was. I guess that’s what you get with a fat airplane 😁 ! As to handling qualities I think the 4 wins hands down !
 
The best of both worlds and faster than both the -4 or -8. Sorry, couldn’t resist. :))
 

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160hp RV4 with a fixed pitch metal sensenich cruise prop. I am thinking of building a 180hp RV8 with a fixed pitch sensenich cruise prop as well

Yes, performance will be similar. But you will loose the perfect handling and sexy cheeks ;)

RVs with standard engines have very similar performance when respecting RPM limitations.
We’ve done some speed runs around here, WOT, same RPM (2600), equipped with same MT 3 bladed CSP with the following ships:
A IO-360 RV-8, a O-360 RV-6, and a O-320 RV-4… ended head to head, all at the same top speed (max speed diff 1kt).
Guess similar aerodynamics speak for themselves here, fat wings remain fat ;)
 
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