Volvo Penta 290 gear ratio's

BruceK

BruceK

Well-Known Member
Joined
8 Feb 2015
Messages
8,361
Location
Conwy
Visit site
My brain is addled. I'm trying to work out what gear ratio's in my 290 legs I have and then marry them to the published ratios.

For every three turns on the crank pulley wheel my props spin once in live observation. to me that appears to be 1:3 but it cant be.....can it? I believe they should be 1:1.76 or so?
 
Thanks, I have those. I believe mine are either DP-D, DP-D1 or DP-E. Any ID plate seems long gone but the engines are KAD42a's so would probably narrow it down.

The ratio's still do not marry though in my mind. Also I am certainly not getting those speeds from my setup using C4's. The chart shows ~38 knts. I get 27 at best at the moment and cruise at ~23 hence my questions re weight previous thread and gear ratio's.

I reach max revs real easily on turbo's but getting out the hole on super chargers seems a bit sluggish so if I step up a pitch I may not get out the hole.
 
Last edited:
The speed is just a guide and clearly not boat specific. My own boat on the relevant chart would do 30 to 34 knots on the chart for A series props but 29knots is more like it in real life.
The prop chart suggests the outdrive with a kad42 should have 1.78/1 gearing.
To get best performance out of kad engines it seems best to apply plenty of throttle once into the supercharger range and push promptly up to something over 3000rpm . Then throttle back to cruising speed. Also legs tucked all the way in to minus 5. Then possibly leave it at minus 5 or trim the leg out - to whichever setting is best seems boat specific. Apologies if you already know that.
I guess you might have the incorrect leg ratio such as 1.95 rather than 1.78 which could explain lack of top speed.
.
 
Thanks for your input Martyn. I understand all those what I am struggling with is there is no 3:1 ratio in these outdrives. So how is it I am turning the engines over 3 revolutions on the crank pulley for every revolution of the props? I could understand if it was two turns on the pulley and marry it to 1.95 to 1. But I get 3 turns. That is what is confusing the hell out of me.
 
When you did your "turning" test, are you sure that the drive cones were locked hard together before you started?
i.e. you tried to turn the prop the opposite direction first with a wrench, yes?
 
In gear I started turning crank pulley. Once the props engaged and started turning I turned until one blade was vertical and marked it and the pulley wheel. I had someone watch until the blade had turned a full revolution before calling a halt while I counted the pulley wheel revolutions. Turning the pulley was a slow affair a) because of the compression and b) because I was nervous of a engine start while I was head down hanging on to a spanner. I don't believe their was any slip and both engine drive combo's recorded an exact 3:1 pulley : prop within 10 degrees of the pulley wheel. (hard to be absolute when the engine is under compression)
 
BruceK said:
In gear I started turning crank pulley. Once the props engaged and started turning I turned until one blade was vertical and marked it and the pulley wheel. I had someone watch until the blade had turned a full revolution before calling a halt while I counted the pulley wheel revolutions. Turning the pulley was a slow affair a) because of the compression and b) because I was nervous of a engine start while I was head down hanging on to a spanner. I don't believe their was any slip and both engine drive combo's recorded an exact 3:1 pulley : prop within 10 degrees of the pulley wheel. (hard to be absolute when the engine is under compression)
Click to expand...

I might be talking b*****ks but can you measure the reduction ratio of duo-props like that, as two props are turning do you have to effectively half the result? so you have approx. 1.5:1.
 
You must log in or register to reply here.

Share this page

Top