tcschweitzer
Cadet
- Joined
- Jun 9, 2015
- Messages
- 6
I have a 21 ft crownline deckboat, about 4000-4500 lbs wet weight. Our lake has a 200 hp limit on inboards so I purchased the merc 4.3L instead of the 4.3LX or 5.7. The boat had an aluminum 19 pitch prop that seemed to work ok. I had a mechanic tune the engine and carbs for performance, he told me it would run more like the LX and I could expect about a 10- 20 hp boost. I've never verified this other than feeling a significant power increase. My WOT speed was always about 40, not sure about RPM, i'll verify tomorrow. After the tune-up the boat still runs about 38-40 but it will do that now with 8 people in the boat and my holeshot with skiers is awesome. Because of the power increase and worry about redlining the engine I bought a 21 pitch stainless prop. WHAT A DIFFERENCE, my top speed is now between 42-46 mph and I have good holeshot with 6 or less people in the boat. Last season I had too many people in the boat for that 21 pitch prop. We had 9 men and gear and although I could run 35-38 mph it took WOT to get on plane. Worried about ruining the engine I went to the local marine store and bought a preowned quicksilver 19 pitch SS prop. The boat ran great after that, in fact, I can only run on about 80% throttle with the SS prop or I redline. I always wondered why I could run WOT with the aluminum prop but not with the SS. I'm assuming the aluminum would flex to a 20 pitch or so under the load.
My mechanic doesn't believe me when I told him I was redlining with a 19 pitch. He was surprised I could even get on plane with the 21 pitch. I showed him video and couldn't believe it. He told me my tach was probably off. I told him that I've been around engines all my life and I can HEAR when an engine is redlining and I was redlining at WOT with the 19 pitch.
After we got back from a 3 hour run down Table Rock lake I noticed the drive oil reservoir was full, expanded and under pressure. The outdrive was pushing oil up into the reservoir. I changed the fluid and noticed the 19 pitch SS prop I just bought had about a 1/4 play on the shaft. And no, I didn't forget the thrust washer when I swapped the props. I googled the serial number of the prop and it is in fact a quicksilver prop built for mercruiser alpha one's. Why would this prop not fit? The vibration was causing the oil to heat up. I swapped props and never had a problem again. No one can seem to tell me why this prop has so much play on the shaft. Advice is appreciated.
Also, am I crazy for running at 21 pitch 3 blade on a tuned 4.3L?
My mechanic doesn't believe me when I told him I was redlining with a 19 pitch. He was surprised I could even get on plane with the 21 pitch. I showed him video and couldn't believe it. He told me my tach was probably off. I told him that I've been around engines all my life and I can HEAR when an engine is redlining and I was redlining at WOT with the 19 pitch.
After we got back from a 3 hour run down Table Rock lake I noticed the drive oil reservoir was full, expanded and under pressure. The outdrive was pushing oil up into the reservoir. I changed the fluid and noticed the 19 pitch SS prop I just bought had about a 1/4 play on the shaft. And no, I didn't forget the thrust washer when I swapped the props. I googled the serial number of the prop and it is in fact a quicksilver prop built for mercruiser alpha one's. Why would this prop not fit? The vibration was causing the oil to heat up. I swapped props and never had a problem again. No one can seem to tell me why this prop has so much play on the shaft. Advice is appreciated.
Also, am I crazy for running at 21 pitch 3 blade on a tuned 4.3L?
