Something isn’t adding up. Speed vs. RPM’s?

[smbarcelow]

Well, I’ve gotten a little seat time now since getting the engine firing reliably on all eight cylinders, and I’ve done a little experimenting with the GPS. My findings are puzzling to me and I’m fairly sure some of the members here will have useful comments. [See my signature for specs.]

Last year, while still struggling with a misfire, I was able to make a top speed run of 59 MPH at 5,100 RPM’s with the trip stop in the top setting. The same day, I ran at top speed of 54 or 55 MPH at 4,900 with the trim stop in the middle setting.

On Saturday, I made a top speed run and achieved 56 MPH at 5,800 in the middle setting. I didn’t have time or lake conditions to make a top trim setting run.

What puzzles me is this: How I can turn 900 more RPM’s and only get 1 or 2 MPH out of it in the middle setting. Am I slipping the prop that much more? I was expecting to get 5 or 6 MPH out of the additional 900 RPM’s. Feedback would really be appreciated. Thanks!

[mrfixxall]

Well, I’ve gotten a little seat time now since getting the engine firing reliably on all eight cylinders, and I’ve done a little experimenting with the GPS. My findings are puzzling to me and I’m fairly sure some of the members here will have useful comments. [See my signature for specs.]

Last year, while still struggling with a misfire, I was able to make a top speed run of 59 MPH at 5,100 RPM’s with the trip stop in the top setting. The same day, I ran at top speed of 54 or 55 MPH at 4,900 with the trim stop in the middle setting.

On Saturday, I made a top speed run and achieved 56 MPH at 5,800 in the middle setting. I didn’t have time or lake conditions to make a top trim setting run.

What puzzles me is this: How I can turn 900 more RPM’s and only get 1 or 2 MPH out of it in the middle setting. Am I slipping the prop that much more? I was expecting to get 5 or 6 MPH out of the additional 900 RPM’s. Feedback would really be appreciated. Thanks!

Yes your slipping the prop,are you using a gps? My boat runs the fastest on the 3rd hole,you need to put a heavy cup in yout ultra prop if that what your running..

[smbarcelow]

Yes, I'm using GPS. I still need to find out for sure what the prop is but, based on your feedback about it last week, I'm nearly certain it's an Ultra. I also still need to look at the drive to determine the ratio. Saturday was more about playing than it was about working. Gotta keep my wife and boy happy. :D Thanks again for the feedback.

[mrfixxall]

Yes, I'm using GPS. I still need to find out for sure what the prop is but, based on your feedback about it last week, I'm nearly certain it's an Ultra. I also still need to look at the drive to determine the ratio. Saturday was more about playing than it was about working. Gotta keep my wife and boy happy. :D Thanks again for the feedback.

I your drive ratio is higher then a b it wont matter what prop you run, it will slip like crazy..

[BigGrizzly]

I figured you would be a little faster. Out 16 does 58 with a 302 with a solas 21 on a good day at . Maybe your tach is screwed up.

[Ghost]

I figured you would be a little faster. Out 16 does 58 with a 302 with a solas 21 on a good day at . Maybe your tach is screwed up.

Piling onto that, doesn't 5800 seem high on an absolute scale? (I admit I don't know anything about your motor as listed in your sig, but isn't 5200 about the max it should be doing unless you're way underpropped?) I'd think the tach is lying now, or was lying before. Now seems more likely. I'd think others here would know for sure. -Mike

[mattyboy]

not sure what prop you are turning but the ultra seems to get less effecient as it spins faster, in general they are around 15% slip which is high
what gear ratio is the volvo, the gears are set in the lower so the numbers on the top of the drive can sometimes mean didley. check the tach also

[smbarcelow]

I'll have to put a timing light with a tach on it and check it against my guage. Once I gather drive ratio and prop info, I'm sure you guys will have a lot more to go on. I doubt this V8 has ever run on all 8, due to the fact that the alternator bracket was so close to the number 1 plug. It may have been propped for the HP it was making on 7 by trial and error. I'll update this thread once I gather the info.

[smbarcelow]

I attempted (briefly) to find some numbers on the outdrive that would tell me the drive ratio. All I could find was a tag listing patents and suggestion lube check intervals. Where would I look to find info about the ratio? I haven't pulled the prop yet to find out what it is. I haven't pulled it out of the lake yet and that seems like an easier job to do in the driveway.

[mrfixxall]

I attempted (briefly) to find some numbers on the outdrive that would tell me the drive ratio. All I could find was a tag listing patents and suggestion lube check intervals. Where would I look to find info about the ratio? I haven't pulled the prop yet to find out what it is. I haven't pulled it out of the lake yet and that seems like an easier job to do in the driveway.
facing the top of the outdrive theirs a hat,theirs a allen center bolt,follow it down where the bellow for the ujoints attach to the out drive..their should be a plate riveted their with the serial # if theirs a b its a 1.61 c 1.89 d 2.15


http://www.donzi.net/forums/showthread.php?t=58387 look here!

[smbarcelow]

Thanks, mrfixxall. That's very helpful. :)

[Just Say N20]

My 16 has a 310 hp Volvo SBC and I'm told it ran 62 on GPS running a Solas 19 prop, I don't know the rpms. I have a Volvo 290 outdrive (with power trim), with a ratio of 1.61:1 (the outdrive is off the boat, and I just went out and counted it. The prop shaft went around 1 time when the upper went around 1.61 times.)

I have never run this prop. I bought it from Grizz shortly after I bought the boat. If your lake is relatively free of prop destroying crap, you could try it.

[smbarcelow]

I might just take you up on that, N2O. Our lake is pretty safe for props and I grew up there so I know it like the back of my hand. I've been talking to Grizz about his Solas props and I'd love to try one out.

[smbarcelow]

The stamp on the top of the outdrive says "D", but I was told that gears were replaced at the time of the engine transplant. I assume that the gear ratio could have been modified and may not match the tag. (Is that a correct assumption?) I'll probably just have to spin the prop and count the number of times the upper shaft spins.

I still have to pull the prop. Tonight was more about tubing with my neice and nephew than working on the boat...I just peeked at the tag as I was getting her off the lift.

[MOP]

Put a chalk mark on the engine balancer and on one prop blade, make careful note of their position. The slowly tap the engine over One turn until the chalk mark is where it was, go back and look where the prop ended up. A 1:50 will be 180 degrees out from where it started a 1:61 will be about 1" less then 180. Phil

[smbarcelow]

At times like this, it would be really nice to have access to the front of the engine. It's so much easier turning it over with a wrench rather than bumping the starter.

[mattyboy]

not really all that big a job to pull the drive and test it that way if it is a 250 to a 280 with no trim any way.