A bit of theory

[Mark75H]

um,ware dose your co-pilot sit? my co' be hangin on to the canard, so the Torque don't drive the hull over

Well then it should be an even race because you predict it will take me "days" to get on plane

[RichardKCMo]

Small wheel turn fast ,Big wheel turn slow. So simple, torque. This has to be done in the range of the h.p. unit used.?
RichardF

[Skoontz]

That wheel diamter sure would have been a good thing to try for the old V-4 75, 80, and 90 HP OMC's. The prop diameter was small and dad always said if we could add an inch or so some really decent speeds might have been achieved with the stock gearcases.

[Tim Chance]

Sam - Your earlier post about prop diameter and pitch as applied to different gear ratios makes a lot of sense, it's something I never thought of. Your recollection on when Mercury went to the 16:21's makes me think back to my early days with an Alky Hot Rod. I got beat on a regular basis by Alky Merc's with 1:1's. So, I adapted a 1:1 Konig to the Champion, found a small prop that worked and still got beat by the Merc's (Not to mention the deflector Konig B's and the Anzani's).

And now all I am is older, not one bit smarter. With my Super E I plan on running a 14:15 Konig (or maybe it's a 13:14 or 15:16, I can't remember, I just know it is one tooth off, not 1:1). If I end up getting a Bass unit I plan on 16:17. Anyhow, someone told me at one time that a lower unit that is not a 1:1 has better wear that a 1:1 as all the gears mesh each other, not just the same tooth-to-tooth over-and-over??

I'd like to throw one more thing into that gear ration prop size discussion. we had two A Konigs that were nearly identical. One had 12:15's and a big prop; the other 1:1's and a little prop. They were pretty much the same speed around the race course. The one big difference is the 12:15's would work with either expansion chambers or megaphones, but the 1:1's would not work with chambers, it would only work with megaphones.

So, I'm wondering did the gear ratio change for the Mercury allow it to gain the advantage of the tuned pipe in the lower unit? I had a stock 20-H conversion that I ran a little, only with 16:21's I wonder if it would have done anything with 1:1's?

I sold that 20-H about 1973 for $250.00. Seeing what they go for on e-bay, I wish I'd had a crystal ball.

[Mark75H]

Tim I had to think about your 2 motors and I think the difference was most likely that the expansion chamber motor had a narrower power band and the megaphone motor had a wider power band. The 1:1 prop may have had proportionally more pitch that the narrower power band expansion chamber could pull.

As far as the toilet bowl mid section and the 16:21's ... I've done the math over and over with the rpm/gear ratio/speed numbers - I don't think the 16:21's do anything beyond allowing you to use a larger diameter prop that helps with acceleration

The toilet bowl on the other hand is very important to the 20H to add power. The original leg just plain kills the 20H's power; originally Merc's research intended to make a mid that just didn't have the original leg's power robbing effect ... no plan at all to make a tuned exhaust - out of frustration they came up with the toilet bowl and just built it to get the job done. Some times ya just gotta "Get'er done!"

[Tomtall]

This may make no sense but I have had it proven to me by a very respected mod racer of many years. Not only gear ratio affects the punch and top speed but the gears diameter makes a differance also. If you can make the gears live on a smaller diameter gear set of the same ratio, they will outpull a competetor out of the corners running a larger diameter gear of the same ratio. I've seen this bring a peaky mod engine from a pooch to rocket with no other changes.

[David Mason]

Tom, you are on track with that science.

Most people don't stop and think about that, they only think ratio's.

One VERY important lesson I have learned over the years. Never trust a theory that is on paper, or in a book. To many times I have been told that won't work based on this and that formula. Well, me being a hard headed lad, I tried it anyways. Sometimes it works, sometimes it don't. One thing I believe, is that just because it works on Snowmobiles, does mean it will work on an outboard or motorcycle. And the flip side is true also. While principles are the same, the variables are very much different. Weight distribution, different drag coefficients, can change performance power curve enough to make or break the theory.

[16andy]

Thats the funny thing about theory, no matter how much someone knows or doesn't know it seems the biggest factor conserning who solves the problem faster is luck. Theory is often applied to reality, while reality should be applied to theory. It seems like a risky approch, but after a lot of time is spent testing based on a theory, this is often the end result.

But that doesn't make it any less fun to discuss .

[Fast Fred]

how about a bit O' history, the CC FR

Known not to be all that out of the hole, why?, cuzz it's got a 1 to 1.

change the foot and the mid to 1.85's and she Leaves like a Dragsta

[Mark75H]

how about a bit O' history, the CC FR
Known not to be all that out of the hole, why?, cuzz it's got a 1 to 1.

change the foot and the mid to 1.85's and she Leaves like a Dragsta

Ratio is only one part of the set up that makes a boat acellerate. Like I said, if you doubt it, watch me blast out of the pits with my 1:1 set up for short courses ... 0 to 50 in about 5 seconds, maybe less ... change my set up to long course style, just a couple inches change in pitch, more rake angle, about half an inch higher on the transom, tilt the motor out a little and now my 1:1 set up is "not all that out of the hole" just like the CC FR - now it might take me 25-30 seconds to get to 50 mph

Fred, Jon Wright (156+ mph in a quarter, I think the time was 8 and some change) and the other top drag racers all use 1:1, why? because it is only one ingredient of set up ...