Where do you want the sweet spot?

[mdaspit]

I have a question, and there probably isn't one clear answer, but... as a general rule, if your motor is turning the RPM's where it is producing the most horsepower, and the most mph, where in the straight-away do you want that "sweet spot"? Half way? 3/4? or should it be pulling the entire length?
Or, maybe it doesn't work that way? I'm asking about a CSH 302.

Thanks-

[ZUL8TR]

Sweet spot

I have a question, and there probably isn't one clear answer, but... as a general rule, if your motor is turning the RPM's where it is producing the most horsepower, and the most mph, where in the straight-away do you want that "sweet spot"? Half way? 3/4? or should it be pulling the entire length?
Or, maybe it doesn't work that way? I'm asking about a CSH 302.

Thanks-

I do not have a 302 but have a Y80 and a 25ss (1974 model). When I was actively racing in 20ssh and 25ssh I had the props and engines set up to provide the fastest acceleration to get the engine to max speed as quick as practical. I figured any delay to reach max speed was wasted time around the course. The props were Pinner and they flexed a bit under high load and slower speeds around the turns and therby reducing pitch slightly to allow increased rpm at the lower speeds around the turns to keep the revs up so the engine remained closer to its max torque range. Both these engines were proped to turn about 7200 at max speed. It worked for me with many wins in Region 5.

[mdaspit]

Novice Logic?

Yeah, I was just thinking that there has to be a law, that the faster it gets you there,the more you lose something on the top end once you get there.

So, in my novice brain, (which has limited capacity anyway), I think there must be a point of diminishing returns...

So, lets say you were testing a new prop, and you are pleased with the top end speed on a set course length, but maybe you suspect that you aren't getting it untill too far down the course.

Is there a point where others have an advantage over you by getting to their top end before you, even though it may not be quite as fast over all?

Is there a point when you are willing to give up a little at the top, in order to gain some in the amount of time it takes to get there?

And if that is true, then where on the race course do you want to be when you get to that point?

[Silas_53A]

I'm not sure what the answer is my self, I'm new to this as well. But if you have multiple props you are trying at a particular course, you want the one that give you the quickest lap time, not necessarily the greatest top end. Maybe by testing multiple props and finding the one that give you best lap time, you could then start to figure out why it is fastest. Were in the strait away do you reach your max? Find were that perfect point of top end and acceleration is. Which will obviously be different for each course.

[Bunker hill]

The answer is test, test some more then test again!

There are several questions here:
Is top end really the all important factor? or do you want lap times?
Does RPM really mean everything? too many revs can make an engine decline in power, you rev past the optimum
There is aways course differences, long vs. short and elevation humidity issues
There are many variables and combimations!
Testing is the only way to really find out

Bunker

[B Walker]

There are actually alot of questions here, but the most important one is the one about lap times vs top end.

Figure out how to accurately test for lap times and you have figured out more than most racers.

Hint: Seat-of-the-pants is not accurate. There is an amazing amount of technology to assist in making informed decisions about props, boats, motors, and setups.

Results from a quick google search:

http://www.advantagemotorsports.com/Ult30.htm
http://www.rcatsystems.com/telemetry/telemetry_rc.php
http://seniordesign.engr.uidaho.edu/...l/pdf/prop.pdf

I know several Stock Outboarders have worked with data acqusition. But not many are willing to share their experiences.

gl
BW

[Dennis Crews]

Hey Mark I follow your logic here but like you I am nowhere near able to devise that mathematical formula to calculate this. But....if you ever want to test the snot out of your rig at Lake Bryan some Saturday just let me know and I will be there to help you lug your boat in and out of the water and to work the stop watch.

[ZUL8TR]

sweet spot - difficult to achieve

The answer is test, test some more then test again!

There are several questions here:
Is top end really the all important factor? or do you want lap times?
Does RPM really mean everything? too many revs can make an engine decline in power, you rev past the optimum
There is aways course differences, long vs. short and elevation humidity issues
There are many variables and combimations!
Testing is the only way to really find out

Bunker

Yes ideally the fastest lap times are the goal but many conditions make it difficult to achieve. Especially if you are late at the start lap times do not mean as much when there are 11 other very competitive boats.

I remember after all the testing I did on acceleration, straight a way speed and running a course for best times to find how the different: props, motor heights, shaft angle, magneto set up, spark plugs, carb jet settings, etc. performed and all was changed during the race with 11 other boats. Because the line you take or forced to take is not always the best, the water is different everywhere on every lap, the wind changes, temp and relative humidity is different during the day, etc. The final result is to know your equipment and what different setting can be expected to do and make adjustments for the course conditions even from one heat to another. Just like the NASCAR boys. Some things work in testing and do not work during the race.

[bill van steenwyk]

quickest is always better than fastest xcept in the kilo

There is a reason why, when races with multiple heat winners are tied on points, the tie is broken and a winner decided by elapsed time.

A good example is drag racing. The fastest car is not always the winner.

A lower elapsed time, against the other competitors, no matter the highest speed attained, will always get you to the finish line ahead of a competitor with a slower elapsed time. The exception would be if you were very far behind on a clock start, but if everything is equal, and you are the quickest around the course, you will win.

As others have said, TEST, TEST, TEST!!!

If you don't have a GPS that can be used to give elapsed time around the race course, use a stop watch, either operated by the driver or a helper on shore. IMHO the speedometer comes last in order of importance when testing. First the stop watch or other device to give you elapsed time, and then a tach to let you know which props keep the motor in the proper power band. If you can only have one, the stop watch or timer is best.

[jtower3941]

RPMs

Who makes or sells the tini tach.

[17W]

Who makes or sells the tini tach.

http://www.tinytach.com/tinytach/index.php

[B Walker]

http://www.tinytach.com/tinytach/index.php

click on the tiny tach link and pick the model for the motor your interested in.

Y-302 is model number TT226R-2C.......I think....can someone verify?

BW

[Boatracer4fun]

Who makes or sells the tini tach.

The tiny tach does not work for the Y80. I have tried it and it doesnt give a true accurate reading. I talked with TJ and for the Y80, The only 1 to date that is accurate is the digitach which is used in go karts, costs $300.00 for the setup and it comes with downloadable software for computers.

Now I know the tiny tach works for theY302.

[ZUL8TR]

Tiny Tach

The tiny tach does not work for the Y80. I have tried it and it doesnt give a true accurate reading. I talked with TJ and for the Y80, The only 1 to date that is accurate is the digitach which is used in go karts, costs $300.00 for the setup and it comes with downloadable software for computers.

Now I know the tiny tach works for theY302.

Which Tiny Tach model did you use on the Y80, the 1c or the 2c?