HP Curve and Tourqe Generic Question

This post is meant to be innocent, I don't run D, do not plan to and don't intend to stir the pot - just want to learn.

1. What does a Dyno Test do?
2. How do I read the charts on the other treads about HP Curve and Tourqe. I'm interested in learning how to look at/read the chart. How are the points plotted, what does it mean and why are they significant.
3. What does it mean as far as speed and acceleration as the two lines rise, come close to crossing and then drop?
4. Could the same thing be done to compare two identical Yamato 102s to see which would be a better motor?

[sam]

dyno racing

Very good questions.

A dyno test measures how much force can be applied 12 inches from the center of the shaft. The output is expressed as torque in foot-pounds (not feet pounds as G. Gordon Liddy insists, because a single 12 inch foot is involved, not feet plural).

"Corrected" torque allows fudge factors to slightly change the points you plot on the chart based on air conditions (temperature, humidity and barometric pressure) that vary from "standard". Basically you take your actual observed torque readings and change them based on how much the air conditions varied from standard ideal conditions while you were running the test.

Each dot representing a torque reading on the chart should represent a load test at the rpm noted across the bottom of the chart.

Horsepower is derived from torque and time and is not directly measured, instead it is calculated by comparing how fast the motor is turning and how much torque is measured at that particular speed. The standard for power 100 years ago was a horse, so a conversion factor was worked up to compare steam engines, gasoline engines and electric motors to a horse. When using foot pounds of torque as the first measurement the conversion to horsepower is done by dividing motor rpm by 5,252 (the standard conversion factor) then multiplying by the measured torque.

One of the flukes of this mathematic formula is that horsepower will always be less than torque at rpms less than 5,252; horsepower will be equal to torque exactly at 5,252 rpm and horsepower will be greater than torque at rpms higher than 5,252. This causes the horsepower and torque lines on the chart to cross at 5,252. If they don't the chart is not correctly labeled or graphed.

So, each horsepower dot represents a torque reading converted by the math at that rpm.

Generally the higher and flatter the torque line is from low/mid rpm up to high the more accelleration you will see. Motors that have torque lines that suddenly bulge up like a mountain could have more peak horsepower with less exciting accelleration {or more like sudden dramatic accelleration after bogging for a while}.

Dyno readings do not always represent racing results. It sometimes happens that the highest torque reading acheived at a particular speed (esp in the mid and lower rpm range) occurs with the throttle slightly less than fully open (and opening the throttle full gives less power) - or - the prolonged stable operation necessary to get a smooth torque reading moves the motor out of a temporary accelleration lag that won't show on the chart, but happens over and over in the vehicle. The inverse of both of these conditions is also possible.


Bottom line ..... dyno results are a tool to compare motors, but unless the competition is restricted to the dyno room, the results are not written in stone.

We are racing boats here, not dynos. The results are basically a 5% difference on the dyno and these results are not conclusive in my opinion. How many 44's were compared to see how much variation exists between them? How much variation can we expect from Tohatsu to Tohatsu? We do not know these answers.

Answer to question #4: Yes, certainly.

[Bill Huson]

Oooohh, very technical, Sam . . .

But you forgot the ol' rule - There ain't replacement for DISPLACEMENT! :-)

DougMc - Sam is on it. Outboards are hooked to a dyno via the prop shaft which drives a hydraulic pump which shoots hydraulic fluid into a the dyno-mo-chine which gives you a "readout" which may not be dead on the absolute truth but engines can be compared on the same dyno.

[sam]

David Christner has one of his father's dynos for sale right now. Only rated for 50hp, but would be perfect for motors smaller than D's.

[David_L6]

Bottom line ..... dyno results are a tool to compare motors, but unless the competition is restricted to the dyno room, the results are not written in stone.

We are racing boats here, not dynos. The results are basically a 5% difference on the dyno and these results are not conclusive in my opinion. How many 44's were compared to see how much variation exists between them? How much variation can we expect from Tohatsu to Tohatsu? We do not know these answers.

You know.... That's one of the better explanations I've ever seen on the internet for any technical question about boat racing. Good job Sam. You made me think (and re-think).

[kws]

Sam that is the most clear & concise (sp?) definition of horspower i have seen anywhere including a few college courses (that nut took 2 class periods to confuse most of the students ) can i just follow you around for a couple of weeks and increase my knowledge base??? \
thanks Sam

[hydroplay]

HP Curve and Torque

"the prolonged stable operation necessary to get a smooth torque reading moves the motor out of a temporary accelleration lag that won't show on the chart, but happens over and over in the vehicle. The inverse of both of these conditions is also possible."

While your statement may be true when using an older or more simple dyno where each rpm/torque measurement is made when the engine is in a steady state at that rpm, modern dynos/software systems are run in an acceleration mode with a computer recording the inputs at the designated rpms as those rpm points are passed as the engine accelerates. The rate of rpm increase is determined by the operator based on his experience. This greatly decreases the time necessary to run each test and the running time on the engine as well as giving a more realistic map of engine performance in a racing environment.

Dyno testing can certainly be done on any of our racing outboards. However for the stock type motors, it is a bit more involved than simply bolting a powerhead to a univeral plate on your dyno and running it. Stock type engines use the driveshaft housing as a component of the exhaust system so to be reasonably accurate, it must be used on the dyno. So now you have to make a far more elaborate system to fixture the powerhead and the driveshaft housing in the dyno, make a long driveshaft to get the power from the crankshaft to the torque absorber and fashion something to collect the exhaust gases/cooling water and pipe it away. This could be done for a 102 but takes some work. We did make a fixture for the 302 and ran ran a number of powerheads and component tests several years ago when we were trying to beat the 102s. The results paid off as our 302 stuff won the only APBA Stock championship so far in CSH. However the transom height rules have eliminated that. The last several nationals winning 25XS motors have also seen dyno testing. It can be useful and certainly is a big help in finding small adjustments/tuning that may not seem apparent on the boat. The dyno is not the ultimate judge, it's just a tool that can be useful.

[ryan_4z]

Hydroplay,

Since you have done dyno testing with the Yamatos, I am curious, what is the approximate difference in Hp and torque between the 302 and the 102. Also, how much difference did you find in motors of the same model?

Is the Championship you are talking about when Brian won? I didn't know that that was a 302.

[Bill Huson]

The dyno I used . . .

was sety up for outboards and I/Os and was driven off the prop shaft. Cool rig. Major problem - that various adaptors for different make/model Ob or I/o units were designed to fit a splined shaft so I couldn't use it on our smooth shaft, drive pin racing outboards without machining wierd parts. Bummer. Anyhoo, at the time my Yamahonker 115 outboard ran the dyno over 130HP! Cool. Probably close to right `cause it swings a 21" pitch prop onna 18 1/2 foot hull.

[hydroplay]

Ryan,

Yes, the championship was a Winternationals out in Bakersfield that Brian Palmquist won. He took my boat and 302 motor, not sure whose prop he used.

While we did test a number of 302s on the dyno, we were only interested in them because we were trying to win with them and didn't have any 102 stuff (at that point). So we never ran a 102 on the dyno to give you any real accurate info. In our experience this year playing with OSY, we tried both and have opted for the 102 as it runs faster and allows almost any prop without any hassles. I suspect that the two curves would be very interesting but would GUESS that the 102 has 1 to 2 more peak hp and that the torque doesn't fall off at higher rpms as much as the 302 does. Give the 302 a bit more power at lower speeds but the 102 seems better from 6500 rpm up. Back when we could run the propshaft level with the bottom, we thought we could win with the 302 but down at 1/2 inch, the 102 has a pretty good advantage on a big course.

We're going to build two boats for next year. One will be a really light one for OSY-20SS and suitable for the 80 and 102 motors. The other will be strictly a CSH now that Bill is old enough for C. We'll build that one mainly for the 302 but adaptable for a 102. Hopefully the data ac***ulated over a season will give us a better idea of both the 102/302 merits by running each motor most every day and comparing lap times, top speeds, etc.

[14J]

Great Information

Great thread

Sam -

Hows does all this factor in when considering a 102 vs a 302 powerhead in a MOD application? Without height restrictions, etc. do things equalize or is one still prefered?

[crankbearing]

K&O garbagbe pump 2000

Hey bill,

What we do with our K&O dyno series 2000, is bolt the race powerhead to a fishing mid-section and lower unit with a 2:1 gear ratio and reverse the math when we find out what the output pressure is and factor that back to see what kind of power we are making. Crude but it works, but sam H is right. the newer attachments I am currently looking into the attachment for the dyno that will give me all the measurements that hydroplay is talking about. for the K&O 2000 dyno without buying a new one. We experiment with different exhaust tuners from the fishing motors until we get pretty much the righ temp at each cylinder. so we no we are on par with what is in the 44 housing for racing.

I had another scheme drawn up for that dyno the allowed the use of a 2:1 merc gearboot (fishing) as a gear reduction unit to test with as well. I had it all figured out and lost the plans.

Regards,

[Ken G]

Wow!

great question doug mc. amazing info coming out to fill the absorbing head... thanks to Sam and Hydroplay for sharing the results to your passionate quest for racing and performance domination.. you both get major kudos for schoolin us wet behind the ear, greenie new schoolers. your knowledge being shared totally helps our sport grow.,12kenF