Scarb sj build/dyno run

[douglee25]

Not sure how HE arrived at that, but since the equation that Matt_E gave is linear and involves a proportionality constant AND hp and torque are on opposite sides of the equation, there will be some number at which they are equal.

Move torque to the left side of the equation (by dividing both sides by torque; this is 7th grade algebra). Then you have hp/torque = rpm/5252.

When hp equals torque, the left side is 1. To hold the equality of left and right sides, rpm must be 5252.

There's nothing magic aout 5252 rpms it just happens to fall out of the numbers and happens to be a tangible rpm that motors can reach. It comes from the fundamental definition of horsepower. Had the fundamental definition of horsepower been different, the rpm at which torque and horsepower are equal may have been something like 18000rpm, unreachable by most motors. The interesting thing is that torque will be greater than hp below 5252rpm and less than hp above 5252rpm.

I'm well aware that it divides out that way according to '7th grade algebra', but there are multiple engines that I've seen on the dyno where torque and horsepower are not equal at that specific rpm.

Edit: I'm going to have to check some old dyno graphs I have. If it works in the math, it should work in real life unless something is messed up with the dyno. I just can't seem to recall off the top of my head that they cross at that point.

Doug

 

[njfl]

but there are multiple engines that I've seen on the dyno where torque and horsepower are not equal at that specific rpm.


Doug

I think you'll find that they ARE indeed equal at 5252.

 

[K-SCARB]

So we just got done with the runs and It made 121hp at 7200rpm, I don't have the whole run printed in front of me but that's the peak hps. I'm very happy with the results and b-roll owes me lunch. The motor that we pulled out a 760 lightly ported, race gas etc made 92hps at 6500rpm so this will be a big improvement for me plus the mag pump will help a ton also.

 

[RiverRat]

Nice bump in power, however I think you will appreciate the improved torque values as well.

 

[#ZERO]

Horsepower = (Torque x RPM) / 5252

BTW that mathematical formula is just an approximate conversion factor and not to be used with internal combustion engines.

http://en.wikipedia.org/wiki/Torque

 

[#ZERO]

I think you'll find that they ARE indeed equal at 5252.

Penn & Teller just said.... BULLSH!T! :biggrin:

 

[Matt_E]

BTW that mathematical formula is just an approximate conversion factor and not to be used with internal combustion engines.

http://en.wikipedia.org/wiki/Torque

Are you sure about that? All my literature about 2 stroke design claim that formula, without exception.

Also, to quote the Wiki article you linked :fingersx:

Some people (e.g. American automotive engineers) use horsepower (imperial mechanical) for power, foot-pounds (lbf·ft) for torque and rpm's (revolutions per minute) for angular speed. This results in the formula changing to:

\mbox{Power (hp)} \approx \frac{ \mbox{torque(lbf}\cdot\mbox{ft)} \times \mbox{rotational speed (rpm)} }{5252}

This conversion factor is approximate because the transcendental number π appears in it; a more precise value is 5252.113 122 032 55... It also changes with the definition of the horsepower, of course; for example, using the metric horsepower, it becomes ~5180.

Use of other units (e.g. BTU/h for power) would require a different custom conversion factor.


It seems the article states clearly that SAE uses that formula for automotive engines - e.i., internal combustion engines.

 

[RiverRat]

Torque is more a measure of the work that a motor can perform, hp is the rate at which that "power" can be done.

 

[#ZERO]

It's just a matimatical forula for explaning how the relationship between torque, power and energy works for a rotating object.

It's not to be used as a formula for figuring out the torque of an engine once the peak horse power is known.

 

[Matt_E]

I concur. It is used to calculate HP after a dynorun determined torque over RPM.

 

[Speedfreak]

So we just got done with the runs and It made 121hp at 7200rpm, I don't have the whole run printed in front of me but that's the peak hps. I'm very happy with the results and b-roll owes me lunch. The motor that we pulled out a 760 lightly ported, race gas etc made 92hps at 6500rpm so this will be a big improvement for me plus the mag pump will help a ton also.

I have a few questions about your motor. I am making a guestimation of my power numbers. What is the diameter of the exhaust manifold? There were 2 sizes the 42 and 47mm. Or is your bored out. They say that going from 42 to 47 makes 7 more horses on a limited motor. Also what pipe was that with? And what was your compression?

 

[K-SCARB]

I have a few questions about your motor. I am making a guestimation of my power numbers. What is the diameter of the exhaust manifold? There were 2 sizes the 42 and 47mm. Or is your bored out. They say that going from 42 to 47 makes 7 more horses on a limited motor. Also what pipe was that with? And what was your compression?

I'm using a mod pipe rite out of the box I will measure it but think 42, compression is about 16.5:1. We were going to try a couple of different things carbs and ignition timing but ran out of time so were going to try them out on b-rolls motor next week. His motor is a 6mm 82mm not as aggressive porting but 46mm black jack carbs and a pro-tec cdi mine was running a msd enhancer. as regards to the lamey motor making 159hps I would think that it is possible with the better carbs and ignition than what was run on this motor.

 

[njfl]

BTW that mathematical formula is just an approximate conversion factor and not to be used with internal combustion engines.

http://en.wikipedia.org/wiki/Torque

Can you explain what you mean by stating that it is not to be used with internal combustion engines?

This equation is what is used to calculate horsepower on dyno runs. On the dyno run, torque is what is directly measured, not horsepower. Horsepower is calculated from torque (with this equation).

As far as it being approximate, that is because pi 3.1415927... is involved because of the rotational aspect. Therfore , this equation can never be exact (to a mathemetician). Then again, most engineering, in practice, is not exact (i.e., machine tolerances, etc.).

 

[njfl]

So we just got done with the runs and It made 121hp at 7200rpm, I don't have the whole run printed in front of me but that's the peak hps. I'm very happy with the results and b-roll owes me lunch. The motor that we pulled out a 760 lightly ported, race gas etc made 92hps at 6500rpm so this will be a big improvement for me plus the mag pump will help a ton also.

That's just about what I thought your motor would do. That's not to shabby either. The thing to consider is that you have most of the major mods and key aftermarket components. Don't go crazy trying to see another 10hp from this motor. As you may be aware, the higher you go in horsepower with a given motor, the harder it is to incrementally extract more power from the motor (and more expensive per additional hp also).

To make significant gains in power from this point you need to start increasing air flow volume through the engine (i.e., increase displacement).

I'd be interested to see your data from 3000 to 7000 also. This is the more usable rpm band. Just curious how flat it is.

Keep in mind also, that the mag pump will not gain you more power, it will just put more of the power into thrust as it is more efficient than OEM pumps (at least under most riding conditions).

 

[crammit442]

I'm using a mod pipe rite out of the box I will measure it but think 42, compression is about 16.5:1. We were going to try a couple of different things carbs and ignition timing but ran out of time so were going to try them out on b-rolls motor next week. His motor is a 6mm 82mm not as aggressive porting but 46mm black jack carbs and a pro-tec cdi mine was running a msd enhancer. as regards to the lamey motor making 159hps I would think that it is possible with the better carbs and ignition than what was run on this motor.

Also remember that accurately modeling water flow is very difficult and is responsible for a great deal of how your pipe will make power. The carbs you are using are excellent and for a given diameter, flow MORE than the carbs used in the other "test". Factory Pipe employs one of the only genuinely accurate watercraft dynos. They've spent years learning how to duplicate water flow on the dyno. Many of the other dynos(if they even exist), are sketchy at best and the numbers are "fudged" a bit or fabricated altogether to sell goods. Sounds like you're on the right track.:smile:

Charles

 

[K-SCARB]

We still don't have the water exact but are going to set up some gauges to get #s when the ski's are running in the water with the load from the jet. We still have a lot of info to gather to make this as exact as possible.

 

[B-ROLL151]

Also remember that accurately modeling water flow is very difficult and is responsible for a great deal of how your pipe will make power. The carbs you are using are excellent and for a given diameter, flow MORE than the carbs used in the other "test". Factory Pipe employs one of the only genuinely accurate watercraft dynos. They've spent years learning how to duplicate water flow on the dyno. Many of the other dynos(if they even exist), are sketchy at best and the numbers are "fudged" a bit or fabricated altogether to sell goods. Sounds like you're on the right track.:smile:

Charles

Charles,

I dont know if you remember but Kyle (K-SCARB) and I are the guys woundering if you still had a connection for some ADA cylinders with the smaller bore. I just never had the time to get back to you once you gave me your numbers:frown: . I have been talking with ART and he thinks we are fairly close. The pipe sizzles the water right after the run and makes the power at a little lower RPM which is what we where looking for in our boats. If you have seen the Factory Pipe Dyno set-up let me know what kind of flow valve or pressure valve they are using to duplicate the water flow into the motor. Like you said we have been brianstorming how to duplicate but I think the only way to do that would be to have a injection box that accualy goes by the RPM of the engine and increase water flow as the RPMS rise. If you have any ideas where we can have one of these custom made let me know. Art and I talked about this exact factor and he did not say he could have a injection box made, I did not ask either. Let me know what your ideas are. Aaron (B-ROLL)

 

[K-SCARB]

Got the motor off the dyno and in the boat heres some pics, b-roll and I are going to ride tomorrow cant wait to see how the new power and pump work. Still wating on the trim should be next week.