Scarb sj build/dyno run

Speedfreak

Speedfreak

Location
So. IL
Ummm I think your shorted yourself a few cc's. I thought 770 sounded small for a +6mm. 82mm bore and a +6mm stroke figures out to be 781.5 Unless I missed something I could be wrong I can't do all this in my head...

Plus I needed to post so that I could find this after the dyno pulls. I wish you had a few extra pipes to throw on there really fast just to see how the numbers change.
 
FLY6584

FLY6584

Location
Clearwater, FL
Speedfreak said:
I wish you had a few extra pipes to throw on there really fast just to see how the numbers change.
Click to expand...

Yeah I'd love to see a comparison of the following chambers:

Limited
Mod
Blaster Mod
TNT

Someone send this guy some chambers and a case of beer so we can find out which chamber really is better on a highly modified motor.:biggthumpup:
 
K-SCARB

K-SCARB

HELLS YEAH!!!
Location
Belding MI
FLY6584 said:
Yeah I'd love to see a comparison of the following chambers:

Limited
Mod
Blaster Mod
TNT

Someone send this guy some chambers and a case of beer so we can find out which chamber really is better on a highly modified motor.:biggthumpup:
Click to expand...

I do have a limited chamber and the mod is on it now. We are going to run it tommorow but do have another motor we will be running soon so pm me if you would like to lend some chambers for the next run.
 
#ZERO

#ZERO

Beach Bum
Location
Florida - U.S.A.
K-SCARB said:
Whats the idea behind this?
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I've been told by more than a few engine shops that when the 44 carbs are mounted in the original position they perform better because the bypass holes and the inner venturi are closer to the manifolds strongest signal. It would make jetting a bit more difficult because you will have to remove the carbs each time but it would be interesting to see since you're on the dyno to prove this theory right or wrong.
 
N

njfl

X-H2
I'm also anxious to hear the results. I've never had the opportunity to dyno my motors, but would like to get an idea where mine stand.

I've heard claims of these 701-based motors making 200+hp.

Here's a thread with a Jr. Magoo (now LPW) motor claiming 159hp:

http://www.pwctoday.com/showthread.php?t=52908

What's really interesting is that in this month's Watercraft World magazine on p.42, there is a writeup of the EME800 (Malone) Polaris claiming 150hp. I'm surprised that it is only 150hp considering the price of the EME800.
 
#ZERO

#ZERO

Beach Bum
Location
Florida - U.S.A.
Matt_E said:
Don't you have to remove the carbs for rejetting anyways?
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On the dyno I would have to say no, with the cabs mounted with the diaphragm plates on the outside.

If it's on the ski you just have to lower the exhaust tube on the back end to make it easier.

I use a ratcheting stubby screw driver to remove the diaphragm plates, valve bodies and jets.
 
Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
njfl said:
I'm also anxious to hear the results. I've never had the opportunity to dyno my motors, but would like to get an idea where mine stand.

I've heard claims of these 701-based motors making 200+hp.

Here's a thread with a Jr. Magoo (now LPW) motor claiming 159hp:

http://www.pwctoday.com/showthread.php?t=52908

What's really interesting is that in this month's Watercraft World magazine on p.42, there is a writeup of the EME800 (Malone) Polaris claiming 150hp. I'm surprised that it is only 150hp considering the price of the EME800.
Click to expand...

HP isn't everything. Torque plays a big role, and target RPM.
 
tor*p*do

tor*p*do

Squarenose FTW
Site Supporter
Location
NW NC
Matt_E said:
HP isn't everything. Torque plays a big role, and target RPM.
Click to expand...

Bingo - I has a "discussion" with a Kawi rep about how a Ultra 250 turning 250hp compares to my 19 foot MasterCraft pushing 250 hp out of a 351 c.i. V-8. He tried to tell me the two boats had the same power based on hp rating but he couldnt come up with the torque rating (neither does the Kawi website).
Comparing a boosted 1.5 liter engine to a 5.8 liter V-8 based on hp rating alone is bull!
 
Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
But where does the number 5,252 come from?

To get from pound-feet of torque to horsepower, you need to go through a few conversions. The number 5,252 is the result of lumping several different conversion factors together into one number.

First, 1 horsepower is defined as 550 foot-pounds per second (read How Horsepower Works to find out how they got that number). The units of torque are pound-feet. So to get from torque to horsepower, you need the "per second" term. You get that by multiplying the torque by the engine speed.

But engine speed is normally referred to in revolutions per minute (RPM). Since we want a "per second," we need to convert RPMs to "something per second." The seconds are easy -- we just divide by 60 to get from minutes to seconds. Now what we need is a dimensionless unit for revolutions: a radian. A radian is actually a ratio of the length of an arc divided by the length of a radius, so the units of length cancel out and you're left with a dimensionless measure.

You can think of a revolution as a measurement of an angle. One revolution is 360 degrees of a circle. Since the circumference of a circle is (2 x pi x radius), there are 2-pi radians in a revolution. To convert revolutions per minute to radians per second, you multiply RPM by (2-pi/60), which equals 0.10472 radians per second. This gives us the "per second" we need to calculate horsepower.

Let's put this all together. We need to get to horsepower, which is 550 foot-pounds per second, using torque (pound-feet) and engine speed (RPM). If we divide the 550 foot-pounds by the 0.10472 radians per second (engine speed), we get 550/0.10472, which equals 5,252.

So if you multiply torque (in pound-feet) by engine speed (in RPM) and divide the product by 5,252, RPM is converted to "radians per second" and you can get from torque to horsepower -- from "pound-feet" to "foot-pounds per second."
Click to expand...

:biggthumpup:
 
N

njfl

X-H2
douglee25 said:
How did you arrive at that?

Doug
Click to expand...


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.
 
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