Rotational torque

alvin l nunley said:
You're right, my bad. I mis-read the scale.
I've never seen a chart where the horsepower and the torque dropped in near unison that much. I'm going to blame it on my faulty vision. lol
I did notice there's an increase in fuel flow at the same time that both the other curves are falling, what's that?
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Tiny carb. Engine looking for airflow. Will take whatever atmosphere pushes to the low pressure area. Thus more fuel.
I never noticed if governor was connected. Easy to see why 4900 is target rpm.
 
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95 shaw said:
Tiny carb. Engine looking for airflow. Will take whatever atmosphere pushes to the low pressure area. Thus more fuel.
I never noticed if governor was connected. Easy to see why 4900 is target rpm.
Click to expand...
Consider this; lower airflow (then needed), higher vacuum, more fuel flow, richer mixture means less HP. Might explain why the KT100 high speed jet is set so lean, and the reverse on the low-speed. Might explain some 4 cycle posts I've seen where they run a much bigger low-speed jet than normal?
 
alvin l nunley said:
I did notice there's an increase in fuel flow at the same time that both the other curves are falling, what's that?
Click to expand...

I think I can answer it.
Piston speed has increased with the rpm increase and the reduced amount of time to burn unneeded additional fuel per burn drops out put.


maybe ??????????
 
alvin l nunley said:
Consider this; lower airflow (then needed), higher vacuum, more fuel flow, richer mixture means less HP. Might explain why the KT100 high speed jet is set so lean, and the reverse on the low-speed. Might explain some 4 cycle posts I've seen where they run a much bigger low-speed jet than normal?
Click to expand...
Now add a restrictor plate!!
 
yep the two basic high speed fuel problems which have been addressed since the beginning of engines.

Vacuum controlled fuel feed at high rpm will exceed fuel need for combustion and the solution has always been to restriction set maximum possible high speed fuel flow.

Mechanical fuel feed same thing when mechanical fuel pump at high rpm will mechanically and forcefully exceed what's needed for available air flow and the solution has always been to bleed off unwanted fuel flow.

It has always been that way before the electronic age because the only other way to control it would rely on unreliable springs and levers because there is no mechanical way to directly relate an increase in rpm to a linear motion, without springs, weights and levers.

All mechanically not possible before my bucket system. ... :)
 
Ted Hamilton said:
A question..... If I'm doing LTO, and my typical RPM drop is only 400 rpm, why wouldn't I gear the engine so that it had the most power in that range? Are we really saying that in typical LTO kart racing, we're running at the upper RPM limit, so far beyond the engine's "normal" powerband, that we see some sort of difference in the curve that is forcing us to compensate elsewhere?

It's kinda' like a v12 spinning at 8000 rpm vs a turbo 4 at 17000.... they're both doing the same amount of work, and both have equal HP ratings, but if you need shear grunt, you'd better go with the v12 because its' torque potential is much higher. Since its got a smaller powerband, it will be more sensitive to disturbances in speed, however... yes, no?
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95 shaw said:
You would want peak horsepower in that range. Where in the range would depend on if you need more grunt off the corner, or if you need a little speed at the end of the straight.

Huh
Kinda sounds like the reason for this thread.

You are kinda on the right track.
I would consider the engines normal powerband to be between peak torque and peak horsepower. So over rev a little to make sure you are using all the work your engine can do.

Below peak torque, any load you add will also lower rpm, dropping torque. Adding load above peak horsepower will drop rpm, but torque will rise.

Might have gave away the farm there.
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I'll do some math for you.

Peak torque based on the sample dyno chart

14.10 ft/pd @ 2300 rpm = 14.10 x 2300 / 5252.1 = 6.17 hp
Peak horsepower = 9.83

6.17 hp x 550 pounds/ft/sec = 3393.5 pounds moving 1 ft in 1 second
9.83 hp x 550 pounds/ft/sec = 5406.6 pounds moving 1 ft in 1 second.

Which do you think will accelerate your 400 lb kart faster?
Potential speed; lifting straight up, of course.
8.5 feet per sec vs 13.5 feet per sec.
 
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alvin l nunley said:
Consider this; lower airflow (then needed), higher vacuum, more fuel flow, richer mixture means less HP. Might explain why the KT100 high speed jet is set so lean, and the reverse on the low-speed. Might explain some 4 cycle posts I've seen where they run a much bigger low-speed jet than normal?
Click to expand...

I believe the chart shows air/fuel ratio, not fuel flow.

PM
 
Pete_Muller said:
I believe the chart shows air/fuel ratio, not fuel flow.

PM
Click to expand...
You are correct, Pete.
The engine actually leans out, then goes rich well after peak horsepower.
I think this is a component of loss of control of the valvetrain. ie intake valve bounce during compression stroke disrupting carb fuel signal.
This is not a problem for 2 strokes as the crankcase and reeds isolate the carb from the cylinder.
Before that happens, the carb bore size is limiting potential hp by restricting airflow.
 
For maximum speed, I'd want to keep the engine where the most work is being done, assuming there was still enough hp there to keep the whole assembly at speed.... Typically, as high an RPM as I can get... UNLESS I expected big RPM disruptions, then I'd favor quickest acceleration... If the breathing (carb throat too small, or bad porting, restrictor plate) or RPM (governor, drag, etc.) were artificially limiting things somehow, I'd gear accordingly.

Which, I presume, is why engine makers are always trying to make more power, and more rpm simultaneously...

EDIT: An interesting consideration for a tangent....when doing FSAE in college, one of our ideas was to use a small (relative to other teams) engine, but a big flywheel assembly with a clutch. Kind of a mechanical KERS. Our theory was to store that kinetic energy, dump it on launch from a standstill, then maintain speed with the smaller motor (and greater efficiency at less total weight.) For FSAE at the time, most teams were using 600cc motorcycle engines, but we were all limited to an airbox venturi of 35mm, or something like that.

EDIT 2: Hmmmm.....I wonder why nobody's made a clutched flywheel....basically a huge drum clutch that had no gearset....would allow for quicker acceleration, but also retain flywheel effect when/where needed...
 
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1597237487698.png

For reference... Kartpartsdepot is wondering why its' site traffic blew up...lol
 
Ted Hamilton said:
EDIT 2: Hmmmm.....I wonder why nobody's made a clutched flywheel....basically a huge drum clutch that had no gearset....would allow for quicker acceleration, but also retain flywheel effect when/where needed...
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I was dreaming of this when we ran a stock appearing restricted flathead class on a larger track with only 3 rules.
stock appearing 5 hp briggs
stock 5 hp flywheel
proper restrictor plate.

Guess which 2 rules were always being broken.

They moved go karts to an extremely small track, and engine power basically went out the window.

lol
 
alvin l nunley said:
EDIT 2: Hmmmm.....I wonder why nobody's made a clutched flywheel....basically a huge drum clutch that had no gearset....would allow for quicker acceleration, but also retain flywheel effect when/where needed...
Click to expand...
Are you talking about the engine flywheel? How would that affect the timing?
 
Your gonna want the squirrel emoji for this one .
James watt , the world recognized horsepower founder .
So if you have two horses a draft horse and a quarter horse . They are going too do two different types of work . One is high torque , one is high horsepower .
The draft horse can pull a heavy load slowly a long distance , where the quarter horse can pull it for a short distance quickly .
Then the quarter horse can haul a bag of mail a long distance quickley , where the draft horse can haul the same mail but at a much slower pace
 
^^ I used to manage 34 horses. You think sitting sideways in 3-4 is scary? I played tag with a trained horse....takes some brass ones to not cower when its' the horses turn to tag you... (he used his nose.) Now that I'm working a "normal" job, I tell people, "In the horse world, at least I could SEE the manure..." And all the work those horses did were 1 hp. (each.) But I've been stepped on by draft horses and quarter horses, and I'd rather have the quarter. The above analogy would've been better with a quarter horse and a thoroughbred... Cowboys like the brute strength of the quarter, mixed with its' agility, vs. the fast but fragile thoroughbreds.
 
alvin l nunley said:
You could be right Pete, but then what is the graph showing us? Is that an 02 censor reading? Flow reading? I really don't know. I didn't read the whole article, does it explain in there?
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O2, I'm sure... maybe lambda (wideband O2), since there appears to be a good amount of detail in the A/F trace.

The graph is showing air/fuel ratio, not fuel flow.

PM
 
95 shaw said:
You are correct, Pete.
The engine actually leans out, then goes rich well after peak horsepower.
I think this is a component of loss of control of the valvetrain. ie intake valve bounce during compression stroke disrupting carb fuel signal.
This is not a problem for 2 strokes as the crankcase and reeds isolate the carb from the cylinder.
Before that happens, the carb bore size is limiting potential hp by restricting airflow.
Click to expand...

To me (admittedly far more experience with 2-strokes than 4-strokes), it does appear that something dramatic happens at about 4900 revs. Have you seen intake valves bounce on the upstroke after closing? If so, this must be a function of something other than purely valve spring force, yes?

Btw: reeds on a 2 stroke don't really isolate the carb from the crankcase, as there are parts of the rev range will reeds will never fully close. Nowhere near the positive control of a rotary valve, or well-designed valve train.

Is there any place on these engine where a strobe could be used (on a dyno) to study what's going on with the valves up there at the top end?

PM
 
Pete_Muller said:
To me (admittedly far more experience with 2-strokes than 4-strokes), it does appear that something dramatic happens at about 4900 revs. Have you seen intake valves bounce on the upstroke after closing? If so, this must be a function of something other than purely valve spring force, yes?

Btw: reeds on a 2 stroke don't really isolate the carb from the crankcase, as there are parts of the rev range will reeds will never fully close. Nowhere near the positive control of a rotary valve, or well-designed valve train.

Is there any place on these engine where a strobe could be used (on a dyno) to study what's going on with the valves up there at the top end?

PM
Click to expand...
Yes
Smokey Yunick did a lot of research on the subject using a tool he invented, which he called the Spintron. Hysterisis, was the word he used to describe the actions of the valve train during these events.

Harmonics, camshaft design,(valve closing ramps), weight of components, and valve spring pressures all play a role in this.
Keep in mind, this is a mass produced industrial engine, designed to turn 3600 rpm max, that can be bought for $99 when on sale at Harbor Freight.
The spirit and intent of the class is to use this item "out of the box" for a racing power plant.
 
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