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VRA National President
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Discussion Starter #1
I have Hard Krome Big Straights on my 800A. Their LOUD and they're higher-pitched than most other pipes I've heard. I like them but the neighbors don't so I tend to keep the rpms low when I'm riding especially when people are riding behind me.

My question is this... I've been told that giving a handful of throttle at very low rpms is hard on the motor. Is that true?
 

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VRA National President
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Discussion Starter #2
I've been studying a graph from my aftermarket kits booklet and thanks to WoodChucks800, I've got rpm numbers to reference. I'm just talking out loud here as I figure this through so bear with me....



The trio of horizontal lines shows the torque and the trio of long 45 degree lines depicts the horsepower. (the lower, middle and top line of each set are for stock, pipes and jetting, and thunder kit respectively) The bottom numbers of the graph are RPMs (x 1000)

With a stock gearing setup, an 800A is spinning 2750 rpm at 45 mph in 5th gear. At that speed, I still had ample pull. At 40 mph in 5th gear, the engine felt dogged and roll-on power was all but absent and felt like it was "bad on the motor" to give it a lot of throttle. 40mph is only 2500 rpm.

I'm thinking that it takes more power to accelerate in 5th than it does in 4th or lower so the motor wouldn't be working nearly as hard to accelerate quickly at 2500 rpm in 1st gear as it would in 5th gear.

I think this is going to end up bringing up the age-old horsepower vs torque thing... According to the graph, I have around 40 footpounds of torque available at as low as 2000 rpm. Under 2000 rpm, the torque falls off considerably. This would presume that I have the same "pulling power" at 2000 rpm that I have at 2750rpm. 2000 rpm in 5th gear is 30mph. There ain't no way that I have any pulling power at 30mph in 5th gear!

So now I look at Horsepower and see that it's incrementally higher as the rpms increase. This is what I get from the graph:

50 mph = 3000 rpm = 31 horsepower = 44 footpounds of torque
45 mph = 2750 rpm = 28 horsepower = 43 footpounds of torque
40 mph = 2500 rpm = 25 horsepower = 42 footpounds of torque
35 mph = 2250 rpm = 20 horsepower = 41 footpounds of torque
30 mph = 2000 rpm = 17 horsepower = 39 footpounds of torque

My bike weighs around 600 lbs and I weigh about 175 lbs so we'll figure the motor is trying to push 800 lbs. Apparently, you need at least 25 horsepower to push 800 lbs. Any less horsepower and I guess it would be like hooking two donkeys up to a tractor trailer and making them pull it - they'd pull a muscle trying.

Gearing reduces work so althogh 20 horsepower isn't enough to push 800 lbs of weight, the gearing reduces the perceived weight so I guess you're motor feels like it's only pushing like 200 lbs in 1st gear.

Alright, I think I understand horsepower and I think I understand why giving her a handful of throttle at too low of an rpm is bad for the motor - too little muscle pushing too much weight will like make pistons do bad things. (Can you tell I'm not a mechanic? :eek: )

So since I'm on a roll, where does torque come into play in this scenario?
:?:
 

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AZ's Official Mechanic
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as long as your not LUGGING the motor your not hurting a dam thing. ill keep my comment to myself about your "hardley wanna-be pipes" :wink:
 

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Horsepower is the amount of torque at a cetain rpm.

HP = (Torque * RPM)/5252

or something like that :idea:

Thats why we look at HP on high revving motors ie sportsbikes and we look at torque on low revving cruisers. If two bikes had identical perfectly flat torque curves and 1 redlined at 5000 rpm while the second redlined at 10,000, the second bike would have twice the HP, but they'd both have the same torque. At least this is my understanding.

Phatboy
 
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