Drivability + Reliability = Fun Factor
Dec 22, 2005 | 03:25 AM
#1
Thread Starter
|
Pro Rider
Joined: Dec 2001
Posts: 400
Likes: 0
Drivability + Reliability = Fun Factor
Drivability + Reliability = Fun Factor
I would like to present an overview of atv modifications.
Upon buying an atv we become overwhelmed with the need for speed.
We come to the conclusion that if a few mods increase our fun factor, then more is better.
Some of us buy parts from a retailer. We liked the words in the catalog and ordered them because the kid behind the counter said that they would make your machine fly.
You install the parts or have this local retailer do the installation. You take the machine out for a ride and notice that even though it seems to run better on the top end, the bottom is real bad. You race your friend and he beats you so bad off the line, that by the time you catch up with him, the race is over. You wonder what is wrong.
You go to the local retailer or retailers and his(their) answer is that you need to buy some more additional parts. You buy additional parts and things just get worst.
Your Fun Factor is very low because your Drivability is low. You slip the clutch a lot to try to have better takeoff and then find the need to replace it. You have to rev the motor to the moon to win a race. Then one day all hell breaks loose. The motor just eat itself up. Reliability was not there and now you have a disaster. Many guys end up selling their quads and state that quads are money pits.
DO NOT GET CAUGHT IN THIS SCENARIO.
When you have to open the motor up to enhance its performance, do it around your driving conditions. Build the motor to fit your Drivability requirements.
If you plan and execute correctly you will have Reliability.
Thus with Drivability and Reliability, you will have enhanced your Fun Factor.
Motor Mods
Every motor has two features that control its power output.
First is cylinder head flow, measured in terms of cubic feet per minute.
Second is piston speed, measured in terms of feet per minute.
The stock head flows around 250 –260 cfm. This is equivalent to roughly 55-60 hp.
45/46mm carb, endcap, 11 piston and mid cam. 8200rpm 4400fpm
Mild port job to flow 275cfm. 65hp
45/46mm carb, better exhaust, 12.5 piston and mid/top cam 9000 4900fpm
725/730 kit Port to flow 300cfm 70hp
48mm carb, better exhaust, 12.5 piston and mid/top cam 9000 4900fpm
Motors that exceed 5000fpm are better suited for race only.
14 to one pistons are also for race only. I know they are being used for non race but that’s my opinion. My mods above are only training quidelines.
When you see a dyno chart of a stock head with a big cam, note that for a few horses how much torque he gave up. Head flow and cam have to be balanced to achieve the broadest torque and hp curve. This width is what is referred to as acceleration output.
Good engine builders do not like peaky motors. Highest hp may not have good acceleration. You will note I think the big bore kits are a natural for high hp and reliability. Pay me now or pay me latter
OMR
I would like to present an overview of atv modifications.
Upon buying an atv we become overwhelmed with the need for speed.
We come to the conclusion that if a few mods increase our fun factor, then more is better.
Some of us buy parts from a retailer. We liked the words in the catalog and ordered them because the kid behind the counter said that they would make your machine fly.
You install the parts or have this local retailer do the installation. You take the machine out for a ride and notice that even though it seems to run better on the top end, the bottom is real bad. You race your friend and he beats you so bad off the line, that by the time you catch up with him, the race is over. You wonder what is wrong.
You go to the local retailer or retailers and his(their) answer is that you need to buy some more additional parts. You buy additional parts and things just get worst.
Your Fun Factor is very low because your Drivability is low. You slip the clutch a lot to try to have better takeoff and then find the need to replace it. You have to rev the motor to the moon to win a race. Then one day all hell breaks loose. The motor just eat itself up. Reliability was not there and now you have a disaster. Many guys end up selling their quads and state that quads are money pits.
DO NOT GET CAUGHT IN THIS SCENARIO.
When you have to open the motor up to enhance its performance, do it around your driving conditions. Build the motor to fit your Drivability requirements.
If you plan and execute correctly you will have Reliability.
Thus with Drivability and Reliability, you will have enhanced your Fun Factor.
Motor Mods
Every motor has two features that control its power output.
First is cylinder head flow, measured in terms of cubic feet per minute.
Second is piston speed, measured in terms of feet per minute.
The stock head flows around 250 –260 cfm. This is equivalent to roughly 55-60 hp.
45/46mm carb, endcap, 11 piston and mid cam. 8200rpm 4400fpm
Mild port job to flow 275cfm. 65hp
45/46mm carb, better exhaust, 12.5 piston and mid/top cam 9000 4900fpm
725/730 kit Port to flow 300cfm 70hp
48mm carb, better exhaust, 12.5 piston and mid/top cam 9000 4900fpm
Motors that exceed 5000fpm are better suited for race only.
14 to one pistons are also for race only. I know they are being used for non race but that’s my opinion. My mods above are only training quidelines.
When you see a dyno chart of a stock head with a big cam, note that for a few horses how much torque he gave up. Head flow and cam have to be balanced to achieve the broadest torque and hp curve. This width is what is referred to as acceleration output.
Good engine builders do not like peaky motors. Highest hp may not have good acceleration. You will note I think the big bore kits are a natural for high hp and reliability. Pay me now or pay me latter
OMR
Dec 23, 2005 | 11:44 AM
#2
Thread Starter
|
Pro Rider
Joined: Dec 2001
Posts: 400
Likes: 0
Drivability + Reliability = Fun Factor
Torque Versus Speed
All 4-cycle engines running on gasoline without supercharging, tend to develop approximately the same maximum torque per cubic inch of displacement. This number is approximately 1.35 to 1.55 lb-ft of torque per cubic inch of displacement (about 110 to 130 Nm per liter). This can also be expressed as a BMEP of 200 to 230 psi (1380-1590 kPa).
Despite the best efforts of engine builders over the past 20 years, nothing has improved this number appreciably. (Again, this number is valid only for 4-cycle engines without supercharging running on gasoline, no matter what the size.)
A more telling determinate of power is stroke. The speed at which an engine develops its engine power is usually determined by the stroke. Typically, maximum power is developed when the average piston speed is between 4,000 and 4,500 ft/minute (20 to 23 meters/second).
Because power is equal to torque multiplied by speed divided by a constant (HP = lb-ft x speed / 5,252 or kW = Nm x speed / 9549), and because the maximum torque for a given displacement is constant, the power per cubic inch is directly proportional to engine speed. Since engine maximum speed is inversely proportional to engine stroke, the shorter the stroke, the more power per cubic inch the engine can develop.
As a case in point, an engine with a 3-inch (76 mm) stroke will develop maximum power at approximately 8,000 rpm, while an average engine with a 1.5-inch (38 mm) stroke will develop maximum power at approximately 16,000 rpm. While the maximum torque per cubic inch will be exactly the same for both engines, the maximum power per cubic inch will be twice as great for the shorter stroke engine.
All 4-cycle engines running on gasoline without supercharging, tend to develop approximately the same maximum torque per cubic inch of displacement. This number is approximately 1.35 to 1.55 lb-ft of torque per cubic inch of displacement (about 110 to 130 Nm per liter). This can also be expressed as a BMEP of 200 to 230 psi (1380-1590 kPa).
Despite the best efforts of engine builders over the past 20 years, nothing has improved this number appreciably. (Again, this number is valid only for 4-cycle engines without supercharging running on gasoline, no matter what the size.)
A more telling determinate of power is stroke. The speed at which an engine develops its engine power is usually determined by the stroke. Typically, maximum power is developed when the average piston speed is between 4,000 and 4,500 ft/minute (20 to 23 meters/second).
Because power is equal to torque multiplied by speed divided by a constant (HP = lb-ft x speed / 5,252 or kW = Nm x speed / 9549), and because the maximum torque for a given displacement is constant, the power per cubic inch is directly proportional to engine speed. Since engine maximum speed is inversely proportional to engine stroke, the shorter the stroke, the more power per cubic inch the engine can develop.
As a case in point, an engine with a 3-inch (76 mm) stroke will develop maximum power at approximately 8,000 rpm, while an average engine with a 1.5-inch (38 mm) stroke will develop maximum power at approximately 16,000 rpm. While the maximum torque per cubic inch will be exactly the same for both engines, the maximum power per cubic inch will be twice as great for the shorter stroke engine.
Dec 23, 2005 | 10:51 PM
#5
Pro Rider
Joined: Mar 2001
Posts: 1,121
Likes: 0
Drivability + Reliability = Fun Factor
WOW!!!!
That is an awfull lot of formulating, calculating, and theorizing. With all that math, a person should be able to predict the exact HP and TQ #'s of any motor that could be built, even if they haven't done that type of motor before.
The problem is, as anyone that has built a motor before knows, reality seldom follows theory that closely.
The statement of "maximum torque for a given displacement is constant" would be one constant that absolutely baffeled me. I, personally, would love to hear what the maximum torque is for a 760CC motor. I'll take it as a personal challenge to excede that #, if I haven't already.
Durring the hundreds of hours I've spent on dyno's, with many different configurations of DS motors, I've proven quite a few "theories" to not hold water.
While I disagree with the logic [for lack of a better word] behind your disertation/advertizement ["pay me now or pay me later"], I actually agree with the result. For generations the same thing has been said, by motor builders and hot rodders of all types. Simply stated, "THERE'S NO REPLACEMENT FOR DISPLACEMENT!"
OMR- I hope your not taking this as any type of an insult, it's not meant that way. I just want to explain to people that building power is every bit an art as it is a science.
That is an awfull lot of formulating, calculating, and theorizing. With all that math, a person should be able to predict the exact HP and TQ #'s of any motor that could be built, even if they haven't done that type of motor before.
The problem is, as anyone that has built a motor before knows, reality seldom follows theory that closely.
The statement of "maximum torque for a given displacement is constant" would be one constant that absolutely baffeled me. I, personally, would love to hear what the maximum torque is for a 760CC motor. I'll take it as a personal challenge to excede that #, if I haven't already.
Durring the hundreds of hours I've spent on dyno's, with many different configurations of DS motors, I've proven quite a few "theories" to not hold water.
While I disagree with the logic [for lack of a better word] behind your disertation/advertizement ["pay me now or pay me later"], I actually agree with the result. For generations the same thing has been said, by motor builders and hot rodders of all types. Simply stated, "THERE'S NO REPLACEMENT FOR DISPLACEMENT!"
OMR- I hope your not taking this as any type of an insult, it's not meant that way. I just want to explain to people that building power is every bit an art as it is a science.
Dec 23, 2005 | 11:33 PM
#6
Thread Starter
|
Pro Rider
Joined: Dec 2001
Posts: 400
Likes: 0
Drivability + Reliability = Fun Factor
You will note I think the big bore kits are a natural for high hp and reliability. Pay me now or pay me latter.
What I ment by this statement was that to exceed 65hp and have reliability it would be better to spend the extra money now for a 725/730 big bore, rather than spend the money to repair the 650 after it has blown from over revving. I wrote this in the middle of the night and I have enough problems having clarity in the middle of the day.
What I ment by this statement was that to exceed 65hp and have reliability it would be better to spend the extra money now for a 725/730 big bore, rather than spend the money to repair the 650 after it has blown from over revving. I wrote this in the middle of the night and I have enough problems having clarity in the middle of the day.
Thread
Thread Starter
Forum
Replies
Last Post
ATVC Correspondent
Polaris Side by Sides
1
Sep 15, 2015 03:33 AM
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)