The need to change Acc. Torque with pulley swap...
10-01-2005, 06:22 PM
#1
The need to change Acc. Torque with pulley swap... Let me know if this makes sense to you all and if anyone has done it. Ok so lets say you just change out your crank pulley to keep thing simple. The size of the pulley is smaller now so the accesory torque seen from the motor will now be less. I need to take measurements of the stock and March pulleys for accurate numbers but lets say that the stocker is 8 inches in diameter and the aftermarket one is 6 inches in diameter.
if you look at the moment the force from the belt would put on the pulley with the stock one it would be F*4=torque in inch lbs, the aftermarket one would be F*3=torque in inch lbs. Since the torque of the accessories remains constant, given that you didnt change any other pulleys, then the torque that the crank sees will be reduced by 25%.
What I am getting at here is, shouldn't all the engine torque settings, including AC, be multiplied by 0.75 to get the proper settings now? This should help give the motor a better chance at making calculations. What do you guys think? Are there any voltage tables for the alt that need to be altered as well. I cannot think of any off the top of my head. That may help problems at idle from electrical loading.
REMEMBER THAT THOSE NUMBERS ARE MADE UP AND NOT ACCURATE, SO IF YOU TRY THIS DO NOT USE THE NUMBERS I DID. SIMPLY TAKE THE STOCK RADIUS AND DIVIDE BY THE NEW RADIUS FOR THE FACTOR.
if you look at the moment the force from the belt would put on the pulley with the stock one it would be F*4=torque in inch lbs, the aftermarket one would be F*3=torque in inch lbs. Since the torque of the accessories remains constant, given that you didnt change any other pulleys, then the torque that the crank sees will be reduced by 25%.
What I am getting at here is, shouldn't all the engine torque settings, including AC, be multiplied by 0.75 to get the proper settings now? This should help give the motor a better chance at making calculations. What do you guys think? Are there any voltage tables for the alt that need to be altered as well. I cannot think of any off the top of my head. That may help problems at idle from electrical loading.
REMEMBER THAT THOSE NUMBERS ARE MADE UP AND NOT ACCURATE, SO IF YOU TRY THIS DO NOT USE THE NUMBERS I DID. SIMPLY TAKE THE STOCK RADIUS AND DIVIDE BY THE NEW RADIUS FOR THE FACTOR.
10-02-2005, 09:58 AM
#4
The torque for the alternator doesn't directly depend on pulley size, but on the current it's drawing. The current draw should stay the same with a smaller pulley unless it's turning so much slower that the voltage regulator can't compensate (for most of us it's not).
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10-02-2005, 11:29 AM
#8
its torque seen by the crank, if you change the pulley out then the motor will see less torque from the ac. so it does need to be changed. think of it like a mountain bike. the rear gear stays fixed and you use the big one at the pedals, its hard to pedal, put it to the smaller gear, you feel less torque from the same fixed wheel and its easier to turn, the motor acts the same way and needs to know this.
i just got dont doing it. the dynamic airflow line has smoothed out considerable, dont know if its related or not but i did notice its a lot smoother. the rom recovery before was good but there was maybe 50 rpm over or under shoot at times and now that is not there. the airflow values didnt change. it seems smoother but that may all be in my head...which it prob is lol. whenever i go out on a ride next ill see how it and if it effects anything while cruising.
i just got dont doing it. the dynamic airflow line has smoothed out considerable, dont know if its related or not but i did notice its a lot smoother. the rom recovery before was good but there was maybe 50 rpm over or under shoot at times and now that is not there. the airflow values didnt change. it seems smoother but that may all be in my head...which it prob is lol. whenever i go out on a ride next ill see how it and if it effects anything while cruising.
10-02-2005, 11:42 AM
#9
I understand how torque multiplication works. It will see less torque from the ac, but since the ac is then turning slower it is then putting out less pressure. Since the table is torque vs pressure, it's already compensated for.
Your mountain bike analogy doesn't hold up because when you switch gears on a mountain bike the steepness of the hill doesn't change. When you change the size of the pulley, the pressure does change.
Your mountain bike analogy doesn't hold up because when you switch gears on a mountain bike the steepness of the hill doesn't change. When you change the size of the pulley, the pressure does change.
10-02-2005, 12:22 PM
#10
ok well i was refering to the accessories not the ac with that one, just for those that dont understand what i was meaning, not directed towards your previous comment. i see your point on the ac pressure, im sure it will change but it wont be as simple as a multiplication factor. i wonder if the table could use some more work, since the acc dont spin at the same rate im sure there is a difference right there as well. since they spin at a reduced rate like you said. might just need to find the rpm shift, move the cell and then do that. i think this is something that would help out for ac tuning more than with the ac off. im gonna think about what you said more and see if i cant find a way to relate the change in speed as well
10-02-2005, 12:28 PM
#11
You're right, i kind of simplified it because ac pressure isn't just based on pulley speed. But changing the pulley radius 25%, the changes to the ac torque vs pressure table would be much smaller than 25%, so I think the simplification is valid.
Anyway, I still don't see where these changes will show the effect. Somehow it should show up in an airflow value, but it seems like the airflow calcs only come from the raf tables, ac adder, fans adder, and trims.
I guess the proper way to tune the ac torque table would be trial by error until the stit doesn't change when you turn the ac on. I have no idea on the accesory drag though.
Anyway, I still don't see where these changes will show the effect. Somehow it should show up in an airflow value, but it seems like the airflow calcs only come from the raf tables, ac adder, fans adder, and trims.
I guess the proper way to tune the ac torque table would be trial by error until the stit doesn't change when you turn the ac on. I have no idea on the accesory drag though.
10-02-2005, 04:11 PM
#12
i just did a quick interpolation because the speed of acc will slow 25% as well. so i found the torques if the einger speed was 100 rpm less, since its in increments of 400. dont know how much this will help if it will even matter, its just peace of mind i guess knowing its set up for what it see. maybe be seen better on a stock car that the airflow stays more consistent. i dont have continual logs of my car to where i can tell a difference in airflow. ill post up my acc table if someone want to try and see if they can see a difference, but p mack your prob right, does a whole lotta nothing lol. main test would be to see for ac torque seeing that will be effected a lot more since those numbers are higher. maybe cause the acc are low torque as it is, only about 3-5 N-m where teh ac is over double that or higher
10-02-2005, 04:12 PM
#13
p mack, how did you take the pressure table? does that have to deal with line pressure? line pressure should be constant AFAIK. as long as there is the right amount of ref in the system the speed of the compressor wont matter. at least that is what i saw in testing i did over the summer at IR with dryer testing in the labs. i may be thinking of it wrong so let me know
