Calculating duty cycle based on RPM and PW
12-29-2000, 03:26 PM
#1
TGO Supporter
Thread Starter
Join Date: Jul 1999
Location: The Bone Yard
Posts: 10,907
Likes: 0
Received 3 Likes
on
3 Posts
Car: Death Mobile
Engine: 666 c.i.
Calculating duty cycle based on RPM and PW
I am looking for a formula that will calculate the % duty cycle based on the RPM and Pulse Width of the injector.
I think I have derived a formula, and I want to run it by you guys to "pick it apart".
The formula I have came up with is PW * RPM /60,000. This will give you a decimal with .5 = 50% and 1.0 = 100%.
How I came up with the constant was to figure out total Pulse width in a minute @ a given RPM. I worked on the assumption that the PW is based on the duration of firing for each revolution. Also there is 1,000 ms every second, so there is 60,000 ms in a minute.
At 6,000 rpm, and engine requires 10 ms to complete a revolution (60000/6000. Thus if my max PW @ 6,000 rpm is 10 ms.
I have done various "cross calculations" and I have related it to the standard (HP*.5BSFC)/(#Inj*%DutyCycle).
Using the above formula, and the following is the max PW @ 100% Duty Cycle for various RPMS.
RPM.....PW ms
1,000....60 ms
2,000....30 ms
3,000....20 ms
4,000....15 ms
5,000....12 ms
6,000....10 ms
I should point out, that this is if we measure PW being measured over a single revolution at a given RPM. If we measure PW every power cycle, then the constant would be 120000 (60000 x 2) and all the values about would have to be doubled.
[This message has been edited by Glenn91L98GTA (edited December 29, 2000).]
I think I have derived a formula, and I want to run it by you guys to "pick it apart".
The formula I have came up with is PW * RPM /60,000. This will give you a decimal with .5 = 50% and 1.0 = 100%.
How I came up with the constant was to figure out total Pulse width in a minute @ a given RPM. I worked on the assumption that the PW is based on the duration of firing for each revolution. Also there is 1,000 ms every second, so there is 60,000 ms in a minute.
At 6,000 rpm, and engine requires 10 ms to complete a revolution (60000/6000. Thus if my max PW @ 6,000 rpm is 10 ms.
I have done various "cross calculations" and I have related it to the standard (HP*.5BSFC)/(#Inj*%DutyCycle).
Using the above formula, and the following is the max PW @ 100% Duty Cycle for various RPMS.
RPM.....PW ms
1,000....60 ms
2,000....30 ms
3,000....20 ms
4,000....15 ms
5,000....12 ms
6,000....10 ms
I should point out, that this is if we measure PW being measured over a single revolution at a given RPM. If we measure PW every power cycle, then the constant would be 120000 (60000 x 2) and all the values about would have to be doubled.
[This message has been edited by Glenn91L98GTA (edited December 29, 2000).]
12-30-2000, 12:49 AM
#2
Supreme Member
Join Date: Jun 2000
Location: In reality
Posts: 7,554
Likes: 0
Received 1 Like
on
1 Post
Car: An Ol Buick
Engine: Vsick
Transmission: Janis Tranny Yank Converter
Originally posted by Glenn91L98GTA:
Using the above formula, and the following is the max PW @ 100% Duty Cycle for various RPMS.
RPM.....PW ms
1,000....60 ms
2,000....30 ms
3,000....20 ms
4,000....15 ms
5,000....12 ms
6,000....10 ms
Using the above formula, and the following is the max PW @ 100% Duty Cycle for various RPMS.
RPM.....PW ms
1,000....60 ms
2,000....30 ms
3,000....20 ms
4,000....15 ms
5,000....12 ms
6,000....10 ms
forra single batch fire.
SEFI just double the numbers
02-05-2007, 09:27 PM
#6
Supreme Member
iTrader: (1)
Join Date: Jan 2002
Location: garage
Posts: 4,432
Likes: 0
Received 1 Like
on
1 Post
Engine: 3xx ci tubo
Transmission: 4L60E & 4L80E
Grim Reaper,
Your math is correct. With that you can see why the SEFI can run a larger injector and not complain about idle BPW problems. One thing to note is that code like the $8D does not actually report the BPW via the ALDL that is sent to the injector. It also brings attention to what a BPW actually is........including the turn off/on time or not, voltage correction, etc.
EDIT: Wow, old post. Info above is for batch fire port injection.
Your math is correct. With that you can see why the SEFI can run a larger injector and not complain about idle BPW problems. One thing to note is that code like the $8D does not actually report the BPW via the ALDL that is sent to the injector. It also brings attention to what a BPW actually is........including the turn off/on time or not, voltage correction, etc.
EDIT: Wow, old post. Info above is for batch fire port injection.
Last edited by junkcltr; 02-05-2007 at 09:38 PM.
02-05-2007, 09:33 PM
#7
Supreme Member
iTrader: (2)
Join Date: Jan 2005
Location: Hurst, Texas
Posts: 10,041
Received 395 Likes
on
337 Posts
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Calculate it based on RPM
Let me take 6,000 rpm, it is a nice round number
With TBI you have 4 injector firings per crankshaft rotation. That is 2 per injector driver.
At 6,000 rpm the engine is turning 100 times per second
That means that you have 10 msecs per rotation.
The injector has 5 msec's per firing @ 100 % DC.
1 millisecond is equal to 1/1000th of 1 second.
Let me take 6,000 rpm, it is a nice round number
With TBI you have 4 injector firings per crankshaft rotation. That is 2 per injector driver.
At 6,000 rpm the engine is turning 100 times per second
That means that you have 10 msecs per rotation.
The injector has 5 msec's per firing @ 100 % DC.
1 millisecond is equal to 1/1000th of 1 second.
Thread
Thread Starter
Forum
Replies
Last Post
mrestrictrplate
Engine/Drivetrain/Suspension Wanted
3
09-21-2015 11:24 AM
MikkoV
TPI
2
09-09-2015 04:25 PM
60, based, calculate, calculating, calculation, calculations, cycle, duty, formula, gen, generation, pw, relating, relation, rpm, rpms
