pulley discussion - Jeep Commander Forums: Jeep Commander Forum
Performance Modifications If you plan to modify your Jeep Commander, tell us about it in here.

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 33 (permalink) Old 10-01-2008, 05:33 PM Thread Starter
Senior Member
Points: 4,505, Level: 42 Points: 4,505, Level: 42 Points: 4,505, Level: 42
Level up: 78% Level up: 78% Level up: 78%
Activity: 0% Activity: 0% Activity: 0%
 
Join Date: Apr 2008
Posts: 282
pulley discussion

hasnt been a new post here in a while so i figured id start one. had an underdrive pulley for my civic and noticed my engine was more responsive. currently have an udp on my 6cyl altima and noticed the difference. my xk has much more electronic bs than the two other cars and id prefer to keep the same diameter. would the weight from the iron pulley to the aluminum make that much of a difference? 2 to 3 lbs compared to 15 to 20. ive seen the kits for the other hemis, but not specifically the xk. new to the pushrod world so feel free to discuss the harmonic balancer issue also.
tripod is offline  
Sponsored Links
Advertisement
 
post #2 of 33 (permalink) Old 10-01-2008, 07:48 PM
Senior Member
Points: 11,816, Level: 71 Points: 11,816, Level: 71 Points: 11,816, Level: 71
Level up: 42% Level up: 42% Level up: 42%
Activity: 0% Activity: 0% Activity: 0%
 
robby's Avatar
 
Join Date: Jun 2008
Location: Desplaines IL.
Posts: 3,262
It is not so much the difference in inertia as it is the reduced crank load due to the underdrive.
A graphic example would be, Stock pully is say the same diameter as all driven pullys (it isn't, this is an example). So, for every full turn of the crankshaft, every belt driven accessory also makes one full turn.
Now, the example becomes the underdrive crank pully and this time we'll visualize it as 1/2 the diameter of the original pully.
Now, for every full turn of the crankshaft, each belt driven accessory only turns 1/2.
So, you have doubled the mechanical advantage the crank has on the driven accessories, and it becomes that much easier for the engine to overcome the drag of the belt driven accessories.
Your small displacement, low torque engines in your past cars would show a rather dramatic response to this mod.
Low R.P.M. high torque v-8s don't show a lot of improvement as they have little trouble overcoming parasitic drag like this.
And since they are low operating R.P.M. engines, usually there are more downsides along the lines of poor a/c output, low amperage output, poor power steering response, etc. at low speeds.
And of course, if you're ever off road, you're not going 50 M.P.H. (I hope)
The Vibration Damper absorbs torsional vibration ringing through the crankshaft and prevents work hardening and ultimatly cracking of the casting/forging.
If there is a underdrive pully available, this would be incorporated into it.

Believe it or not, that was a short answer,
..........Rob
robby is offline  
post #3 of 33 (permalink) Old 10-01-2008, 07:55 PM Thread Starter
Senior Member
Points: 4,505, Level: 42 Points: 4,505, Level: 42 Points: 4,505, Level: 42
Level up: 78% Level up: 78% Level up: 78%
Activity: 0% Activity: 0% Activity: 0%
 
Join Date: Apr 2008
Posts: 282
not looking to reduce the diameter, just wondering if the the same size pulley, but in a lighter material would be beneficial. alt/pwr stering/crank. the whole rotational mass idea
tripod is offline  
 
post #4 of 33 (permalink) Old 10-01-2008, 08:20 PM
Senior Member
Points: 11,816, Level: 71 Points: 11,816, Level: 71 Points: 11,816, Level: 71
Level up: 42% Level up: 42% Level up: 42%
Activity: 0% Activity: 0% Activity: 0%
 
robby's Avatar
 
Join Date: Jun 2008
Location: Desplaines IL.
Posts: 3,262
Well then, I can't imagine a change in inertia for that diameter would be very benificial on a V-8.
Let me try to explain.
Lets say we have a 20 lb sleeve that has 1/4 inch wall thickness and is 3 ft long.
Visualize it as a pipe attached to the crank snout pointed forward inline with the crank.
Now, we start the engine and with wide open throttle, see how long it takes to reach 6000 R.P.M. It generally takes a bit more than 1 second to accelerate the crank to that speed.
OK, now we exchange our sleeve with one that only weighs say,5 lbs, but is dimensionally the same.
We perform the same crankshaft acceleration process.
So now we find it took only 1 second flat to hit 6000 r.p.m.
Not much change for a 15 lb reduction.
Similar results will be obseved with a lighter crank pully only because the diameter is comparatively speaking, not very large and the high torque production has no problem overcoming any pullys inertial moment.
Now, if our discussion involved a manual transmission and aluminum verses iron flywheels,
well, thats where the much larger diameter and weight reduction of aluminium would be very noticeable.

Am I doing any good here or am I just muddying the water more?
........Rob
robby is offline  
post #5 of 33 (permalink) Old 10-01-2008, 08:34 PM
Senior Member
Points: 11,816, Level: 71 Points: 11,816, Level: 71 Points: 11,816, Level: 71
Level up: 42% Level up: 42% Level up: 42%
Activity: 0% Activity: 0% Activity: 0%
 
robby's Avatar
 
Join Date: Jun 2008
Location: Desplaines IL.
Posts: 3,262
I have to apologize Tripod,
As I read my responses and your question, I have gone into way more detail then you may have been looking for.
Anyways, what I'm trying to say is, you probably will experience no change beyond a lighter wallet with this mod

Again, sorry for hyperdetailing,
Rob
robby is offline  
post #6 of 33 (permalink) Old 10-01-2008, 08:35 PM
Points: 6,704, Level: 53 Points: 6,704, Level: 53 Points: 6,704, Level: 53
Level up: 77% Level up: 77% Level up: 77%
Activity: 0% Activity: 0% Activity: 0%
 
Join Date: Oct 2005
Posts: 1,397
Quote:
Originally Posted by tripod View Post
not looking to reduce the diameter, just wondering if the the same size pulley, but in a lighter material would be beneficial. alt/pwr stering/crank. the whole rotational mass idea
The benefit would be nearly nothing. Not even measureable. As Robby pointed out, the benefit is in having your accessories underdriven. That's why they call them underdrive pulleys.
TR4Runner is offline  
post #7 of 33 (permalink) Old 10-01-2008, 09:04 PM
Senior Member
Points: 15,238, Level: 79 Points: 15,238, Level: 79 Points: 15,238, Level: 79
Level up: 78% Level up: 78% Level up: 78%
Activity: 0% Activity: 0% Activity: 0%
 
adamag25's Avatar
 
Join Date: Jul 2008
Location: Northwest Central Jersey
Posts: 2,629
Adding a ture underdrive pulley (smaller) will affect the alternator performance right?

Bright Silver 4.7L 2.25 RR/OME lift, Kumho KL71 265/70/17, Flashpaq, Lights, rack, intake, Super44, mopar skids, 4x belly guard, rear fog lights, MM9500 winch, GetLost4x4 winch mount

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

HILLBILLY DELUXE
adamag25 is offline  
post #8 of 33 (permalink) Old 10-01-2008, 09:30 PM
Senior Member
Points: 11,816, Level: 71 Points: 11,816, Level: 71 Points: 11,816, Level: 71
Level up: 42% Level up: 42% Level up: 42%
Activity: 0% Activity: 0% Activity: 0%
 
robby's Avatar
 
Join Date: Jun 2008
Location: Desplaines IL.
Posts: 3,262
Yes, less output at a given engine R.P.M.
.........Rob
robby is offline  
post #9 of 33 (permalink) Old 10-01-2008, 10:01 PM
Senior Member
Points: 11,210, Level: 69 Points: 11,210, Level: 69 Points: 11,210, Level: 69
Level up: 90% Level up: 90% Level up: 90%
Activity: 0% Activity: 0% Activity: 0%
 
CrzCajun's Avatar
 
Join Date: Jan 2007
Location: Northern Virginia
Posts: 2,789
Correct me if I'm wrong robby, but those pulleys are usually used for racing because of the high rpms that the engine turns. If the alternator turns too fast too many times, it could ruin it. At least that's what I've always been taught.
CrzCajun is offline  
post #10 of 33 (permalink) Old 10-01-2008, 11:15 PM Thread Starter
Senior Member
Points: 4,505, Level: 42 Points: 4,505, Level: 42 Points: 4,505, Level: 42
Level up: 78% Level up: 78% Level up: 78%
Activity: 0% Activity: 0% Activity: 0%
 
Join Date: Apr 2008
Posts: 282
just playing devils advocate. With the lighter materials, in theory the engine would be more efficient possibly getting better mileage, as well as being more responsive. that 6000 rpm over 5 gears and tenth/s of a second each gear would add up? if we keep discussing this someone will buy a set and let us know. Would the pulleys synergize additional bolt ons also cai, chip, exhaust?
tripod is offline  
Sponsored Links
Advertisement
 
Reply

  Jeep Commander Forums: Jeep Commander Forum > Jeep Commander Discussion > Performance Modifications

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Jeep Commander Forums: Jeep Commander Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome