nemss1
Full Access Member
Looking to increase gas mileage and free up power
What companies make headers and underdrive pullies for the KJ...???
- Thread starter nemss1
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kjweston
Full Access Member
JBA makes headers. idk about underdrive pulleys
heres the link
http://jeepinbyal.com/prod-JBA_Performance_Headers-652.aspx
heres the link
http://jeepinbyal.com/prod-JBA_Performance_Headers-652.aspx
nemss1
Full Access Member
Thanx for the link
kjweston
Full Access Member
no prob
Powerslave
Banned
I haven't seen any Underdrive pulleys for it. I know there are headers, saw them.
Ahh, here they are, nothing a little Google can't find: Crankshaft Pulley, Serpentine, 5-Groove Aluminum Nitride, for Dodge/Jeep, 3.7/4.7L, Each: $285.39 - Kind of steep! http://www.summitracing.com/parts/ASP-501150/
http://www.lmgtfy.com/?q=jeep+3.7+underdrive+pulley
Ahh, here they are, nothing a little Google can't find: Crankshaft Pulley, Serpentine, 5-Groove Aluminum Nitride, for Dodge/Jeep, 3.7/4.7L, Each: $285.39 - Kind of steep! http://www.summitracing.com/parts/ASP-501150/
http://www.lmgtfy.com/?q=jeep+3.7+underdrive+pulley
sleeve
Full Access Member
Question:
Will an underdriven accessory system really free up power? Or would the KJ's computer compensate for the slower moving alternator by upping the idle to maintian proper charge?
Also - I thought the computer also cut off torque output at a certain point to keep the drivetrain intact.
Not sayin it doesn't work. Just questions I have myself about the idea.
Will an underdriven accessory system really free up power? Or would the KJ's computer compensate for the slower moving alternator by upping the idle to maintian proper charge?
Also - I thought the computer also cut off torque output at a certain point to keep the drivetrain intact.
Not sayin it doesn't work. Just questions I have myself about the idea.
kb0nly
Full Access Member
Under-drive pulleys are snake oil on most vehicles. Sure they can have their place, but on these modern vehicles its not worth the cost involved to squeeze out maybe 2-3hp if your lucky. And what's worse is your not going to gain any fuel economy.
After reading on a bunch of other forums about these pulley's your just asking for trouble. Most of them are poorly made crap that vibrates because they aren't perfectly balanced, and many have had them crack or chip because the aluminum used for them was too soft, etc..
The alternator question is a good point.
I have noticed this... If i leave some lights on or use my radio gear for a while with the engine off when i next start it the engine will stay at that higher idle speed for much longer, i assume this is because the computer sensed the lower voltage of the battery and is running faster to top off the battery. If i don't use any accessories with the engine off and start up it usually jumps to 1000-1100 for 3-5 seconds and then drops down to 600-800 and once its warmed up it hovers around 600. However, if i turn on a bunch of accessories the idle will increase to 700-800.
So if you had an under-drive pulley on the alternator the computer would sense the lower voltage and increase the engine speed to compensate.
After reading on a bunch of other forums about these pulley's your just asking for trouble. Most of them are poorly made crap that vibrates because they aren't perfectly balanced, and many have had them crack or chip because the aluminum used for them was too soft, etc..
The alternator question is a good point.
I have noticed this... If i leave some lights on or use my radio gear for a while with the engine off when i next start it the engine will stay at that higher idle speed for much longer, i assume this is because the computer sensed the lower voltage of the battery and is running faster to top off the battery. If i don't use any accessories with the engine off and start up it usually jumps to 1000-1100 for 3-5 seconds and then drops down to 600-800 and once its warmed up it hovers around 600. However, if i turn on a bunch of accessories the idle will increase to 700-800.
So if you had an under-drive pulley on the alternator the computer would sense the lower voltage and increase the engine speed to compensate.
sleeve
Full Access Member
Sorry to pester - but did you buy the pulley kit?
I am actually curious about the performance change now that I've been thinking about this for a few more days.
Edit: Did some searching and found a couple threads on LOST:
Looks like someone tried them long ago
Another person who experiemented
Not too much information on them, but given the previous history and the fact that no one seems to use them regularly it must not have been a popular choice.
I am actually curious about the performance change now that I've been thinking about this for a few more days.
Edit: Did some searching and found a couple threads on LOST:
Looks like someone tried them long ago
Another person who experiemented
Not too much information on them, but given the previous history and the fact that no one seems to use them regularly it must not have been a popular choice.
Last edited:
Powerslave
Banned
The underdrive pulley would be the Crank pulley, and if; an alternator pulley. BASICALLY, you are essentially changing the gears for the devices being driven by your engine in order for the engine to do less work. The underdrive pulley kit replace your stock pulley(s) with larger pulley(s). Less work for your engine (freeing up power lost to parasitic drag) = more work it can do on moving your car. It does not ADD any more HP, just requires less work for the engine. You will need a new serpentine belt too, it will have to be slightly larger. When you buy a pulley kit for your engine, they usually have a part# for which belt to use. If they cannot find a belt, or can't get the slack from backing off a tensioner, then they probably won't make the UD pulley for that motor.
HP is robbed in so many places, that's called parasitic drag; especially an automatic. Auto transmissions eat about 20-30HP, and your accessory pulleys about 3-5 to as high as 12. As stated, you may not notice a difference, they do not make a difference on some vehicles. The ECM doesn't play a role in it, so nothing will change or re-compensate. These jeeps are what? 4800 - 5000 pounds? It may not be noticeable, but still may help with MPG. If you are looking for that "every little bit adds up" kind of mod, then its for you...
A 5.0 Mustang can get an easy 15HP freed up for less than $100, and installed in under one hour. This was a crank pulley, and alternator pulley.
I drove a Dodge avenger with just the UD Crank pulley, and could feel the difference compred to mine.
HP is robbed in so many places, that's called parasitic drag; especially an automatic. Auto transmissions eat about 20-30HP, and your accessory pulleys about 3-5 to as high as 12. As stated, you may not notice a difference, they do not make a difference on some vehicles. The ECM doesn't play a role in it, so nothing will change or re-compensate. These jeeps are what? 4800 - 5000 pounds? It may not be noticeable, but still may help with MPG. If you are looking for that "every little bit adds up" kind of mod, then its for you...
A 5.0 Mustang can get an easy 15HP freed up for less than $100, and installed in under one hour. This was a crank pulley, and alternator pulley.
I drove a Dodge avenger with just the UD Crank pulley, and could feel the difference compred to mine.
sleeve
Full Access Member
I fully understand what undriving the accessory system does. I've owned 2 Fox Body Mustangs, A SN98 and a F-body.
I suppose what I should ask is: Does anyone have actual user experience with the UD kit? I want to know what problems / benefits it might cause to the KJ if possible.
I still believe that the computer systems in the KJ will compensate for lower than normal alternator ouput by increasing idle. Which is why I'm looking for real world experience... And no, I am not going to put a UD pulley kit on the KJ.
I suppose what I should ask is: Does anyone have actual user experience with the UD kit? I want to know what problems / benefits it might cause to the KJ if possible.
I still believe that the computer systems in the KJ will compensate for lower than normal alternator ouput by increasing idle. Which is why I'm looking for real world experience... And no, I am not going to put a UD pulley kit on the KJ.
Don't spend a lot trying to increase mileage. If you can't at least double your mileage (which will never happen-- not even close) it'll take you forever to recover your investment.
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