I had a friend with me at FFW last Sunday. He just purchased an 02 Harley. We went by LFP's booth and he bought a lower pulley from Mark. He wants to go to 10lbs. of boost (from the stock Harley's six). I told Mark we wanted a four pound lower and he said because of the larger size of the Harley top pulley that we needed a Lightning six pounder to get to 10lbs. of boost. The reason he wants to do this is the same as what I'm doing on my 03 L. I am running a two pound lower (10lbs. total) so I (and he) can run the stock plugs (for now even though Sal does not like them at any boost) and if I need to, I can run without a chip installed (while it is between here and NY getting reburns and such). I need to know if Mark is correct for obviously reasons. I'm sure Mark knows what he's talking about but I noticed on JL's web site that he shows a 2 or 4 or 6 pound pulley as the same part numbers for either a Lightning or a Harley. Please help as my friend is scheduled to have the pulley installed tomorrow!


Thanks,
Jerry

 

I think he's right. It's the ratio of upper to lower that determines the boost increase.

There's a spreadsheet out there somewhere that you can plug pulley sizes into to determine the boost increase. AWHITTLE should know where it's at.

 

I never really looked at it this way................Ummmmmmm

 

Does the HD come with the same size lower pulley that the L has??

I know the HD upper is larger and thought that was how it was 6lbs stock and the L's smaller upper was 8lbs stock.

would make sence to go with a 6lb lower if your trying to reach 10lbs with the stock HD upper.

Not sure if the HD can go without a chip & plugs with a 4lb gain vs. your 2lb chipless set up though.

 

He should be able to add 4 lbs of boost without a chip. I have been running my 03 L with a 4lb and no chip for awhile now. Plenty of people run 4lb and 6 lb without a chip.

 

I would not run a 4 pounder without a chip but that's just me (Sal say's not to and that's good enough for me. Just not worth the risk unless you did a dyno pull and made sure A?F was ok). Sal said he thought running 10 lbs. of boost without a chip should be about the same as running 10 lbs. without a chip on a Lightning.

Jerry

 

Yes he is right.

The stock lower for the Harley and the Lightning are the same. Its the upper thats different size.

harleys need a 6# to get the same as the Lightning 4# if you keep the uppers stock for both.

VINNIE

 

I have dynoed it and the A/F was just fine.

 

Vinnie now you have me really confused. We are trying to get to 10 lbs. If you add a four pounder to an L, it now has 12 pounds. If Mark is right a six pounder will only add 4 pounds to the Harley giving you 10 pounds (and that is what we want). I just do not want to mess this guy's truck up!

Jerry

 

Yep...you have it right...6lb on the HD to get 10lb

 

Thanks!

Jerry

 

Harley and L both have a 7.4" lower pulley. L has 2.93" upper and Harley a 3.25" upper.

What you are concerned about is not "pulley rating numbers" as they apply to the ratios of the L lower and upper. What you are concerned about is the final ratio of the combined upper and lower.

Use this:

Lower/Upper for a ratio to compare by. Multiply times RPMS for blower speed.

For example:

7.4/2.93=2.5256 ratio on L
7.4/3.25=2.2769 ratio on H

2.5256 times 5250 = 13,259 rpms
2.2769 times 5250 = 11,953 rpms

If you are wanting your Harley to have 10lbs of boost, equating to the same 10lbs that would occur on an L, you need:

8+2 on the L... A couple of mfrs have one at 7.8" (a couple are bigger). That's 7.8/2.93 or a ratio of 2.6621 and 13976 RPMs at 5250 engine rpms.

To achieve same on the Harley, solve for X. X/3.25=2.6621. That gives you a value of 8.6518. The 4# pulleys out there are rated at 8.5" and the 6lbs are 9".... You need bigger than a 4# and smaller than a 6#.

I guess you can take it from here and make your decisions.

Just as an FYI, the assumption that because the harley starts with 2# less means that an L lower pulley of X will net X-2 lbs is completely inaccurate. You have to do the math.

**Edit**

If you really want to read about this ad nauseum, go here:

https://www.f150online.com/forums/sh...ghlight=pulley

Ken

 

All I am saying is with if both uppers are OEM then you need 2# more lower for a Harley to be equal to the lightning,

If you have a 2# then he needs a 4# to be equal.

You have a 4# then he needs a 6# and on and on.

Sorry for any confusion.

VINNIE

 

Vinnie,

Ken's point is that since the uppers are different between the L and the H, a 2# L pulley will increase an H's boost LESS than 2#.

-Edward