BlairTruck

From what i have read on here in the past month about pully size is that a lightning pully will add basically 2 more pounds of boost then if you put it on a harley

IE. 6lb pully make approximatly 4 pounds on a Harley

here is my question, if this is true, does that mean if i put a 2lb Lightning pully on my Harley i will get zero boost gains out of it?
This has me stumped

Am i totally missing something here?

2002GreyHD150

ok... this is simple... everyone over thinks this.

an L has a 2.9X" upper pulley the HD has one X.XX" that & ECM tuning are the main reasons for the 2lbs less boost. If you swap an L upper pulley or snout you will gain 2 lbs of boost. Period.

{edited:} Ryan explains this perfectly below... I was working off bad information & faulty logic...

the bigger issue is the discrepancy between one company's quoted "6# lower" versus another's which is not the same diameter. If they are different diameters they both can't be a 6# pulley.

A couple of the original guys started a table of Vendor "X" has a 6# pulley X.XX" in diam & Vendor "Y" has a 6# X.XY" in diameter.

All you can do is look at your boost gauge (you did put one in right?) & see what your truck makes before & after.

Rob W.

BlairTruck

Thats what i was thinking, doing the searching i seem a million times that a 6lb is only 4 on Harley
And a few people say that 6lb was 6lb,

When i get this 6lb pully i should see closer to 12lbs then 10 right

my boost gauge is in the mail and was supposed to be here before xmas. And The LFP 6lb and predator should have gone in the mail this week

2002GreyHD150

{edited} since I was th idiot

You will like the parts for LFP mark is agreat, Stand up guy... next E-Fan & Factory Tech Valve Body (FTVB!) you'll be screamin!

Rob W.

Madferraristi

If you put a +2 0n a Lightning you will see ~10 psi, same pulley on a Harley will give ~8 psi. A +4 will yield ~12 on an "L" and ~10 on a HD.

The increase will be about the same, just a different baseline.

The confusion lies primarily in the name the various pulleys were given by somebody.

I have all sizes available, $199.90 with Gatorback belt, for any size.

__________________

Click here to visit MAD's site.

lerandell

Can this be made a sticky or added into the FAQ? I was totally confused by all the back and forth from everyone's post about 6=4 or 6=6.... this thread and specifically 2002GreyHD150's explanation nails it.

__________________
Randell Kelly
Black 2003
http://www.kellymanor.com

Speedin Bob

Stuck...

Ryan@RhynoTune

People need to reference their pullies in terms of diameter, not gains in PSI. Bottom line is a 8.5'' pulley will not gain the same on both engines.

This is a simple calculation, the hardest part is figuring out why people can't grasp this simple concept.

7.5/2.93= 2.55 blower ratio for a Lightning @ 8 PSI
7.5/3.25= 2.30 blower ratio for a HD @ 6 PSI
8/2.93= 2.73 blower ratio w/ 8'' lower (2#) for a Lightning
8/3.25= 2.46 blower ratio w/ 8'' lower (2#) for a HD
- Time out, so with a 8'' lower, you still aren't even at the same blower speed as a stock Lightning. So how do you gain two pounds? Do I really need to go on? I guess I must.
8.5/2.93= 2.90 blower ratio w/ 8.5'' lower (4#) for a Lighting
8.5/3.25= 2.60 blower ratio w/ 8.5'' lower (4#) for a HD
- Another time out, so with a 8.5'' lower on your HD, your not even at the same rate as a Lightning with a 2lber. So you start w/ 6PSI, buy a so called 4lber, slap it on with your stock upper, and bam your at 10PSI!!! But the odd thing is, your still spinning your blower slower to get that same 10PSI than a Lightning does. It's magic
I assume after reading that, someone is saying that isn't much of a difference. These numbers are small and meaningless. This is the part where I multiply the given ratio times 5250 RPM.
5250x2.73 (L blower ratio for a 8'' lower aka 10 PSI)=14332.5
5250x2.60 (HD blower ratio for a 8.5'' lower aka 10 PSI)= 13650

So you have a difference of 900 RPM for the supposed same amount of boost. Bottom line, you do not get the same amount of increase on the two engines with the different uppers.

__________________
2002 HD - 631 RWHP - 757 RWTQ
Currently fabbing twin-turbos

PgreenSVT

Thank you Ryan. That is exactly what I was thinking as I read the above posts. The larger the crank pulley the more difference in final boost between the L and the HD for the very reasons you explained. As the lower becomes larger the difference in the ratios for the 2 setups become larger resulting in a increasing disparity in boost levels as the lower pulley becomes larger. Swap on a 2.93 upper and then the pulley will be the advertised increase.

2002GreyHD150

thanks for clearing that up so perfectly Ryan... that makes a HUGE difference in my understanding...

learned a new math forumla today... I hate math but like boost...

Ryan, just to be sure I am clear where are the measurements taken? on the ribs I assume no the outer lip correct?

Rob W

Ryan@RhynoTune

I usually take the measurement on the outermost rib wher the belt rides... Somewhere inside the pulley, not the lip that holds the belt if that makes sense?

2002GreyHD150

total sense to me... I am slapping myself for not thinking about the upper interms of ratio before.... it is just one of those "DOH!" things I guess..

thanks again for the great info!

Rob W

tonysailor

if you do the above all you need to know is the pulley size. If you do not know, do another search for that also.

Do your math and compute the boost for your truck.

T

__________________
02 DSG #50, What mods? I don't need no stinkin mods!

Danko

Rob and Ryan are to be commended for their efforts to help us understand, but this old fart has gotten nowhere in two tries, so far. Rob's X.XX is not for me and Ryan's details are great but I do not know what the L and HD start with. To make it simpler for this blockhead, could someone tell me what is the difference between the L and HD powerplants? Is it just pulleys? If so, is it upper and lower that are different? Thnx for this info and your patience but I know nothing about this stuff and own two HD's. Do I want to mess with them? Yes? How? No? Why not? thnx again!

bgstew6

lightning upper pulley = 2.93 stock size
Harley Upper pulley = 3.25 stock size

both stock lowers are the same size.

The lightnings smaller upper pulley increases the RPMs of the blower which in turn provides 2 more pounds of boost (8lbs) over the Harleys (6lbs).

The lightning also has a more agressive stock tune. Couple this tune with the smaller upper pulley and that is why the Ligtning puts down Higher HP/Tq numbers than the Harley.


How is that?