Boost pulley combo question

[Big Jay 02DSG]

I did a search but could'nt figure it out. From what I found 14lbs
is safe on stock internals with the right tune. OK, so here is my question. I am looking to run 14lbs of boost. Here is a list of mods so far. I see 10-10.5lbs on my boost gauge now.

Airaid intake, NGK tr6 plugs, 170 thermo, 2.80 upper(is on now) Also have 2.93, Bassani cat back etc.

I just bought the FTVB and 4x4 pan. I am looking to get the Predator and a lower pulley.

What size lower should I do and with what upper 2.93 or 2.80 to get 14lbs? Who would be good to tune it I live in NY?

[MRBLUEOVAL]

A 6 lbers will net you between 14-15 depending on how cool the weather is. In the summer you will lose a little boos t from the heat

[cayman150]

I am trying to figure out the same type of thing, Here is what I found somewhere that may help you decide.

I've also attached a .zip file of the Excel spreadsheet that you can use to plug in the upper and lower pulley values to show you what the final boost numbers will be with various pulley combinations.

Here are the forumlas. L and HD have a 7.4" lower pulley. L has a 2.93" upper, Harley 3.25.

2# is 7.8" 3#:8.17 4#:8.5" 5#:8.75" 6#:9" 8#:10"

Lower/Upper=ratio ratio times 5250=blower rpms at shift point of 5250. You can plug the values into a spreadsheet and see what I am talking about...

Here is the formula to calculate maximum potential boost

a = lower pulley diameter.
b = upper pulley diameter.

1.84 x ( a / b )
------------------ x 14.7 - 14.7 = BOOST
2.7

14.7 is PSI at sea level, 1.84 is eaton blower displacement in litres, and 2.7 is the engine displacement divided by 2.

Plug in the values for an L with a 4lb and a HD with a 6lb and see what you get. Hint: they are not the same.

[bgstew6]

good post cayman, mighto ought to think about making this a sticky

[harleytruck9144]

well according to that formula i am supposed to be making over 16 lbs of boost with a 10" lower but i only see at most 14/15 on a VERY cold day, usually around 12/13?

[Big Jay 02DSG]

Originally posted by MRBLUEOVAL
A 6 lbers will net you between 14-15 depending on how cool the weather is. In the summer you will lose a little boos t from the heat

Been away for few days

Do you mean run the 6 lber with the 2.80 or 2.93? As far as losing a little boost would the heat exchanger or E fan help?



cayman150
I don't have excell spreadsheet, cant open Thanks anyway

[cayman150]

If you don't have MS Office that comes with Excel then look for Microsoft Works. Most computers come with it as bundled software. It will work with that too.

If not you can still plug that formula into any spreadsheet or even use it on a calculator to see your results.

[BlairTruck]

when i enter the numbers for a stock harley My answer comes out to be 8.10
and stock lightning is 10.6

[cayman150]

Yes that's what it works out to.
I don't know how acurate this is 'cause like I said when I posted it...I found it somewhere, can't remember what site or forum.

I don't have my boost gauge on yet but I think I remember that the HD's come with around 6-8psi stock?

Anybody know the true posistion on this?

[bgstew6]

6 pound for the HD stock
8 pound for the lightning stock

Difference is the upper pulley that gives the lightning 2 more than the Harely.

[BlairTruck]

my gauge showed 6 lbs today at WOT
first itme i opened it up since i got it

It was warm enough for the highwya to be clear for the test.
I got pictures also

[cfradam]

cayman, good to see that you made it home safe. the calculations on the spread sheet seem to be a little agressive, and very helpful. on my truck I saw 15/16 lbs. today with temps @ 48deg. and I'm running an 8lb lower. Blair lets see the pix.

[cayman150]

Thanks Adam.....I wish I could remember where the h3ll I found that write up. I followed the blurb and put the formula together in the spreadsheet. There is a mistake in the column title ...where it says 7# it should be 8#.

Can anybody see any mistakes or where something is wrong in order to try and get those stock numbers back down to 6 lbs for the HD? I tried looking at the formula and reworking some of those numbers but they look right according to the blurb. Maybe something in the blurb is off?

HELP...you mathematicians!
(anybody watch the tv show Numbers last night?)

[BlairTruck]

Its a blurry picture,
Its hard to take a pic of the needle and keep it in focus
I took like 8 pics, and this one shows the most boost.

When i wasnt trying to take a pic it hit 6 even

That was at 42 degrees

[fordbyfour]

keep both hands on the wheel over 120 mph!