Heres the story:

Bought a 4 Lb Lower from RPMoutlet.com

This one Pulley

It says adds 4 additional pounds of boost like every 4 lb should do (or very close atleast).

Took it out the first night and yeah it seems faster and def screams louder, but both of my boost gauges read 9lbs MAX.
I've read the stock one and the recently added Ford Racing Boost Gauge on my steering column. Whats going on here? never driven another truck with a 4 lb lower so i dont know how it should feel. I dont know if it just felt faster because i just put the FTVB in the same night or if it really is and both of my gauges are screwed up. Should all 4 lb be the same diameter? If so what is it?
Thanks Jim

MODS:

4 LB Lower
Predator by RWTD
FTVB
Boost by pass
Modded air box

 

measure it and then try one of these, you'll find pulley diameters:

 

One other thing to check is the tensioner for the supercharger to see if the belt is slipping. I just changed a tensioner for
1-menance last Sunday he is seeing 13 lb of boost again. Here is a few quick ways to check it...

Clean around the supercharger upper pulley and the face plate of the s/c. You will find black belt dust. After you have cleaned it run it a few time s hard to see if you have more black dust there. If so it's slipping. Next if you can squeez the belt together with very little force just under the upper pulley it should be changed.


Hope this helps,

Suavy

 

i'm gonna try that belt idea. thanks

Wait we have a search button?!?!?! HOLY ****! Thanks for pointing that out
Some people are too full of themselves.

 

I'm seeing 15 lbs of boost with my JDM/Metco 4 lb lower.

FYI: I have a ported eaton.

 

rpmoutlet sucks they are big @ssholes i wouldnt trust them for *****.

 

Also RPM is known for shipping the wrong belt with there pulleys. I have a freind who got a belt that was to big, and he was getting a lot of belt slippage. We put a smaller belt on and all was well.

 

Don-

what size belt should be used for a 4 lb? thanks

 

I have dealt with them more than once and was shipped the product as promised in a timely manner. They were extremely reliable, everything they said was in stock shipped out the next day and with 2nd day air how I paid for it.

I wouldn't buy a tune or motor from them, but I do trust their service and website.

Care to share why you hate them so much?

 

Suavy you wouldn't happen to have the part number for that tensioner? I think I might need to change mine....Thanks

 

I think the belt for a 4# should be 67 inches long. In my experience, the ribbed belts seem to be available in 1.5 inch increments. I believe the stock belt is a 65.5 inch and the 8# belt is a 68.5 inch. If you translate the 67 inch belt to Gates part numbers, it will be something like 50800670. The last four digits (0670) are the actual length. Likewise, a 68.5 inch belt will be a 5080685. I'll be replacing my 2# (which barely uses the stock belt) with a 4# in the morning. I'll post another response to this thread about the length based on how it works.

 

Goodyear Gatorback 4080675 SC Belt
1999-current Ford Lightning & 2002-current Harley-Davidson F-150, 4lb. Lower SC Pulleys

67-1/2 "
I've been runnning this belt over 2 years and not once has it slipped.

Bro you should be seeing A LOT more boost.
Stock is 8-9, a good filter adds up to 2lbs alone. Then 4 more for the Lower Pulley and there you have it, @ 15lbs on a cool day.
I have a 4 lower, 1 - 2 upper, and a Ported Eaton, schitt I see 10lbs of Boost at 1/8 - 1/4 throttle in 1st gear
And AN EASY 15lbs at WOT

 

Check the tensioner.

FOOD for thought.

My stock tensioner was stamped at 9 pounds of pressure and it was slipping all over place.

My new one is stamped at 12 PSI so it is much tighter.

like Suavy said No more belt slippage.

The part number is on the box which is in the parking lot, but I'm too busy to run out right now and grab it, I'll get it later.

When you get your tensioner make sure it is a 12# one. (the navigator uses the same TYPE of tensioner but it may be more stiff)

NO sense spending $200 on a metco system when all you have to do is replace the stock tensioner!

BTW:
Thanks a Ton Suavy for hooking me up. i was seeing 10PSI, now I'm seeing 13PSI.
(not bad for a 3# lower and stock upper)

 

i'm gonna check the belt length and then check for a lot of dust. But yeah somethings def wrong. thanks

Anyone have a part # for the 12lb tensioner?

 

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