R3ckl3ss

Wanted to start a thread specific to pulley diameters. I've read a few posts where folks have gone down as small as 3.625" (at least one example). Recently had the system installed with the 3.875" pulley. Don't necessarily feel the need to change as I'm reasonably happy with the power.

What's everyone else have?

Related is actual boost measurement. Whipple says 1 psi / 0.125" change. Anyone have a boost gauge and any data?

-R3ckl3ss

engineermike

Great question! The supplied pulley is 3.875 which Whipple rates at 9 psi. I measured 10 at redline. I dropped to the 3.75" pulley, which is what comes with the mustang kit. Since the truck is lower compression than the mustang, I feel this is still pretty safe. I normally run a mix of 91 pure and 93 gas and would feel comfortable on 91 since, again, the mustang is higher compression and still rated for 91 octane. I spoke with Whipple about going to 3.625 and they said 93 octane only and NO towing. I personally feel like they are being conservative here because, again, the mustang guys are upgrading to the 3.625 pulley running .5 higher compression on 93. I recently heard a rumor that Whipple is working on a new cal that might allow running a 3.5" pulley but we shall see.

Personally, I'm looking for a little more power (593 rwhp not quite enough) so I'm looking at the ic fan upgrade and 3.625 pulley, but reliability is pretty important to me so I'm on the fence. However, there have been no publicized failures of Whipple 5.0's so that gives me some assurance.

1 psi is about 20 hp and 20 ftlb at the wheels.

jmeo

iTrader: (1)

I've been running a 3.625" since day one with zero issue. I live in MA and use 93 octane. I have used my truck once to tow a 20' flatbed trailer with a 3,000 lb 4 post lift for about 100 miles with no issue.

I have spoken to Whipple and the new tune is supposed to allow a drop to 3.50" pulley and provide as much as 60 rwtq

JSEDECKER

I ordered 3.875", 3.75" and 3.625" pulleys with my kit. When I first installed the kit I put the 3.875" pulley on and ran it for about 2 weeks but then put on the 3.75" pulley. I didn't go with the 3.625" pulley since I was heading on vacation across the continent to the Canadian east coast and I was sure there would be no availability of good quality fuel above 91 octane at my destination. I have access to 94 octane in my home province of Alberta so the 3.625" pulley will be going on as soon as I get home.

As for the boost gauge, I have did some programming with FORScan software (and some help from Livnitup) and I enabled the factory boost gauge on my cluster (same gauge that is in the cluster an ecoboost) and although there are no markings on it besides 0 and 20psi I can report that it reads at half way when at full boost with the 3.75" pulley installed which should be about 10 psi. I can't comment on the boost gauge reading with the 3.875" pulley since I didn't do the programming for the boost gauge until after the 3.75" pulley was installed.

BlueFlame2015

Is this in a 5.0 that you enabled the gauge?

minniehill2

Yep, on a 5.0!

R3ckl3ss

Really helpful input. Think I need to reconsider my pulley size. Ignorant question - that require anything more than a hardware change? Need a different calibration file or settings changes?

jmeo

iTrader: (1)

Just a simple pulley swap and Bob's your uncle

JSEDECKER

Yes sir!

One thing to remember guys is that the boost numbers are rated at sea level, so as your elevation increases boost will drop slightly. A positive displacement supercharger is unable to compensate for elevation like a turbocharger because it moves a fixed amount of air per revolution and the RPM of the supercharger is just engine RPM x the gear ratio: engine RPM x (Crank pulley diameter/Supercharger pulley diameter) = RPM of supercharger

All a turbo has to do to compensate for altitude is spin a bit faster since it is non-positive displacement and is exhaust driven. Most turbochargers' max speed is limited by the waste-gate which is opened by the manifold pressure signal, that is transmitted by a signal line or electronically via the MAP sensor.

JSEDECKER

I need to edit my post above but the editing button does not appear so I will correct it here:

I listed the RPM of the supercharger as Engine RPM x (Crank pulley diameter/Supercharger pulley diameter) It should in fact be Engine RPM x (Supercharger pulley diameter/Crank pulley diameter).

To determine gear ratio you need to do driven/drive and in the first way I listed it, it is drive/driven which would give you a false gear ratio.