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Thread: 10% OD vs. 15% OD on MP Inlet/S-Port

  1. #1
    Join Date
    Apr 2002
    English, IN

    10% OD vs. 15% OD on MP Inlet/S-Port

    Finally did some experimenting today and I'll a little surprised at the results.

    I've been running a 5% SC & 5% JS pulley for awhile now and my car has been able to consistently keep the ACT's below 120F, so I decided to swap the 5% JS for a 10% today and datalog both setups on the same day, same conditions.

    The car: 76mm MAFS, 3.5" Tube, 75mm TB, MP Inlet, S-port supercharger, custom FMIC, MP springs

    Weather: overcast all day, 70F - same stretch of road with same warm up and cool down routes/times (although for some reason the 10% run started at 110F ACT )

    *see datalogs for relevant data*

    Runs were only 1 hour apart with no significant changes in the weather

    I expected to see much higher ACT's and higher MAFV with the 15% pulleys, but was surprised to see no huge difference in ACT's! The MAFV @ a given RPM is a little higher for the 15% combo...but the ACT's are nearly the same. Max boost is at 15psi (Autometer boost gauge) with the 15% combo, but I forgot to check the max boost for the 10% combo seems like it was either 14 or 15psi also.

    Does this make sense? I'm wondering if I'm getting belt slip...granted I've not run it many times, but there aren't any obvious signs that this is the case. Maybe a leak somewhere? Any ideas?
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    Matt Haub
    Shootouts: '09 SS 1st | '10 Mod1 2nd | '11 Bracket 3rd | '12 Bracket 1st | 2013 | '14 Bracket 3rd | 2015 | '16 Bracket 1st & Mod2 2nd | '17 Spectator | '18 Freeze-Plug Champ
    Black '89 5spd - 281K miles, MPx, Alky-Inj 387rwhp, 438rwtq (new motor) Best 1/4mi:12.521, MPH:107.23mph (old motor)
    35th Anniversary Auto 46k miles | Red '93 Auto 186k miles
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