MP8 505+ Proper Gearing

Discussion in 'Mack Forum' started by walrus, Jan 28, 2014.

  1. walrus

    walrus Bobtail Member

    6
    1
    Jul 15, 2013
    0
    Thinking about making a move to Mack. We have 2 KW's with Acert C-15s. Both have over 900k miles and we need to make a move. We're going to overhaul one of the Acerts which is in a decent 84" studio T600 but the other KW is an '07 T-2000 which has seen its better days. It's time to take a leap of faith into SCR. We have had CATS for many years and these two get decent mileage because they were set up correctly: 550 hp, 1850 torque, 3.25 rears, 11r 22.5 tires, Eaton RTLO 13's, about 1375 rpms at cruise speed of 70 mph. The torque rating on the MP8 505+ is 1860 when it's in pulling mode in the top 2 gears. But at other times this MP8 is rated at 1660 lb.- ft. Do we want to gear this engine to the same specs as our CATS??? We run mostly I-80 through PA, OH, and IN. I don't know much about Mack engines and would appreciate any help. Thanks!
     
  2. Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.

  3. markster1957

    markster1957 Light Load Member

    65
    20
    Jan 21, 2014
    boise id
    0
    Just talk to a sale man's they can spec it for you
     
    walrus Thanks this.
  4. walrus

    walrus Bobtail Member

    6
    1
    Jul 15, 2013
    0
    Thanks. They did spec it already: RTLO 13, 11 R22.5, 3.36 rears. Just wanted to double check on this site. I've heard stories of salesmen missing the mark when it comes to ratios. Sometimes guys on here know more than salesmen about proper gearing.
     
  5. striker

    striker Road Train Member

    5,906
    6,186
    Aug 8, 2009
    Denver, Co
    0
    I run a '09 CXU with the 445 hp MP8 and 3.70? gears, we run primarily the Rockies out of Denver and the E. plains thereabouts, @ 78,000 lbs I can climb Vail and keep it about 20 to 25 mph. I've test driven two CXU's equipped with pushbutton Mack tranny's, one had 455 and 3.70 gears, governed at 65 mph, it ran like the dickens. The second one was a 505 engine with 2.36 gears, on the flats it took forever to get up to speed, I could get 9+ mpg at 65 mph. However, with that gearing, @ 78,000 lbs climbing Vail EB, I couldn't get out of my own way, I dropped as low as 15 mph.
     
    walrus Thanks this.
  6. walrus

    walrus Bobtail Member

    6
    1
    Jul 15, 2013
    0
    We're going with the salesman's recommended gearing. Thanks.
     
  7. Jokingypsy

    Jokingypsy Medium Load Member

    669
    613
    Jan 4, 2013
    Baltimore, MD
    0
    One question, it sounds like cat has been good for you, why not look at a glider? You get fresh pre-emissions factory cat or Detroit rebuilt with warranty. Just curious.

    Adam
     
  8. markster1957

    markster1957 Light Load Member

    65
    20
    Jan 21, 2014
    boise id
    0
    The mack drive is nice the idaho state dump trucks use them my dealership just sold 53 more to them
     
  9. Mack427

    Mack427 Medium Load Member

    323
    92
    Jan 22, 2009
    0
    some are saying the 445 get better fuel mileage than the 505 and pulls the same
     
  10. Cowpie1

    Cowpie1 Road Train Member

    5,569
    4,646
    Nov 25, 2008
    Kellogg, IA
    0
    I don't mind taking recommendations from a sales guy, but I will usually grab a HP/Torque chart for the engine in question and study how the engine power curves are, then figure from that the RPM's I need to run, and then sit down with a road speed calculator and plug in tire rotations per mile, trans gear ratios, and differential ratios to see how thing line up and fits into what I want to do with a truck. The sales guys are working of canned charts that play a one size fits all kind of game. Only you know how and where your trucks run and the conditions they run in. The sales guy stuff is an ok starting point, but it is just that... a starting point.

    But the sale guy already spec'd it and you seem to be going with that, so good luck.
     
  11. KB3MMX

    KB3MMX Road Train Member

    3,057
    2,572
    Dec 29, 2014
    Orrstown, PA
    0

    Curious what you ended up going with on rears?

    Volvo trucks with the XE package are specing a 2.64 rear on 22.5's w/ the iShift(Mdrive)for 1150RPM @65MPH w/ the same motor to get incredible fuel mileage (7.6-8.3). For a little better pulling, the 3.08 rears are preferred and they only lose about a tenth on MPG as compared to the 2.64's.
     
    20 Mule Team Thanks this.
  • Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.