N14 or C15 or ??? for good power and MPG?

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Turbrospeed, Apr 11, 2023.

  1. mile marker 27

    mile marker 27 Road Train Member

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    I’ve came to the conclusion, that this Performance 9, is what it is and not simple or feasible to make it a 13. And that’s fine, it does a fine job but I like the splits for in the hills, stop lights in town and down shifting. Not a must though. My FIL’s cabover that I’m building the engine for(350 small cam), has a RTO12513, tall 22.5’s and 4:44 rears. He wanted the rears changed to 3:73’s initially but now has talked to someone who thinks it’d be easier/better to flip the gears around in the transmission. Maybe so??? Still not enough power from the engine? Before all this, the SC 290 would turn 2000rpm at 68mph and that was it. Wouldn’t tach up any more. Pros and cons of flipping the gears around?
     
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  3. wore out

    wore out Numbered Classic

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    Don’t flip it he will hate it..the ratios don’t work out exactly like the factory double overs. And like I said speeds the whole trans up so race car reverse and a high low hole seven those rears won’t compensate for it
     
    Oxbow and singlescrewshaker Thank this.
  4. mile marker 27

    mile marker 27 Road Train Member

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    I hear you and I’ll relay the message. Dang, he ain’t gonna like hear’n it but I wouldn’t want what you’re describing. I guess I’ll be back to the original plan of 3:73’s.
     
    Oxbow and singlescrewshaker Thank this.
  5. little cat 500

    little cat 500 Road Train Member

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    ive never heard N14 and big power in the same sentence
     
  6. mile marker 27

    mile marker 27 Road Train Member

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    Well, I relayed the message to my FIL and earlier today he talked to one of the old retired mechanics, that used to work for my extended in-laws. My FIL drove a Superliner dump truck back in the 80’s, that had 350 Mack, 13OD transmission and I think he said 4:6? rears. Said the mechanic flipped the gears around in it and it helped it tremendously. That mechanic is the same guy he talked to today. I told my FIL I don’t know anything about it and that’s why I asked the question on here. My question, Wore out, is the only gear ratios affected are the two that are flipped? Seems to me that 3 & 4 in low, 10 & 12 in direct and 11 & 13 in OD will all be affected. In your opinion what’s gonna happen to this transmission if he has it done this way?
     
    wore out Thanks this.
  7. wore out

    wore out Numbered Classic

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    No ever single gear is affected. It speeds up the whole box
     
  8. wore out

    wore out Numbered Classic

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    You have to press 2 gears off each countershaft swap sides as well as turn them opposite way. Then you have to buy 4th and 5th with the right number of teeth so they mate with these used counter shaft gears you’ve flipped. Once a wear pattern starts you’ll never move it and keep it quiet. Remember high gear is held to main shaft by a snap ring. So we’ve got excessive noise, odd splits now cause we just bought the 2 gears and by changing the number of teeth on what’s splined to the input shaft we sped everything up. You can buy lots a parts and do it “right” and still have a weak back box with no trans cooler… or you can go buy a RTLO16713 get a trans cooler, way better rear box and still have overdrive in the front (.73) the rear is actually an under drive unit. Work’s opposite of what you think. You will still be 13 percent short of an RTOO. But 13 percent faster than where you currently are and way more Money ahead. I know you’re thinking by doin some hoe #### to what you have you’ll get by cheap. And labor and all if y’all pull it and put it back you’ll have 1200 ish to 15…..and a strong dislike. I know he thinks he has had this done but I’d bet money the gear man said I’m not doing that no point in it and bought all the gears to do it right as his name was on it…..bout 3800 parts only. I’m not picking on you when I say this I do understand these trucks are not used in the capacity of soul income providers and something close but cheaper seems like such a better option. Trust me I’ve never seen this short cut took that the long way around didn’t cost 3 times what it shoulda. Part time or not doing it right one time and being done is the money saved. Or continue use as is.

    There is an old sayin big trucks big bucks

    the biggest waste of money in this universe is trying to make what’s close exactly what you want. I was poor once had a heap of free used parts at my disposal. It was a lot of work but I learned that 3.36, 3.70, 3.55 all got the same mileage behind the same motor in same truck pulling same loads. I also learned they topped the same hills at the same speed just different gear positions. Whether I had a 15 over or a 16713A all with tall rubber. Again I wasn’t trying to prove nothing I was broke and using what I had. I’m just sharing real world actual knowledge from experience do with that what you may
     
    Sons Hero, Crude Truckin' and Oxbow Thank this.
  9. mile marker 27

    mile marker 27 Road Train Member

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    Missouri Transmission and Gear in Poplar Bluff, is who he talked to initially about this. Said, if he bring them the transmission, they’d do the swap for around $800. Because he and I don’t know much about it, he got all on board. I’m gonna call this bunch today and talk to them, because my FIL insisted, I talk to them and hear what they say. I hear what you’re saying and in my opinion, if it were me and had to pull it anyway, I’d trade it in for an OO or change the rears. I appreciate the advice and I’m gonna reread your post about two more times before I call that ol baw. My FIL doesn’t want any of it done half arse or detrimental to the truck, he just not as saavy on the mechanical side. When a guy goes around asking advice, he’ll sure enough get it.
     
    Crude Truckin' and wore out Thank this.
  10. mile marker 27

    mile marker 27 Road Train Member

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    I told something of that nature because that what you were eluding to and he acted like the Superliner had no other gears affecting, that he could remember(mid 80’s). He didn’t swear to that though and that’s why he went and asked their old mechanic. I don’t think he’s concerned to much about saving money but he kinda likes the idea of keeping the same parts in the truck as it was. That concept is why I would’ve pulled the small cam and put a bigger and newer motor in it from the get go. It’s caused me a ton of work and time and now this transmission thing, when he’s literally got a set of 3:73 rears from an IH, in a parts truck.
     
    Last edited: Apr 21, 2023
    Oxbow, Crude Truckin' and wore out Thank this.
  11. Crude Truckin'

    Crude Truckin' Alien Spacecraft

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    Subscribed. God I love reading this stuff.
     
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