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Thread: first real drive with the cummins

  1. #1


    engine i put an estimated 85 miles on it today. lots of go from 1st to 4th. 5th seems weak, but usable... it seems to be more of a way to drop the rpm than a top speed enhancement. i would guess i never went over 65.... im still debating a muffler. there isnt one right now.

    gears 4.88 gears may have been a better choice. time will tell. the 4.56 came with the axles. the rear detroit is NOT noticable. first gear is still unusable without a load.

    cooling 79 degrees 65percent humidity and the truck ran 185 to 195 the whole time with no electric fan. including lots of city/traffic driving. thats with the stock radiator.

    brakes hydroboost 4 wheel disks. they stop WELL and the proportionong valve works great too. i barelypush the pedal and they brake well.

    any specific questions, ask.........

    4.88 gears on 35 inch stock tires is 2283 rpm at 65mph, this is what was recommended to me from the 4bt gurus.

    4.56 gears on 38.7 inch tires is 1940 rpm at 65mph, whis is what i have now. this is also close to 3.73 gears that would be on a stock dodge

    i think i would rather do 65 to 70 at the lower rpm for better mileage than the more power at speed. tire wear is an exponential equation, at 75 to 85 the michelins will wear MUCH faster. plus after all the 4bt redlines at 2500 rpm. i plan on turning the injector pump up soon. any other opinions?

  2. #2
    Join Date
    Sep 1998
    North Central Wisconsin


    My opinion....sweeeeeeeeeeeeeeeeeeeeeeeeeet!
    Wish mine was even remotely close to yours!!
    Lord send your Holy Ghost into our hearts and make the desire of our hearts Your Will.

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  3. #3
    Join Date
    Jan 2004
    New Haven, CT


    Congratulations Lee!

  4. #4


    You may be near the line of diminishing return with you gearing. 4.56's don't seem to have the top end power but have lower rpm...but you may need to be putting more fuel to it to maintain. 4.88's will give it more power from more rpm and use the same amount of fuel spinning faster with less load. As far as muffling...I'm looking into perforated stainless exhaust cones used for racing when a muffler is too much and you just need the edge taken off the exhaust note in my CAT motor project in the Blue truck. 636 diesel cubes and no exhaust sounds neat...but will leave the ears pinging after a while. Summit Racing sells the SS cones.
    Big Blocks RULE!

  5. #5
    Join Date
    Jan 2004
    New Haven, CT


    How noisy is it? Can you carry out a conversation inside the cab?

  6. #6


    its loud with no muffler. im looking at getting a sray in liner to quiet it down. you have to talk loud, but its ok

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