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Thread: HP rating for a 321/300 doubler?

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    HP rating for a 321/300 doubler?

    can't seem to find much info on what the max HP would be for one of these doublers. i realize the 300 was found behind a 360 at about 250hp but the 231 was only really ment for around the 200 mark. just curious what if any info anyone else has found. opinions on the doubler holding up to around 345hp/ 375FT#s?
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    Way too many variables there to peg it down to a HP number. Tire size, axle gear and vehicle weight along with the type of terrain and driving style would very important factors.

    The D300 is going to be the weak link in the doubler. The 231 planetary has been proven to be quite strong so I would not be concerned about it in that combo.

    Once you change the outputs on the 300 to 32 spline, the case and input become the weak links. The 231 low range is hard on the small input on the D300 and breakage is common in abusive applications. The other issue is the case can split from too much load.

    You can certainly make a 300 live behind 345 HP....but with big rubber and an abusive environment, it could be a weak link for sure.
    Last edited by CTD NUT; 04-14-2013 at 09:48 AM.

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    ya, guess im not looking for an exact HP # but rather some real world experience. i believe chris broke the intermediate shaft on his with the 350 in BBQ juice. i have seen 300 cases crack. i have upgraded both outputs to 32 spline, now thw 231 only has the 3 gears in the planetary not the 6 (unless i can find one.) any hopping situation i do believe the tcase will be the weak link no matter what. not too sure on ujoints yet. planning on 1410 but 1350 might have to be used for space constraints. so many people have done the doubler but i haven't found any real follow up on their performance.

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    There isn't much point with 1410 joints in a mild 1 ton driveline. 1350 joints are at LEAST as strong as the 32 spline outputs...both of which will dwarf your doubler set up in strength.

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    good to know. i haven't even started to think about drive shaft/ joints yet. only reason i was even thinking about 1400 series joints is the 14 has the 1450 yoke on it. i guess no matter what any shock load is going to be felt greatest in the doubler.

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    HP rating for a 321/300 doubler?

    The only thing that I have broke with a V8 in front of my doubler is the spud shaft between them. Letting a 5000 lb jeep bounce in Ardbeg by black lake isn't the best idea just cause you no longer have to worry about breaking axles.

    The spud broke clean without damaging anything else and it was fixed for $200.

    As long as you use the low range in the 300 before using the 231, it's all good.
    The increased torque the 300 gets is 2.72 times what the factory ever put into it. I'm still running factory output front and rear on the 300 as well. I've broke 2 fronts but that was caused by excessive ujoint angle and bind. The rear has been great.

    I've started the process of swapping in. 5.3 with a 4L60e and am not to worried about the doubler with 300 HP.


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    HP rating for a 321/300 doubler?

    I'm also running a 1310 joints in the front and a toyota cv shaft in the rear.

    The d300 case can crack but it's a real easy fix. You have to make/buy a thicker cover for the bottom. I made mine with a piece of .250" and cut a hole in it for the one gear that sticks out. I then put the stock cover over it sandwich style to cover the gear.


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    now thats a good idea. might just look into a beefier cover.

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    here is a pic of my cover and you can see on the right side where I'm about to weld it to the mount to make sure everything is strong and tied together.


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