How much torque?
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    Default How much torque?

    I have a 3000 - 3500 lb vehicle. I was wondering how large of an engine do I need? How much torque do I need to look at?

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    well my dodge at 7380 lbs has 436 hp / 897 ft/lbs at the rear wheels and that seems to be satisfactory for me especially when towing. i liked it at 507/1060 on my old truck and ive been higher but for balance and scoot movement it seems like with the numbers rounded up a little 1 ft/lbs or torque to every 9 lbs of steel or 1 hp to every 17 lbs of steel keeps my butt o meter happy

    but thats all factored around a rig that tows heavy. my cherokee chief i have the numbers a little lower


    Stock Ford F350 215/440 (7000lbs) from 1997 and a dodge 2003 (7300 lbs) 305/555 truck had torque to weight ratios of 15.9lbs to every ft/lbs torque and 13.15 lbs to 1 ft/lbs torue respectively and around 13 lbs is where things started to feel pretty effortless in stock form with these heavy beasts.



    3500lbs / 13 = 270 ft/lbs should scoot pretty well and would be well within the stock settings of a cpl 857. id turn it up jsut a hair decrease the size of the exhaust housing to improve spool up and call it a done deal you'd easily have 130-140 hp/ 290-300 ft/lbs scoot well and have good economy due to the relatively mild combination


    my chief at 5100 lbs @ 430 ft/lbs will be at a 11.85

    bread trucks at 9000 lbs roughly with a partial load and a cpl 857 4bta were sporting 120 hp+/- & 260 ft/lbs +/- were at a gastly 33.70 lbs per 1 ft/lbs of torque and they still maintained speed and booked right along. theres just my way of deriving a statistic to choose hp/torque number relative to a combination and estimated weight. I also factor in the hp and then after determining the hp/tq that i feel is relative to my objective i choose the gearing to get it all to perform at the speed i want also

    there are a million other therories that work its all dependant on where you want to go, how fast you want it to move and what you are comparing it to. go out and drive a few diesel turbo charged rigs and figure out their hp/torque to weight ratio and that can get you started in a possible direction but then you need to determine what your final objective is. Track time, brute torque for trailering brute power for showing off...... its all relative in the end to what youa re trying to achieve
    Last edited by dusty; 01-28-2009 at 09:37 AM.
    FSJ cherokee chief 4BTA 120 hp ve, piston lift pump, 50 hp lenny's injectors, 03 dodge HY35/9, 1991 dodge intercooler, 13" clutch & dodge nv5600 flywheel, nv4500/D300 3.54's D44 Ploks F&R
    4bt info

    2003 Dodge 3500 4x4 6 spd........

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    Quote Originally Posted by oldschoolboy View Post
    I have a 3000 - 3500 lb vehicle. I was wondering how large of an engine do I need? How much torque do I need to look at?
    That's really an open ended type of question. Depends on your goals. Fuel economy or a something used to haul a load of tools around town.
    BobS

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    I am looking for fuel economy but I don't want to get on the interstate and take forever to get up to speed. So I guess fuel economy with a little spunk

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    Quote Originally Posted by oldschoolboy View Post
    I am looking for fuel economy but I don't want to get on the interstate and take forever to get up to speed. So I guess fuel economy with a little spunk
    I have a mostly stock 4BT (HY35 and 3200rpm spring) in a 6000 lb truck and it does just fine. It will cruise at 80mph all day long.
    1963 Jeep J300, 4BT/NV4500/NP200/D61/D71
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    Quote Originally Posted by oldschoolboy View Post
    I am looking for fuel economy but I don't want to get on the interstate and take forever to get up to speed. So I guess fuel economy with a little spunk

    Stock 105 or 120 HP 4BT will do that nicely, just gear it correctly.

    Mine's still in the 7K LB (empty weight) P-30 with an additional 2.5K LB in it right now (tools, a disassembled 6BT, etc..), and it has no difficulty with on-ramps or hills. Needs OD badly, though..
    A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly.
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    Quote Originally Posted by BobS View Post
    You need to first confirm the problem BEFORE you start buying and replacing parts.

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    Quote Originally Posted by machman View Post
    Stock 105 or 120 HP 4BT will do that nicely, just gear it correctly.

    Mine's still in the 7K LB (empty weight) P-30 with an additional 2.5K LB in it right now (tools, a disassembled 6BT, etc..), and it has no difficulty with on-ramps or hills. Needs OD badly, though..
    HAHA! I'm sitting here thinking mobile shed!
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    Quote Originally Posted by BobS View Post
    HAHA! I'm sitting here thinking mobile shed!
    You should here the clown music he plays going down the road

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    I am looking to find out what torque I need to move 3500 lb car used for daily driving. I am also looking at other engines (small engines) besides the 4bt, that is why I am asking for torque.

    Thank you everyone for your posts

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    Quote Originally Posted by BobS View Post
    HAHA! I'm sitting here thinking mobile shed!
    You Sir, win the prize. There's something about having more dry square footage in a mobile format than some apartments I've lived in over the years that I can't resist.

    Quote Originally Posted by CrewCab59 View Post
    You should here the clown music he plays going down the road
    So THAT'S what we call that whistling noise...

    Quote Originally Posted by oldschoolboy View Post
    I am looking to find out what torque I need to move 3500 lb car used for daily driving. I am also looking at other engines (small engines) besides the 4bt, that is why I am asking for torque.

    Thank you everyone for your posts
    Uhh.. Well...

    Without (hopefully) channeling the ghost of Charles...

    And not intending to take anyone's sacred cows out and grill 'em, or to step on anyone's toes, or any such things like that, but here comes the Torque vs Horsepower thingy again..

    If your concern is accelerating a weight (or, taking a more holistic view, overcoming inertia of a given mass, plus the various other resistances, drag, losses, etc) to a velocity in a given timeframe (which is what I interpreted your prior post to mean), then the thing you're concerned with is HORSEPOWER. (Well, at least in the civilized part of the world that doesn't rely on that abomination known as Metric.. Next they'll be wanting us to use measurements like Cubic Furlongs per Fortnight or some such. )

    Torque is just a force being applied, and by itself has NO reference to the RATE at which that force is applied and (or even if) WORK is being done. If you hang a 1LB weight off an arm 1Ft long that is sitting level, then you are applying 1 Ft Lb of torque (a force). But, if that's not enough to cause something to move, then no work is being done..

    Horsepower, however, does encompass the idea of doing a given amount of work in a specific timeframe.

    The nice thing about it is that doing the math is fairly easy since, for what we're dealing with here, Horsepower is simply Torque (in Ft. Lb.) multiplied by RPM, and then the whole thing divided by 5252.

    Now, back to your question.. How much torque do you need? Well, it's more a question of how much horsepower will it take to accelerate your vehicle at a rate that satisfies you, and then can the engine under consideration produce that necessary horsepower in a manner that is functional for your uses (efficiently and with a minimum of drama doing so for a daily driver)?

    And yes, there are those that will scream that "It's the low end torque" of the diesel engine that does it, not the horsepower.. Well, even though they don't know why, they're right, but maybe wrong in their understanding of it. Or mebby it's just one of those semantic things, but I still say they're taking the long road to saying the same thing:

    "Low end" references an RPM range. So, they say it makes "lots of low end torque". OK. That's giving a torque value at an RPM value.. Whoops, that's one whinny away from saying Horsepower.

    Now, usually when they're saying it that way, what those people are trying to convey is that it's not necessarily the peak horsepower rating (or the peak torque rating, either!) of an engine that you need to look at, but rather where it makes horsepower.

    Attached to this post is a PDF that is the power/torque/BFSC data sheet for a 130HP 4BT. (And, if someone out there has the info for the more common stuff, such as CPL 858 and 857 motors.. Post it up! I want it. Or did I miss it somewhere?)

    If you look at it and compare it with similar charts for many factory small block V8 gas motors (if you can find ones that actually show output starting at 800 RPM..), you'll find that for every RPM point up until the 4BT's horsepower peak / governed limit, it's making MORE horsepower than those V8s. (And, yes, more Torque!)

    And most of those gasser V8 motors have a peak horsepower rating that is nearly double that of a stock 4BT (but their peak torque will generally be less..). Even better, some of the V8s don't equal the horsepower the 4BT puts out at 2500 RPM until they're much further along the RPM curve.

    This means that you'll usually get things moving and initially accelerate faster with the 4BT, but if you keep your foot planted and wind the thing out, the higher horsepower peak V8 will out accelerate it. But it's going to be spinning at a pretty high RPM to do it.

    Or, you gear the V8 to spin faster initially, or put a higher stall torque converter on, or otherwise move it up into a higher RPM range for a given road speed, and then the V8 will out-accelerate the 4BT off the line, but you really pay for it at the gas pump.

    And there's the kicker for the 4BT. You get a lot of the functional bang of the gasser V8, but with much better fuel economy.

    Here's another way to put it. Which one is going to be faster to freeway speed with the same 3000LB vehicle: The 130HP @ 2500RPM 4BT that makes 344 Ft Lb of torque @ 1500 RPM, or will it be the engine from a Shelby Series 1 that pushes out 320 HP @ 6500 rpm, but only makes 290 Ft Lb of torque @ 5000 rpm?

    Even though the Cummins is pushing out gobs more peak torque, and is going to come off the line with a bit more authority (if they're geared the same), something tells me that the Shelby engine is going to maybe be a little bit faster up the onramp if running both wide open. But the Cummins is going to be a bit nicer to drive (if you ask me..)
    Attached Files Attached Files
    Last edited by Machman; 08-26-2009 at 06:58 AM. Reason: Torque figure for 4BT quoted wrong..
    A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly.
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    Quote Originally Posted by BobS View Post
    You need to first confirm the problem BEFORE you start buying and replacing parts.

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    Quote Originally Posted by machman[B
    edit...
    If your concern is accelerating a weight (or, taking a more holistic view, overcoming inertia of a given mass,
    cut......cut....cut...

    ,But the Cummins is going to be a bit nicer to drive (if you ask me..)
    Well said.
    my $.02
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    charles charles charles

    he back yet??

    just kidding

    personally i liked the idea of the 4bt because no matter where I am, i am not that far away from someone that carry's parts. 4/6bts and cummins in general are everywhere. i can go to autozone and get a water pump. can you do that if you have a b3.3?

    i drive about 30k miles a year, so that's important to me.

    edit: for those that weren't here, this is charles: http://www.4btswaps.com/forum/member.php?u=238 looks like he last visited 12/10/08, but he hasn't posted since 9/27/07
    Last edited by Diesel Durango; 01-28-2009 at 06:49 AM.
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    Quote Originally Posted by machman View Post
    chop, cut, edit.... HORSEPOWER. (Well, at least in the civilized part of the world that doesn't rely on that abomination known as Metric.. Next they'll be wanting us to use measurements like Cubic Furlongs per Fortnight or some such. ) .....grind, grind, remove
    nah

    Decca Gills per Hecta Dram.

    At least they aren't measuring fuel economy in Rods per Hogshead.



    Thanks for the concise description on power, in it'a various 'but-o-meter' (as mentioned previously in this thread) forms.
    Erik
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    Quote Originally Posted by scout4bta View Post
    Well said.
    my $.02
    Sorry, I was in verbose mode..

    Quote Originally Posted by Diesel Durango View Post
    charles charles charles

    ..snip due to image limits in one post..

    personally i liked the idea of the 4bt because no matter where I am, i am not that far away from someone that carry's parts. 4/6bts and cummins in general are everywhere. i can go to autozone and get a water pump. can you do that if you have a b3.3?

    i drive about 30k miles a year, so that's important to me.

    edit: for those that weren't here, this is charles: http://www.4btswaps.com/forum/member.php?u=238 looks like he last visited 12/10/08, but he hasn't posted since 9/27/07
    Agreed on the parts availability being a prime consideration.

    The thing about Charles was that, he was technically correct. But something got lost in his delivery. (Or others' interpretation.. Your pick.) I must have revised and pondered my take on it for an hour before hitting the Submit Reply button for fear of stirring that pot again. And even then it's still not quite what I was hoping to deliver.

    Quote Originally Posted by nexxussian View Post
    nah

    Decca Gills per Hecta Dram.

    At least they aren't measuring fuel economy in Rods per Hogshead.
    Just had to go there, eh?
    Last edited by Machman; 01-28-2009 at 04:34 PM.

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