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how important is making power down low

Discussion in 'The Garage' started by Paxx, Apr 21, 2006.

  1. Paxx

    Paxx 1/2 ton status

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    Ok we all know that you want your torque down low for a truck engine right. Well what about when you add a doubler? With all the gearing does it change where you want your power to come in? It would be nice to have the power come in a little higher for mud and sand if your gearing could compensate for the lack thereof down low. What is everyones opinion on this?

    I plan on using 4.56 gears with 42's though so it might still be necessary to have the power come in lower but then again maybe just starting in 1st gear instead of 2nd would work? For those that don't know I am trying to build this truck for all around use with the least amount of comprimises. I need to plan the engine to fit with the rest of the build plan. I already know it will be a BB probably a minimum of 500cid so I can get a good long flat torque curve. Maybe something that makes peak power mid-range? I need opinions on this though so everyone feel free to chime in.

    ~Max
     
  2. trailblazr81

    trailblazr81 1/2 ton status

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    With 42's I would run more gear. Maybe 5.13's or more. Ive run 4.56's with 35's in a DD before. I run 4.10's now cuz thats what was in the axles. Put gears in it so its close to what RPM's you were turning stock. Maybe a couple hundred RPM more. Then build for low end torque and mid range power.
     
  3. hack500

    hack500 1/2 ton status

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    the higher you have to rev it the more gas you'll use/need so.
    a 6000lb caddy ran about a 26" tire with a rear ratio around 2.73:1.

    as long as you stay with the stick and the doubler you'll have plenty of gearing options to keep it in whatever sweet-spot the engine wants.
     
  4. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    What do you mean by "all around use"????

    Are you talking about all forms of offroad driving, but NOT street driving.....???


    Remember that lower gearing is used to increase "torque" at the wheels. If you don't have the motor to get the torque you need (like a 4-cyl Toyota)...then you put lots of gear reduction to make up for it.

    An engine that makes more bottom-end power doesn't need as much gear reduction (torque) because it's available from the engine already.

    Ultimately, your magic number for "torque at the wheels" is the multiplication of the engine torque (at a given RPM) times all of the gear ratios that it passes through on the way to the tires. As you can imagine, there are MANY combinations that can yield the same magic number....

    One thing that IS worth considering, is that a setup using more engine torque and less gear will be more able to give a "burst of speed" to clear an obstacle....whereas a deep-geared, small motored rig will spin a lot of RPMs quickly, but won't make much forward progress by just "goosing" the throttle.


    :usaflag:
     
  5. Paxx

    Paxx 1/2 ton status

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    yeah i did mean all around offroad use, not street use. And I will have both the gearing and the torque. I already have the doubler and I am going to use a big block, I would just like to know if I would be better off having an engine that makes power at 2500-5000 instead of 1000-3500 since i have a doubler going in.

    Does that make sense?
     
  6. sdavid

    sdavid 1/2 ton status

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    Also consider where your RPMs will be when you shift from gear to gear on the 465. That is not a very close ratio trans in the first couple of gears, so if it is higher than a 2500 rpm torque curve you will have to ride the clutch a little or rev during the shift to hit peak power. My experience in mud with a 465, you got to have some momentum and know your clutch throw and rpm shift point very well to get the best result.
     
  7. 1977k5

    1977k5 3/4 ton status Vendor

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    Go with the 2500-5000 torque curve. You can use the real first gear in the tranny on the street if you need. The doubler will be plenty low off road. 4.56's will be fine with your setup, IMO. That's what I have and I think its too low. I won't be changing gears when I go to 42's.
     
  8. 85-m1028

    85-m1028 1/2 ton status

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    I run a 6.2 diesel and 4.56 gears, I will run 42"s and 4.56 as well. without an overdrive rpms can get up there quick, thats about 2500 rpms at 65mph
     
  9. RootBreaker

    RootBreaker 3/4 ton status Premium Member

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    well I am running 40" hawgs (38.8 true measured0 and 4.56's with a smc465 trans.... my motor was my problem... 195hp/295lb-ft torque... out of a 1991 caprice police car. Problem was truck made power at about 2500rpm's and up... so on the pavement it would start off slow until the power band then launch.....

    well I re-cammed... went with a 4x4 xtreme cam... vortec heads and intake..... MUCH MUCH BETTER.... I was going to go with a bigger cam but the rpm's power range were higher like 1200 or 1500 and up vs my current idle to 5000..... personally I lost some HP/torque due to going with a smaller cam but I now have power off of idle...

    depends on what you are looking for. I do mud, trails... no rocks... so yeah ya figure higher rpm's but I can bang gears out in the mud with 0 problems....

    all in all it is going to depend on what you are looking for...

    one of the biggest things to me is in the mud... I have WIDE tires plus detroits front and rear... I watch people with tires smaller and up to mine.. they have to work their trucks through the mud... I just go in nice and lay into it a bit.. the lockers help so much......

    whatever ya do it is trial and error.. good luck...:wink1:
     
  10. Paxx

    Paxx 1/2 ton status

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    sdavid I understand what you are saying about the gears with the 465. My current engine makes power at about 25-2600 rpm and your right when you shift it seems to miss the powerband. It usually grabs the next gear at about 2000rpm. So I guess if the powerband started at 2000 it would always catch in the right spot. It's been a while since I have gotten to drive the thing so I kind of forgot about that. Thnx for reminding me.

    So rootbreaker, what your saying is that even in the mud your happier with your powerband being lower? Thats kind of where I had figured the higher powerband would be more desirable. (I'm trying to omit the trial and error part lol)
     
  11. RootBreaker

    RootBreaker 3/4 ton status Premium Member

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    I think the detroit lockers also help this factor but yes... even under powered I had no problems enjoying it.... I will be going out hopefully soon and will bring my camcorder.. to take some movies....:wink1:
     
  12. Paxx

    Paxx 1/2 ton status

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    awesome. shoot me a pm when you get the video, i would love to see it.
     
  13. Hossbaby50

    Hossbaby50 3/4 ton status

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    Whatever you do make sure your engine idles well and can have at least some torque off idle. When you are crawling with a manual you just let it ride alot of the time and if you get into some heavy crawling spots you want your motor to be able to torque itself over things. A doubler is alot of gear but even with that much gear you still need to have throttle response and power off idle.

    From what I have always read about peak fuel mileage vs. torque is your best mileage will happen when you are at or near your peak torque band. So if you are still going to street drive the truck I would build the motor to have most of your torque at your cruising RPM and have the peak HP above your cruise RPM.

    I would build the motor to have good off idle power but have all its power down low.

    Harley
     
  14. FOR MUD

    FOR MUD 1/2 ton status Premium Member GMOTM Winner

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    I have a 350cid and 203/205 and I'm running 4.88 gears with 44" tires the only thing dif is a th350 trans . It gives me good wheel spin in mud in the higher ranges and still good lower end for slow stuff . I would wait until you instal the BB and see what it feels like and then swap if needed , why spend the $ if you don't have to
     
  15. Paxx

    Paxx 1/2 ton status

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    i'm not really all that concerned with street driving. I'll probably buy a tow rig this fall that will serve as a DD. I just want the best offroad performance possible. Mileage will suffer but oh well. As long as I get about 6-10mpg that will do.
     

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