mpg difference between 4bt vs. 6bt? If 6bt is cheaper, why not as popular?
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Thread: mpg difference between 4bt vs. 6bt? If 6bt is cheaper, why not as popular?

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    Default mpg difference between 4bt vs. 6bt? If 6bt is cheaper, why not as popular?

    If it is cheaper to do a 6bt, why is everyone doing a 4bt? it would be fore a jeep wrangler for me, so what would be easier/chaper a 4 or 6 cylinder?

    Also, what would get better mpg?


    Thanks,

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    I have a 01' Dodge Diesel 5spd and I get 20 MPG at the best with no load. But I had to invest $3500 in motor mods to get that. I have heard of 6BT'S getting as high as 28 MPG but only if it is put in a much lighter, aerodynamic, vehicle with perfectly matched gears and tires at sea level. I am in the middle of my swap now but I have seen posting on this site with numbers as high as 32MPG with very minor tweeks. I went with the 4BT due to weight, size, price, and most of all V8 power with 4CYL MPG. The choice is yours but unless your converting a 3/4 ton or bigger I would go, and did, with a 4BT.

    GOOD LUCK ON YOUR SWAP 4 or 6BT
    Last edited by COLOJEEPGUY2K; 10-25-2007 at 09:37 PM.

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    Quote Originally Posted by rubicon lover View Post
    If it is cheaper to do a 6bt, why is everyone doing a 4bt? it would be fore a jeep wrangler for me, so what would be easier/chaper a 4 or 6 cylinder?

    Also, what would get better mpg?


    Thanks,
    4 cylinder is smaller and lighter
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    i asked myself the same question before doing my swap. i contemplated using a 6/354 perkins. i found the 4BT, and it had the same hp/tq numbers, with easier upgrades. also, the 4BT is only 350kg, versus 500-odd for the sixes. smaller and lighter ( relatively ! ) cars like my F100 suit the 4BT better.
    It pulls like a 14 year old with a playboy !

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    Default Milege figures and truth

    keep running into people with vehicles similiar to mine, I own 7 diesel vehicles that my family member and myself drive, and many people I meet report extraordinary mileages superior to what I get. I have well maintained equipment, and good, reasonalbe speed driving skill. The only difference is I never quote one tank, I quote a 2-3 thousand mileage average.

    For instance, my mercedes station wagon got just one tank that measure 32.5 MPG, my low is 25 (with a leak), average is 29.5. Does the car get 29.5 or 32.5?

    My pickup gets not towing lows of 16, high is 19.5 averages is 17 or was it 19.5?

    My best example is my tiny little old VW pickup. My average is 39-40. I keep meeting people that say these things get 50 MPG, 55 MPG. everybody knows that, they say. Having owned 5 diesel VW, I can hardly squeeze more than 40 out of it or any I have owned.

    Talking to a guy today, who (not much diesel experience) asked me what kind of milege I got in my pickup. 16-17, I said. At the price of diesel, why would I buy diesel, he said, I get that with my gas SUV. The difference I said, I said is my 1T can tow 15-25K loads, and still get 16-17 empty. Well, the reason, I asked he said, was a guy with a Duramax at the station said his bulley dog kit is leting him get 30 mile per gallon on his crew cab dually. Wow, I said, that is amazing mileage.

    Amazing, or is it just what he said, and not really a scientific measurement (or even true).

    Few years back, on the TDR, 4WD Dodge Cummins were getting 24-28 MPG, yet I have not met anyone who could prove over 22-23 with 2-3 K averages.

    Mileage and truth. My 2 cents.

    Wayne

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    I have noticed this phenomenon myself, and have reached the conclusion that most folks are not very scientific when it comes to figuring mpg. The fellow with the 26 mpg Dodge probably has not verified his odometer with a GPS, probably does not fill his tank at the same pump until fuel is coming out of the neck, and most likely has not averaged his figures over several tanks. My neighbor thought something was wrong with my 91 Dodge because it only gets 20 mpg instead of the 26 mpg that his 93 was getting. After I fixed his speedometer, he wasn't getting 26 anymore, more like 19.

    Back to the original question, I would speculate there are just as many, if not more, 6BT swaps as 4BT swaps. Deciding which engine to use is contingent upon the prospective vehicle, the vehicle's intended use, and countless criteria specific to each individual. The 6BT's weight and length make it more prohibitive for swapping into a smaller, lighter vehicle than a 4BT. If the vehicle intended for the swap has a short engine compartment, the front end is incapable of safely supporting the 1200 lbs a 6BT weighs, mileage is an important factor, and does not necessarily need the power a 6BT is capable of producing, then a 4BT is the obvious choice.
    "If it ain't broke, fix it till it is"

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    I was talking to someone yesterday that was amazed that i wasn't getting 40mpg with my swap... 40??? holy crap. I'm getting between 20-24 depending on what i'm doing, light towing or just travel. it is a slush box and has lost 1st gear, still 20-24mpg in a 4600lb vehicle is pretty darn good, it got about 12-14 with the stock engine. I'm hoping that it goes up a little bit with an NV4500 in there instead. We will see though.

    mileage figures from people drive me nuts, it's like an ego booster or something, blah blah blah. Everyone else seems to get amazing mileage and i don't. I don't think it's my driving, i think it's mostly just general exageration for dramatic effect...

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    It all depends on what the vehicle is, what you will be doing with it, the area you live in, etc. For a small vehicle, or 1/2 ton truck, a 4bt is the way to go. You would never get a 6b to work well in a Wrangler. It would destroy your frame, you would need a Dana 60 front axle to handle the weight, and you would never be working it very hard (diesels like to be worked). You could do fine with a 4bt in most 3/4 ton or larger trucks if you use them more for commuting than towing big trailers. You could even haul some pretty good loads in the bed, especially if you live in flat terrain. A 4bt would move just about any load across Iowa, but forget the Rockies with a 30 foot trailer behind it.

    Comparing mileage is the same. If you have a 5000 lb. vehicle in a flat area, you'll get great numbers out of a 4bt. But if you have a 10k lb. truck and live in the mountains, you would be much better off with a 6b.

    For costs, I don't see any difference between a 4bt and a 6b. They require almost all of the same components to make them work, and the engines cost very close to the same (at least from what I have found). The cheapest I have found a 6b is $1500-$2000. I see 4bts for those prices all over, including ebay.

    Jim
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    Default Fuel consumption thoughts...

    Here is a technical question pertaining to mileage and fuel consumption between the 4BT and 6BT. I realize to get accurate results it would take dyno and a lot of other equipment to verify the results.

    If you take a 4BT rated at 120 hp and a 6BT rated at 160 hp and compare the factory fuel consumption at 1800 rpm the 4BT will normally require less fuel in gallons per hour to operate at the same rpm, right? Now lets increase the fueling rate of the 4BT to equal that of the 6BT. Will the results then be a 4BT producing 160 hp or will it be less than or more than 160 hp? If you placed both engines in identical vehicles - would the highway mileage not be the same due to the equal fuel delivery rates?
    BobS

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    There are three things you can't argue about with a guy:

    How pretty his wife is

    How smart his dog is

    What mileage his ride gets

    Seriously, most people don't properly check mileage in the first place. Tire size changes don't get compensated for, etc. Tuners on diesels completely screw up the onboard computer calculators. I heard a story about a guy who bought a VW bug back in the 60s. He was telling everyone at work how good the mileage was. One prankster decided to mess with him. At night he would put gas into the VW in small amounts. The owner kept telling everyone "My car is getting better and better mileage as it breaks in." After a few months of doing this, the prankster started taking gas out at night. All the sudden, the car was getting worse and worse mileage! The guy kept taking it back to the dealer and they couldn't seem to find anything wrong with it.

    I put a 4BT in my 'burb because I knew it would be much easier to do than the 6BT because of the length, and I don't tow with it to need the extra power. It is a 3/4 ton, so it could have handled the extra weight, but I didn't feel that the 6BT was necessary. The 4BT pulls it great, and other than the idle vibration in gear, I really like it.
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    Quote Originally Posted by marcdeluca View Post
    There are three things you can't argue about with a guy:

    How pretty his wife is

    How smart his dog is

    What mileage his ride gets

    Seriously, most people don't properly check mileage in the first place. Tire size changes don't get compensated for, etc. Tuners on diesels completely screw up the onboard computer calculators. I heard a story about a guy who bought a VW bug back in the 60s. He was telling everyone at work how good the mileage was. One prankster decided to mess with him. At night he would put gas into the VW in small amounts. The owner kept telling everyone "My car is getting better and better mileage as it breaks in." After a few months of doing this, the prankster started taking gas out at night. All the sudden, the car was getting worse and worse mileage! The guy kept taking it back to the dealer and they couldn't seem to find anything wrong with it.

    I put a 4BT in my 'burb because I knew it would be much easier to do than the 6BT because of the length, and I don't tow with it to need the extra power. It is a 3/4 ton, so it could have handled the extra weight, but I didn't feel that the 6BT was necessary. The 4BT pulls it great, and other than the idle vibration in gear, I really like it.
    how is mileage with the 4L80E? How do you like it, what is your computer setup?

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    Quote Originally Posted by BobS View Post
    Here is a technical question pertaining to mileage and fuel consumption between the 4BT and 6BT. I realize to get accurate results it would take dyno and a lot of other equipment to verify the results.

    If you take a 4BT rated at 120 hp and a 6BT rated at 160 hp and compare the factory fuel consumption at 1800 rpm the 4BT will normally require less fuel in gallons per hour to operate at the same rpm, right?
    Correct!
    Quote Originally Posted by BobS View Post
    Now lets increase the fueling rate of the 4BT to equal that of the 6BT. Will the results then be a 4BT producing 160 hp or will it be less than or more than 160 hp?
    It'll have more HP but you cant tell w/o a Dyno - need more info

    Quote Originally Posted by BobS View Post
    If you placed both engines in identical vehicles - would the highway mileage not be the same due to the equal fuel delivery rates?
    Nope, the 4BT still might have a slight edge, due to the weight difference of the engines (<1mpg) in a small vehicle. As the vehicle weight increases the mileage of the 4BT would eventually equal, then drop off quicker than the 6BT (Insert Line Graph here )

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    Quote Originally Posted by marcdeluca View Post
    Seriously, most people don't properly check mileage in the first place.
    QFT

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    Quote Originally Posted by COLOJEEPGUY2K View Post
    I have a 01' Dodge Diesel 5spd and I get 20 MPG at the best with no load. But I had to invest $3500 in motor mods to get that. I have heard of 6BT'S getting as high as 28 MPG but only if it is put in a much lighter, aerodynamic, vehicle with perfect mathced gears and tires at sea level. I am in the middle of my swap now but I have seen posting on this site with numbers as high as 32MPG with very minor tweeks. I went with the 4BT due to weight, size, price, and most of all V8 power with 4CYL MPG. The choice is yours but unless your converting a 3/4 ton or bigger I would go, and did, with a 4BT.

    GOOD LUCK ON YOUR SWAP 4 or 6BT
    shoulda got a 12v... 20mpg empty is cake. bump the timing and turn up the fuel a little, and a couple more isn't out of the question

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    Quote Originally Posted by Forrest Nearing View Post
    shoulda got a 12v... 20mpg empty is cake. bump the timing and turn up the fuel a little, and a couple more isn't out of the question
    Yeah turning up the fuel sounds like a perfect way to consume less fuel...

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    Quote Originally Posted by mooktank View Post
    Yeah turning up the fuel sounds like a perfect way to consume less fuel...
    it is... amazing how that works, isn't it?

    same with adding a mild programmer to a computer controlled truck... mileage comes up.

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    Quote Originally Posted by BobS View Post
    Here is a technical question pertaining to mileage and fuel consumption between the 4BT and 6BT. I realize to get accurate results it would take dyno and a lot of other equipment to verify the results.

    If you take a 4BT rated at 120 hp and a 6BT rated at 160 hp and compare the factory fuel consumption at 1800 rpm the 4BT will normally require less fuel in gallons per hour to operate at the same rpm, right? Now lets increase the fueling rate of the 4BT to equal that of the 6BT. Will the results then be a 4BT producing 160 hp or will it be less than or more than 160 hp? If you placed both engines in identical vehicles - would the highway mileage not be the same due to the equal fuel delivery rates?
    You should get a little better mileage with the 4bt. Less inherent friction, and less weight to move=less rolling friction.

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    Quote Originally Posted by Forrest Nearing View Post
    shoulda got a 12v... 20mpg empty is cake. bump the timing and turn up the fuel a little, and a couple more isn't out of the question
    My '96 Ram Cummins 4x4, auto trans, 2500, 3.54 gears with 235/85/16 tires gets an average of 22mpg around town. One tank best was with my friend driving on the highway at 55-60 mph, where he got 25mpg. Increase speed and the motor left the sweet spot and sucked more fuel.

    Jim
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    a 6bt wont fit in your vehicle and also its too heavy for it. 4bt,s get alot better milage also

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    Quote Originally Posted by bcowanwheels@aol.com View Post
    a 6bt wont fit in your vehicle and also its too heavy for it. 4bt,s get alot better milage also
    I agree, way to heavy for a Wrangler!

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    There are alot of ways to get phenomenal mileage with a 4bt. My 4bt once went over 100 miles on 1/2 pint of fuel!!! The secret is that it was in the bed of my ford on the way home and 1/2 pint is what dripped out of the fuel lines. Putting your truck on a trailer and towing it is another great way to get phenomenal mileage. It actually won't burn any fuel at all while it is on the trailer, but it is still moving. Some guys get 10% mileage increase driving from the mountains to the coast(downhill). Another way is the alternate method of figuring fuel used. Most peoples tanks have a couple gallons above full and 1/2 tank is actually less. So you figure you have a 20 gallon tank and you figure mileage when the needle hits 1/2 full and say you've burnt 10 gallons. (Actually you've burnt more like 12-13)..........Serious diesel mileage figures-71 chevy 4wd with 4bt-22mpg, 4spd diesel rabbit 43-47, Mitsubishi 4wd delica van turbodiesel 24mpg, new Ford ranger diesel (Thai version) 27 MPG at 70-75mph, New toyota diesel pickup nonturbo 2wd(thai version) 29mpg, mercedes 240D 28-30mpg, mercedes 300CD turbo 25-28mpg, 81 isuzu pickup 37 city 40-42 highway, military HMMWV (highway at 80mph 6mpg,on road normal driving 12mpg, tactical mix 8mpg, cross country 4mpg), Military LMTV(new 2.5 ton) 8mpg, Sheridan armored recon vehicle 5mpg.........Based on what I've seen I don't see where the super high mileage figures come from either.

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    Quote Originally Posted by nhdiesel View Post
    It all depends on what the vehicle is, what you will be doing with it, the area you live in, etc. For a small vehicle, or 1/2 ton truck, a 4bt is the way to go. You would never get a 6b to work well in a Wrangler. It would destroy your frame, you would need a Dana 60 front axle to handle the weight, and you would never be working it very hard (diesels like to be worked). You could do fine with a 4bt in most 3/4 ton or larger trucks if you use them more for commuting than towing big trailers. You could even haul some pretty good loads in the bed, especially if you live in flat terrain. A 4bt would move just about any load across Iowa, but forget the Rockies with a 30 foot trailer behind it.

    Comparing mileage is the same. If you have a 5000 lb. vehicle in a flat area, you'll get great numbers out of a 4bt. But if you have a 10k lb. truck and live in the mountains, you would be much better off with a 6b.

    For costs, I don't see any difference between a 4bt and a 6b. They require almost all of the same components to make them work, and the engines cost very close to the same (at least from what I have found). The cheapest I have found a 6b is $1500-$2000. I see 4bts for those prices all over, including ebay.

    Jim
    I 100% agree with this post. More over, it is what I have found with my swap. I looked and looked for a year and a half for a 6BT that was affordable and found that I couldn't get the whole truck, only the pulled motor. I did find that it was cheaper for me to go with a 4BT rather than a 6BT, although I didn't know I would have to go to Chicago to get it. Since the vehicle I'm puttng the motor in is a rock wheeler, snow plower, daily driver, and weekend camping vehicle, I know the 4BT will serve me better. Becuase I live in the mountains of Colorado I don't intend to tow heavy with it, that's what the Dodge is for
    Last edited by COLOJEEPGUY2K; 10-25-2007 at 10:07 PM.

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    I have an 87 V3500 chevy....that is a 1 ton, 4x4, long bed, 4 door. Add to this has 35" tires and the 6BT becomes the obvious choice. I need 500lb/ft of torque just not not feel like I am driving gramma's car.

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    Quote Originally Posted by Diesel Durango View Post
    how is mileage with the 4L80E? How do you like it, what is your computer setup?
    I have only put about 300 miles on the rig, so I can't give you mileage numbers yet. Also, I run alot of propane, so that completely clouds the issue. I am hoping for 25 mpg on #2 only. I should be able to achieve at least 60 mpg on #2 when doing propane. I have gotten that on my Duramax, so this 'burb should be able to.

    This 'burb had the electronic 6.5L before. I am using the same computer. I welded a throttle linkage onto the existing TPS lever in the cab. This way, I have mechanical control over the 4BT pump, but still retain TPS for the computer. I took the crank sensor from the 6.5 and put it directly in front of the crank pulley bolts. This way it counts the 4 bolt heads, which gives the same amount of pulses per rev as the 4 lobes on the timing gear of the 6.5. I am having a custom EEPROM written for the computer to remap the throttle. I currently have to back off the pedal to get it to upshift for each gear. With the propane, this little engine has plenty of power to pull my 3/4 burb around. It is governed at 2900, which is 81 mph with the 4.10 rear.
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    Quote Originally Posted by robmobile1970 View Post
    Some guys get 10% mileage increase driving from the mountains to the coast(downhill).
    I have experienced similar with a 4.0L Cherokee. I've made numerous trips from Louisiana to Colorado. I always get better mpg returning home to Louisiana.

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    Quote Originally Posted by 95Z28A4 View Post
    I have experienced similar with a 4.0L Cherokee. I've made numerous trips from Louisiana to Colorado. I always get better mpg returning home to Louisiana.
    In reality, do you get 10% worse mileage (than average) on the way home?

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    Louisiana To Colo. Is All Up Hill And Reverse Back.

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