Engine Choices --3.3l vs. 3.9l
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Thread: Engine Choices --3.3l vs. 3.9l

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    Default Engine Choices --3.3l vs. 3.9l

    Hey. I'm fairly new to this forum and stumbled onto it by accident. However, reading all this has gotten me very interested in doing a diesel swap in my YJ. I currently have a '95 YJ with the 2.5l. It is mostly stock and retains the AX-5 tranny and the NP-231 t-case and d30 and d35 axles with 4.10's (I know a lot fo you know this already so sorry for the repeat). I don't know which engine to choose from between the 3.3l and 3.9l however. I know the 3.3 has less torque and hp but I have read that it gets better mileage and that you can put aftermarket injectors and an intercooler on it to make as much or more hp and torque than the 3.9 but I was wondering if anybody knew how this affected the mileage of the engine. I have heard of a lot of people getting in the high twenties and low thirties with the 3.9's, but I have also seen a lot of people get in the low to mid twenties with it and was wondering why this was. I was also thinking of swapping in the NSG370 6-speed manual transmission used in the '05-'06 TJ's. I also wondered why the o/d trannies get worse gas mileage than non. I was also thinking about swapping in a d44 rear and getting the d35 from an old rubi. However, I don't want to get a huge 6 inch lift and 35's. I would like to get by with a 2 in. lift to a 4 in lift at the most and was wondering if I would have to trim the hood or anything like that to make the engine fit. I know the 3.9l would require similar fabrications. Sorry for asking so much at once, I just have a lot of questions. Thanks.
    Last edited by sbartolic; 08-15-2008 at 11:39 PM. Reason: needed to add more to it

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    Quote Originally Posted by sbartolic View Post
    Hey. I'm fairly new to this forum and stumbled onto it by accident. However, reading all this has gotten me very interested in doing a diesel swap in my YJ. I currently have a '95 YJ with the 2.5l. It is mostly stock and retains the AX-5 tranny and the NP-231 t-case and d30 and d35 axles with 4.10's (I know a lot fo you know this already so sorry for the repeat). I don't know which engine to choose from between the 3.3l and 3.9l however. I know the 3.3 has less torque and hp but I have read that it gets better mileage and that you can put aftermarket injectors and an intercooler on it to make as much or more hp and torque than the 3.9 but I was wondering if anybody knew how this affected the mileage of the engine. I have heard of a lot of people getting in the high twenties and low thirties with the 3.9's, but I have also seen a lot of people get in the low to mid twenties with it and was wondering why this was. I was also thinking of swapping in the NSG370 6-speed manual transmission used in the '05-'06 TJ's. I also wondered why the o/d trannies get worse gas mileage than non. I was also thinking about swapping in a d44 rear and getting the d35 from an old rubi. However, I don't want to get a huge 6 inch lift and 35's. I would like to get by with a 2 in. lift to a 4 in lift at the most and was wondering if I would have to trim the hood or anything like that to make the engine fit. I know the 3.9l would require similar fabrications. Sorry for asking so much at once, I just have a lot of questions. Thanks.
    Take a look in the build up section there are several people that have done diesel swaps in vehicles similar to yours
    Turbo D

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    Everything you need to know about the 3.3:

    http://www.dieseltruckresource.com/d...d.php?t=112807

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    Quote Originally Posted by sbartolic View Post
    I know the 3.3 has less torque and hp but I have read that it gets better mileage and that you can put aftermarket injectors and an intercooler on it to make as much or more hp and torque than the 3.9 but I was wondering if anybody knew how this affected the mileage of the engine.
    I have a hard time believing that if you did the same mods to both engines that the 3.3 (non common rail) would produce more than the 3.9. But the 3.3 would more than likely be plenty adequate for your platform and be easier to fit due to smaller dimensions. What is your intended use for this vehicle? If you are all about mileage than I'd go with the 3.3.

    I have heard of a lot of people getting in the high twenties and low thirties with the 3.9's, but I have also seen a lot of people get in the low to mid twenties with it and was wondering why this was.
    I've only heard of a select few getting high 20s/low 30s with the 3.9. If you read up on the builds you'll see the 3.9 being put into all different kinds of mostly trucks (i.e. aerodynamic bricks) running different transmissions, pulling varying weights, turning different gearing, pushing different tires. Lots of variables so mileage fluctuates from one rig to the other. Not to mention the different conditions of the engine from previous wear to current mods. But a general average does seem to be in the 20s.

    I was also thinking of swapping in the NSG370 6-speed manual transmission used in the '05-'06 TJ's. I also wondered why the o/d trannies get worse gas mileage than non.
    The only way I see OD trannies getting worst mileage is from improper gearing and in OD the engine is being lugged (this is under driver control). In general at today's highway speeds an OD will return better mileage and if you plan on running the highway the consensous is that OD is a wise requirement with a diesel.

    Welcome aboard and know that you found a site with plenty of addicited diesel fanatics.
    85 Landcruiser FJ60, 4BTA, 4L80E Optishift controller, 203 doubler to splitcase tcase, SOA, 38s, and more.

    Family Haulin' FJ60

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    -Jon
    79 CJ5 4bt CTD/SM465/D20/D44 f&r/4.56 gears/spools/about 6" of lift.
    Quote Originally Posted by WC53 View Post
    My rod is a bit short and I need a longer one or I need to lengthen the one I have.

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    Quote Originally Posted by boots4 View Post
    ...
    The only way I see OD trannies getting worst mileage is from improper gearing...
    A properly geared Direct Drive transmission can return marginally better mpg than a properly geared Over Drive transmission. The DD is driving straight through the mainshaft of the transmission in top gear while the OD is compounding from input to a counter back to the main which is inherently less efficient.

    How much better mpg? Likely not enough to matter to a vehicle manufacturer.

    There are various reasons OD vs DD is used but it's not normally the gearing. The exact same final drive ratios in each gear can be achieved with a DD transmission as an OD one.

    A DD setup stresses the transfercase, the driveshaft, u-joints and differential more than a similar final drive ratio OD setup. The DD must use a 'higher' r/p ratio to achieve the same final, given the same tire size. Thus the transmission gears are 'lower' to account for the higher r/p. This results in more torque being transferred through everything between transmission and r/p. The OD setup stresses the driveline less due to more torque multiplication taking place after it, in the differential. So for a DD, the need for slightly tougher components to achieve the same service exists. This costs more...

    Ken

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    Looks like I stepped into the direct drive vs OD debate with my poorly worded "only" statement. While it seems most of that debate centers around the trucking industry I'm sure the principles cross over. It just seems that with a light vehicle (compared to the semi trucks) using an OD will allow more flexibility with being able to use a deeper axle ratio for easier take-off with the added benefit of an overdrive for the highway cruising instead of having to aim for one side or the other. OD kinda lets us have our cake and eat it too. I suppose this could be duplicated with a direct drive tranny with a granny gear and running a higher r/p but I wonder what the drivability would be. Perhaps there is a less-known/popular tranny that can be adapted to the cummins that closer matches the semi tuck trannies and has better gear spacing making a DD setup work like the semi's do. Most auto manufacturers seem to be running ODs now in manuals and autos (focusing on non-comercial vehicles).

    You are right Ken that the OD gearset is less efficient than direct drive and your insights on tranny stresses make sense. Guess I tend to side with the OD crowd.
    85 Landcruiser FJ60, 4BTA, 4L80E Optishift controller, 203 doubler to splitcase tcase, SOA, 38s, and more.

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    Quote Originally Posted by sbartolic View Post
    Hey. I'm fairly new to this forum and stumbled onto it by accident. However, reading all this has gotten me very interested in doing a diesel swap in my YJ. I currently have a '95 YJ with the 2.5l. It is mostly stock and retains the AX-5 tranny and the NP-231 t-case and d30 and d35 axles with 4.10's (I know a lot fo you know this already so sorry for the repeat). I don't know which engine to choose from between the 3.3l and 3.9l however. I know the 3.3 has less torque and hp but I have read that it gets better mileage and that you can put aftermarket injectors and an intercooler on it to make as much or more hp and torque than the 3.9 but I was wondering if anybody knew how this affected the mileage of the engine. I have heard of a lot of people getting in the high twenties and low thirties with the 3.9's, but I have also seen a lot of people get in the low to mid twenties with it and was wondering why this was. I was also thinking of swapping in the NSG370 6-speed manual transmission used in the '05-'06 TJ's. I also wondered why the o/d trannies get worse gas mileage than non. I was also thinking about swapping in a d44 rear and getting the d35 from an old rubi. However, I don't want to get a huge 6 inch lift and 35's. I would like to get by with a 2 in. lift to a 4 in lift at the most and was wondering if I would have to trim the hood or anything like that to make the engine fit. I know the 3.9l would require similar fabrications. Sorry for asking so much at once, I just have a lot of questions. Thanks.
    Responses in bullets:
    * 3.3 is a bit over 500 lbs
    * 3.9 is well over 700 lbs
    * your original 2.5 is not even 400 lbs.
    * If you want to use the NSG370 - get a 2.8l VM Motori 4 cylinder from a Liberty CRD (in USA, many vehicles in Europe) or a Mercedes Benz 2.7l 5 cylinder from a Sprinter. Both Cummins put out too much torque for the NSG370.
    * 3.9 is VERY tall.
    * with any of the diesels, you want to gear them for around 1500 rpm at 60 to 70 mph - the final drive ratio will depend on tire size and transmission selection.
    * as mentioned: http://www.dieseltruckresource.com/d...d.php?t=112807 is excellent.

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    Hey guys, just some more info on the Cummins 3.3L. This engine is a Kamatsu designed engine. I haven't taken a real close look at it, but it also might be indirectly injected which is common of japanese engines. If so, there goes the efficiency. Another thing to consider is the price of replacement parts. I know for a fact that no 3.3L are made in this country.
    2005 Dodge 2500 HO Cummins ISB5.9, 4x4, 4dr, 6 sp, II SPS 62/71/14, New Bosch Stainless Bodies with Bosch Motorsport nozzles from Exergy, Gauges, AFE stage 2 intake, MBRP 5 in. exhaust with FTE resonator, Smarty SSR, FASS 150, Firestone air bags, B&W gooseneck hitch. Back to 20mpg with the injectors.

    1997 2dr Tahoe 4x4, 4BT cpl 858, VE pump, aftercooled, HX30W, NV4500

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    Is the 3.3 taller than the 3.9? I have been looking at it and the link posted above only had a hood scoop to compensate for the height of the 3.3 and if that's all I would have to do for a 3.9 that would be fantastic. I am going to get a 2.5" lift with a little lift from shackles and wondered if you guys knew anything.

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    Quote Originally Posted by sbartolic View Post
    Is the 3.3 taller than the 3.9? I have been looking at it and the link posted above only had a hood scoop to compensate for the height of the 3.3 and if that's all I would have to do for a 3.9 that would be fantastic. I am going to get a 2.5" lift with a little lift from shackles and wondered if you guys knew anything.
    Here you go:

    www.4btswaps.com/forum/showthread.php?t=6169

    NOTE: There are lots of variants - High mount turbo - water to air cooler - etc. The dimensions of the engine that you buy may vary!
    1986 Ford F150 with 1952 Bell Telephone System service bed, 4BT, CPL 727 with 3,400 RPM governor spring, small aftercooler, AC, PS, Cruise, 1997 M5R2 5 speed overdrive transmission, Stock P215/75R15 tires, 2.75 rear axle ratio, approx 25 MPG average, Driven in 10 states in 2013, 2014 Diesel Confab - 22 states in 15 days
    http://www.4btswaps.com/forum/showth...rtbed-with-4BT
    Still plays with trucks

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