How do I up the MPG's on my Willys Jeep???

Discussion in 'Flat Fender Tech' started by mikec4193, Apr 4, 2012.

  1. Jun 19, 2013
    Bob-The-CJ

    Bob-The-CJ Member

    Waxahachie, Texas
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    One of our Jeeps on the farm had it and unless you want to drive real real slow I would not recommend it.

    But concerning the conversion, it is simple - many forklifts have the Lhead engine and run on propane, you just take the stuff off one or work out one the part numbers. You are talking a few hundred dollars

    Since I commented on this I want to say something else. I always see people bring up air resistance, that is more or less an urban myth with these Jeeps. The air resistance on these Jeeps (well CJ5, not sure on the flat fenders exactly) is very close to that of a Suzuki Samurai, the Samurai gets over 35 MPG when new and they could drive 100 MPH. So I am not saying there is not a lot of wind resistance but what I am saying is it is not affecting top speed and gas mileage as much as people make out.

    If your Jeep was setup right, and had the right gears you could easily see MPG near 30 mpg. I don't however see that happening with either the FHead or the LHead engines, those engines and low gears are the real problem.

    For the record, I suspect our propane driven flat fender got what is roughly equal to 28-30 mpg with stock gear and no OD, but I will say this again, it was insanely slow. I would venture to guess the HP went down to about 30 hp
     
    Last edited: Jun 23, 2013
  2. Jun 19, 2013
    duffer

    duffer Rodent Power Sponsor

    Bozeman, MT
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    I think the biggest problem with using propane would be the limited refueling locations. If you wheel in the boonies, it could be a big problem. Most pitstop "towns" will have a gas pump but not many are going to have bulk propane, at least anything more than maybe a 10 lb tank.
     
  3. Jun 19, 2013
    tarry99

    tarry99 Member Sponsor

    Northern California
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    I would agree with Duffer...........hard to find refueling stations in a lot of area's not withstanding trying to place an adequate sized fuel vessel somewhere in a Jeep...........lower cost per gallon but also less BTU's by about 10-20% which equates to questionable mileage increase per gallon when compared to gas while the engine still has to perform the same work load with less power. Lots of Major Trucking carriers have fleets of trucks now running on propane.........they of course do well when they are on flat ground.
    Probably the major benefit has been the reduced maintenance cost as the cleaner burning fuel does promote less engine wear & damage and has extended the oil change cycle's out to 20-25k miles from about 12-15k. Higher compression is also nice for maximum efficiency.
     
  4. Jun 20, 2013
    nickmil

    nickmil Super Moderator Staff Member Sponsor

    Happy Valley, OR
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    This.

    And I'd have to disagree with the comment above about a Samurai driving 100mph. Not likely. Possibly, under test conditions, on a test track, but certainly not on an Interstate with crosswinds and other traffic like large trucks.
    I've modified several and have had several students who owned them. In stock form, running well, most were good up to about 55-60 mph. We put a Datsun/Nissan A-15 (1500cc) 4 cylinder and 5 speed in Dad's and it would handle a max of 80mph and that was extremely spooky. That was with offset and wider than stock wheels and tires and anti-sway bars.
    The stock 1100 or 1300 cc engines (depending on model), no way.


    Sent from my iPhone
     
  5. Jun 20, 2013
    aallison

    aallison 74 cj6, 76 cj5. Has anyone seen my screwdriver?

    Green Cove...
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    I have a suzuki and I can say the MPG was not impressive. I'd say around the mid teens. It has not ran since the early 90's so I'm going from memory. And I can say with confidence if you take the little motor, toss in bigger pistons, a hot cam and quad carbs, with 4.56 gears and 33's it does pretty well. But top speed is around 65 in 4th gear. To motor runs like a raped ape and the Sammy takes off like a shot from about 3K RPM to around 8K RPM. And as long as you keep the RPM's up, it goes.

    But bottom line is you have a slow jeep that was never made to get MPGs, it was a work horse and it still is. You can work to improve them but they will never be "good". And when you look at spending a bunch of money on something that gets better MPG, or improves the jeep's MPG, you really need to look at the amount of fuel that could buy and what kind of return on investment you will get.

    I drive a dodge diesel truck. I get 22 mpg and drive 80 miles round trip each day. To get a different car, it takes too long to get ROI for me to do it. So I drive the truck.
     
  6. Jun 23, 2013
    Bob-The-CJ

    Bob-The-CJ Member

    Waxahachie, Texas
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    The farmers that use propane get it delivered in bulk and keep it on site. They don't fill up while driving about.
     
  7. Jun 23, 2013
    Bob-The-CJ

    Bob-The-CJ Member

    Waxahachie, Texas
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    If your Suzuki got in the mid teens there was something seriously wrong with it, plus it must have been a carb version. Even running 30 inch tires mine would get in the mid 20's. When my Samurai was brand new, and I was still running the stock tires I was getting very close to 40 mpg in it. Most of the time it was 37-38 mpg.

    But I agree with the part about tires and the gearing (RPM's) - without changing the gears you are stuck around 30 inch tires on the Samurai.

    Nickmil you can disagree with the Samurai going 100 mph all you want, it is a fact they could do it. Saying they are good to 55-60 is a joke, I never drove mine below 70 mph on the interstate, and I drove it for 11 years and 280,000 miles - never going below 70 mpg on the interstate unless the wind was really bad. And even then I did not go slower because it couldn't go faster, I slowed down in case a side wind hit it. I even got a ticket on 635 in Dallas going 89 mph. I owned one from brand new and 3 used. The new one with fuel injected was great, I owned one with carb and it was complete junk, I got rid of it as fast as possible - so maybe if your experience was with carbed ones then I could almost see your point. Not completely but almost, but being as I helped people work on the stock carbed ones and got them driving in the mid 70's easy, I can't see anyone with even basic mechanical skills could not do the same. I know for certain your skills are far above basic.

    When my 91 Samurai was brand new it would easily do 100 mph. I once drove it over 95 mph for 4 hours and it did not even get hot. My 91 was a bone stock 1.3 liter fuel injected JL model. Absolutely would drive 100 mph, it would even maintain 70 through modest hills. Funny you mention a Datsun because my first truck was a Datsun with the 1.6 liter - the Samurai was so much more powerful than that truck it was not even close. My little truck did top out somewhere around 80 mph

    No Samurai ever came with a 1100 cc engine - you sure we are talking about the same vehicle? The Samurai was a north America only model and only came in the 1300cc engine. There were two versions - the carb version which was really bad but would still drive in the 80's easy enough and the fuel injected model which had no problem driving 90+ for as long as you could stand to do it. The J410 did come with a 1100 and I would impressed if one of those could hit 60 mph let alone anything more.
     
    Last edited: Jun 23, 2013
  8. Jun 24, 2013
    trawler Scott

    trawler Scott Member

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    My M38 has a sammy frame, toyota running gear(20R,4spd) is running 35's and I average around 21mpg with a best of 23mpg. A more modern 2.7 Toyota engine would put me mid 20's with 50-60 more hp, I can bolt in a Toyota turbo diesel as it sits and would expect mid to high 20's with the diesel.
     

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