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Mopar flathead 6 motors- whats to be expected

Discussion in 'The Hokey Ass Message Board' started by Modeljunkie, Dec 8, 2011.

  1. 1956 Belvedere
    Joined: Jul 1, 2013
    Posts: 15

    1956 Belvedere
    Member

    How does a super interesting thread go so strong and just die?

    Please continue the banter about flat head Mopar 6's.
     
  2. plym_46
    Joined: Sep 8, 2005
    Posts: 4,018

    plym_46
    Member
    from central NY

    looks like most of those whom had something to say said it.
     
  3. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    mustang6147
    Member
    from Kent, Ohio

    Probably cuz of the P15D24 forums.


    That's if you can stomach their arogance
     
  4. Barn Find
    Joined: Feb 2, 2013
    Posts: 2,312

    Barn Find
    Member
    from Missouri

    I've got a 230 in my '42 Dodge Carryall. I believe the military version is rated at less than 100 hp. It takes some patience to pull a nearly 6,000 lb truck, but it does pull it. Check out www.dodgepowerwagon.com or Vintage Power Wagons in Fairfield, IA for sources of parts. 230s are plentiful there.

    I couldn't stand to put a V-8 in this old truck. I'm experimenting with a Chrysler straight-eight. It is 324 cubic inches, 135 hp and 275 lb-ft torque at 1200 rpm. It's gonna take some serious re-engineering for the added length, but I think it is doable in the truck.

    [​IMG]
     
    turboroadster likes this.
  5. 73RR
    Joined: Jan 29, 2007
    Posts: 7,175

    73RR
    Member

    The L8 is an interesting engine to be sure but you will spend some serious time/money trying to get it to fit. The first obstacle you will find is that the bellhousing bolt pattern is completely different than the L6 so it is not a bolt-up.
    Although the idea of a v-8 may make you cringe, they will likely be a lot less work and even a 360 can double the HP/TQ. If you need old-skool then look at the 318 Poly (check out Chrysler Power Magazine for a new engine building series featuring the 318P)
    If you just-gotta stay with an inliner then look at the Jeep 4.0 or go completely wild and look at the JAG 4.2.


    .
     
  6. Barn Find
    Joined: Feb 2, 2013
    Posts: 2,312

    Barn Find
    Member
    from Missouri

    The straight-eight does bolt up to the Power Wagon bellhousing, and I've got my clutch and flywheel all together. The front motor mount even fits, I just need nine inches additonal room between front and back. That was easier than you might think on my truck platform. It would be much harder in a car.
     
  7. mtkawboy
    Joined: Feb 12, 2007
    Posts: 1,213

    mtkawboy
    Member

    My half a bubble off high school buddy joe drove his 50 plymouth up to my dads house. I said Joe the pan is leaking. He replied no it isnt, there isnt one on it, Im going to the parts store to get a pan gasket. We looked underneath and sure enough there wasnt one on it, Id like to report a happy ending but the rods started knocking. They were tough, just dont turn them too high. We put a lot of straight 8 Chryslers in them back then, early 60s
     
    JOHN H EDGE likes this.
  8. 64 DODGE 440
    Joined: Sep 2, 2006
    Posts: 4,421

    64 DODGE 440
    Member
    from so cal

    The big Chrysler flathead 6 works well too.
     
  9. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,657

    Rusty O'Toole
    Member

    Suggest you use the larger Chrysler/DeSoto/ Dodge truck engine. It was actually used in Power Wagons in the fifties, the last vehicle Chrysler built with flatheads was a 68 military Power Wagon with the 251 six.

    In stock form 265 cu in 120HP. Can be bored to 283 cu in. With a little work you should be able to get 150HP without using very high compression or going too radical on the cams etc.

    Also comes stock with full flow oil filter.

    To me this would be easier and better than the straight 8. I like the straight eight but parts are hard to get. I don't think it would have much advantage over a good big six.
     
  10. Barn Find
    Joined: Feb 2, 2013
    Posts: 2,312

    Barn Find
    Member
    from Missouri

     
  11. alsancle
    Joined: Nov 30, 2005
    Posts: 1,572

    alsancle
    Member

    My understanding is that the bolt patterns on the bell housing for the 23 inch, 25 inch and Straight 8 Mopar are all the same. But I don't know that as a fact so any confirmation from somebody that really knows would be appreciated! I've been particularly interested in putting a late 30s 3 speed top shift overdrive from the 8 into a later 3 on the tree 6 banger car.
     
  12. plym_46
    Joined: Sep 8, 2005
    Posts: 4,018

    plym_46
    Member
    from central NY

    The 265 torque out at just about 210, Look for them at airports in tugs and ground support equipment, or if the is old farm equipment about, look for Massey Ferguson combines. They were powered by 251 and 265 flat 6. Beides finding room for 2 inches i length is gonna be easier than 4 or 5 of the Straight 8, and parts for those are scarce and pricey. Plus they gotta weigh close to 850 lbs. w/o the trans.

    Hope that wasn't too arrogant.
     
  13. Barn Find
    Joined: Feb 2, 2013
    Posts: 2,312

    Barn Find
    Member
    from Missouri

    I have them bolted together. I had to source a clutch from a 2-ton truck that would bolt to the eight flywheel and match my 1-ton truck four speed. The bellhousing defintiley bolts up.
     
  14. bigboy308
    Joined: Feb 7, 2007
    Posts: 144

    bigboy308
    Member
    from Merlin, OR

    I know of one person that is installing a 308ci Hudson Hornet flathead engine in an early Plymouth Coupe. 1/2" stroker crank takes it to about 350ci. Using a 700 R4 o/d behind all.

    Might fool some of the people!!
     
  15. 73RR
    Joined: Jan 29, 2007
    Posts: 7,175

    73RR
    Member

    Either you have a bell with dual bolt patterns (which Chrysler did on occasion) or, there are two very different L-8 blocks out there (which I kinda doubt).
    Last year I made a one-off adapter for an L-8 and the back of the block wasn't even close the an L-6 design (I have those adapters on the shelf)...just sayin'...

    .
     
  16. Tim Keith
    Joined: Jan 1, 2010
    Posts: 65

    Tim Keith
    Member

    Per conversation with Mr Asche I wouldn't be too concerned about occasionally turning 4,500 RPM in a 265. The motors were popular in mid-duty trucks and were very dependable in hard use when properly maintained. George told me that he's ran the flatheads hard since he was a teenager and never had a failure that wasn't anticipated. He said that odds are that when rods have been thrown in flathead that the bearings were badly worn with low oil pressure and the oil level in the sump was also low. Now, that being said these motors can run for years in badly wounded condition without making much of a complaint. That is also a reason that these motors have a reputation for being a dog - many of them are flat worn out but seemingly running smoothly. He said that the rods won't cut loose without advance warning, that if you pay attention to the condition of the motor - watch the oil pressure and temperate as you should with any motor, there is little to worry about. Even at 150 HP the internals are not highly stressed. These motors make torque at low speeds so that unless you have a light car you won't have a need to operate at high RPM anyway. With modern oils there is an extra margin of safety, and you can do the oil system mods. I got my 265 from George, it has a standard spec crank. Although not traditional I might consider fuel injection to help distribute fuel more evenly, the two and three carb setups are cool, but EFI might be a good, although I'm sure that's not popular on this board and fully agree, yet fuel injection was used back then, although not on vehicles. I think 150 HP wouldn't be on the ragged edge, I think you could drive across the US at that level of output in a 283 ( 4.6 liter ) flathead six. A 5 or 6 speed would be good to keep the motor in its torque curve, the 200R4 is gaining some popularity with these sixes.
     
    Richard Hartman likes this.
  17. Bmartin
    Joined: Jul 22, 2013
    Posts: 35

    Bmartin
    Member
    from mesa,az

    Love this thread. Great info on the flat 6. Does anyone have a link to a writeup installing the 25" block in a 1940 Plymouth or similar? I'm battling with this decision right now. I know the 230 can make good power, but I'd like to start with the larger engine. Thanks.
     
  18. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,657

    Rusty O'Toole
    Member

    Transmission and bell housing bolt up, motor mounts must be relocated 2" farther forward (some frames come with extra bolt holes drilled). Rad must be moved forward. That's about it.

    There are variations in starters, flywheels, 6 vs 12 volt starters but pretty straight forward swap. P15D24 can help with the details.
     
  19. ^^Diddo^^

    Posted using the Full Custom H.A.M.B. App!
     
  20. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,657

    Rusty O'Toole
    Member

    I don't know if I linked this before on this thread but it is interesting anyway. If you want to know what is to be expected of a flathead Chrysler here is a guy who bought one new and drove it 185,000 miles.

    Happens to be a DeSoto Suburban 8 passenger sedan. If the old flathead can make good in that whale it can do anything.

    My favorite quote, at high altitudes at 70MPH it smooths out like a perfectly balanced turbine. This in a 6000 pound car with 4:11 gears.

    http://www.allpar.com/cars/desoto/suburban-1951.html
     
  21. 64 DODGE 440
    Joined: Sep 2, 2006
    Posts: 4,421

    64 DODGE 440
    Member
    from so cal

    Pretty impressive bit of automotive history there. Treat them right and they will return the favor.
     
  22. Hemi Joel
    Joined: May 4, 2007
    Posts: 1,528

    Hemi Joel
    Member
    from Minnesota

    I need a little advise on my 48 Plymouth convert: It has the 218 that had a stock rebuild from Gopher engine about 15,000 mile ago, and an overdrive out of a '53 Plymouth. I'm going to hop it up a bit with an Edmunds high compression aluminum head, 2 carb intake, Fenton headers and dual exhaust. I also have on old NORS dual point conversion kit for the stock distributor. My question is about a NORS Howards 3/4 cam that I have. if I stick the cam in there, how bad will it hurt the low end tork, and how much will it help the power and in what RPM range? I'm not sure if it is wise or not for street use?
    Second question is about carbs. I have different intake manifolds to choose from, set up for either the B&B carbs or for Stromberg 97 3 bolt carbs. I have rebuildable cores of both styles of carbs on hand. Which would work better?
    Thanks, Joel
     
  23. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,657

    Rusty O'Toole
    Member

    You need a cam to get the most out of the extra carbs and headers. It sounds like an excellent combination for street use. It shouldn't hurt the low end too much, your engine idles down to 400 RPM now, you might have to boost it to 500 or 600.

    I don't know about the carbs.

    One suggestion. If you have the trans or engine out, or need to renew the clutch, have the flywheel lightened. This gives whippier acceleration and doesn't hurt the running any. It is an old hot rod trick from the days of 3 on the tree and flywheels like manhole covers ha ha.
     
  24. A chrysler marine manifold would give your in line six a unique look, they are hard to get, but they are intake and exhaust in one. Here is a few pics of one i have.
     

    Attached Files:

  25. 64 DODGE 440
    Joined: Sep 2, 2006
    Posts: 4,421

    64 DODGE 440
    Member
    from so cal

    I believe that those are designed to have water running through them when operating.
     
  26. daliant
    Joined: Nov 25, 2009
    Posts: 692

    daliant
    Member

    You'd also need an updraft carb to go with it. Also the exhaust would have to run through the firewall.
     
  27. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,657

    Rusty O'Toole
    Member

    The amazing thing is, it's still quieter than a brand new 216 Chevy six. Don't be surprised if you find broken pistons and broken rings when you take it apart. These engines will continue to run in an advanced state of neglect and wear, without complaining.

    A good engine would have at least 100 pounds compression, 110 - 120 on a newer, higher compression model.
     
  28. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,657

    Rusty O'Toole
    Member

    Re: oil filters. Leave the original on there. They only need to be changed every 5000 miles and it isn't that big a deal. New, modern filters are far inferior to the original and you can't adapt a modern full flow to your engine.
     
  29. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,657

    Rusty O'Toole
    Member

    If the engine is that badly worn it is probably only making about half the HP it should. In other words, a straight rebuilt will DOUBLE your power.

    I know guys who thought their old flathead Dodges and Plymouths were too low powered until they rebuilt the worn out engine, then they had plenty of power for all normal driving. Just having them run right, took away all desire for a hop up or V8 swap.
     
  30. Bought an old 49 4 door Plymouth in 1974 for 75 dollars replaced the ball and trunnion u-joint and drove it 100,000 plus miles. Good little cars gave its remains to a local college kid in 1984 and he drove it some more then drove it back up north when he finished school..........
     

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