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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. Modeljunkie
    Joined:
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    Modeljunkie Member

    I'm really wanting to build up either my 40 plymouth 201 flathead six or a newer/larger version but have heard alot of bad press on them in the way of "no high RPMS", intenal oiling issues, and not worth the money spent - by some folks.
    I like the motor because it's different from the sual SBC and SBF around here, but I want to have all the facts before I fully decide to do the build.
    1) just how high should one rev a flathead 6 and live to tell about it...what's the agreeable limit? I'm planning on an automatic 4 speed behind it....3000...4000?
    2) I hear the crank is the week part, and since forged cranks are not available, what can be done to improve the life of a crank sans limited revs.
    3) Multi carbs and twin exhaust manifolds help her breathe, but aside from internal mods and a head shave, what's the actual HP gains from any of the above mods - I'd like to add on an AC compressor and worry about the power loss from that...stock hp for my 201 is only 87HP...I'd like to see around 150HP to 175HP when done and still have the motor as a daily driver on pump gas{87 octane}.
    4) I hear the flathead 6 motor production ran for quite a while into the mid 50s, with the exception of a larger displacement block, are there better choices for a starting point...a good application{industrial?} or year?

    Sorry for the ton of questions here, I just want to get the facts straight.
    Thanks for lookin- Happy Holidays, Bob
  2. bct
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    bct Member

    can't help other bumping to the top and to say my dodge flat6 is the long head version out of canada . it is very reliable and cheap to maintain and fix , it has tons of torque but sounded labored at high RPM untill i swapped out the rear for some hwy. friendly gears.
  3. Dynaflash_8
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    Dynaflash_8 Member

    150 to 175 is asking alot for these little motors. Start off with a chrysler or desoto to get away from the crank issue. I built a pretty gnarly motor from a 218. Dont rev above about 4k unless you inprove the bottom end oiling. 3800 was factory redline.

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  4. RAR1947
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    RAR1947 Member

    I'm no expert but would think those HP numbers are a bit high for the smaller flathead that you have. The big block flatheads would be a better option for numbers like that. I have a slightly hopped up 218 in my 47 Plymouth and can say the best thing I did was get an overdrive trans from an early mopar. Really keeps the RPM down when cruising down the interstate.

    You should check out the P15/D24 site. They are all about the old flatheads.... and I mean ALL about them. Good guys too.
    http://www430.pair.com/p15d24/mopar_forum/index.php
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  5. RichFox
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    RichFox
    ALLIANCE MEMBER

    They made the 230 version of your motor until 61. Newer is usually better. You might find one with a Powerflit 2 speed automatic. I always heard, in the day, That the bad thing about Plymouth/Dodge six cylinder engines is that the oil line from the main gallery is drilled straight through. So as much oil goes to the cam bearings as the mains and rods. The fix is to tap the feed to the cam and install a restriction. Maybe with a 1/16 hole. Then the crank gets what it needs.
  6. 73RR
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    73RR Member

    I will suggest swapping a larger 25" Chrysler or DeSoto. You will need the extra torque to drive the ac pump and depending on which 'auto' trans you plan to use you may have additional hp losses there.

    .
  7. plym_46
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    plym_46 Member

    There are several threads regarding these engines, rule of thumb, if you build a 201 you will end up pretty close to a stock 218, if you build a 218, you will end up pretty clost to a stock 230, if you build a 230, you will have something. I have a built 230 that I have driven on several long distance trips, it has been reliable, and fairly economical. So if you are going to spend the money to build an engine start with a 230. The chrysler and Desoto versions are 2 inches longer so they are not a direct bolt in, at the minimum you need to move the radiator forward, you may need to notch the front crossmember to clear the crank pully. And yes they do not like high rpms, you are talking nearly 5 inches of stroke for the larger engines. Which in and f itself makes higher RPMS an excersize in piston friction.

    Do a search for material here and look at the p15 D 25 forum. For all stuff mopar flat six.
  8. Dale Fairfax
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    Dale Fairfax Member

    Strange that this subject came up and you described the real problem and the fix. Just yesterday I was in a shop where an old timer is working on a '49 or '50 Dodge. He said the very same thing you just did. At 74 and having hung around auto shops for 62 of that, I'd never heard this until yesterday and now again today.



  9. Modeljunkie
    Joined:
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    Aurora Illinois

    Modeljunkie Member

    I figured a larger cubed block would be a better choice...finding one might be a challenge though.

    As far as the max revs are concerned, I didn't know it was as low as only 3800 rpm....dang good thing to know!

    The trans in question, at the moment, would either be a GM 700r or the 200r4 since I can only find one adapter for the back of the block for either of those two in 4 speed auto transmissions...my wife has requested that if I change transmissions that I make it an auto so she could drive it too. I'd kind of prefer to keep it all mopar, but I haven't seen any mopar 4 speed auto trany adaptors for the flathead 6.

    If using, say, a 230 cube block, what's the modded HP that I could really expect?...120...130? What would it take to get to that point after a good block was found- $2000-$3000 in mods?
  10. plym_46
    Joined:
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    plym_46 Member

    230 were 125 to 135 stock. and 3800 is a number from Where??? Factory peak HP was at 3600, to suggest that the rev limit is only 200 higher is somewhat dubious.

    The factory used to take engine of the line and strap them into test stands, and then run them at 3600 for 50 hours, against a load. So they are not as frail as some would have you believe. But are you going to make a full race engine for the street, not likely, so you up the compression by milling the head and maybe decking the block, you open up the intake, with etiher a 2bbl set up (available from the factory in 1956) or 2 singles (www.rustyhope.com) or check member moose profile for a link to his site for other intake and exhaust options. Going much past 4000k is pretty futile but you don't build them that way.

    My engine is a 56 230, 30 over, 060 milled, dual carbs and single exhaust. at 3200 rpm on a chasis dyno its running 62 mph, and putting 127 HP to the rear wheels. The factory rated the engine at 125 at the flywheel, so adding 25% for drivetrain loss, that makes it about 140 to 150 at the flywheel. It pulls the car around pretty smartly, climbs hills with little or no effort and gives me 19 to 20 mph this withthe stock 3 speed and the stock 4.11 rear end.

    I do believe that are a couple of folks that make an adapter for a torque flite, and if you look real hard you maybe could find a 55, 56, 57 doner car or truck with the powerflite, which was the engine that preceeded the torque flite.

    Egge has rebuild parts, and Terrel Maching in Terrel texas also carries rebuild parts and so does Vintage Power Wagons.


    some ideas here

    http://www.jalopyjournal.com/forum/showthread.php?t=429644
    Last edited: Dec 8, 2011
  11. thekid1950
    Joined:
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    new york state

    thekid1950 Member

    I have a 39 Chrysler Royal coupe w/ a 1954 Chrysler 265 flathead w/ a 39 overdrive transmission, dual small webbers, electronic ignition & a/c. The rear is a modern ford 3.8 ratio.

    I bought the car cause it didn't have a modern v8. I couldn't be happier w/ the performance. Tons of torque...great gearing 2300 rpm at 70mph and I get 23 mpg at that speed.

    It would be perfect with a 700r or the like. My a/c condensor is a remote mounting unit (I think for 18 wheelers) that is mounted under the driver's floor & blows straight down. Never any overheating....in any weather...moving or not.

    My car was built by a man in Turlock, CA that restores & sells machinery for the agriculture industry. All his equipment is old style & powered by flathead Chrysler, Dodge, Plymouth engines. He's an expert on these flatheads

    I've driven it 15,000 in 3 years & it runs great.

    Now I'm not singing but it runs Mobil 1 and after 3,000 miles (oil change time) it still hasn't used any oil (knock on wood)....guess I'm lucky...I'm not singing etc....etc...

    The builder originally had a 3.5 rear but thought that it was too high. The 3.8 is perfect. The overdrive drops it about .3.

    I don't know about mounting it in your car....earlier posts said it is slightly longer & mounts might need tweeking.

    There's an old timer (in his 70s) near Oil City PA that builds & sells these engines hopped up. I've ridden in his 29 DeSoto Coupe (that he's had for over 50 years) & he runs the RPMs way up...a brass knuckles ride. I can get his name if you are interested.
  12. 73RR
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    73RR Member


    ...seems that this was covered in another thread of yours...

    .

    Attached Files:

  13. RichFox
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    RichFox
    ALLIANCE MEMBER

    O)ne good thing about the HAMB is passing on experiance to the younger Hot Rodders. I don't mean you at 74. But the younger guys that won't get much about 218s at the local speed shop. I hope you have seen the many pictures of my '32 Plymouth engines. Both OHV with a '57 Ford head.And the flathead that went 113.75 in my roadster. I hope somewhere somebody will see them and get an idea. Like I did when Dave Dozier told me about his.
  14. Mopar Jack
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    Collinsville

    Mopar Jack Member

    No matter which moter you choose to build,i think its great your keeping it mopar...
  15. George Miller
    Joined:
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    NC usa

    George Miller Member

    I worked on them back in the day. They were not a bad engine, but did not have much torque . The problems I seen was with the lower end. The rod bearings went out before most cars of the time. I would go with the Chysler 6 they also used that engine in trucks, marine, and industrial. Much stronger engine that looks a lot like the Plymouth, or Dodge.
  16. Modeljunkie
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    Aurora Illinois

    Modeljunkie Member

    Hey, do you have any plans for a 588{?} mopar 4 speed auto behind a flathead 6 adaptor....904s and 727s are fine, ran my share in late 60s and early 70s cars, but I'd like a 4 speed auto...mopar.
    edit/ I just looked up "A-500 trans"...well, what do ya know! -cool, now to find a trans!
    Last edited: Dec 9, 2011
  17. Modeljunkie
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    Modeljunkie Member

    ...that'd be me coming in at 46, soon to be 47. ;)
  18. Modeljunkie
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    Modeljunkie Member

    Yes sir!, while I have owned other makes, the majority of my old owned car were mopars...heck, I'm driving a 99 gran voy daily so running a fallen flag car is noooo problem for me!
  19. Modeljunkie
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    Modeljunkie Member

    That's what I'm shooting for!...a good lookin old flathead engine, good power, and good reliability - within her limits{all engines have some sort of limit, right?!}...the trifecta! I'm not going to bracket race the car...a 40 plymouth touring sedan...don't think so! I'm not going to race it against any BBmotor car, or SB motors...nope...just a good reliable cruiser with style and good looks.
  20. Modeljunkie
    Joined:
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    Aurora Illinois

    Modeljunkie Member

    Here's what I was shooting for since my 201 couldn't be much more than a 220 pending over bore{218 base crank/rods}.
    The 265 cube block, is that one of the 25" motors? I can move the radiator farther forward but I'd have to use a remote filler and a different radiator since the oem rad filler cap would be covered up by the overhead core support when moved forward enough{2"}...a more modern rad {griffon?} wouldn't hurt anyway. I can pocket the firewall too if need be.
    Is there a place where I can find a good rebuilt or rebuildable 265 block...no replacement for displacement- right?!...it would gain me 45 more cubes than where I'm at now with a little shoe horning and tweeking.
    I've seen a lot of the flahead 6s here and on you tube, but around here where I live they're non existant...that just cries to me, "Do it!".
    Anyone have any lincs to online sources for motors
  21. plym_46
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    plym_46 Member

    check massey furgeson combines if yo live in an agricutlural area, if you have a regional airport check and see if they have any clark equipment that they might be surplusing, especially if there are charter operations at the airport.

    Chyrlers, dodges and desoto had longer wheelbases than plymouth, that difference was between the cowl and the centerline of the front wheels. Which do you think accepts the longer engine with the least hassle???

    If I were you i would be looking for a late model or industrial 230, with an .060 overbore you are looking at about 250 cubes. I have to disagree with the fellow who suggested they are low on torque, it is their forte. I can slow down to about 10 miles per hour make a hard turn and then pull a substantial hill easily in third gear.

    video evidence to support claim

    http://www.dailymotion.com/video/xhywtf_mmmmmmm-torquey_auto
  22. My dad's old portable welder had a mopar flat 6 in it. In the Army I put many miles on the old M-37 dodge powerwagons with the bigger 6....always ran 'em up to the governed RPMs and left the foot on the floor.
    Got home from the service to get a job where my service truck was...yep, an old surplus M-37 Dodge. It'd go 60-62 MPH all day long with no complaints and with the low gearing I pulled many a fully loaded 1 ton ford outta the ditches...only restriction was traction and the things had 4 wheel drive. I have respect for these engines.
  23. Modeljunkie
    Joined:
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    Aurora Illinois

    Modeljunkie Member

    1- Wife's uncle ralph owns a fordson/new holland dealership in mendota..I could have him look for that...
    2-isn't there always some kind of hassle - but isn't it usually worth it all in the end?
    3-I'll look for that one too...that 230 should be a 25" block, wonder how much longer the 265 is from that? 218 and 201 blocks were the 23" version as I recall.
    Nice vids...Thanks!{keep off the grass-lol}
  24. Modeljunkie
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    Modeljunkie Member

    PLYM 46, when you get the time, can you measure the length of your block for me, just for a reference point for length?
    I just measured my 201 and yup, it comes in just under 23"- 22 3/4" to be exact. This is simply measuring the head length.
  25. plym_46
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    plym_46 Member

    All Plymouth, Dodge, and Dodge trucks had 23 1/2 inch long blocks, as does mine. All Desoto, and Chrysler, and All Canadian built Cars and trucks used the 25 inch block. US 217.8 and 230 blocks from 1935 up are the same, the difference between the 217.8 and the 230 is the crank and rods. No plymouths used fulid drive and all early plymouths had a 4 bolt cranckshaft flange (till 53/4) All dodges with fluid drive regardless of transmission, used an 8 hole crank shaft flange (to accomodate the extra weight and length of the fluid drive unit) Plymouth 4 bolt flywheels will fit on the 8 bolt cranks but need to be alligned properly to the assymetrical hole pattern. Some later Plymouth 230 (mid year 54 and newer) used a 6 bolt flange. Some Dodge drive shaft flanges are thicker than Plymouth and some dodges. Dodge bellhousing are deeper than Plymouth to accomodate the fluid drive unit, Dodge transmissioin input shafts are longer than Plymouth when equiped with fluid drive. Most Dodges from 41 through 55 will have fluid drive, some Desoto and very few Chrylsers were not equiped fluid drive.

    All mopar flat 6 setup use the bellhousing as the mounting and locating assembly. Bolting to a frame chrossmember in cars and to the frame rails on trucks and industrial applicatioins. that said the accomodation of the longer block will of necesity be forward of that mounting point. As noted sometimes it is as simple as moving the radiator to the front of the support, others will require modification of the front crossmember, and swaping of the oil pan and oil pump pickup.

    Fluid drive is NOT THE TRANSMISSION.

    Confused yet???
    Last edited: Dec 10, 2011
  26. 73RR
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    73RR Member

    Now that (Plym 46) is about as informative as a short reply can get!

    .
  27. plym_46
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    plym_46 Member

    Well yea, without going into the 33 inch HD truck blocks........
  28. 73RR
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    73RR Member

    Yeah, someday I'd like to find one of 'those' 331 or 413 jobs...:eek:

    .
  29. plym_46
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    plym_46 Member

    look for "K" series HD trucks. Wouldn't be suprised if there weren't some up in grain growing country.
  30. marv norton
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    happy rock, missouri

    marv norton Member

    If you are looking for the bigger 6 cylinder I have one. The engine is all new from top to bottom. The block has been bored .060 oversize with new pistons. The crankshaft was machined to .010 on the mains and .010 on the rods. New oil pump and screen. Both new timing gears and chain. Like new camshaft with new lifters. New valve guides and good valves. New valve cooling tube and water pump.

    If interested call me at 1-816-721-7558 or E-mail me at OLEMWN442@aol.com

    Marv Norton


    Greater Kansas city, Missouri area

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