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Old 10-03-2007, 04:03 PM   #1
bbuswell
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Default Mopar Flathead 6 Horsepower vs. Production Year

Iím a newbie in the process of doing some upgrades on my 39 Plymouth P7 coupe and I have a question about flathead 6 horsepower that one of you guruís may know. I recently purchased a 230 ci flathead 6 out of a 1950 Dodge (from a fellow hamber) to replace the 201 ci that is in it now. When I look at specs on the carnut.com website, they show a 1950 Dodge having 103 hp from the factory and a 1959 Dodge Coronet 6 having 135 hp from the factory. My question is, what is the reason for the difference in horsepower ratings between a 1950 flathead 6 and a 1959 mopar flathead? According to the specs on carnut.com, the only difference I see is that in 1959 the compression was 8 to 1 and in 1950 the compression was 7 to 1. Is that where the additional hp is found or are there other factors like 12 volt electrical, different cam, different carb, different head, etc? Iím obviously not looking for great horsepower from this setup but if I can pickup an additional 35 hp on my 1950 engine I would like to.
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Thanks in advance
Brett
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Old 10-03-2007, 04:41 PM   #2
squirrel
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

looks like compresion is the big change, it gradually increased from 53-58, and hp gradually increased also. valve timing appears to have changed slightly in 54, but not after.

I don't know enough about them to tell you what else might have changed over the years. Head design might have played an important part.
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Old 10-03-2007, 05:38 PM   #3
plym_46
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

Compression was the biggest factor. Internally the 230 engines are the same and parts are interchangeable. In 56 there was a 2bbl option that picked up 8 hp. Here is something you can try. Supposedly the head on your 201 engine has a smaller squeeze zone as the bore is smaller. So putting your old head is good put it on your newer engine. I have a 56 230 in my car. I found a fenton intake and am running dual carbs. I had the head shaved .040 and the blocked decked .010. pistons are .030 over. The machine shop guy calculated the Compression ratio at about 8.7 to 1. It is much more stout that the 218. Easily pull grades on the interstate, and is probably as fast from 40 to 70 as our daily drivers.

There are a couple of fellows who do split intakes and split exhaust. One of them says you can go to .080 off the head block and still run regular gas (don;t even need lead substitute cause the old MOPAR engineers included hardened valce seats).

Check out this wesite for split manifolds and front disc brake kits.
If you don't want to split the intake, you can get on of those aluminum adapters and put a 2bbl on it either a Carter BBS or a carter weber. Check tom langdons site for other inlline 6 stuff.

http://langdonsstovebolt.com
http://rustyhope.com.

Also you might want to drop in on the P15 D25 forum. A good community of MOPAR Flathead 6 enthusiasts.

http://www430.pair.com/p15d24/mopar_...isplay.php?f=1

And the rest of the wesite for some good info on 40's Dodges and Plymouths

http://www40.addr.com/~merc583/mopar...eframeset.html


One caution, Chrysler made 2 styles of flat 6 engines. Short blocks 23 1/2 in long head for Plymouths and Dodges, and the long blocks 25 inch long heads for Desoto and Chrysler. Then they complicated the mix by using 25 inchers for all displacement engines in Canada. So when ordering parts and accessories for your car measure the head and specify that measurment, specially if you find vintage manifolds at swaps or on auction sites.
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Old 10-03-2007, 06:20 PM   #4
rockabillybassman
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

All good advice from Plym46. There are some very knowledgeable folks at the p15-d24 forum mentioned above, it's worth your while. An example of how the compression crept up.... my 55 Plymouth 230 has 7.4 stock and is rated at 117hp. The good thing about that is it BEATS A 239 INCH FLATHEAD FORD V8 @ 100HP!!!!!
Some handy parts sites for ya....
www.oldmoparts.com
www.rockauto.com
www.vintagepowerwagons.com
www.kanter.com
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Old 10-03-2007, 07:37 PM   #5
blackp-15coupe
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year


What a coincidence - I have a '39 Ply business coupe with a dead motor ( '46 Ply 218 cube). After some discussions and checking around, I'm going for a Dodge engine. The info I got is that the Dodge has a stronger bottom end and I want to start with a 230. I located a motor and expect to pick up tomorrow, a '55 dodge 230. It will undergo a rebuild (bore at least +.30), 3/4 cam, and I already have a Fenton head (which should boost compression to approx 9-1), Edmunds 2x1 intake, and Langdon headers. Exhaust system - duals with Smithys.
This is pretty much what I have in my '46 coupe; Dodge 230 (out of a truck), Sharp aluminum head, Edmunds 2x2 intake (2 Holley Weber 2 bbl with re-popped Helling and Stellings cleaner), tube headers, tweaked dizzy with mechanical advance, and duals with glass-packs.
Make sure to check out Tom Langdon's site and give him a call. he's a wealth of info. Also check Bluesky's site ; www.50Plymouth.com Pete is also a good source of info.
Good luck with your project,

Dave


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Old 10-03-2007, 07:43 PM   #6
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

The '59 passenger car head is the best flowing of the 230 heads. The chamber is shifted in the head casting towards the valves, unshrouding them somewhat, making it easier for the air to get in and out. The head I'm designing for the 230 is based around the '59 car head.

The problem with shaving the head for compression is that you loose flow because the valves are more shrouded. I've seen a very few people that had offset their heads using turned down head bolts. Obviously this isn't for everyone, but if you're chasing every last HP in your Mopar powered pulling tractor...

Dave, you have Fenton and Sharp heads? Could you post some pics of both sides? I've never even seen a Sharp head before.
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Old 10-03-2007, 09:21 PM   #7
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

Quote:
Originally Posted by Bugman View Post
Obviously this isn't for everyone, but if you're chasing every last HP in your Mopar powered pulling tractor...

Dave, you have Fenton and Sharp heads? Could you post some pics of both sides? I've never even seen a Sharp head before.
Do you have such a tractor? What kind?

I'd like to hear some more about your head design and see some of those Fenton and Sharp heads too.

Hud
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Old 10-03-2007, 09:28 PM   #8
rockabillybassman
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

Blackp-15coupe...... there's no difference in the bottom end between Dodge and Plymouth.... a 230 is a 230, end of story. I like your mods, but are you sure about the 9:1 of the Fentons? If they are stock I doubt they would be more than 8:1, although you'll pick up some from the overbore.
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Old 10-03-2007, 10:07 PM   #9
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

Quote:
Originally Posted by rockabillybassman View Post
Blackp-15coupe...... there's no difference in the bottom end between Dodge and Plymouth.... a 230 is a 230, end of story. I like your mods, but are you sure about the 9:1 of the Fentons? If they are stock I doubt they would be more than 8:1, although you'll pick up some from the overbore.

Plymouth 218's don't have a cross drilled crank for oil.
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Old 10-03-2007, 10:26 PM   #10
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

Quote:
Originally Posted by 53dodgekustom View Post
Plymouth 218's don't have a cross drilled crank for oil.
Nor does the '59 Dodge 230 crank in my '55... To my knowledge, none of them are factory cross drilled.
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Old 10-03-2007, 10:28 PM   #11
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

The link below is to a string on the P15-D24 site that has a head milling chart that shows how much you can safely mill your head and the expected compression increase.


http://www430.pair.com/p15d24/mopar_...ht=milled+head
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Old 10-03-2007, 10:31 PM   #12
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

Quote:
Originally Posted by Bugman View Post
Nor does the '59 Dodge 230 crank in my '55... To my knowledge, none of them are factory cross drilled.
oops. Must have been thinking of something else. I think BlueSkies did his.?
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Old 10-03-2007, 10:46 PM   #13
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

Old Mopar Fan adage: Ply-Do sixes only knock once...then the bad soft crank throw pops the rod and grenades the piston.
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Old 10-03-2007, 10:49 PM   #14
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

www.inliners.org
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Old 10-03-2007, 10:57 PM   #15
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

My Dad, decided to trade in the ol 47 Dodge coupe, in 56. It was a fancy car in its day. In Mopar land Dodge occupied the comparable price range as a ford deluxe.It had 'fluid drive' which was a standard trans with a fluid coupling. Not the speediest car in accelration. But man what an interior , big mohair seats front and rear, was a great makeout car! It was a great hiway machine too' we cruised 65 and 70 mph and when i started to drive and my folks got enuff confidence to nap while i was driving I would sneek it up to 75 and 80 I inherited it when he traded, and it took me thru hi skool. It was a great car and i trusted it to take me whever I wanted to go , and it performed great.
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Old 10-03-2007, 11:08 PM   #16
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

SO, have any of you guys with a built up flathead 6 ever run it through a quarter mile strip? I mean, just what kind of times/mph are you running and with what car/drivetrains? I need to know if I should hide away my "modern 6" at the drags should I come up against one with a the hot rod flathead six. Gene
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Old 10-04-2007, 04:31 AM   #17
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

This page has all the variations of Flathead 6 with horsepower and application info
http://en.wikipedia.org/wiki/Chrysler_Flathead_engine
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Old 10-04-2007, 05:05 AM   #18
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

I had a '39 Plymouth with a 40 something Windsor engine( Spitfire cast into the head).pretty much a bolt ion deal.The radiator support had been reversed to allow for the extra length( I think it just unbolts and can be turned around ). There is no substitute for a few extra cubes.
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Old 10-04-2007, 09:32 AM   #19
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

Rockabilly,
Sorry I wasn't clear the comparison is really between the 218 and 230. The difference in strength may/may not be true, that is just what i was told.
Bugman,
The Sharp head looks like the Fenton except there is no freeze-out plug and it says Sharp in the same location as the Fenton. I've never seen another Sharp head no one I've spoken to has seen one either. I'm curious how many were ever made. I'll try to get a picture posted as soon as I can. FYI, my friend cc'd the Fenton head and it was significantly different ( i don't have the #s handy) than the stock head on the '46 218 and he guessed at the compression ratio. The Fenton head I have is new never put on a motor. The guy I got it from brought it in 1962 and never used it or the headers and in-take which I have been trying to get from him. I got the head for $300 and I was hoping to get the other parts for about the same price. It's probaly too much to hope that I'd get everything at these prices considering a used Fenton head just sold on e-pay for $1,330.......

Dave

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Old 10-04-2007, 09:43 AM   #20
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Default Re: Mopar Flathead 6 Horsepower vs. Production Year

I haven't been down the 1/4 mile, but I have had one at full bore down the pulling track. All I can say is, tenacious.

The crank cross-drilling is absolutely necessary if you intend on running high rpms. As is making the oil grooves in the main bearings larger to accomodate more oil flow to the rods. That is the only holdup to sustained high rpm operation in those engines.

I haven't seen a 230 crank yet that doesn't oil #5 from the rear main or #2 from the front main, which are your two culprits for failure. You have to drill from #5 to the 3rd main and #2 from the 2nd main to fix it. I'd say that if a person widened and deepened the main bearings to accomodate more oil flow, particularly the front and rear main, you'd help the rod starvation problem - but not completely cure it. To do both the main oil grooves and cross drilling makes you nearly bulletproof - until you rev it so high you twist your crank in two.

Stock valve springs will pull you up to 5500 rpms when new, but will start to float under no load at 5500 after a while, but will still pull 5500 under a heavy load. Neat little rev limiting characteristic, because valve float in a flathead does no damage as in an OHV.

I really regret not spending more time on flow improvement with the 230 we built. I didn't give it much consideration as I had no faith in flatheads at the time. It taught me better and I fell in love with it after we put it on the track.

Launch at 3200rpms, buzz it up to 5500rpms, and it would pull down to about 4700-4500 rpms at the end of hard pull on a super sticky track and never give up. The pull-down was likely a function of its cam grind more than anything else.

The build was nothing spectacular. All stock components with the crank mods and what would be considered a slight cam increase. We did find and run the late model head, which was shaved to an unknown amount when we acquired it. Dual B&B carbs with a split stock exhaust. It ran and pulled best on 87 octane pump gas.

It was a winner against some big cubed inlines, until the rules changed in favor of higher revving engines to catch us. I still love to get it out and hear it run, and I'm about 15-20 ft away from the pack. If the rule change hadn't brought in the 292 Chevy, we'd probably still come away with a trophy or two with the little bugger as is.

I also know where there is room to improve over what's in the tractor right now, so it could do better than it is.

You won't hear me badmouth the mopar 230, and most that do either haven't messed with them or don't want to. They caused me to change the way I thought, and I liked the change.

Hud
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