I'm brand new to this forum having been on the P-15 forum for years. The old flatty started spitting piston rings out the tail pipe and needs a complete rebuild costing lots of $. It's time for a change. I opted for a '75 225/904 conversion. I'm a retired antique car restorer and old time hot rodder so I'm capable of doing a swap like this. The info provided by those on the forum reasures me that this can be done with much less cost than messing with the old flatty. I plan to use as much of the original Plymouth parts and componets as possible. I will try to post updates on my progress and post some pics if I can figure out how. [/img]

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’48 Plymouth Club Coupe
'63 Corvair Conv.

I drove a '48 P15 Special Deluxe for years... loved it! Can't wait to see your car and the work you are putting into it.

Pictures must be hosted elsewhere (like PhotoBucket) and linked in. See the FAQ section for details on how to do it.

- Mac

Oh, and I just noticed you are on your second post. Welcome to the Board!

Gees that Slanted Opinion sure has an eagle eye hasn't he?
Good advice too, re uploading pics.
It's a little dickie until you've done it a couple of times - like everything.
Welcome aboard
Gary

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Gary from Downunder
2 weeks ago I couldn't even spell mukanic - now I are one!

Flatheads aren't costly to rebuild, probably less than a slant six. The 218 or 230 is simple. Some rebuilds of Kohler or Onan motors can cost as much as a rebuilt flathead. The original motors often wore out at 85,000 miles, sometimes less when driven hard or when oil changes are missed.
That wear pattern was generally superior to competing makes. They don't overheat like the Ford 8 did.

Faster wear is due in 4-ring pistons and inferior motor oils - as much as the long stroke. With current oils flatheads can last for more miles. The flatheads can keep running in wounded condition leading many to think that they are dogs. Broken rings are common on high mileage motors, maybe because worn wrist pins allows the top ring to hit the cylinder ridge. They do run out of steam at an RPM where an overhead valve six builds its mid range, but the HP ratings on these motors were listed at 3,600 RPM, which is fast enough to go 70 MPH with the gearing of the day. The problem is the peak torque is 1,200 to 1,600 RPM. Some late '50s 230s were rated at 140 HP, not much below the slant six. Flathead Mopars are tough. When the oiling system are in good shape they can be safe at 4,500 RPM and a little more. They do work best in a light car. When rebuilt with modern pistons, dual carbs and more compression they can be spunky, in a light car. The optional overdrive really helps these motors on the freeway.

Anyone who is interested in the flathead Mopars should give George Asche a call. He is in Venus, PA. His number is posted on the P15-d24 site, Google can return it as well. George is 80 years old and has been working with these motors since 1949. He has a '29 DeSoto roadster with a 265 which I believe he claims can hit 140 MPH. Its a light car. He can exagerate but his enthusiasm for these motors is like a teenager. His daily driver is a '52 Plymouth that he rebuilt in the 1980s, now with over 300,000 miles. I get some details wrong, but he is quite knowledgeable. Talk to him. He rebuilds the popular Borg-Warner overdrives when he can find them. Somewhat like Doctor Dodge he has dealt with a foundry to cast his own design of manifolds which he sells.

The crankshaft journals of long stroke inlines can act like a centrifugal pump and direct most of the oil flow to the center cylinders, causing sustained high speed use to throw #1 and #6 rods. That's also true for a sludged and worn Toyota 7MGE, which has a 3.58-inch stroke(same as the Mopar 360). Attention to the oil system is critical if you run these motors hard. The old head gasket technology is not up to handling turbo charging. The motors have 6 bolts around each cylinder with greater surface area than an OHV motor. George said one of his customers turbocharged a 218 and it runs like a 318. How long that motor lasted, I'd like to know. At 6.6:1 compression ratio for the P15 era the flatties can use help there. The later 230 ('57-59) had over 8:1 compression ratio and an improved flowing head, thus they are more powerful. The 23 inch motors are designed to be very compact, these have offset rods. In my opinion the 25 inch motors are better to use for performance, but fewer "speed" parts were built for them. Most of the period aftermarket parts are eye candy. Homemade parts are the way to go if you have the skills. As these sixes were built in many different displacements you can easily build different sizes The Canadian 218 is a 25-inch block with a shorter stroke (like a slant six). It's common to bore the 265 1/8-inch to be a 283. Its torque that plays with the flathead.

Improve the oiling system, resolve head clamping, and maybe a turbo would be the the hot ticket. Most of the people who build these are traditionalist and shy away from turbos or EFI. External oil lines might need to drilled to the #1 and #6 crank journals, I'm not an expert. As wrist pin knocking is often a problem that limits the service life of these motor, maybe oil squirters like turbo motors use might help. The long stoke might not get enough oil to the wrist pins. Again, I'm not an expert. I think the common issue of broken top rings on 90,000 mile motors is related to worn wrist pins. Yet, George claims 300,000 miles on his 218. George is great resource for these motors, very helpful.

In my opinion a turbo that gives good torque from 2,500 to 3,000 RPM would awaken many to the potential of these motors. Very high speed is not necessary. Mid range is where its at. But it would take some custom work, that's for sure. Avoid the eye candy parts and build your own. A 230 with traditional techniques: increase in compression, cam regrind, split exhaust and dual 1 barrel carbs will make about 130 HP and be streetable. The few 200 HP 230s which are built are drag race only, those often run at 5,500 RPM - for short distances.