I have a customer who wants me to build his stock motor and use it for cruising in town and to out of town car shows. Stock specs. show it had either 95 or 97 HP stock, I would like to hop it up 25 to 50 HP more so it will cruise fast enough to keep up with traffic on the weekends, not to race it.. He likes the early to late 1950 cruising looks and performance
He already has a 2 one barrel intake manifold and he wants to put twice pipes on it with Smitty glass pack type mufflers
I'm looking for suggestions on camshafts to use and piston brand to raise to compression ratio up to around 9.0 to 1 comp. ratio

No go on pistons for that kind of compression ratio. If you look at the chamber design the bulk of the volume is over the valves and not the pistons. I went with an Edgy head that has a more modern chamber design and is smaller to get you the 9:1 compression ratio. Unfortunately, I also got one of the last sets they made and there are no more new ones. I did see on on Ebay, used, for twice what I paid for my new one. The company that made that head is working on a more stealthy one, same chamber design inside, but looks stock outside whereas mine are finned. So you just deck the block for quench and run a better head. They also do cams.

http://www.moparmontana.com

But these guys are really the 218 cam gurus

https://p15-d24.com/blogs/entry/109-the-all-mighty-cam-flathead-style/

Shot of my new cylinder head's chamber.

As for the intake you mentioned, which one? I am running a Thickstun and in the process of dual TBI injecting it. You can find that intake on Ebay semi-regular

I'd bet that for every flathead Mopar 6 that's been built, 1,000 Ford flathead V8s have been.
I would think a lot of the same tricks would apply, plus the Mopar probably doesn't have the heat issues of the Ford V8.
A racer buddy of mine does single-cylinder (Mustang scooter) motors and gets quite a bit more out of them, and there's almost zero HP parts for them.

218 CI is about what, 3.5 liter?

Leave it stock and put a Turbo on it.
Leave it stock and put an Eaton Supercharger on it.

You can deck the head a bit and re-port the valve crossover pocket but not touch the quench side. Then deck the block 0.040".
I seen a Ford flathead that used golf ball dimpling in the valve and crossover port. The dimples are only 0.020" deep and done with a drill press. I think they got 10 HP and a better flame front.

Not sure what you mean by the valve crossover pocket but the stock combustion chamber is poorly designed for efficient combustion

Stock combustion chamber

I know thats for sure.

An OLD flat head racer told me the area over the valve in the head was the Valve Pocket and Valve crossover passage is the portion going over to the piston. The old flat head racer said to never grind out the area above the piston, only in the valve pocket and crossover. He also polished the whole chamber.

Knowing how hard it is to make compression with most of it trying to fill that valve pocket, thats why I think 10 PSI boost would help. 10 PSI should give 25 HP from this 218 CI

You can mill the head a lot to reduce combustion chamber volume as well. But I figured I'd go with the updated head, not cheap either.

does this engine have an in block water "diverter" tube thing that can be rusted away or missing altogether, causing overheating problems ?
i seem to remember something about this in the dusty cobwebs of my inner cranium space.
or was that on the straight eight flat head ?

Yes, they have the water distribution tube you are thinking of. You can get new ones, vintage powerwagons has them in stainless as well.

I wish I had pictures of the guys flat head shop. He had about 25 different sets of flat heads on the wall. He was mostly into these 218 and other L6 flat heads. Some of his milled ones had to have furnace welded/brazed in the chambers and on the outside to raise the valve pocket up and relocate the sparkplug .

My dad had me as a kid do a head gasket on our family 53 Ply with a six, all I remember is my dad smiled when he said he had the head milled .060"?, the head was really heavy, I painted it silver to look cool, and the local machine shop I believe did a valve job, in the car?

.060" is a mild shave. Zero deck the block and take about 0.85" off the head is a good number, assuming the head hasn't already been milled. Your best bet is to CC and set it up for the compression ratio you are looking for.

In the car valve jobs were the norm back in the day, heck guys used to do them on the weekend in their garage and drive to work Monday.

Yes, they are heavy, which is yet another reason I like my new head, it's aluminum.

I did a couple in chassis valve jobs on Continental motors when I worked at the Hyster dealership.

Buddy of mine has the boring bar from a shop my Dad worked at in the '50s. They bored cylinders with the block in the car.

Well yeah those things needed to be rebuilt every 60,000 miles or so.

Cast iron rings will do that

A back cut on the valves work WONDERS on those.

I can't answer your question. But my old 51 PU sat for 25 years or so. All I did was change the oil, new cap/rotor/coil, plugs, plug wires and sent the carb to be rebuilt. Started up and ran great. I think to get any power you'd have to mill the heads. I'm guessing a "cam" guy to grind you up something. You can check https://p15-d24.com/forum/6-mopar-flathead-truck-forum/ that's where I got all my info. They also have a "parts" section.

Keeping up with traffic could be better served with a transmission and axle ratio combo that keeps the engine in an RPM range it's happy with, that is to say lowish. Flatheads were notorious for breaking cranks if you spin them up over farm tractor RPM for extended periods.

I'd look at a T5 or similar and a 3.23 or 3.55 depending on tire size.

If I was building the engine for long term reliability I'd build it like any other, a light piston and H-beam rod combo with the crank properly machined and balanced. If the crank needed to be turned down to make an off the shelf rod work, I'd offset turn it for some extra displacement.

Add dual carbs and exhaust to suit.

Kevin

The '53 218 in my '55 Plymouth wagon has no problem running at highway speeds. Although, with the deep rear gears and the 3-speed manual, it can be quite noisy if you try and run over 70. All I've really done to it was an HEI distributor and a new carb.