Inliners International Forums General Discussion MOPAR 8 cylinder casting numbers

How do you ID a Chrysler straight 8 flathead motor? Were they basically 6-bangers with 2 extra cylinders?

Chry flathead 8's started in 1931 and continued until 1950. I believe the engine ID is left side of block at top front between first two cylinders. 1931 had 298 ci and 100 hp. 1950 had 324 ci and 135 hp. Not much get up and go for what the motor weighs!

What year car are we talking about, if you know?

It's out of a 1940 Chrysler coupe. I was looking into putting it in a 1940 Plymouth coupe but I'm starting to wonder if it'll fit now.

Update - I just found out it probably won't fit. That kinda sucks. What is the most desirable flat six, and how do I identify it (casting#)? I'm guessing the one in the 1940 Plymouth is a 230?

johnny, the 218/230 is probably the most common. the 265 truck engine is very strong and if you're very lucky, you might find one with factory dual intake and dual-outlet exhausts! semi tractors, dump trucks could be bought with 265s in 'em, but i can't remember the years....like '49-'51.

i rode in a '29 desoto a while back with a '50- something 265 truck engine and the performance was amazing. i believe chrysler and desoto had a 251 cubic inch engines. the 218/230 sixes are the same length. the 251/265s are about 2" longer. if you could squeeze the straight-eight into your car, you'd really have a smooth machine, but i don't know about the differences in your ability to build power into them. check with don coatney...he's really into these engines and he's a storehouse of info, too.

It is possible to get some power out of these 8's, if you look at the bonneville section, there is a member named Haggerty who ran a really cool airflow 8. I'm still thinking this might be the way to go on my current project (which is in "remission" because I'm moving) Do you want to sell that 1940 lump? Where are you located?

go for it, lief! i'd love to see some big ol' extra long inliners back on the road again. i remember a couple of buick straight-8s, powering rail jobs back in the '50s. an old buddy in florida is been in the process of building a packard inline-8 powered rail job, but between raising citrus, flying radio controlled model airplanes and a building a '46 ford, his plate is pretty full.

The longer block 6-cyl engines came in smaller capacities than 245 as well. They ran capacities pretty much parallel to the small block engines as well as going to the larger sizes.

Because they had the larger bore, of course, they were shorter in stroke... here's the list of sizes from Allpar.com for long and short block engines:

Size Bore Stroke CID
175 3.000 4.125 174.9
190 3.125 4.125 189.8
201 3.125 4.375 201.3
205 3.250 4.125 205.3
212 3.250 4.250 211.5
218 3.250 4.375 217.8
224 3.250 4.500 224.0
230 3.250 4.625 230.2

The 'big' block flathead sixes (block reworked in 1935 for full-length water jackets) :

Size Bore Stroke CID Use
201 3.375 3.750 201.2
218 3.375 4.063 217.8
228 3.375 4.250 228.1
237 3.438 4.250 236.7
242 3.375 4.500 241.5
251 3.438 4.500 250.6
265 3.438 4.750 264.5

The specific cars that used these are listed on that site, information provided by Bill Watson.

Well, it's definitely a 323. Do these have the same bolt pattern as the six that Edgy makes a head for? If it does, I can make one for the 8 by welding 2 of them together. I still can't find specs on this thing...

Maybe this book ?

A couple of small mentions on the Allpar engine pages:

"What made the flathead so versatile was its dependability and torque. The largest flathead six Chrysler used in its automobiles was 265.5 cubic inches that produced 218 ft/lbs of torque at 1600 RPM. So, at just off idle, this engine produced maximum torque, making it ideal for the applications above.

In comparison, the last flathead 8 was used in 1950, with 323.5 cid and 270ft/lbs @ 1600 rpm. Although the 8 was more powerful, most people found the smooth power produced by the six was sufficient, and so a vast majority of older Chryslers found today are equipped with sixes. These figures are at the rated compression of between 7 and 7.5 to 1.

Webmaster's note: the flathead eight-cylinder engine was used in a large variety of vehicles, and was a straight-eight (not a V8) design. It was used in the revolutionary Airflow models - they had to be lengthened to accommodate it."

From my Chrysler book:

The 40 Chrysler Series 26 and 27 motors came with the updated 6 main bearing crank and same 2 bbl carb. They were 323.5 ci. The lower priced C26 had an option for a high compression "Silver Dome" aluminum head.

The more expensive C27 Crown Imperial had both low and high compression options that used the same aluminum head. The head raised compression from 6.8:1 to 7.45:1 and torque from 250 to 270. HP went from 135 to 143.

C26 engine numbers start at C26-1001 and end at C26-18700
C27 " " " " C27-1001 " " "
C27-1875

Just a note. Your motor may not be the original 1940. Lots can happen in 66 years! They needed overhaul or replacement much sooner than they do now. A common practice was to get one from the wrecking yard that may or may not be same year as mfgr. Check your "cereal" number.

Thanks for all the info. The only info I could find online before posting here was the Allpar blurb. Does someone on this forum have more detailed specs (ie casting numbers, clearances, manuals, tune-up info, parts interchange, pictures etc). Wait a second, I think I have a 1948-1958 Motors manual(!) I'm gonna dig it out of the closet and check it over.

I've been knocking around the idea of fabbing up a multi-carb intake and dual exhaust but I'd like to get some more compression out of it. It sounds like I may have to go with a billet aluminum head which is not cheap or easy to make with the factory water passages. Roller lifters would be cool too. Anybody ever tried adapting the ones Crower makes for Ford V8's to the Mopars?

If you know the 8 won't fit your car I suggest the 230 ci 6. Information and parts are easy to find along with web sites that offer lots of help on these motors.

People have put the long block six(25" head) in smaller 40's-50's PlyDos, which requires some minor mods but the 8 would require some major modification in my opinion.

On the other hand, if you can weld, have metal fabarication ability and good mechanical skills I suppose anything is possible. Did I forget to mention money too? !

This is going to be a mild street rod, not a restoration. The old powertrain, front (and rear) suspension, part of the floor, firewall, and cooling system are all going to be reworked and upgraded. If I can make the 323 fit I'll build it. If not, I have 2 hemis waiting in the corner. I'll keep you posted...

Saw one not so long ago... a '39, I think... the car's only had two drivers in all its life, the present owner knew the car from new and bought it from the second owner, who had formerly driven it for the first owner!

Fully and lovingly restored.



Lives in Sydney, I caught sight of it at Tamworth. Very nicely done, here's the rest of it:

I hate to admit it but the darn thing won't fit without major mods. If you're interested in it email john.avram@t-mobile.com.