The Venerable Slant 6 vs Our Beloved Flathead 6s

[Don Coatney]

As options are now available on this thread here are a couple of thoughts. I have swapped out a 218 CI Flathead for a 255 CI Flathead. Yes drive ability pleasure increased and it was worth doing. I do not have any documentation such as dyno results so this is a seat of the pants observation.

 

On slant engines. I have owned a couple and they were good engines. Back in the early 60's others were also producing slant engines besides Mopar. International Harvester sliced a 304 CI V-8 right down the middle and created a slant 152 CI 4 cylinder engine for use in Scouts and smaller trucks. I owned one of these and it was also a good engine. This makes me wonder about the development of the Mopar slant 6 and the Viper V-12. Was the slant 6 used in the development of the V-12?

 

[Plymouthy Adams]

the Viper was a V10, based on the LA engine...the LA is very versatile also, it has had two cylinder lopped off for the V6, two added for the V10 and was also available in the four as a racing engine only.   Other companies did the half engines also...the Porsche 5.0 V8 of 928 fame was the building block for the 2.5 4 cylinder of the 944...not to be confused with the 924 Audi engine.  At this time, VW owned all the three.  I am however right with you in the concept....a V12 of twin tower of power would have been awesome in my thinking.  I also wish Mopar would have marketed their latest straight 8 of the 90's.  I believe the novelty of that engine alone would have been successful venture. 

Edited January 28, 2018 by Plymouthy Adams

[Don Coatney]

Having never owned a viper I thought they were  V-12 powered. My apologies for bad information.

[55 Fargo]

34 minutes ago, Don Coatney said:

As options are now available on this thread here are a couple of thoughts. I have swapped out a 218 CI Flathead for a 255 CI Flathead. Yes drive ability pleasure increased and it was worth doing. I do not have any documentation such as dyno results so this is a seat of the pants observation.

 

On slant engines. I have owned a couple and they were good engines. Back in the early 60's others were also producing slant engines besides Mopar. International Harvester sliced a 304 CI V-8 right down the middle and created a slant 152 CI 4 cylinder engine for use in Scouts and smaller trucks. I owned one of these and it was also a good engine. This makes me wonder about the development of the Mopar slant 6 and the Viper V-12. Was the slant 6 used in the development of the V-12?

 

Options? Think this is still a Slant 6 and Chrysler flathead 6 thread.

Is that Viper for your Dodge?

[P15-D24]

Had a 225 in a '68 Dart with auto. Found neither performance nor mileage to be that good. Auto choke was pure junk, near impossible to start in cold weather. Eventually changed it out to a manual choke.  From my experience not a big lover of the /6.

[55 Fargo]

3 minutes ago, P15-D24 said:

Had a 225 in a '68 Dart with auto. Found neither performance nor mileage to be that good. Auto choke was pure junk, near impossible to start in cold weather. Eventually changed it out to a manual choke.  From my experience not a big lover of the /6.

Now thats interesting. 

So your vote is for the Beloved Flatheads.

Flatheads are great powerplants..

[Plymouthy Adams]

Sorry you had a bad experience with the /6  They were reliable and while not stingy with gas...they did fair.  Other than the factory hyper pack of 1960 fame...little was done to the slant till the introduction of the 2 bbl much later in the 70's.  I owned many of these over the years, never a problem, depending on where your car was sold often dictated its ability to start and idle smoothy, our local dealership could not set a carb up if their life depended on it due to emission requirements....if a California car in 1968 you may have been more a victim of the newly established CARB than Mopar.

[P15-D24]

5 minutes ago, Plymouthy Adams said:

...if a California car in 1968 you may have been more a victim of the newly established CARB than Mopar.

It was purchased new, location was Indianapolis. It gets cold there...  

[55 Fargo]

Well.the good news is for 99.97 % of us.

These engines will be run at leisure and in warmer temps outdoors.

No we dont have to go outside at 0530 and warm up the car at -30.

At any rate the Slant 6 is listed #6 in the worlds 10 best engines, love em or hate em that's the facts.

Our Flathead 6s were reputed to be real lousy starters in cold temps especially 0 or below.

But those were different times 50 to 80 years back.

Edited January 28, 2018 by 55 Fargo Spitfire

[dpollo]

I put a 72 slant six with 904 torqueflite and a 8 3/4  3.23 rear from a full size Dodge into a 50 Plymouth Club Coupe.  I used a rear sump pan from a van. 

This would be back in 76 and I last ran that car about  1988 after many miles.  I later swapped that 225 into  a 68 Valiant and used that until about 2000.

I think the engine had about 150 000 miles of use when I sold the Valiant.    

All my cars  are now flathead powered, a 201, a 217, a 230 and two 251s.   I am preparing a fresh 230 for a 52 Dodge D40 Kingsway Convertible.  Although it looks like a Canadian car,

this model was built in Detroit for export.  Unfortunately the speedometer was missing so I do not know if it was in Kilometers.

Every one is quite satisfactory.  The 201 is no ball of fire in the 40 Plymouth coupe  but as the car is all original with 73 000 miles and the engine has good compression, I am content to leave it alone even though I have to add a quart of oil in 250 miles.

I built a stock 265 for a friend's 50 Plymouth and performance was impressive.  He tore up two transmissions and a rear end which rarely happens otherwise.

In my 50 and 51 Plymouths and my 52 Fargo, I have installed  R10 overdrives .  Each has a 3.9 ratio in the rear.  The 40 also is 3.9 but the 35 has a 3.7.   The 52 D40 came with overdrive and has a 4.3 ratio which I will likely change to 3.9.   " Positive ground six volt six cylinder and a flat head is the norm around here "  

 

[55 Fargo]

17 minutes ago, dpollo said:

I put a 72 slant six with 904 torqueflite and a 8 3/4  3.23 rear from a full size Dodge into a 50 Plymouth Club Coupe.  I used a rear sump pan from a van. 

This would be back in 76 and I last ran that car about  1988 after many miles.  I later swapped that 225 into  a 68 Valiant and used that until about 2000.

I think the engine had about 150 000 miles of use when I sold the Valiant.    

All my cars  are now flathead powered, a 201, a 217, a 230 and two 251s.   I am preparing a fresh 230 for a 52 Dodge D40 Kingsway Convertible.  Although it looks like a Canadian car,

this model was built in Detroit for export.  Unfortunately the speedometer was missing so I do not know if it was in Kilometers.

Every one is quite satisfactory.  The 201 is no ball of fire in the 40 Plymouth coupe  but as the car is all original with 73 000 miles and the engine has good compression, I am content to leave it alone even though I have to add a quart of oil in 250 miles.

I built a stock 265 for a friend's 50 Plymouth and performance was impressive.  He tore up two transmissions and a rear end which rarely happens otherwise.

In my 50 and 51 Plymouths and my 52 Fargo, I have installed  R10 overdrives .  Each has a 3.9 ratio in the rear.  The 40 also is 3.9 but the 35 has a 3.7.   The 52 D40 came with overdrive and has a 4.3 ratio which I will likely change to 3.9.   " Positive ground six volt six cylinder and a flat head is the norm around here "  

 

Thanx for sharing this Dave.

The 265 sounds like it was a beast...

[Dozerman51]

I swapped out the 23” 230 that had been bored 40 over for a 25” IND-7(236) in my WC-12. The 230 was stock with the exception of a 1957 230 head and distributor out of a Plymouth fury. The 236 has been statically balanced, ported, bored 30 over and the ‘41 Spitfire Head shaved and an Isky 44-3/4 grind cam installed. Tell you the truth the, 230 had more snap than the 236 has. Now maybe I need to fine tune the distributor some. I do like the smoothness of the 236 though. Wish I could find a 265 near me. I would probably swap that in. Anyone have a good rebuildable 265 in California?

[55 Fargo]

37 minutes ago, Dozerman51 said:

I swapped out the 23” 230 that had been bored 40 over for a 25” IND-7(236) in my WC-12. The 230 was stock with the exception of a 1957 230 head and distributor out of a Plymouth fury. The 236 has been statically balanced, ported, bored 30 over and the ‘41 Spitfire Head shaved and an Isky 44-3/4 grind cam installed. Tell you the truth the, 230 had more snap than the 236 has. Now maybe I need to fine tune the distributor some. I do like the smoothness of the 236 though. Wish I could find a 265 near me. I would probably swap that in. Anyone have a good rebuildable 265 in California?

Well that doesnt make sense.

Only thing that might be a limiting factor is this.

The 236 has a 4 1/4 stroke and the 230 is 4 5/8.

Did the 230 have more bottom end power?

Perhaps your Isky cam sacrificed bottom end power for power higher in the RPM.band.

[P15-D24]

2 hours ago, 55 Fargo Spitfire said:

Well.the good news is for 99.97 % of us.

These engines will be run at leisure and in warmer temps outdoors.

No we dont have to go outside at 0530 and warm up the car at -30.

At any rate the Slant 6 is listed #6 in the worlds 10 best engines, love em or hate em that's the facts.

Our Flathead 6s were reputed to be real lousy starters in cold temps especially 0 or below.

But those were different times 50 to 80 years back.

THe /6 would start, just wouldn't run!

My P15 started easier and ran better in the cold. 

[T120]

"Venerable", Maybe a term better applied to describe some of our forum members rather then a  /6 engine...LOL

[55 Fargo]

24 minutes ago, P15-D24 said:

THe /6 would start, just wouldn't run!

My P15 started easier and ran better in the cold. 

Even in cold weather climates?

My current setup ( dual carbs/ exhaust) from George Asche is not as good as my stock setup in cold weather until its good and warmed up.

[Dodgeb4ya]

I swapped out the original 218 in my 1952 dodge truck in the early 70's and rebuilt a 53 Chrysler 265 to put back in...

What a difference in pulling up hills. Also the engine is a lot smoother running than the original six which was a good running engine 70,000 mile engine.

The 265 today still runs great. Sodium valves bronze exhaust guides forged pistons etc.

[55 Fargo]

4 minutes ago, Dodgeb4ya said:

I swapped out the original 218 in my 1952 dodge truck in the early 70's and rebuilt a 53 Chrysler 265 to put back in...

What a difference in pulling up hills. Also the engine is a lot smoother running than the original six which was a good running engine 70,000 mile engine.

The 265 today still runs great. Sodium valves bronze exhaust guides forged pistons etc.

Bob sounds like a big difference in performance.

Sodium filled valves bronze guides, your addition or was the engine an Industrial?

[Dodgeb4ya]

2-1/2 ton truck 265 engines used the Sodium/ bronze guides set-up.

I must have read that in the 1953 B4 dodge truck manual I stole from my high school!

I rebuilt it as a truck engine.

[palmersparts]

A buddy of mine had a s-6 in a volare in high school...  it wasnt anything to write home about   it got crummy mileage for a 6 it had no power  and was just a dog (dang electric choke)..  but i dont know how many miles it had either...  on the other hand i have worked on may s-6 chryslers in many industrial applications from case combines john deere swathers  fire pumps  generator sets etc etc  and they seem to live forever

[Flatie46]

I work with a guy who drives an early to mid 70's Scamp with the slant six. Gave $350 for it about 5years ago.  Other than a crushed quarter panel the car is very solid and straight. He was telling me months back it needed a tune up really bad.  He's been in a tight spot financially and thru  the holidays he didn't have the extra cash to tune it up. Last week he said he had to do something at this point because it was so hard to start and ran so poorly it was about to lay down.  He brought the plugs in to work and had them laying on a table. I walked by and noticed a strong smell of gas,  it was coming from the plugs.  He questioned me about how difficult it was to put a kit in the carb, and a few other things.  As the week went by he would tell me how the tune up had progressed.  Last thing I asked was, when the last time it had an oil change.  He said he didn't know, he would have to ask the family of the deceased previous owner. Said he really needed to change it,  it smelled of gas pretty bad.  Said it didn't use much oil at all.  I think that says a lot about one.  Over 5 years as a daily driver, a lot of it in a poor state of tune. The oil saturated with gas and it still doesn't use much oil. 

[55 Fargo]

Great posts guys and thanx for participating in this thread, want to throw something out for discussion on this topic.

Those of you who may have driven and owned vehicles or equipment powered by 225 Slant 6s and 265 Chrysler Flathead, got some ideas for discussion.

Lets compare power specs, to real world comparisons.

The slant 6,

Bore 3.4

Stroke 4.125

Horse Power 145 at 4000 RPM

Torque 215 Ft Lbs at 2400 RPM

Compression Ratio 8.4:1

 

The 265 Flathead 6

Bore 3 7/16

Stroke 4 3/4

Horse Power 123 at 3600 RPM

Max Torque 228 Ft Lbs at 1600 RPM

Compression Ratio 7:1

 

So there is the specs, let us know these 2 compared to each other in either work, driving racing, you name it.

They are different in a few ways for sure, but how much do they differ in seat of the pants power in stock form to each other....

[55 Fargo]

On 1/27/2018 at 9:54 AM, bob westphal said:

When my old dual carbed flattie went south, I installed a SL-6/904 in my P-15 with dual Carter single barrels. I gained an easy 50 hp. and a much better car. Since I'm using a  Satellite 273 rear axle, its a slug of the line but has lots of go after I'm moving. The mileage is about the same. I imagine, that if I had a lower rear ratio, It would be a screamer. 

Good stuff Bob, you should post some pics of the swap.

Now how about performance changes, off the line, and on the highway?

Much better car out of the swap, in what ways?

[keithb7]

When I was about 16, in Grade 10 I bought a 1976 Dodge Dart. If I recall it had a 225 slant 6 engine in it. My Father was dead set against me buying any "P.O.S. import" he called them. North American built or nothing at all, I remember him saying. I spent what seemed like forever trying to find a car that Dad approved of. Finally I settled on the Dodge Dart. He gave it his blessing after going over the car with me. Within a few days I noticed it was hard to start when it was hot. It would crank fast but never start until it cooled down again. Dad was no mechanic. He had no idea what to do. I was new to cars but my brother who was 18 at the time in Grade 12, was totally a gear head. He was planning to be a heavy duty mechanic. 

 

Bro and I spent a couple of days troubleshooting together. We had few specialized tools. Finally we begged and borrowed a compression tester. Yup low compression across all 6. We quickly made a decision to pull the engine and rebuild it. Ourselves. In the back yard. No garage. We borrowed an engine hoist and by day's end the next Saturday, we had the engine out on the ground. Pulled the head. Found a tired engine with a considerable ridge at the cylinder top. Flipped it over on a piece of plywood and pulled the oil pan. I removed mains and rod bearing and lifted out the crank. Then out came all the pistons.  Bay day's end Sunday I was staring at a pile of parts and starting to add up the bills. I was in high school and working part time as a dishwasher in a restaurant. If I recall I had about $300 in savings and I got paid again soon. I ordered an engine rebuild kit. I bought a reman exchange crank. Block and head was brought to a local car wash pressure washer where I blasted it as clean as I could. Next trip was to drop the block and head off at a local machine shop.

 

I worked every Friday night after school and all day Sat and Sunday for weeks to pay for the needed parts and machining. Timing chain, carb kit etc. Dad convinced me to pull the torque and have it checked over too. I was tired of school and working, but I wanted my car bad. I had a sweet girlfriend and wanted to take her on dates. With no car, we could not meet very often. She was patient as I worked my butt off to buy everything I needed. She even came and hung out with me sometimes while I was re-assembling the engine. She was an angel.

 

Finally after probably a month we were re-installing the slant 6 engine in my Dart. There was no way we could line it up to the 747 auto transmission bell housing. Finally we determined that the exchange crank I installed was for a different transmission. Drat! More delays. We pulled the torque again and had it machined to fit the crank. All went together well finally. The car started! I was excited. It was idling a little rough but I had no money left for new spark plugs, cap, rotor and wires. My brother took it to his Grade 12 shop class on Monday and hooked up to a scope. Hmm.. Spark looked off. He pulled all the plugs again. I had installed them. Several had zero gap as they had been dropped and kicked about for the past month. I had  little experience and overlooked the plugs. He cleaned and gapped my plugs. Set timing and adjusted carb. He was my hero. The car was running in top shape now. I could not have done the engine rebuild without my brother. I had a ton of respect for him for helping me.

 

Next came the courting again! Dates and ice cream often with my slant 6 Dart. Good memories with my girl. She's still with me today. It was just our 25th wedding anniversary in early January. I was a young dumb 16 year old. I drove the Dart for about 6 months and sold it for something faster. That was a huge mistake. I bought another car that I soon had to rebuild it's engine as well. I repeated the whole process again. I learned the hard way. This time big Bro was in trade school. I was on my own and rebuilt the V6 engine myself. Lots of frustration but what does not kill us makes us stronger. 

 

Below is a pic from 1987.  Here we all are man handling the slant 6 engine. I'm in the blue coveralls. Big bro in the white T-shirt. Dad pulling the hoist. Good memories.

 

 

How does all this relate to the flat head six? Well today I own a '53 Chrysler with a 265 L6 flat head. The story is a little similar. I bought my '53 last May and drove it home. Within a month I had the head off and did a full valve grind and all new valves. I'm a little smarter today with more experience. Today I can afford to order parts as needed. Today my best girl is home with me every night. No stress as I have other vehicles! LOL.  My '53 is not my only car. My old Dart was.

 

I believe the 225 slant 6 was rated at 94 HP. My flat head is rated at 119 HP. I am unsure of the actual torque of each. I would say that my flat head '53 has considerably more torque. It lugs down nicely and pull hills smooth. It was over 30 years ago that I owned the slant 6. The performance details are a little blurry. I do recall street racing my Dart against a 1974 Ford Pinto 4 cylinder, standard 4 speed tranny. It beat me off the line. Today I'd say I prefer the flat 6. I love how it sounds. It idles so quietly. It runs so smooth. It seems easy to maintain. I like it!

Edited January 31, 2018 by keithb7

[Dodgeb4ya]

Very nice story!

Nice Kaydee 1500 knock down  hoist too!