How did Flathead Motors Hang on So Long?

[B Jake Moran]

As some of you know, I am looking for a project vehicle (yes, still looking) to restore with a young friend.  Not many, but a couple of my saved vehicles are Flatheads.  One is a 1947 Studebaker Coupe Express truck with a small flathead 6.  

That got me thinking about why Flatheads stuck around so long even when the trend was toward OHV engines, and OHV engines, especially at Buick, had been around so long.  

 

I have never worked on a Flathead.  I have owned a few, but never opened them up.  Should I avoid them since I have no experience rebuilding them?  

Packard had a Flathead through 1954.
Kaiser used the Continental based 6 through 1955

Hudson through 1954. 
Ford through 1953. 

[Matt Harwood]

Flatheads were cheap to build, reliable, and simple to work on and for the most part, they got the job done. Retooling for overhead valves was expensive and convincing the general car-buying public (cars like low-cost Plymouths, for example) that overhead valves were superior and worth the extra money was a bit of an uphill battle. It wasn't until highways started to become a real transportation option in the early 1950s that higher speeds were necessary and it was at higher speeds that the flatheads had trouble keeping up.

 

Just think about how long and loud this group here biatched and moaned about, say, the loss of the venerable pushrod GM 3800 V6 when it was replaced by overhead cam engines. An important step forward but one that few people appreciated or understood, and they certainly were not happy about paying extra for a replacement they didn't respect. Same thing.

[ply33]

We happened to have an early 1960s Encyclopedia Britannica in the house growing up and the article in it on internal combustion engines had an interesting tidbit: Above about an 8:1 compression ratio an L-head (“flathead”) engine geometry made it difficult or impossible to avoid restrictions in the flow of intake mixture and exhaust gasses.

 

Prior to the 1950s the octane rating of gasoline did not permit compression ratios as high as 8:1 so an L-head really did not have performance disadvantages compared to an overhead valve design.

 

Once higher octane fuel was commonly available and you are taking advantage of that by raising the compression ratio above 8:1 then the L-head design is a liability and you move to overhead valves to get better breathing.

[dodge28]

The racing giant Louis  Chevrolete developed the overhead valve engine around  1914.The bottom was babbit bearings. At first the cylinder heads to the gasket were flat. The pistons  reached about 2 inches below the head. That was the firing chamber. That is where firing took place .There was no valve cover .Oiling of the valve train was by a heavy piece of felt soaked with oil sitting on top of the valve train. The felt had to be soaked regularly with an oil can. There was a broad oil pan  siting below the oil pan to catch oil spill over. In 1928 a valve cover was added but there was no gasket. In 1929 there were some improvement and the first 6 cylinder introduced.   

[Rusty_OToole]

In the early days meaning before 1920 there were a variety of engine designs tried. Flathead, T head, and OHV engines were popular. Duesenberg made an excellent engine with the valves at 90 degrees to the cylinders called a Walking Beam engine.

 

Flatheads were popular because they were simple, quiet, cheap to build, easy to repair, and if you broke a valve spring (which was a common thing at the time) it did no harm as the valve could not crash into the piston.

 

But the OHV engines, while more expensive, complex and noisier had a slight advantage in efficiency.

 

Then came a major breakthrough called the Ricardo cylinder head. Invention of an English inventor Harry Ricardo and brought to the market in 1922. It introduced the idea of squish or quench. This did 2 things, it reduced the effective size of the combustion chamber at TDC and it caused turbulence. This allowed higher compression and faster combustion.

 

With the new high compression Ricardo design OHV engines had little or no advantage over a flathead. While the flathead still had all the advantages above. Plus, you could use bigger valves in a flathead. With the valve chamber beside the cylinder, it could be wider than the cylinder, while OHV engines were restricted to the diameter of the cylinder. This was an important point with the small bore, long stroke engines then in vogue.

 

So, from 1922 on, the flathead held all the cards. This is why there were practically no new OHV engines from then on, with the exception of a few old line companies that were committed to the OHV principle, and some all  out racing engines with hemi heads, that would do anything to eke out a few more Horsepower.

 

This was the rule until the early fifties. There were several technical developments that led to the use of OHV engines, the biggest one being the use of high octane leaded gas.

 

Top compression ratio for a flathead is about 7.5 or 8:1. The highest I know of is 8.2:1 in a 1954 Packard straight eight, and they had to pull every trick in the book to get it that high.

 

If you raise the compression beyond a certain point you cut off the breathing. This is not an issue with OHV engines.

 

Now you know why the flathead was king from the early twenties to the early fifties, and why the OHV took over. There is still nothing wrong with a good flathead. They are smooth, reliable, quiet and a pleasure to drive as the long stroke and high torque make driving easy with almost no shifting required. And with low compression they run fine on the lowest octane regular, in fact, they run better on low octane fuel than high octane.

 

If you want to go fast you need an OHV V8 but for driving pleasure a good flathead is hard to beat.

 

By the way don't think all flatheads are deadheads on the road. The big Packard 400 straight eight could top 100MPH and was only a few tenths of a second behind its OHV competitors in acceleration.

Edited December 14, 2023 by Rusty_OToole (see edit history)

[Rusty_OToole]

3 hours ago, B Jake Moran said:

Packard had a Flathead through 1954.
Kaiser used the Continental based 6 through 1955

Hudson through 1954. 
Ford through 1953.

We could add to the list, Plymouth and Dodge to 1959, some Dodge trucks to 1962, Rambler to 1964. Not sure when Hudson made their last flathead but believe you could still get one in 1956.

 

Studebaker's small Champion six was only 170 cu in and 85HP later raised to 185 cu in. Rather underpowered.  The bigger Commander six at 226 or 245 cu in would give more power.

 

Don't be afraid of a flathead because it is a flathead. They are much easier to work on than more modern engines. I would be concerned about the parts supply. Any Chrysler product six cylinder is very easy and cheap to get parts for. The straight eights, not so much. Flathead Fords are well supported but good blocks without cracks are getting hard to find. Packards seem to be ok except for some prewar senior straight eight and V12 engines which are something of a nightmare to work on. Studebaker, Nash, Hudson,Olds, Pontiac,  etc I'm not so sure, you could look into the parts situation before you buy one, possibly by contacting the owner's club.

[Grimy]

8 minutes ago, Rusty_OToole said:

They are much easier to work on than more modern engines.

Well, except for valve jobs (note that all my collector cars are flatheads).  It was much easier for me to pull that Buick straight 8 head and take it in for cleaning and a valve job, and the price of sending it out was well worth it to me rather than having to lap valves in (never mind grinding seats) with the block in the car.

[Rusty_OToole]

If you find it easy to lift the head off a straight eight Buick you are a better man than I am. Back in the day you could get the auto machinist to come to you to grind valves, true cylinders and grind crank throws. Today you would probably have to tow the car to his shop if you could get it done at all.

[Grimy]

4 minutes ago, Rusty_OToole said:

If you find it easy to lift the head off a straight eight Buick you are a better man than I am. Back in the day you could get the auto machinist to come to you to grind valves, true cylinders and grind crank throws. Today you would probably have to tow the car to his shop if you could get it done at all.

Exactly!  Even in my long ago youth I used a cherry picker hoist to remove and replace a Buick head.

[oldford]

4 hours ago, Matt Harwood said:

It wasn't until highways started to become a real transportation option in the early 1950s that higher speeds were necessary and it was at higher speeds that the flatheads had trouble keeping up.

That is, except the Hudson Super Six. They blew the doors off the Olds Rocket V8 at the 1953 Daytona 500....

 

Frank

[B Jake Moran]

1 hour ago, Rusty_OToole said:

Studebaker's small Champion six was only 170 cu in and 85HP later raised to 185 cu in. Rather underpowered.  The bigger Commander six at 226 or 245 cu in would give more power.

 

That is kind of bumming me out.  I don't have to go fast with the 47 Coupe Express, which is a neat truck featured in the last issue of Vintage Truck that I received.  But wow 170 cid only?  

[Angelfish]

If you can't get one of the common flatheads running, it's time to sell your tools and go into social work.

 

On a personal note, there was a time when I almost had to go into social work.   I couldn't get a Ford flathead V8 running after reassembly.   Fought it for weeks, or so it seemed.  Spun over but would not fire.  Friend of mine came by to help,  "Are you sure that's cylinder #1?  Usually this is cylinder #1."  My hand drawn diagram (before the internet age) had all the plug wires swapped one side for the other.  Swapped them back and away we went.

[58L-Y8]

4 hours ago, B Jake Moran said:

That is kind of bumming me out.  I don't have to go fast with the 47 Coupe Express, which is a neat truck featured in the last issue of Vintage Truck that I received.  But wow 170 cid only?  

Studebaker was designing and building half-ton pickup trucks for Ole to drive to the Feed and Seed to get his milled grain, doing so with miserly economy.  Only the higher tonnage trucks came with the 226 ci and 245 ci flathead sixes. 

[Bryan G]

8 hours ago, Rusty_OToole said:

By the way don't think all flatheads are deadheads on the road. The big Packard 400 straight eight could top 100MPH and was only a few tenths of a second behind its OHV competitors in acceleration.

Recently I was reading Tom McCahill's test of "my car", a '49 Chrysler flathead straight eight. He ran it foot-to-the-floor on the highway and got up to, as I recall, 96. I fully believe the larger Packard engine could beat 100.

 

Engine was stuck when I got mine. I did a ring & valve job in my driveway. A great learning experience. And there really wasn't too much they could have done to make an engine easier to work on.

[Twisted Shifter]

15 hours ago, B Jake Moran said:

...One is a 1947 Studebaker Coupe Express truck with a small flathead 6.

 

10 hours ago, B Jake Moran said:

  I don't have to go fast with the 47 Coupe Express, which is a neat truck

I learn something every day...

I thought the "Coupe Express" name ended in the '30's with the great looking Studebakers of '37 or '38. Now I find out that the post-war Studebaker M-5 pickups were also identified as a "Coupe Express". When did that terminology end?  ...with the M-5's or later on?

 

 

 

[f.f.jones]

3 hours ago, Twisted Shifter said:

I find out that the post-war Studebaker M-5 pickups were also identified as a "Coupe Express". When did that terminology end?  ...with the M-5's or later on?

 According to the knowledgeable gods of the internet:

Design and specifications:

The M series sported a more aerodynamic shape than most trucks of the time, with easily recognizable "wind wing" vents on the driver and passenger windows, a feature not found on any other make of American truck during World War II. When Studebaker introduced the M-series pickup truck in 1941, the company used the Coupe Express name from its 1937–1939 Coupe Express coupe utility in advertising for a time, but no M-series trucks were ever officially designated as the Coupe Express.

 

So, Mr. Shifter, you have been correct all along. Mr. Moran needs to revise his terminology.

 

 

[B Jake Moran]

3 hours ago, f.f.jones said:

 According to the knowledgeable gods of the internet:

Design and specifications:

The M series sported a more aerodynamic shape than most trucks of the time, with easily recognizable "wind wing" vents on the driver and passenger windows, a feature not found on any other make of American truck during World War II. When Studebaker introduced the M-series pickup truck in 1941, the company used the Coupe Express name from its 1937–1939 Coupe Express coupe utility in advertising for a time, but no M-series trucks were ever officially designated as the Coupe Express.

 

So, Mr. Shifter, you have been correct all along. Mr. Moran needs to revise his terminology.

 

 

Mr. Jones - 

 

Perhaps you are correct, but there are many references to the post war Studebaker small series pickup as the "Coupe Express". Studebaker introduced an all new truck - the R2 - in 1949 that was even more modern styled than the Chevy Advance Design. 

To my knowledge, the Coupe Express was more of a slogan than a name plate. 

A 1946 Studebaker advertisement touts:

"With the war at an end, thousands of truck users will welcome this announcement that Studebaker is again producing commercial vehicles - with the popular Studebaker Coupe Express Pick-up in the vanguard."

The Saturday Evening Post referenced the advertisement's full color painting of the half ton Coupe Express explaining " that Studebaker Coupe Express Pick-up you see above is a full-fledged teammate of 197,661 Studebaker military trucks that wrote brilliant new pages of transport history at the fighting fronts."

 

 

So, Mr. Jones, M-5 was the model number, but it was a Coupe Express, borrowing heavily from the passenger line for the interior, which was very untruck like.   We call that splitting hairs here in central Iowa.  

 

Edited December 15, 2023 by B Jake Moran (see edit history)

[Rusty_OToole]

For an interesting comparison of flathead vs ohv let's look at 2 brand new V8 engines for 1949. Everyone remembers the Cadillac but Lincoln also had a brand new V8 that year, a flathead.

 

Both made by experienced makers of luxury cars, using the state of the art engineering and manufacturing of the time.

 

Both all new V8s

Cadillac 331 cu in Lincoln 337 cu in

Cadillac 160HP  Lincoln 155HP

Both had 7.5:1 compression ratio.

 

As you can see there was not much to choose between them. Caddy had a trifle more HP but was it worth the extra cost and complexity?

 

This comparison only lasted a short time. In a few years the Cadillac was improved with higher compression, hotter cams, more carburetors and got up to 230HP in the Eldorado version.

 

Meanwhile Lincoln quietly dropped the flathead after 1951 and replaced it with their own OHV V8.

 

The lesson is, as long as compression ratios stayed below 8:1 and fuel was no better than 70 or  75 octane there was not much point to an OHV engine. If you go back to the thirties and forties and compare HP per cubic inch of Buick and Chevrolet OHV engines to their flathead competitors you will wonder why they bothered to make an OHV engine.

Edited December 15, 2023 by Rusty_OToole (see edit history)

[AzBob]

One thing I don't think anyone has mentioned yet is the mechanical advantage that can be gained by offsetting the rocker arm pivot point to achieve greater lift using the same cam in an OHV setup. 

[pfloro]

1 hour ago, Rusty_OToole said:

The lesson is, as long as compression ratios stayed below 8:1 and fuel was no better than 70 or  75 octane there was not much point to an OHV engine.

Thank you, Rusty...  I gained more knowledge...

 

Paul

[joe_padavano]

1 hour ago, Rusty_OToole said:

The lesson is, as long as compression ratios stayed below 8:1 and fuel was no better than 70 or  75 octane there was not much point to an OHV engine.

CR and operating RPMs. The improved port flow from OHVs made a huge difference once the rest of the engine was upgraded to take advantage of that. We could be having this same discussion about pushrod motors vs OHC motors.

[rustyjazz1938]

3 hours ago, Rusty_OToole said:

The lesson is, as long as compression ratios stayed below 8:1 and fuel was no better than 70 or  75 octane there was not much point to an OHV engine. If you go back to the thirties and forties and compare HP per cubic inch of Buick and Chevrolet OHV engines to their flathead competitors you will wonder why they bothered to make an OHV engine.

@Rusty_OToole, I'd like to offer a counter to your statement. In discussions with @Stude Light, we both came to the realization that his 1923 Studebaker Light Six and my 1927 Buick Standard 27-27 have the same displacement engine. Both have 3.125in bore by 4.5in stroke for a displacement of 207 cubic inches. The Studebaker is a flathead engine whereas of course, the Buick is OHV. Factory ratings (always taken with grain of salt) were 63 HP for the Buick, and I believe 35 HP for the Studebaker (Scott please feel free to correct me). I believe the compression ratio for the Buick was in the 6:1 or slightly higher range which was high for the era, I don't know the number for the Studebaker.

 

It really isn't an apples to apples comparison of course as age/price point differences come into play, but I felt it would be a valid observation to share that given the same displacement, one engine makes 28 horsepower more than the other with one major difference being OHV configuration versus flatheads.

 

I won't get into the fact that the Buick being a significantly heavier car, the overall vehicle performance is about the same... 🤪.

 

Just my two cents in the discussion.

 

Happy Motoring,

 

Rusty

[ply33]

38 minutes ago, rustyjazz1938 said:

@Rusty_OToole, I'd like to offer a counter to your statement. In discussions with @Stude Light, we both came to the realization that his 1923 Studebaker Light Six and my 1927 Buick Standard 27-27 have the same displacement engine. Both have 3.125in bore by 4.5in stroke for a displacement of 207 cubic inches. The Studebaker is a flathead engine whereas of course, the Buick is OHV. Factory ratings (always taken with grain of salt) were 63 HP for the Buick, and I believe 35 HP for the Studebaker (Scott please feel free to correct me). I believe the compression ratio for the Buick was in the 6:1 or slightly higher range which was high for the era, I don't know the number for the Studebaker.

 

It really isn't an apples to apples comparison of course as age/price point differences come into play, but I felt it would be a valid observation to share that given the same displacement, one engine makes 28 horsepower more than the other with one major difference being OHV configuration versus flatheads.

 

I won't get into the fact that the Buick being a significantly heavier car, the overall vehicle performance is about the same... 🤪.

 

Just my two cents in the discussion.

 

Happy Motoring,

 

Rusty

What is the compression ratio for those two engines? 1923 is a bit early for the Ricardo combustion chamber design in the US so it is likely that even though the two engines have the same displacement they have quite different compression ratios and thus different efficiencies.

 

An internal combustion engine is basically Carnot Cycle engine where the hot gas to expand is created by burning a fuel/air mixture in the cylinder. The power/efficiency of a Carno Cycle is dependent on the amount you can expand the hot gasses, call it "expansion ratio". On an Otto Cycle gas engine the expansion ratio is the same as the compression ratio, so higher compression ratios deliver more power for the same fuel input. So it is not just a matter of displacement, it is also a matter of compression ratios.

[Rusty_OToole]

34 minutes ago, rustyjazz1938 said:

@Rusty_OToole, I'd like to offer a counter to your statement. In discussions with @Stude Light, we both came to the realization that his 1923 Studebaker Light Six and my 1927 Buick Standard 27-27 have the same displacement engine. Both have 3.125in bore by 4.5in stroke for a displacement of 207 cubic inches. The Studebaker is a flathead engine whereas of course, the Buick is OHV. Factory ratings (always taken with grain of salt) were 63 HP for the Buick, and I believe 35 HP for the Studebaker (Scott please feel free to correct me). I believe the compression ratio for the Buick was in the 6:1 or slightly higher range which was high for the era, I don't know the number for the Studebaker.

 

It really isn't an apples to apples comparison of course as age/price point differences come into play, but I felt it would be a valid observation to share that given the same displacement, one engine makes 28 horsepower more than the other with one major difference being OHV configuration versus flatheads.

 

I won't get into the fact that the Buick being a significantly heavier car, the overall vehicle performance is about the same... 🤪.

 

Just my two cents in the discussion.

 

Happy Motoring,

 

Rusty

If you read my post you would know that before the Ricardo head came out, OHV engines did have the advantage over the flathead in power. You car comparing 1923 engines. The Ricardo head came out in 1922. If the Studebaker was an older design it would explain the difference.

 

References I find online say the 1923  Studebaker was a 40HP car and the1927  Buick 60HP. But the difference in year is significant. If you compared both from the same year you would not see such a big difference.

 

I could throw in the 1924 Chrysler flathead six of 201 cubic inches, one of the first "high compression" motors at 68 HP. You notice this outdoes the Buick even though it is slightly smaller and a flathead.

 

This illustrates my point that before 1922 the OHV engine had an advantage in power but with the new head design the advantage largely disappeared.

[Rusty_OToole]

If you want to compare flathead to OHV engines in the twenties there was a dandy contest in 1927 to determine the stock car champion at Daytona Beach.

The main contenders were the Auburn and Stutz speedsters.

Both had straight eight engines of identical bore and stroke but the Auburn had a conventional Lycoming flathead while the Stutz had a very sophisticated overhead cam engine.

The Auburn produced 88 HP while the Stutz made 115 HP.

In the event they were very close within a couple of MPH of each other but the Stutz pulled off a win.

 

The more powerful Stutz also weighed 700 pounds more than the Auburn. It had a heavier more powerful engine, a heavier drive train and heavier chassis. It also cost twice as much as an Auburn.

 

Given the fact that the two were so close in size and performance, the Auburn for half the money seems like a bargain.

 

2 years later Auburn brought out an improved engine with 115HP.

 

This was an extreme contrast between the most technically advanced overhead cam engine in America and the most basic flathead. Yet speed and performance were close.  The typical pushrod OHV engine would not have done as well as the Stutz.

 

For the ordinary motorist the flathead engine was the best choice.

Edited December 15, 2023 by Rusty_OToole (see edit history)

[Rusty_OToole]

3 hours ago, joe_padavano said:

CR and operating RPMs. The improved port flow from OHVs made a huge difference once the rest of the engine was upgraded to take advantage of that. We could be having this same discussion about pushrod motors vs OHC motors.

Joe we both know there was a lot more to the changeover to OHV engines in the early fifties. There was the chance to go to higher compression than was possible with a flathead because of the better high octane leaded gas. There was also the change to a short stroke big bore configuration from the previously fashionable long stroke designs. Then there was the fact that most of the new engines were V8s which have a very short,  stiff crankshaft compared to a straight eight.

All these factors, and a few others, went together to make a more powerful, low friction, high revving engine that could exceed the typical flathead in power and economy.

Combine this with new automatic transmissions which encouraged even higher compression and hotter cams.

 

So yes, there was a revolution in design and the flatheads did become "old hat". But I believe this has been exaggerated. A good flathead is far from the useless junk a lot of people think it is. And, in the period of 1922 to 1949 the flathead often had the advantage.

[Rusty_OToole]

4 hours ago, joe_padavano said:

CR and operating RPMs. The improved port flow from OHVs made a huge difference once the rest of the engine was upgraded to take advantage of that. We could be having this same discussion about pushrod motors vs OHC motors.

Just looking at improved port flow. You can have as large and well shaped intake and exhaust ports on a flathead as on an OHV engine, right up to the valve seats. The flathead can have larger valves than an OHV because the valve chamber can be wider than the cylinder bore. In the days of the small bore long stroke engine this was significant. Where the flathead loses is the 180 degree turn from the valve seat down into the cylinder. To have enough room for gases to flow you can't bring the head down too low or make the combustion chamber too small. This is not a big deal if you are aiming for a CR of less than 8:1.

 

So  the flathead had the advantage of large valves and the disadvantage of a sharp turn between the valve and cylinder. The OHV had the advantage of straight gas flow but the disadvantage of smaller valves. This of course was before the short stroke big bore era.

 

In terms of power and efficiency it was a tossup for ordinary road use as long as fuel was no better than 70 or 75 octane.

 

As soon as high octane leaded gas became available, along with short stroke big bore high compression OHV engines, the flathead became obsolete.

[Gary_Ash]

Even lawnmower engines have moved to OHV configuration.  I have read that even a few pounds of supercharger boost will really wake up a flathead.  Perhaps the Graham Supercharger is a good example of extending the capabilities of a flathead.  The Graham got 124 hp from 217 cu in six with about 3.5 lbs of boost.  Earlier, there was a supercharged eight making 135 hp from 265 cu in.  There were also aftermarket superchargers for Ford flathead V8s.

 

For many years, the website at Uncommonengineering.com showed examples of Hudson 306 cu in six-cylinder engines that had been modified to beat the band, including superchargers.  That site is now gone.  I'll have to look for any photos I downloaded.

[Rusty_OToole]

31 minutes ago, Gary_Ash said:

Even lawnmower engines have moved to OHV configuration.  I have read that even a few pounds of supercharger boost will really wake up a flathead.  Perhaps the Graham Supercharger is a good example of extending the capabilities of a flathead.  The Graham got 124 hp from 217 cu in six with about 3.5 lbs of boost.  Earlier, there was a supercharged eight making 135 hp from 265 cu in.  There were also aftermarket superchargers for Ford flathead V8s.

 

For many years, the website at Uncommonengineering.com showed examples of Hudson 306 cu in six-cylinder engines that had been modified to beat the band, including superchargers.  That site is now gone.  I'll have to look for any photos I downloaded.

For various technical reasons flatheads respond very well to supercharging especially centrifugal superchargers and turbochargers.

We have already covered the fact that they have low compression ratios. This is an advantage for supercharging. Suppose you add 7 pounds of boost, this will increase cylinder filling by 50% which means your 6:1 compression becomes 9:1 which is about what you want to run on pump premium.

Flatheads are tuned for best cylinder filling and power at low to medium RPMs and run out of breath at high RPMs. Centrifugal superchargers mate well with this as they add little boost at low RPMs and more at higher RPMs.

 

In the thirties you had centrifugal supercharged sixes with the same HP as a straight eight, and supercharged eights with the same HP as a V12.

 

In the early fifties the flathead six Kaiser with supercharger had the same HP as  a typical small block V8. Later the supercharged Studebaker 289 had the same HP as a 352 Packard.

 

There has been some discussion of this on the HAMB bulletin board. A couple of guys have tried centrifugal superchargers on old Ford flathead 4 cylinder engines. They were impressed with the results. With no changes other than the supercharger they got much higher speeds, in fact they did not seem to have a top speed, they just kept slowly gaining speed until they ran out of room. This was in the beach races on sand that they call the race of gentlemen.

 

Edited December 15, 2023 by Rusty_OToole (see edit history)

[B Jake Moran]

I was going to mention the Kaiser application.  It boggles the mind really.  So Flatheads were safe reliable engines and were started at 4.5 to 1 compression and ended - in normal application- at 6:1.  
 

How in the heck do you explain supercharging a motor not able to go above 6:1?   Let’s supercharge it and go to 9:1 !  How is that possible?   
 

It begs the question- why not increase the compression ratio to 8:1 or in line with the OHV compression ratios of that early 50s era?  
 

What happens to a Flathead when the compression ratio is increased?  

[AzBob]

5 minutes ago, B Jake Moran said:

What happens to a Flathead when the compression ratio is increased?  

In the case of the Model A Ford engine at 4.22:1 stock CR to the currently available 6.0:1 CR which I installed on my "A" engine.

So approximately a 15 HP gained (40 HP stock) along with a cooler running engine. (More efficient combustion.)

 

The chart below is with a stock carburetor and a Stipe touring cam. Sorry, couldn't find a chart with the stock cam. If the bottom end is in good shape, no problem with the bearings handling the increased compression.

 

[Rusty_OToole]

7 minutes ago, B Jake Moran said:

I was going to mention the Kaiser application.  It boggles the mind really.  So Flatheads were safe reliable engines and were started at 4.5 to 1 compression and ended - in normal application- at 6:1.  
 

How in the heck do you explain supercharging a motor not able to go above 6:1?   Let’s supercharge it and go to 9:1 !  How is that possible?   
 

It begs the question- why not increase the compression ratio to 8:1 or in line with the OHV compression ratios of that early 50s era?  
 

What happens to a Flathead when the compression ratio is increased?  

To increase the compression you have to make the combustion chamber in the head smaller. But if you do this you cut off the air passage between the valves and cylinder. So the engine can't breathe. You can get up to 7.5:1 or maybe 8:1 compression, depending on engine design, but that is about the limit.

 

Now about supercharging. With a normally aspirated engine you depend on atmospheric pressure to fill the cylinder. This is 14.7 pounds per square inch at sea level. Less at higher altitudes.

 

So let's say you have 14 PSI filling your cylinders. Now you add a blower that gives it another 7 PSI. It stands to reason that you will force 50% more air into the cylinders since 7 is 50% of 14. I hope this is clear.

 

Now let's say each cylinder holds 36 cubic inches and you have a 6:1 compression ratio. That means the combustion chamber must be 6 cubic inches. Now if you over fill the cylinders by 50% to 54 cu in and compress that into the same combustion chamber you will have the equivalent of 9:1 compression.

 

There is a rule of thumb that your octane should look like your compression ratio. A 6:1 compression motor will run fine on 60 octane gas. But a 9:1 compression motor needs 90 octane gas. This is not a hard and fast rule just a guide. But you see where I am going with this.

[Rusty_OToole]

Ricardo's original patent. Perhaps this will help explain how the Ricardo head made the flathead competitive with the OHV engine and why the OHV eventually won out.

PATENT SPECIFICATION  148,046.
Application Date: July 22, 1919.    No. 18,235 / 19               
Complete accepted: July 29, 1920

 

• The drawing shows a cross section through the cylinder block and head of a typical side valve engine in which the valves lie side by side in the Cylinder block.
• The plan view shows the combustion chamber relative to the cylinder bore, please note the small gap between the combustion chamber and the cylinder bore as this is the basis for the invention.
• In the opening paragraphs of Ricardo`s specification he describes all the problems which plague this type of side valve engine, the main one being the lack of turbulence in the head.
• Another problem he outlines is “that increase of the compression beyond a certain and fairly low figure merely results in a greatly increased tendency to detonation without affecting any appreciable improvement in either the power output or economy”.
• The text then goes on to explain that “all things being equal” an overhead valve engine with a symmetrical cylinder head will give 10% to 20% improvement in power output over the side valve arrangement.
• Having set down the disadvantages of the side valve layout, Ricardo then goes on to outline the basis of his invention.
• The cylinder head would be flat with a minimum clearance between it and the piston, the combustion chamber would be formed over the valves and connected to the cylinder by a small passage created by overlapping the combustion chamber with the cylinder bore, the passage having the same area as the inlet valve port
• Ricardo argues that this layout will create turbulence in the combustion chamber and with the sparking plug placed centrally in the combustion chamber will give conditions for greater power and economy and will permit a much higher compression ratio to be used without a tendency to detonation.

 

You can see from the drawings that this design reduces the combustion chamber by half from the wide open design previously used. That when the piston comes up it will squirt the mixture towards the spark plug, causing turbulence which makes it burn quicker.  And you can see why you can only make the combustion chamber so small before you cut off breathing.

Edited December 16, 2023 by Rusty_OToole (see edit history)

[Littlestown Mike]

Thanks for the history on Ricardo's head design.  I knew of Ricardo, but never had  the context.  patented in 1919/1920--hmmm.  

What makes this interesting to me is I was reading in James Eickman's " The FORD Y-Block" where he discusses the head design,
 "While Chevrolet was busy developing a free-breathing V8...Ford was working on new combustion chamber shapes.  The Y-Block development crew was concerned about the move to ever-increasing compression ratios.  ... the combustion chamber of arch rival Chevrolet's V8 had not taken kindly to compression ratio increases.  This same publication stated that the Y-Block could accomodate still higher ratios than were in use at the time.  It is unfortuante that the auto industry did not continue on this path toward higher ratios and greater efficiency instead of engaging in a horsepower and cubic inch race.  The full potential of the Y-Blocks combustion chamber design was never fully to be realized.  Indeed speed tuners in the fifties and sixties did not understand the intent...and labeled it a poor deswign becasue it did not lend itself to modification  for huge hoursepower gains " ...." The combustion chmaber of the Y-Block was a high turbulence Ricardo design..."  He then went on to dicuss the way the design created turbulence which blended the fuel and air for better efficiency.  He also noted that the design prevented the formation of two flame fronts which would lead to detonation. 

IIRC, that same principle of swirl and turbulence was used in the Indirect Injection design used in diesel engines which had a separate compustion chamber from the piston area.  All the air was forced thru a small hole into a sperical (more or less) chamber and the fuel was injected into that swirling mass and the combustion process forced the expanding gases back out thru that same small hole and into the cylinder

 

[Stude Light]

Speaking of supercharging a flathead….this is the 1936-1948 Cadillac flathead design with a little extra boost 😁

 

 

[Joao46]

On 12/14/2023 at 2:52 PM, Rusty_OToole said:

fact, they run better on low octane fuel than high octane.

Hi. Can you explain that? I would think if a car does not need hi octane you’re just wasting money, but why would a low compression car run ‘better’ with lower octane gas.

[Rusty_OToole]

1 hour ago, Joao46 said:

Hi. Can you explain that? I would think if a car does not need hi octane you’re just wasting money, but why would a low compression car run ‘better’ with lower octane gas.

Octane is a measure of knock resistance and nothing else. If you have a low compression engine it does not need high octane fuel.  It will run better and cooler, and develop more power on low octane fuel.  The rule of thumb is the octane should look like the compression ratio. In other words, if you have a 9:1 compression engine you need 90 octane hi test. If you have a 6:1 flathead 60 octane is fine. Naturally this is not a hard and fast rule, just a guide. There are other factors involved but it will get you close.

[JV Puleo]

One aspect of this that seems to be ignored is that vast majority of car buyers have never been particularly interested in the mechanical aspects of their cars or overly concerned with horsepower. Long-term reliability was far more important and the flat head was a fully developed, mature technology that satisfied them. I'm thinking here of my own father, who wouldn't have been able to tell the difference between a flat head and an OHV engine...it was just an engine and if the car got him to work in the morning and home at night and didn't require lots of expensive maintenance he wouldn't have cared what engine it had. I suspect his attitude was far more common in the general population than it would be with car enthusiasts.

 

In the 70s my everyday car was a '54 Plymouth Cranbrook. It got me to work just fine and I only scrapped it when the rear springs broke. Still, I took the engine out, overhauled it, and put it in a ? (I forget now but it may have been a '49 Dodge) and as far as I know it may still be on the road.

Edited December 24, 2023 by JV Puleo (see edit history)

[Tom Boehm]

New question about flathead engines: A method I have heard of to revive engines that have sat unused for a long time is to remove the spark plugs and fill the cylinders with Marvel Mystery Oil. If the engine is suspected of being stuck the MMO soak could loosen it up. Is this method possible with a flathead engine? If a valve is open, wouldn't the MMO fill the intake or exhaust manifold rather than filling the cylinder? Especially if the spark plug is over the valves and not centered on the cylinder. 

[Harold]

21 minutes ago, Tom Boehm said:

New question about flathead engines: A method I have heard of to revive engines that have sat unused for a long time is to remove the spark plugs and fill the cylinders with Marvel Mystery Oil. If the engine is suspected of being stuck the MMO soak could loosen it up. Is this method possible with a flathead engine? If a valve is open, wouldn't the MMO fill the intake or exhaust manifold rather than filling the cylinder? Especially if the spark plug is over the valves and not centered on the cylinder. 

On Plymouths I've used a pump oiler with a long, skinny flex nozzle.  I go in through the spark plug hole and aim the nozzle towards the driver's side of the engine to get the lubricant above the piston where it has to go.