Over head valve vs. Flat Head

[Leif in Calif]

I'm the care taker of a '25 Chevy. It's overhead valve...I used to own a Model A (Flathead). I have an engineering background. I wonder why manufacturers like Chevy would bother with overhead valves, which are more expensive to manufacture. The main advantages are better breathing and higher compression, but in the '20s the fuel did not support higher compression ratios, and the breathing was only better at higher RPM than was used in those days (at least in Fords and Chevys...we're not talking Stutz here). What do you think? 

[TerryB]

Buick and Chevrolet under Wm Durant might explain Chevy having overhead valves.  I would think it showed the customer the “better engineering” going into the cars or at least the impression it’s better.  Certainly a few more bragging hp claims over a flathead design could be used in advertising.  Didn’t Louis Chevrolet make an aftermarket OHV for Ford engines?

[1957Birdman]

Zora Arkus-Duntov of Corvette fame was the man behind the Ardun hemi heads that were used with some success on the flathead Ford V8s. I believe that Louis Chevrolet was involved with hopping up the Modet T engine if I am not mistaken.

Lew Bachman

1957 Thunderbird

[Leif in Calif]

Right on both counts...there were many overhead conversions for Model T's and A's and one famous one for the v-8, but their purpose was to greatly increase performance outside the normal passenger car operating envelope. My question is why did some manufacturers go to the additional complication and expense of overhead valves in the first place when (in the period) there was little performance gain over the simpler and cheaper flathead. 

[hidden_hunter]

I wondered if easier maintenance was a factor during those times, the cads valves are awful to adjust and they claim it’s “easy” 

[Bloo]

Buick and Chevrolet started out in the early days of the car with overhead valve engines, never made anything else, and had been advertising for years that it was an engineering advantage. They didn't breathe better or have higher compression, even though both were technically possible. The fuel octane and the RPM limits imposed by the engine lower ends of the time made that irrelevant. Overhead valves also made more noise when "smooth and quiet" and "you can hardly hear it running" were huge selling points. By the mid 30s it was pretty clear that there was no performance benefit to overhead valves in an ordinary car. At that time almost all new engine designs were flatheads. Buick and Chevrolet had the last laugh though when high octane gas came along and the horsepower race took off. Almost overnight the tables turned when overhead valves proved to be the way forward.

 

Edited April 8, 2022 by Bloo (see edit history)

[hook]

I would think that the overhead valve engine people back then could also talk of easier maintenance. Valve jobs, cleaning out carbon (normal job back then), valve adjustment (rather than grinding the valve stems to fit) and with the exception of adjustment, all could be handled on the bench.   Also, less mass and easier casting of block, not to mention better cooling.

Edited April 8, 2022 by hook
left out (see edit history)

[TerryB]

In the history of things I was surprised both Pontiac and Packard held on to flathead only until the mid 1950s.  Dodge in the lower price field had an OHV V8 option in the early 1950s but the price leader Plymouth did not get that option until 1955. Of course both Dodge and Plymouth held on to the flathead six until 1959.  
 

Chrysler industrial engines used the flathead design for a long time. I guess they worked out quite well in applications where slow and steady power was required.

 

Didn't British cars adapt to OHV use very early compared to US manufacturers?  Perhaps the small displacement and need for higher rpms made the OHV design more desirable.

[Leif in Calif]

21 minutes ago, TerryB said:

 

Didn't British cars adapt to OHV use very early compared to US manufacturers?  Perhaps the small displacement and need for higher rpms made the OHV design more desirable.

I think you are right about European designs.

At least in the 20s, overheads weren't less maintenance. The '25 Chevy I look after requires the rocker arms to be oiled before every use, and the oil used eventually drips down the sides of the engine. I can't imagine what a mess it must have been when it was new and almost all roads were dirt. Many WWI aircraft had exposed valve gear, so maybe that feature was seen as more cutting edge, but the operating environment of an aero engine is quite different than the City of Petaluma's egg delivery truck.  

[DonMicheletti]

One of the "nice" things about OHV engines that had to be manually and frequently oiled, is that the owners often didnt clean the engines. Thus they were coated in a preserving oily gunk.

I pulled two 1918 Buicks, that had been sitting under trees, (with the hoods off) for over 40 years. They were really filthy. However, once the crud was cleaned off they were in surprisingly good shape. One had an oak tree growing up between the frame and starter/generator.

I ran one in my car for a while when I was rebuilding thy original engine

[LI_BENTLEY]

19 hours ago, Bloo said:

Buick and Chevrolet started out in the early days of the car with overhead valve engines, never made anything else, and had been advertising for years that it was an engineering advantage. They didn't breathe better or have higher compression, even though both were technically possible. The fuel octane and the RPM limits imposed by the engine lower ends of the time made that irrelevant. Overhead valves also made more noise when "smooth and quiet" and "you can hardly hear it running" were huge selling points. By the mid 30s it was pretty clear that there was no performance benefit to overhead valves in an ordinary car. At that time almost all new engine designs were flatheads. Buick and Chevrolet had the last laugh though when high octane gas came along and the horsepower race took off. Almost overnight the tables turned when overhead valves proved to be the way forward.

 

Buick made flat head engines, this is a normal error.  See model 5.

[LI_BENTLEY]

The first Chevrolet in 1912 was a T head and the first 6 cly was an L  head.

[keithb7]

Chevy touted OHV design, yet didn't they use a non-pressurized main and rod oil lubrication system into the 50's?

I watched a 1953 Dodge truck sales training video recently on you tube. They were pointing out that the Chevy still had a splash oil system.

Seems like splash lube was pretty stale dated for that time. No?

 

Sorry about my ignorance on Chevrolet products.  I have zero experience with them. I am pretty in tune with old Mopars, my marquee of choice.

Edited April 9, 2022 by keithb7 (see edit history)

[Bloo]

1 hour ago, keithb7 said:

Chevy touted OHV design, yet didn't they use a non-pressurized main and rod oil lubrication system into the 50's?

Yes. The last ones were the 53 stickshift cars. I had one. It had squirt nozzles pointed at the rod dippers and poured babbitt bearings. Cast iron pistons, too. I believe the mains had direct oiling, but not at high pressure. Great car but not modern my any stretch.

 

@LI_BENTLEY I stand corrected.

 

[Mark Shaw]

In 1902, Buick established the Buick Manufacturing Company. This was intended to produce engines for use in other manufacturers’ cars and make its own cars. The money again ran out in 1903. By now, however, Buick had managed to produce an engine that offered far more power than anything else being built at the time. The overhead valve engine, or “Valve-in-Head” as it was known at the time, was revolutionary and offered car manufacturers benefits unavailable from any other engine then on the market. 

 

The Great Scot who invented the overhead valve engine and the Buick Motor Company – Great Scots Foundation

 

[Layden B]

Buick 1907 1908 Models D H S K 5 are all T head

Buick 1911 Models 14 14B are L head

[TerryB]

The prevailing thoughts on Chevy 6 engines when I was young and impressionable was that the pre 1954 engines were good runners as long as you avoided long operations at higher speeds like turnpike speeds here in PA.  The Chevy sixes had the advantage of low price and plenty of spare parts to keep them running.

 A lot of the trucks I remember were Chevy.  We had our heating coal delivered in an old early 1950s Chevy truck equipped with a scissors lift box that held two tons of coal.  The truck wasn’t fast but it had enough power to carry the two tons of coal for several miles up and down hills to deliver it to us.  You always wanted to avoid getting behind these trucks on a hill as they were very slow and the coal was wet to keep the dust down. That blackish water running off the load would get all over your car and make a complete mess of your windshield.  Ah the good old days😀.

[bryankazmer]

On 4/9/2022 at 12:22 PM, Mark Shaw said:

 Buick had managed to produce an engine that offered far more power than anything else being built at the time.

I'm a little doubtful of that.  This may be just before the Lozier and Pierce Great Arrow, but the FIAT 24 hp was out.

[Mark Shaw]

30 minutes ago, bryankazmer said:

I'm a little doubtful of that.

I expect they were referring to engines being built in the US...

[bryankazmer]

6 hours ago, Mark Shaw said:

I expect they were referring to engines being built in the US...

Not what it says - GM has a history of claiming to invent more than they do.  Benz and Mercedes were certainly well above Buick's power also.  For an American firm, Winton.

[hidden_hunter]

1 hour ago, bryankazmer said:

Not what it says - GM has a history of claiming to invent more than they do.  Benz and Mercedes were certainly well above Buick's power also.

GM’s bigger claim to fame is probably more that they mass produced or popularised stuff as opposed to being first 

[Larry Schramm]

Buick's claim that an over head valve offered more power and performance has been played out over the years.  Buick went from being about the only manufacturer at the time with an overhead valve to all engines that I know of today have over head valves.  The industry migrated to the best design for performance.  Just saying.

[edinmass]

Without good fuel, the OHV was a benefit but probably not worth the extra expense early on. T heads and F heads came and went. By 1936 war clouds made the demand for high octane fuel for aircraft. It didn’t take long after the war for car companies to make engines that could use the fuels that were easily and cheaply available.

[m-mman]

On 4/8/2022 at 12:07 AM, Bloo said:

Overhead valves also made more noise when "smooth and quiet" and "you can hardly hear it running" were huge selling points.

Ford dropped their flathead and began with overhead valve V-8s in 1954. Surveys of owners of the new cars frequently said that the motor ran OK but it was "too noisy".  

Ford brought out their overhead 6 cylinder in 1952 (a really under appreciated engine) but nobody seems to have asked buyers what they though of them. Maybe because it was a 6 nobody cared?

The horsepower on the 6 was understated so that it would not embarrass the legacy flathead V-8. 

[Bryan G]

I've read reviews of the 52 Ford (Consumer Reports and either Popular Mechanics or Popular Science) and they both heaped praise on that 6. The consensus was that it was a much better engine than the old V8. 

 

I agree that the noise part of the equation gets downplayed today. An old Chrysler or Packard is great for sneaking up on folks at a car show! Just tonight my neighbor was commenting how he can never hear me drive by.

[Mark Shaw]

5 hours ago, bryankazmer said:

Not what it says - GM has a history of claiming to invent more than they do.

I don't want to argue, but I think it is interesting to point out these documents:

 

 

[bryankazmer]

Excellent article.

To be clear, I'm not disputing Buick's 22 HP claim - it's just that it's not the most in the industry.

The Buick  period article's claim is backed up.

The later  "Great Scots" article exaggerates.

 

I'm not knocking these fine cars.

[Mark Shaw]

3 hours ago, bryankazmer said:

The later  "Great Scots" article exaggerates.

I don't disagree, However, your previous post stated: "GM has a history of claiming to invent more than they do."  

That article was not written by GM.  

[jwbrew15]

Overhead valve setup always had efficiency advantages over the side valve, L head, Flat head. True they were noisier unless silent lash adjusters were installed but air flow both in and out were drastically better. A flow bench shows this dramatic difference. Best flow was always the sleeve valve having no valve stem to interrupt flow and an added uninterrupted hemi head. OHV was able to get the exhaust out better in a V-8 rather that the Flathead Ford flowing the hot exhaust thru the head and water jacket. The 1917 Scripps Booth was a mono block V-8 with OHV as one of the early to exhibit this efficient configuration.

For quality in the mid-price range the early 30's Nash advanced engines were at the top. OHV, 2 sparkplugs per cylinder for double flame propagation, forged alum rods with steel caps, pressure oiling to cam, mains, rods, rockers, timing chain, piston wrist pin and oil spray from rods to thrust areas on cylinder walls.  

[Larry Schramm]

My 1908 Buick, 2 cylinder has overhead valves and roller valve lifters.

[Frank DuVal]

On 4/7/2022 at 10:40 PM, Leif in Calif said:

there were many overhead conversions for Model T's and A's

Historical note:

 

If you got an AAA Trip Tic for central Virginia, the town of Colonial Heights was stamped with Speed Trap for many years. I remember seeing it in the early 70s. How did it get the reputation? Back in the 30s they had Model T police cars, so people would speed through on US 1 seeing the slow police car, and then they would get pulled over, as the Model Ts were modified overhead conversions.....

[Leif in Calif]

On 4/11/2022 at 6:16 PM, edinmass said:

Without good fuel, the OHV was a benefit but probably not worth the extra expense early on. T heads and F heads came and went. By 1936 war clouds made the demand for high octane fuel for aircraft. It didn’t take long after the war for car companies to make engines that could use the fuels that were easily and cheaply available.

Exactly my point. Overhead is far superior at higher RPM and/or Higher Compression, but neither situation was normal for the first 30 -40 years of automotive production. when everybody a 4 to 5 compression ratio and 2800 was the red line, a flat head had near identical performance at lower manufacturing cost. 

[Stude Light]

I think it’s interesting that Buick and Chevrolet and others had overhead valves but it was Oldsmobile that took advantage of an OHV, short stroke and higher compression technology in 1949 to put an end to the Ford Flathead dominance in street rods and they dominated NASCAR in the early 50s. The 1949 Olds Rocket engine and Cadillac’s OHV were really the first post war modern designs. It took Chevrolet five years to catch up. 
 

It’s a lessen learned many times - you don’t necessarily have to be the inventor of  new technology to win. Just figure out how to best use and market it.

[Rusty_OToole]

In the early days - meaning before WW1 - a large variety of engine designs and valve arrangements were tried including flathead, F head, T head,  OHV, the Duesenberg walking beam engine with valves at 90 degrees to the cylinder, even valveless designs with sleeve valves, and 2 stroke engines.

OHV and flathead were the most popular and both had their advantages, the OHV said to be more efficient and the flathead simpler quieter easier to service and cheaper to build. Also, a broken valve spring did not mean a bent valve and broken valve springs were a common occurrance.

The big breakthrough for the flathead was the invention of the Ricardo head design in 1921 or1922. This introduced the principle of squish or quench, effectively reducing the size of the combustion chamber by half and increasing compression without causing spark knock. For the first time a flathead could match the OHV in efficiency meaning power and fuel economy.

After 1922 I don't believe there was a new OHV gas engine other than those who were already committed to the OHV principle like Buick, Chevrolet and Nash. They had nailed their colors to the mast so to speak, and refused to admit there was something better or at least, just as good and cheaper. Yet even Buick and Nash introduced flathead models, in Buick's case under the Marquette name.

Another factor that came into it was the popularity of long stroke engines after about 1915. A long stroke, small bore OHV engine does not have room for very big valves. While a flathead can have a valve chamber wider than the cylinder, in some cases, as the Harley Davidson 45, quite a bit wider. This too tends to negate the breathing advantage of the OHV.

So why are we not all driving flatheads to this day? The last part of the equation is fuel octane and the max compression ratio allowed by available fuel. A flathead loses the ability to breathe if you make the compression ratio too high. You have to bring the roof of the combustion chamber down too close to the valves and don't leave enough room for air to pass from the valve chamber to the cylinder. The practical limit is about 7.5:1 compression ratio. Packard did manage 8.4:1 by using every trick in the book, including tipping the valves towards the cylinder and an aluminum cylinder head. But after that the OHV has all the advantage. The short stroke, big bore, high compression, high speed OHV engines of the fifties, took advantage of technology not available in the twenties thirties and forties such as high octane leaded fuel, automatic transmissions and high speed hiways. But for a generation the flathead was the way to go.

[Rusty_OToole]

It might be interesting to compare different engines of the past, OHV vs flathead and see how much difference there was in power and economy. I can think of one such comparison, the 1927 Stutz and Auburn. They were involved in a battle for stock car supremacy at Daytona Beach that year. It is interesting because both had straight eight engines of identical bore and stroke and 298 cu in displacement. But the Auburn was a conventional Lycoming flathead while the Stutz featured a very sophisticated overhead cam, overhead valve design.

You would think the Stutz had an advantage in power and speed and it did  - it beat the Auburn but by less than 2MPH. The Stutz also cost $5000 vs $1000 for the Auburn, and the Stutz with its heavy complicated engine and drive train weighed 700 pounds more even though both had light weight boat tail speedster bodies.

Stutz also finished second at LeMans a couple of years later, coming second to another OHV, overhead cam sport model, the Bentley. But two Chryslers with flathead sixes came third and fourth. Once again we are comparing cars in the $5000 class to cars in the $1000 - $1500 class. I will concede that back in the day a really good OHV car could beat a flathead, but at what a cost! For all practical purposes I would take the flathead for smoothness, silence, easy service, reliability, and low cost and concede the last 2 MPH. In other words settle for a top speed of 88 rather than 90MPH.

[TerryB]

The idea of cost vs performance had to be a deciding factor for many manufacturers.  As I mentioned earlier I was surprised Pontiac used the flathead straight eight as long as it did. My first car, purchased in 1970, was a 1951 Pontiac with the straight eight.  It seemed to fit the description “slow and steady”.  Nice car that I did not appreciate fully at the time.  

[JRA]

Where are the F-head design in this battle? The Hurricane engine of my 1954 Willys-Overland CJ3B Jeep has this design, and I have never understood the reason of this engineering solution for such type of car. 

[JV Puleo]

F Heads allowed you to use larger valves...with one in the block and the other in the head you could get a larger overall diameter than you could when the valves were side by side or on opposite sides of the combustion chamber. They also allowed you to put the intake and exhaust manifolds on opposite sides of the engine. It seems the most common was IOE (intake over exhaust). My own car is EOI...the exhaust valves are on top.

[JRA]

The hurricane engine is great, very strong for the Jeep usage, but I have always questioned its application in a utility vehicle. Anyway, it works very well.

Edited April 17, 2022 by JRA (see edit history)

[Rusty_OToole]

One of the hottest performing cars of the teens and twenties was the Hudson Super Six and it had an F head engine. There were a few F heads on the market,  made by companies known for their quality engineering and expensive products. Hudson, Rover, Rolls Royce and Harley Davidson all featured F head motors at one time or another, the last being Rolls Royce and Willys in the fifties.

I don't know why they weren't more popular as the layout offers advantages over both flathead and OHV designs or at least, did in the early days. I suspect the Ricardo head made the flathead so efficient most designers looked no farther.