Wondering if anyone has bothered to better understand the claims an OHV 4 cycle small engine is better than a flat head? OHV versions are reported to be higher compression, more efficient yet I’ve never seen how much and I’m interested to see a write up backing that claim.
When NHRA started the junior dragster class, my understanding was it was and is based on a B&S 5hp flat head. Of course you prob never seen ones as rules let the users use some super tricked out ones, but still a flat head small engine.
Somewhere along the line, the small 4 cycle engines also stopped being advertised by HP. Seems like all of them are OHV and advertised by the size in CC’s wo a mention of the peak power

The HP rating disappeared because someone sued, because the advertised 6 HP engine only produced 5.4 HP, and they were injured because of it. Seriously.
They advertise cubes only, kinda like Modified Production.....

quote:

Originally posted by Goob:
The HP rating disappeared because someone sued, because the advertised 6 HP engine only produced 5.4 HP, and they were injured because of it. Seriously.

How in the world does 10% less power cause a serious injury and litigation strong enough to pluck something as useful as rated power? Wait never mind, I almost forgot the times we now live in.

No more Hp rating because they go on so many different applications that the hp could be more or less than advertised. Briggs along with other got sued and stopped using hp and went to cc or gross torque. Kawasaki which has been known to under rate their motors still uses HP. Can't kill the flat heads but OHV and technology has them being more efficient. It's amazing how they even stay together when you see some of the parts.

All the well built HD last forever USA made flathead engine makers folded

In their place are rinky dink built OHV engines that routinely break, puke, fail and are anything but HD

Only OHV engines I have that are well built are Hondas

A Honda generator at least 20 years old and a Honda mower that is kick a-s-s good I bought a couple years ago...

My 15-20 year old Tecumsah snow blower engine is a little brute....maybe 8 hp and will not stop no matter how heavy the load is....

Old Onan flatheads were pretty much bulletproof with some good maintenance

Modern Robin built Onan engines are ok but require a ton of maintenance and still fail if you use them a lot in hot weather

Onan made zillions of flatheads used in all kinds of machines.....they were/are tough and HD built....

In the small generator world it was common to have 1.5 HP for the KW.....

So a 4 KW generator had a 6 HP or better engine....but that was a 4 pole 1800 rpm machine

Todays machines are 2 pole 3600 rpm machines mostly and they spin the engine harder to get the power needed for the generators rated load....

The engines don't last anywhere near as well obviously spinning twice the RPM to get the power needed....

Well I do not know about the HP of the B & S motors but someone mentioned generators and I have seen where some put out close to advertised and others not so close.

Any engine driven generator can only produce its rated output if the engine is running properly.

Same as a automotive engine.

No way you can get the advertised HP or really Torque if the engine is not tuned properly or is worn.

It's long been assumed in the JR ranks that allowing ohv engines would make the cars considerably faster, and probably cheaper. The single cylinder flatheads are entrenched in jr racing though.
I would assume that if the flatheads were an advantage, the OEM's would be using that technology.

Well the Jr Dragsters were started as a low horsepower way to get children involved. Some are pretty fast now even with the same basic block design.

The basic design of a flathead is poor for making power.

OHV engines or OHC engines can easily make more power using the same CC or Cu Inch

My point earlier was more about the old flatheads were built to last and most of the modern small OHV engines have very cheap light duty parts that can fail.

Build the OHV or OHC engines with good parts and they will be good and make a lot of power

Back 30+ years ago in my engine building days we had a guy who got involved with some kind of round track mini car that had to use a 5hp Briggs engine. Stock block, crank and head

There was not much in aftermarket parts.

We bolted the engine to a steel bench and ran it......did everything we could think of to hop it up...It easily made nearly double the 5hp it started out as and could see 8500 rpm on one of those little electric tach output meters.....

Vibrated the bench so much it was moving and weighed a lot......

Rich Have you seen any test results, that shows the power and efficiency gains from flat top to OHV small engines like this? That would be a good YouTube for Project Farm.

No Paul I have never seen anything like that..

The basic design of an OH engine vs a flathead makes it better for moving air in and out more efficiently.

Small engines, not a lot of power and lower rpm it's not a big factor.

A Flathead V8 Ford .....Was a ridiculous design to me compared to OHV engines but so many were built and run in cars for years and years...and for the time were real good

They were pretty reliable.....4000-4500 rpm and the were about maxed out... Not really a lot of power but compared to what else was out there was not bad

Flathead straight 6's and 8's also built and run in huge numbers

There were some OHV engines in cars going way back....1920's 1930's ? Can't recall.....