Which is the Best Engine Valvetrain Design? OHV, SOHC, DOHC or Flathead | Pros and Cons
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Publicado 2023-07-01
Valvetrain:
The valvetrain is a mechanical system in an internal combustion engine that manages the opening and closing of the intake and exhaust valves. Its purpose is to regulate the timing of these valve operations to allow the intake of air/fuel mixture into the combustion chamber and the expulsion of exhaust gases.
The intake valves are responsible for controlling the flow of the air/fuel mixture into the combustion chamber during the intake stroke. On the other hand, the exhaust valves regulate the flow of spent exhaust gases out of the combustion chamber during the exhaust stroke. By coordinating the timing of valve openings and closings, the valvetrain ensures efficient combustion and optimal engine performance.
Types of valve train
Different engines may utilize variations in valvetrain designs, such as an overhead valve (OHV), overhead camshaft (OHC), or dual overhead camshaft (DOHC) configurations.
Advanced technologies like variable valve timing (VVT) and variable valve lift (VVL) allow for even greater control over valve operation, optimizing engine performance across various operating conditions.
--- Time Stamp --
00:00 - Introduction
00:40 - Parts
04:16 - Types of Valvetrain
04:42 - Overhead Valve (OHV)
06:25 - Overhead Camshaft (OHC)
07:03 - Single Overhead Camshaft (SOHC)
08:38 - Dual Overhead Camshaft (DOHC)
11:07 - Flathead Engine
16:39 - Thanks For Watching
#ohv #sohc #dohc
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Disclaimer:
This video is just for educational purposes only. We are not in the auto repair business nor publish automotive service manuals. This video is not reviewed or authorized by any vehicle manufacturer. This video is intended only as general guidance. Every system is slightly different, so refer to the owner’s manual of your vehicle for any specific information about your model. Remember that only proper service and repair procedures will ensure your car's safe and reliable operation.
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Todos los comentarios (21)
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Worth mentioning that flat head designs were still very common in small engines until recently. (Such as in lawn mowers and generators)
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@2:07 valve springs do not exert downward pressure on valves, they exert upward pressure on them, which is how they are closed.
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This video helped explain to my son what is going on with my truck.
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OHV engines are ideal in countries that dont tax displacement. They make most of their power in usable revs, are light, compact, very fuel efficient and have very low service costs. The only drawback is that you need to give them a bit more displacement. The market needs another Buick 3800 V6. That engine made the same power (205HP) as most 3.0L DOHC V6s of its time, was smaller, lighter and got 31MPG highway moving large cars around the highway and are extremely reliable. I had a 2005 Mazda 6 and that car was smaller than something like a Pontiac Bonneville and only got 29 highway from a 2.3L DOHC 4 making 160HP.
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One type you missed is the "F"-head, where the inlet valve is push-rod operated in the head and the exhaust valve is [as a side valve engine] in the block. This allows for two things. Smooth power and a huge inlet valve for good breathing. They were used by Rolls Royce and Rover from the early 1945 era until the late fifties in Royces, and right into the 1970s in Land Rovers. They are famously quiet, smooth [especially in in line six form], and robust. Neither Royce nor Rover really made performance cars, but they did build cars to last and be comfortable. Several Bentley variants of the Royces appeared that showed that such an engine could really perform in the grand tourer segment of the luxury are market, such as the Bentley Mark Six and the earlier Continentals, before Royce's own new V8 was adopted across the Royce and Bentley models. Nice video. Thanks from George [in UK].
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The valves in an Overhead Valve engine are not in the block, they are in the head. Flathead engines have the valves in the block.
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Overhead Valve design does not automatically mean more low end, rather OHC allows higher revs with lighter valve springs due to the lighter valvetrain. Camming an engine for higher revs takes away low RPM torque. That is the reason Overhead engines tend to have more low end- OHC engines tend to have aggressive camshafts and therefore have weak low end.
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There never is a best, always an engineering compromise. It is all about the initial design criteria.
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Very comprehensive and clearly explained. Thanks!
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OHV / center cam. Used for decades and time tested.
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Triumph had a lovely Sprint engine that was 16 valve straight 4 engine. One cam, with one set of valves under it and the other side working off rockers but on the same cam! It was a lovely neat design that kept the engine quite compact. I always wondered why this configuration was never used more.
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DOHC does not imply 4 valves per cylinder, although it makes it easier. There are many DOHC engines with 2 or 3 valves per cylinder (for instance the classic Alfa Romeo engines) and there are also 4 valve per cylinder designs with only 1 camshaft (such as the Triumph Dolomite Sprint, as someone else mentions). The main advantages of DOHC are certain kind of simplicity and lightness of the moving parts + ability to regulate the position of the both camshafts individually when you are going for adjustable timing arrangements.
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A fantastic video with one error. At 11:12 the labels for the graphics are mismatched. The OHC label should be on the left, and the OHV label should be on the right.
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Just subscribed excellent video packed with historical and useful information. Thanks for sharing. 👍
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Amazing video. Good pictures as well as good explanations of advantages and disadvantages as well as history. Perfect
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Excellent, well presented and very educational. Thank You and Best Regards.
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Love these videos!
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Some single camshaft engines had the cams directly mounted over the tops of the inlet and exhaust valve’s leaving space for spark plug; for example the Coventry Climax racing engine which was also used in Hillman Imps and fire engine portable water pumps.
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Terima kasih telah berbagi ilmu, smoga bermanfaat.
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I really grateful with all this videos, they`re been helpful for me to learn all this car items. Thank`s again. Congrats, great videos.
