---
title: 'This Tiny Engine Part Changed Everything - Flathead vs OHV vs OHC'
source: 'https://youtube.com/watch?v=y2TuR4fR1W0'
video_id: 'y2TuR4fR1W0'
date: 2026-07-28
duration_sec: 635
---

# This Tiny Engine Part Changed Everything - Flathead vs OHV vs OHC

> Source: [This Tiny Engine Part Changed Everything - Flathead vs OHV vs OHC](https://youtube.com/watch?v=y2TuR4fR1W0)

## Summary

This video explores the evolution of combustion engine valve trains, from Flathead to overhead valve (OHV) to overhead cam (OHC) designs. It explains how these changes impacted engine performance and oil requirements, focusing on the role of ZDDP additive and the transformation brought by roller lifters.

### Key Points

- **Valve Train Evolution Introduction** [00:02] — The video covers the evolution from Flathead to OHV to OHC engines and how motor oil has evolved alongside.
- **Flathead Engine Design** [00:44] — Flathead engines have valves and camshaft in the block with a flat head. They are space-efficient and cheap but have poor airflow and low compression, resulting in low power and efficiency.
- **Overhead Valve (OHV) Design** [01:41] — OHV moves valves to the cylinder head above the cylinders, improving airflow and combustion chamber design, but the reciprocating mass limits high RPM and valve float.
- **Overhead Cam (OHC) Design** [02:09] — OHC places the camshaft overhead, enabling finer valve control, variable valve timing, and high RPM with better efficiency and power. Drawbacks: larger footprint and higher cost.
- **Oil Challenges in Old Engines** [03:04] — Old engines with flat tappets experience high wear at cam-lifter interface. Oils like Mobil 1 Classic use high ZDDP to form a sacrificial barrier, though ZDDP can poison catalytic converters.
- **Roller Lifters: A Game Changer** [05:15] — Roller lifters replace flat tappets, reducing friction and wear. They allow more aggressive cam profiles for more power and reduce the need for ZDDP, benefiting catalytic converters.
- **Oil Formulation Balance** [07:14] — ZDDP competes with detergents for surface area. Too much ZDDP can form high-friction phosphate glasses. Modern oils are balanced for turbochargers, direct injection, and to prevent pre-ignition.
- **Conclusion: Impact of Tiny Change** [09:50] — Switching from flat tappet to roller lifter reduces wear, improves efficiency, enables more power, and lowers emissions by reducing needed ZDDP. It's a win across the board.

### Conclusion

The evolution from flat tappets to roller lifters is a prime example of a small change with outsized benefits, enabling more powerful, efficient, and cleaner engines, while also shaping modern oil formulations.

## Transcript

this very simple part has had a tremendous impact on combustion engines hello everyone and welcome in this video sponsored by mobile one we're looking at the evolution of the combustion engine from Flathead to overhead valve to
overhead cam as well as how motor oil has evolved with these engine changes now it says something very interesting on the back of this bottle of oil their newly launched mobile one classic so it states that it is specifically not for
overhead cam engine designs and that it is for older vehicles with Flathead or overhead valve engine designs all right so first let's understand how engine valve trains have changed over time starting with the Flathead engine here
you can see the valves and the cam shaft reside within the engine block and the reside within the engine block and the head is flat so flat head this design is super space efficient and it's mechanically simple which keeps it cost
effective unfortunately this design has really poor air flow because you've got that air coming in One Direction then it has to completely turn around to go into going out this direction and then again turning completely around and if you
have an exhaust an intake valve overlap then you have the intake air wanting to go this direction while that exhaust air wants to go the opposite direction so again all of this leads to poor air flow the valve design also tends to limit the
compression ratio so once you add it all up it results in an engine that doesn't produce much power and has poor efficiency to improve on this we have efficiency to improve on this we have the overhead valve Design This moves the
valves overhead they're no longer inside the cylinder block and now are located above the cylinders this greatly improves the air flow and the design of the combustion chamber and still keeps the packaging very compact unfortunately
reciprocating Mass here in order to actuate these valves so this limits how high revving these engines can be before running into valve float and the single cam design while simple puts limits on
how much airf flow optimization you can do there is a better way which leads us to what almost all modern combustion engines are using overhead cams so instead of the cam being located within the block overhead cam engines move the
cam over head wow I'm really good at this overhead cams enable much finer control of the valves and make it easier to implement optimization strategies like variable valve timing or variable valve lift for increasing horsepower
these engines tend to be the most efficient the most powerful relative to their displacement and can rev High hence their popularity in modern day of course the design isn't without compromise as overhead cam engines have
a bigger footprint taking up more space and are generally the most complex in design which also increases cost so why would an engine oil be good good for these kinds of engines but not these kinds of engines well engine oil is
about preventing wear and reducing friction right so where is one of the toughest locations in an engine to protect well on old engines where the cam shaft interacts with the lifter is a huge challenge so old engines commonly
use flat tapet so where you have that cam rotating you have this tap it which is then going to lift which is going to actuate your valves now this tap it relative to this cam right here is just remaining stationary as that cam spins
not moving with that cam so you just have metal scraping across this metal and of course that means lots of wear so how do you prevent this well oil formulations such as mobile one classic use a lot more zddp often referred to as
zinc though this molecule does have other elements in it as well like phosphorus and sulfur in addition to the zinc zddp is a super powerful added for preventing wear so this zinc additive that's floating around within the oil is
used to create a sacrificial barrier on your engine parts and so in order for these zinc films to form they want a lot of energy so where does that energy come from well it can come from high oil temperatures but you need temperatures
around 150° C for that faster formation of this film now really oil is going to be sitting around 95 to 100° C within your engine so where else can you get example here we're pressing this cam lobe against this lifter and also from
energy is coming from in this scenario where we have that metal scraping up against another metal putting a lot of energy into that scenario and so that is energy into that scenario and so that is helpful for this zddp film to form and
so it's going to create this sacrificial barrier which then acts as a protector against this cam lobe here this sacrificial layer can wear away but then within your oil and it's going back and
constantly have this cycle of wearing away this film and then replacing it but the important part is is that you're not wearing away the metal from your engine okay well if zddp is so great why not just use loads of it well unfortunately
the sulfur and phosphorus Within These zinc additives act like a poison to catalytic converters so for modern engines you don't want to run an engine oil that has really high zddp but then how do you prevent getting engine wear
well there's a solution solution that fixes both the wear problem and the emissions problem and that is the use of rollers now modern engines are often using rollers on finger followers which have hydraulic lash adjusters but let's
keep things simple with a basic Cam and lifter setup now this is awesome because such a simple part can have such a meaningful impact so instead of having a flat ta it that your cam is then rotating against and creating wear well
instead of that you use a roller so now your cam is rot ating against this roller and thus you have very minimal relative motion between the cam and that lifter so you've greatly reduced the friction in this scenario and you have
less wear and remember our zddp wants lots of energy in order to form this film so in this scenario we've taken out that energy so we don't need as much zddp because it's not really helping in
this scenario anyways but there's another really cool benefit of using rollers so with our flat tets you have to be really careful with the profile of this cam lobe because if you're too aggressive in the ramp up well then you
this taet and it doesn't work you have so much wear so with a roller it can much more easily follow whatever the profile is of that cam lobe so you can have a faster ramp up you can have a wider cam lobe meaning you keep that
intake valve open longer you can bring in more air and you make more power now it is worth mentioning that rollers certainly aren't a modern technology despite them being more prominent on Modern engines there are old engines
that use rollers and there are new engines that don't use rollers instead they can rely on Modern material advances like diamond light carbon Coatings for minimizing valve train wear but as a general rule this style of flat
taet tends to be more commonly related with these engines whereas rollers tend to be more commonly related with modern engines now I want to talk a bit about oil formulations because I think a common misconception is that okay if an
additive is good I want as much of that additive as possible and it's like as is always the case with any good engineering problem everything is a compromise nothing is as simple as more is better except horsepower more is
is better except horsepower more is always better so for example zddp is an additive that acts on the metal surfaces of your engine but okay well so are detergents so both of these additives are competing for real estate on the
metal parts of your engine on surfaces where there isn't wear occurring you want detergents to form a film keeping your engine clean where there is where you want zddp to create a protective layer so if you just crank up one of
these you reduce the effectiveness of other additives here's another example of why you simply don't want to crank up the zddp so if your concentrations are too high you can start to have these phosphate glasses form in regions where
you don't have where occurring and these phosphate glasses actually have really high friction so you're increasing the resist distance within that engine the exact opposite of what that oil is supposed to be doing your engine's
getting hotter and you're making less power one of the main purposes of oil is that it reduces friction and helps cool your engine yet too much zddp does the exact opposite so again everything is a balance for older engines using a much
higher zddp concentration like mobile one classic is beneficial but because it's formulated for these older engines it doesn't meet the the requirements for modern engines hence you won't see any API or illac certifications on the back
of the bottle modern engines are super complex turbocharging is far more popular now so oils are formulated to ensure minimal buildup of deposits on the turbo shaft low-speed preignition is a challenge with modern high boost
engines so oils are formulated with different ingredients that minimize pre-ignition direct injection is prevalent on Modern engines so oils are timing chains from the deposits that direct injection systems can cause so
these types of subjects are misunderstood with the idea being that okay I just need more zinc for older cars with different requirements you mobile one classic having higher concentrations but modern cars have so
facing so the oil formulations will differ accordingly now to me it's just so cool how such a tiny change can have such a huge impact by switching from a flat taet to a roller lifter you've nearly eliminated the meaningful wear
improved efficiency you've enabled greater horsepower through New Cam profiles and you've reduced the need for zddp enabling better Effectiveness from your catalytic converter and thus reducing the amount of pollution from an
engine all of this is done without sacrificing reliability while increasing performance this is a win across the board incredibly cool if you have any questions or comments feel free to leave them below thanks for watching