Reader Question: Switching to Roller Cam?

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Here’s the latest reader question, along with my reply! 

Bryce asks: Should I take into my possession an older car with a flat tappet camshaft? And does it make sense to switch to a roller camshaft in light of low or no ZDDP motor oil?

My reply: Lots of variables here, but let’s leave the cam aside for a moment and consider the car. Is it sound? Is it priced fairly? Do you like the car? In other words, the same basic considerations that would apply to any used car.

Put another way: I would not want to buy a rusted out old heap with not much potential and a too-high price regardless of the type of cam in its engine. But I wouldn’t hesitate to buy a desirable car in good condition at a fair price that had an engine with a flat tappet cam.

Now, to some specifics about the cam.

Flat tappet cams aren’t bad (as in defective) cams; their chief deficit from a functional point of view is that more aggressive/performance  grinds get progressively less and less “streetable” because of lobe profiles. Have a look at the pic below; the roller is on the left and the flat tappet cam is on the right. A flat tappet high-performance cam will have a lopey idle because of the steep pitch – to use a roofing analogy – of the cam lobes. Performance enthusiasts love the sound – but it can be a bear to live with in stop-and-go traffic. These types of cams also usually produce a weaker vacuum signal at idle and often do not work well with automatic transmissions.

In a nutshell, it is tougher to put together a really powerful engine with a flat tappet cam that is also a street-drivable engine. As an example, I installed Pontiac’s Ram Air III camshaft in my ’76 Trans-Am’s 455 V8. This cam is about as aggressive as I can go without compromising the car’s drivability.  But it is a relatively mild cam – in terms of power production –  by today’s standards.

By roller cam standards.

One of the reasons the OEMs (i.e., the car companies) switched over to roller cams  – this began in the ’80s – was because they were able to (literally) ramp up more aggressive profiles in performance cars like the Mustang GT of that era while maintaining good idle quality as well as engine vacuum at low RPM for power accessories such as brake boosters, etc. Roller cams are one of the reasons (along with much better airflow through the heads) that today’s performance V8s make 400-plus horsepower easily, with Camry-like idle quality.

My TA sounds very tough but the 455 only makes about 320 horsepower – about the same as the current Mustang’s 2.3 liter four cylinder engine.

The chief deficit of flat tappet camshafts from a maintenance point of view is needing to find oil with the necessary additives, as you’ve noted. However, it is not hard to find this oil. AMSOIL sells it (see their ZRod line) and you can also buy the additive as a stand-alone and add it to any high-quality off-the-shelf oil.

The AMSOIL costs about the same as any other high-quality oil so provided you plan ahead and have the oil on hand for oil changes – which you won’t have to do as often if you use AMSOIL – it’s not much of a big deal to maintain a car with an engine that has a flat tappet cam.

So, assuming you like this car – and the price of the car is fair – I’d not hesitate to acquire it if I were you.

Finally: Yes, it makes sense to switch to a roller cam, but not because of the ZDDP. It makes sense if you want a big performance bump without sacrificing the streetability of your car.

I am planning to do this myself. The swap is pretty straightforward. If you can change out a flat tappet cam, you can install a roller cam. And if you go with a roller cam, you can go with a more aggressive profile and end up with much more power without that loose nuts and bolts rattling around in a tin can idle quality!

. . .

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5 COMMENTS

  1. So the only difference is the shape of the cam lobe ????

    Somehow I thought there was some sort of literal roller (wheel) on the lifter that “rolled” on the cam ….

      • eric, it’s the roller rockers where the lack of life comes in. You don’t see diesels with roller rockers for a very good reason. They’re supposed to last virtually forever, many times more than a gasoline engine with roller rockers.

        I suppose it’s what you want from an engine. I want long term durability. If I need higher gears as OD for better mileage, I can get a Brown-Lipe 2 or 3 speed gearbox behind the transmission and transfer case. Probably Brown-Lipe makes something to replace the transfer case. They make units with a low down gear like a transfer case, a one to one with the transmission and an OD. That would be an OD over your last gear that’s OD.

        Brown-Lipe gearboxes got fame in the old original military Jeeps. They never went away. It’s not hard to install another bracket behind the final factory outpout and install a Brown-Lipe there. I had a friend do it on his 4WD Ford back in 76 on a new pickup. Of course that transmission, the Slushomatic, didn’t have OD but it wasn’t a powerhouse gas engine anyway. It had a killer stereo though.

        • Morning, Eight!

          You make sense – as usual. I occasionally think: Well, to get my 1950s technology 455 to make 2000s power and be street-drivable, it will need X, Y and Z upgrades, all of which entail modernizing the old Indian. Roller cams, aluminum heads. 1950s engines just didn’t flow the air that modern ones do. Only so much you can do with the factory iron heads. And the old flat tappet cam profiles are analogous to back in the day when you didn’t have OD transmissions and had to pick either “highway” gears in the pumpkin or gears for the quarter mile.

          But then I rethink and reflect. My TA isn’t a 2000s car and even with only say 320 hp, it’s still a damned fun experience to drive it and arguably more fun to drive it than a modern muscle car with 500 hp. If my car had 500 hp, it’d be less fun – unless I upgraded the rest of the car to cope with it. What fun is 500 hp that you can’t put down? You’re not putting it down on 15×7 wheels, so they have to go in favor of 17 or 18-inch wheels at the least. But the suspension needs work, too. And then you’ll want better brakes… and before you know it, you’ve got the shell of a classic car hiding a modern car and what’s the point of that?

          It strikes me the same as going “camping” in an air-conditioned tent with a flat screen.

  2. switching to a roller cam and tappet is doable ok but on vehicles made for roller cams, the cam is a much larger diameter. Not sure you could even put in the same size lobe lifts in a non-roller cam engine. But there is some power and possibly fuel mileage to gain.

    OTOH, it’s always been and still seems to be that flat tappet cams last much longer engine-wise. It may be the reduced power that causes it. There are companies that make old style SBC’s and BBC’s with roller cams and LS heads. If an LS didn’t have variable valve timing and variable oil pump(esp. the oil pump), they’d be much more durable. There’s an O ring on the pickup tube that gets old and doesn’t seal causing the pump to flow less oil. Nothing like stripping the entire engine down to replace an O ring although I have seen it done on a video without removing the pump and everything on the end of the cam. There is a hold down that only goes one way but it’s a little bump on it that makes it this way. You can grind it off flat and use the other hole that’s easily reached. LS engines are notorious for needing intake gaskets replaced. Not a big deal but something to think about. What is available to replace the factory gaskets is much better. I’m considering buying an LS and rebuild it with non-variable everything and damn sure not like the later ones with cylinder deactivation.

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