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10:46:23 - 04/19/2024
General Dakota Board
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robert badia
Dodge Dakota
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3/23/2005
19:07:52
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 Subject: roller to flat tappet convertion
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Just wondering i i cant convert my 97 318 magnum motor from roller to hydrollic flat tappet and what would need to be ghanged if possible.
thank you.
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.boB
Dodge Dakota
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3/23/2005
20:10:43
|  RE: roller to flat tappet convertion
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Sure you can, it's a pretty easy conmversion. Just look in the Comp Cams catalog and they have all the parts listed for you. You'll need a new cam, lifters and puch rods.
But why would you want to? The roller is a much more efficient set up.
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gen1dak
Dodge Dakota
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3/23/2005
20:31:02
| RE: roller to flat tappet convertion
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Maybe because flat tappet cams are much less expensive, come in far greater variety, and eliminating those heavy rollers will remove nearly 2 pounds in valvetrain weight. The pityful 4% improvement in EPA mileage for a stocker (below 4800rpm) with rollers is dwarfed by the free HP from the midrange on up on the same engine with flats. Hardcore racers pay gobs of money to achieve the same thing.
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Yup
Dodge Dakota
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3/23/2005
20:48:33
| RE: roller to flat tappet convertion
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That weight is spread over 16 lifters and most hard core racers use rollers.
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robert badia
Dodge Dakota
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3/23/2005
21:11:48
| RE: roller to flat tappet convertion
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well ya its cheaper and alot more to choose from
just wanted to see if it was possible
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IntenseDak39
*GenIII*
3/23/2005
22:27:27
| RE: roller to flat tappet convertion
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a lot more to choose from??
is your motor EFI??
that's the limiting factor.. ya cant just go get a summit catalog and point out the cam you want from there..
a new, quality, cam/lifter package is about $200. You'll also need to measure for pushrods and have custom length pushrods made... which could easily be another $75-100
that gets ya closer to package of a roller.
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.boB
Dodge Dakota
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3/23/2005
23:36:13
| RE: roller to flat tappet convertion
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There's more to a roller cam than just the rolling action of the lifter itself. The roller reduces friction and heat, but only by a very small amount. You have a lot more freedom in cam profiles, and the additional power potential for the same spec cam is amazing.
You can put roller lifters on a flat tappet cam, but you can't put flat tappets on a roller cam. Why, you ask? Simple. The cam specs for lift, duration, and centerline may appear to be exactly the same. But the valve action is very differant. The roller allows for a much steeper ramp. And the roller will follow a profile much more closely.
A flat tappet cam lobe looks kind of like an egg in profile. "Gentle" ramp up, peak, and gentle ramp down. Has to be that way to prevent excessive side loads.
A roller cam can have a much more agressive ramp. So the lobes are more like a mesa. Rapid upslope to open the valves quickly. Flat top to hold the valve open. And a rapid close with an asymmetrical base to close the valves quickly but not allow them to slam shut.
Performance wise, the roller is far superior to flat.
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Yup
Dodge Dakota
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3/24/2005
00:05:36
| RE: roller to flat tappet convertion
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Flat lifter cams are angle ground to cause a slight spin on the lifter. Also, the lifters are not really flat. They're convex ground. This prevents excessive wear.
Don't forget about the oiling system. That will be a fun chore.
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gen1dak
Dodge Dakota
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3/24/2005
00:58:38
| RE: roller to flat tappet convertion
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You may be able to put rollers on a flat tappet cam, but it won't last long. The lobes have a slanted face that induces a spin in the flat tappet to reduce wear. This "angled deck" will provide an uneven surface for the roller, and incur excessive roller axle stresses. If the axles don't fail, the cam lobes will.
A clarification: The hard core racers I referred to were not big-buck sponsorship types, but the local "hard-core" type driving hot-street cars, not an alcohol digger or Top Fueler. As the price of roller cams has come down, more have begun to use them, where rules allow, because they do offer cam profiles that flats can't touch. Those cam profiles are not what one would usually run in a street-driven vehicle.
Obviously, rollers have been around for a long time, and in ultimate valve action, they are superior. They offer profiles that a flat can't touch. Now, a little perspective. Are we talking about .700" lift cams, or are we talking about street-driven trucks, at best, in the low .500" range? The Saturn V is testament to a superior powerplant....if you're going to the moon! But I just need to go to North Carolina or Denver, so a jet is fine. See where I'm going with this?
The "freedom" in cam profiles is not a factor in street profiles. There are literally hundreds of streetable profiles in flat tappet cams for SB Mopars. The weight being spread over 16 lifters, is still the same amount of weight when added up. This weight also acts on the entire reciprocating assembly. You know....timing chain's connected to the crank on one end, spins the cam on the other end..... Also, that "spread" is handled by 16 sets of springs. Even divided by 16, that's a considerable amount of weight each spring doesn't have to control (meaning reversing valve direction in microseconds). This means, with a given spring, the valves are better controlled at higher rpm. Or, taken another way, it takes a heavier spring to control the extra inertia in the heavy roller lifter, and thus prevent valve float. Two engines with the same cam specs (reasonable with respect to streetable engines), one a roller, one a flat, the flat will rev more freely, and will have a higher effective redline. A roller's advantage comes in where the ramps are getting steep, and over-the-nose pressures start skyrocketing on flat tappet profiles. The 426 Hemi is a perfect example of this. The cam would show considerable wear at only 15,000 miles because the weight of the rocker assembly. Running to 6500rpm required such heavy springs to maintain control for even .480 lift cam. There were no cam coatings back then to reduce friction, and the metallurgy wasn't as advanced. Billet cam? Not then. That's a great example of where roller tappets would save the day, but they were only an exotic, very expensive item then, and the 426 Hemi is a unique case, with rather mild cam specs on a stocker. However, even today, do crate Hemis come with a roller cam? No. Why? Cam coatings, and better cam material. The valvetrain is heavy enough. No need to add another kilo of weight to it with roller lifters unless you want a really wicked cam, and then we're talking a drag engine. It's always a trade-off. Heavier roller lifters for the really exotic cam grinds....exhaust restriction to run a turbo....it takes HP to run a supercharger to make even more HP. We can thank the automotive industry for bringing the roller to common use, thus reducing prices, but in a weekend hot-street Mopar smallblock, I'll take a flat over a roller any day. For the record, I have a roller cam in my 360 Magnum, so don't take this as some sort of personal bias.
As for costs, any decent roller is more like $300, and with the rather limited selection for Mopars, it'll cost even more for a custom grind. Are you gonna use wimpy stock pushrods with it? That negates the cost of the new pushrods arguement for a flat tappet cam right there. A roller cam/roller lifter package costs more than the flat package. Period.
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gen1dak
Dodge Dakota
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3/24/2005
01:01:44
| RE: roller to flat tappet convertion
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What oiling chore? Flat tappets oil through pushrods, just like Magnum rollers. Where's the chore?
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