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Roller Cam

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With the advantages of roller cam designs in engines, why don't we see roller type buckets on top of valve springs on motocross bikes?

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I guess extra reciprocating weight requiring stronger valvesprings (not a good thing, 'spesh with titanium valves), taller engine, more cost.

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I would guess it's because the extra mass and complexity outweighs the reduction in frictional losses. It might be a worthwhile concept for an engine that doesn't rev real high, but there aren't too many of those designed with four valves and cam-over-bucket actuation. However, many OHC and/or four-valve engines use roller followers. Ford's modular V8s and Mitsubishi's 4G63 come to mind.

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It's not the friction loss that's the biggest advantage, but you can run a lot more aggressive cam that opens and closes the valves quicker and holds them open longer. We race super late model stock cars, and the difference in a roller cam motor and a regular flat tappet motor (which we are not legally suppose to run) is between 40 and 70 HP.

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It's not the friction loss that's the biggest advantage, but you can run a lot more aggressive cam that opens and closes the valves quicker and holds them open longer. We race super late model stock cars, and the difference in a roller cam motor and a regular flat tappet motor (which we are not legally suppose to run) is between 40 and 70 HP.

i agree. you can only go so aggresive on the cam profile before the lobe ramp starts hitting the edge of the bucket. rollers get rid of this problem

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1.) It's not the friction loss that's the biggest advantage, but you can run a lot more aggressive cam that opens and closes the valves quicker and holds them open longer.

2.) We race super late model stock cars, and the difference in a roller cam motor and a regular flat tappet motor (which we are not legally suppose to run) is between 40 and 70 HP.

1.) I only just noticed that I neglected to include that. :busted: I'm familiar with roller cams and their benefits as I hang around the later Ford pushrod V8s and have one in my '68 Mustang. :thumbsup:

2.) How much power do those engines typically make?

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Flat tappet camshafts are limited in valve lift velocity (measured in units of distance per degree of camshaft rotation) by the size of the bucket. Roller camshafts are limited in valve lift acceleration by pressure angle and the physical/dynamic limits of the components themselves. This gives the camshaft designer much more flexibility to work with in the roller design with regard to slamming the valves open and holding them open for a longer period. If you can slam the valve open quickly, hold it there, and close it quickly you have a more effective valvetrain.

With regard to why they are not used on MX bikes (except for Honda), it is a weight thing. Honda gets away with it on their forked rocker because you have two valves/springs splitting the control of that component.

I always thought a radiused bucket would work rather well towards eliminating some of the velocity restrictions associated with the flat tappet design, though it could be potentially much heavier and require a taller head to package.

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I always thought a radiused bucket would work rather well towards eliminating some of the velocity restrictions associated with the flat tappet design, though it could be potentially much heavier and require a taller head to package.

Kind of like this?

besteng14hz.jpg

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1.) I only just noticed that I neglected to include that. :busted: I'm familiar with roller cams and their benefits as I hang around the later Ford pushrod V8s and have one in my '68 Mustang. :thumbsup:

2.) How much power do those engines typically make?

In our class there are teams running 415hp crate motors with a 50lb weight advantage as well as 0.5% more left side weight, and there are teams with motors upwards and greater then 600hp. We are currently running a 500hp flat tappet all steal engine. More power in this type of racing is hardly ever an advantage because of the design of the cars and the length of the short tracks (1/3 - 5/8 mile) actually it seems like we are being beat by crate motor cars more ofter then not, not because of the weight advantage, but because of the more controllable power. I believe we will be going to a 415hp crate motor for 2010 in the car I will be driving.

I think this is a very interesting topic and would love to hear more opinions. I personally believe that it could be worth the extra weight and height, but I'm only 16 so I'm still learning.

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Yes......ha.

Where/what is that from?

I don't remember exactly; I dug it up from an old folder on my computer. I want to say it's from a Champ car engine or possibly a BMW product.

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I don't remember exactly; I dug it up from an old folder on my computer. I want to say it's from a Champ car engine or possibly a BMW product.

i was going to ask the same thing. that looks like a bitchn setup. if i had the machining equipment, id love to do a comparison on the same motor/cam specs with the 2 different designs, trying to make the componant weights the same if possible. and i forgot that the bucket diameter dictates cam aggressiveness on a flat tappet, thanks for the reminder

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In our class there are teams running 415hp crate motors with a 50lb weight advantage as well as 0.5% more left side weight, and there are teams with motors upwards and greater then 600hp. We are currently running a 500hp flat tappet all steal engine. More power in this type of racing is hardly ever an advantage because of the design of the cars and the length of the short tracks (1/3 - 5/8 mile) actually it seems like we are being beat by crate motor cars more ofter then not, not because of the weight advantage, but because of the more controllable power. I believe we will be going to a 415hp crate motor for 2010 in the car I will be driving.

I think this is a very interesting topic and would love to hear more opinions. I personally believe that it could be worth the extra weight and height, but I'm only 16 so I'm still learning.

jeez dude ur only 16 and ur running a SLM?? ur running asphalt right

im 20 and im all the way down in ministock dirt but our rules are pretty open so its makin almost 300hp 2200lbs with driver

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