DavidNJ

Different roller lifters have roller diameters f .750, .760, .785, .820 .850, ,940. At least three of those sizes are available in LS1 lifters.

How does the different roller size affect cam timing? Do the larger rollers need large base circles?

What is a reference for this?

Adrenaline_Z

I'm going to stick my neck out here and say the larger diameter roller will act
on the ramp slightly faster on opening and later on closing giving the valve a
touch more duration.

That's what it seems like on paper, and I don't imagine the duration to change
much between those sizes.

racer7088

The larger the wheel on the lifter the more radical the cam lobe acts especially if it was designed with a smaller roller wheel in mind. You need to spec that when ordering a cam otherwise it is assumed you have a wheel .750 or under usually.

DavidNJ

Since any concave radius would need to be larger than the wheel's radius, does it impose a restriction, or are the cam's concave radii always larger than the largest cam wheel?

Does the larger wheel also reduce side loads on the lifter? Are side loads on the lifter an issue?

ProdriveMS

The concave radius will always be greater than the lifter wheel's radius. That's because the concave radius on the lobe cannot be smaller than the radius of the grinding wheel used to grind the cam. Grinding wheel diameters are usually 5" and up.

A larger wheel wont reduce side loads, but it may reduce the stresses from side loading as the load is spread out over a greater area. Generally, the larger the wheel, the lower the hertzian stress on the lobe- which can allow a slightly more aggressive profile for a given stress.

Al

racer7088

To be silly or to make it easier to see, if you could take a lifter wheel down to an impossibly small size or make the base circle really small for the same lobe lift, you do start to turn the lobe into more of a paddle wheel that's for sure and there is more side loading. These cams will eat up lifter bores and the lifters are hanging more out of the bores as well due to the lower base circle too. It's all bad!

DavidNJ

At what ramp/spring pressure/valvetrain mass do larger wheels become important? Are the .750/.760 wheels best for only light duty systems, like hydraulic rollers?

racer7088

Well as Al above said as loads and forces grow so does the lifter and the better stuff in higher rpm and big lift cams (NASCAR and Pro-Stock) and valvetrain all use the largest lifters they ever have. The Nascar guys even use all use the .935 keyed lifters and the same goes for the pushrods. Basically it's hard to get too big. Before you can even get them big enough they are hitting everything.

I would say when you are doing real endurance engines or extreme drag race stuff you should always do these lifters if you can afford them. You probably "need" to over them in the 9000+ rpm range and 1.000 inch lift stuff as well as 400+ PSI seat pressure and 1000+ open. These big lifters with bigger wheels also require different cams, sometimes also with narrowed lobes so you don't operate more lifters than you intend to!

I have used regular good quality .842 roller lifters like the Isky Red-Zones or Morels with .750 wheels even around 350 PSI on the seat and 850 PSI open but I would sure rather have beefier stuff like the .904 or the .935 lifters that Al is talking about! That type of pressure will even take out regular .842 lifters sometimes. Like everyone always says "the valvetrain is not a place to save money!"

NoMoreFWD

iTrader: (1)

Agree.

Steve - Race Eng

iTrader: (1)

Increasing the roller wheel diameter increases both duration and rate of lift (acceleration) of the lifter. You need to be careful with this especially if you increase rocker arm ratio at the same time. It is best to talk to your cam grinder. A larger wheel diameter may be incompatible with inverse flank cams.

I use a software program called "Doctor Doctor" to test camshaft profiles using different wheel diameters, rocker arm ratios. This is a great program for checking quality of grind as well.

There is a really good book available on camshaft design by Don Hubbard: "The Camshaft Reference Manual". Don provides some useful software with the book. You can order direct from Don:

dhubbard7@earthlink.net, Phone 239-936-0866, Fax 239-275-9936.

I'm not sure what the current price is. I paid $149 back in 2000 for it. This book is worth many times that price.

Steve

Wnts2Go10O

iTrader: (12)

same idea as haveing a larger diameter flat tappet. the larger the diameter the more your ramp/lift/i think duration charecterisitics change. the added size is just a different place.

GuitsBoy

iTrader: (4)

Im gonna relate this into another way of thinking... When I was a kid, I used to ride BMX bikes. Some people at teh same trails would ride mountain bikes. A bmx bike has a 20" wheel, while a mountain bike has 26" wheels. Some of the smaller jumps with very tight transitions (curvature of the jump) would work fine for the 20" bikes, but would be really difficult to handle with t he larger 26" wheels. Imagine in slow motion what would happen when a jump with, for instance, a 24" radius transition and a 45* exit angle. The 20 inch wheel would move laterally about 10 inches over the course of being redirected to the 45* angle. The 26" wheel would only have 7" lateral movement to do the same. You could see how the larger wheel reacts more abruptly to the ramp. In many cases it was enough to buck the rider over the handlebars.