i see references to what you can and can't do with a big cam. so what is the group think on what a big cam is. is it over .700 lift. is it lift only or are ramp speeds a concern in it. what does everyone mean for a big solid roller.

I think it depends on the motor. A stock 350 will not run right with a .700 lift cam. As far as what cam fits with what combo, I don't know that. In a street car, IMO, a .650' lift is fairly big. I think 'big' is in the eye of the beholder.

Big solid roller= mechanical roller lifters with a lot of lift.

Chris

There's no such thing as too much cam; only not enough motor. ;)

There is really no such thing as a big cam. You can say that there are big cams in reference to a particular engine, or engine combo, but not exactly its a big cam really. If I were to say to someone thats a rather big camshaft, here is what I would mean. Its either they have a motor that they want to drive a lot and run from 2000-6000rpm and they selected a cam that will run from 3500-6500rpm in that motor. In that case, they have a big camshaft cause its gone above what they are anticipating. Or, youve got a mostly stock motor whose heads, manifold, carb, headers...... only allow 5000rpm, yet they pick a cam that would like to rev well over that rpm. Its too big for THAT motor. I mean, if youve got a cam thats big for a particular 283, yet you put that cam in a 406, its probably not big at all any more. The 100 plus additional cubic inches will all the sudden make that cam tame, which is why you cant say for sure that there are a particular set of numbers that make a cam big. .700 inches of valve lift would usually indicate a big cam, but maybe not at all in a 640 cube motor.

CID and RPM range

Please go over to Pat Kelley's great "Dynamic Compression Ratio Calculator" site the he now calls "Effective" instead of "Dynamic" AND read it through AT LEAST 4 or 5 times!!

It will explain a whole bunch of this to you!!

You can get to Pat's site through his sig.

Great reading and info in general!!

pdq67

I notice that many refer to the valve lift when saying what is a big cam. The valve lift is a dependent value not a defining value. Intake duration is dominant factor to start with for chosing the proper camshaft for an application. Valve lift is dependant the camshaft profile at a given duration and the rocker ratio. Because of the geometry of a cam lobe in a typical V8 you cannot have .750" lift with a @.050 duration of 210 deg. The upper and lower limits of lift are dependant on the duration.

Jim,

Have you ever checked out a lobe on a max. effort Jr. Dragster's Briggs&Stratton motor cam??

You can run any lift you want up to the point of valve-train accelerations getting out of hand AND not hitting the edge of the lifters foot!!

Of course as Harold has mentioned in the past doing so MAY not be veeeeeeeery practical OR cam/valve-train long-lived!!

He, He!!

That's why I got on the "mushroom lifter" kick a while back!! Why bore the Chevy block lifter bores out to a MOPAR .904" when a mushroom lifter can go to about .950"(???) or somewhere bigger then the MOPAR lifter diameter...

pdq67

I think it boils down to your usage of the vehicle
balanced with your tolerance for noise and violence. I run .630/.650 lift solid flat tappet
in a 427 and street drive it regularly. I don't
however load up the family and take it out to
dinner. If you're comfortable driving it, and it
will run safely amongst other traffic, it's up
to you what's too much. I will say that peoples'
reaction to the car is generally strong, either
thumbs up, or dirty looks, who cares.

pretty much like a fiqured, it's a relitive term.with no hard and fast specs.
thanks