Started thinking about some things that BigKid and 02sierraz71_5.3 said about cam base cirlces and their relation to valvetrain noise in this thread: https://www.performancetrucks.net/fo...d.php?t=344887

I think that the nail's been hit right on the head. So what's the cure? Longer pushrods, adjustable rockers? If this is the case, why don't the cam manufacturers recommend these parts as part of the cam swap? Comp recommended their 7.400 hardened pushrods and 915 springs to me with my small cam, but that's it.

I'm really curious as to what kind of valvetrain noise is associated with the GM "Hot Cam" (219/228 .525/.525 112), if any. You would "think" that components engineered by the same company should be made to work together...and not sound like a Singer that's been tweaked by a GENIII engine. I plan on slowly putting together a 6.0 project, 1 piece at a time (as I can afford a piece, I buy a piece), and I want to have it all mapped out when it's time to get serious

Anyone heard a HotCam in a 6.0? howz it sound...better yet, howz it run? I wonder if the General has any special recommendations for pushrods, springs, rockers, etc. for that cam?

Hmmmm

 

GM's hot cam sounds great,but there are{newer designs}better cams for your truck.As far as cam base circle is concerned most cam manufacturers increase duration by undercutting the backside of the cam's lobe which reduces it's base circle,it's easier than adding metal to the lobe.In the good old days,before custom pushrods were widely available it was common to shim the rocker pedestols[not nearly as good a solution as custom pushrods}to align the valve geometry.I would go with a aftermarket cam with matching valvetrain,most manufacturers will help you with the component selection.

 

if your putting this cam in the 6.0 i would think that the valve train noise is going to sound stock. With my cam 223 225 564 571 114 and 915 with stock push rods i have no valve train noise at all. I know 02denali had valve train noise with his cam and 918 and harden push rods. his cam was 224 224 581 581 112. talk to big@black he is running a cam simular to the one you have.

 

As to the base circle issue, reducing the bc is dont to increase lift. Obviously you can't make the lobe height on a cam larger than the cam journals or it just wouldn't go in the motor. Therefore, the over all lobe has to be smaller with a larger profile height. This is why you need a longer pushrod to compensate for the overall smaller lobe. Although most people think that 7.40s are not longer when they are. Stock pushrods are 7.38. In order to find a good replacement pushrod after installing a cam, you can take the stock base circle(sbc) minus the aftermarket base circle(abc) all devided by two then added to stock push rod length(spl). That will give you a new pushrod length(npl) that matches you stock valvetrain geometry. Here is the formula in equation form:
npl = [(sbc-abc)/2]+spl

If you end up milling you heads, you have to subtract that amount from the bc radius difference before you add it to the stock pushrod length.
npl = {[(sbc-abc)/2]-mill}+spl

The problem is that most aftermarket pushrods are only made in 0.050" incriments unless you have some custom made. If you wanted the geometry to be exact you could have some rocker spacers machined. But the good thing is they dont have to be exact thanks to our hydrolic lifters. In order for the lifter to take up the slack, you will want a pushrod that is slightly too long. A pushrod that is too short is going to cause slack in the valve train and be noisy. On the other hand, if the pushrod is so much longer that the lifter cant absorb the extra length, it will also be noisy and not allow you valves to close all the way.

 

Thanks for the equation, that will definitely be helpful as I start a 6.0 build (I've got a clean set of heads coming, gonna start searching for a nice shortblock...It's gonna be a long term project as funds allow...maybe even a stroker )

 

Git some, Bud!!!

 

call comp spend 20 bucks buy a pushrod length checker, the math will get you close but alot of times with milling and other things it wont be exact. The checker is the only way to be sure