Quote:

Here we go with the cam stuff: The way to get more lift per degree of duration is to have a faster acceleration rate. The maximum acceleration rate varies with the diameter of the lifter. Over the past 10 years or so the cam designers have found ways to use a really fast accel rate on the opening with a slower closing rate to set the valve back down so it doesn't bounce.
The standard of the automotive world, the chevy smallblock, has lifter dia. 0.842". Thus you will find that about 90% of all lobes are designed around that limitation. We call them "Chevy lobes". You can tell this in cam catalogs when the lift and duration at 50 lift are the same for all engines with a 1.5 rocker ratio.

One of the advantages designed into Mopar engines is they have a lifter diameter of 0.904" That means if the cam designer wants to he can accelerate the valve faster. This means more area under the lift vs duration curve and more power. For years Hughes has used what it calls "real Chrysler lobes". These take advantage of the larger lifter. The latest Hughes lobe series is closer to the edge than about anyone else. You can see this when the lift for same duration at 50 is higher on the Hughes grind. So it makes sense that it would take more spring to slow down the faster-moving valve and turn it around. One does not want the lifter to fly off the cam lobe (except in certain very specific cases with lift rules).




Well now i feel bad that you typed all that out. I'm way ahead ov you here. The saving grace with what i have i think is that is was spec'd for the Comp version/ripoff ov the Hughes cams. The 924-16 springs are what Comp recommends for their 'Mopar .904" lobe' cams, even the big one.

Quote:

Now onto springs:
There are only a few really pertinent numbers for springs. They are seat pressure at a particular installed height, coil bind height and spring rate.
For example, the Crane 933 springs I am going to use on my 318 project have a seat pressure of 98 lb at 1.700" installed height and spring rate of 328 lb/in. I am going to install them at 1.600" so I have to add the spring rate times the extra compression, in this case it is 328 x 0.100 = 32.8, to the 1.700 seat pressure so now my installed seat pressure is 130.8 lb, perfect for hydraulic roller lifters. Assuming I use a 0.474 lift cam, the open pressure is 130.8 + (0.474 x 328) = 286lb open pressure, in the ballpark for hydraulic roller lifters. Coil bind is 1.08", so 1.08 + .474 + 0.060 = 1.614 which is more than my 1.600 installed height meaning this might not be the spring for the job because one can't run really close to coil bind as it will destroy the spring. In this case I will be saved because my stock rockers come in with less than 1.5 ratio, a 1.45 is more like it, real lift is 0.458 so the springs will have more than the 0.060 minimum clearance between max lift and coil bind.

If you think about it, the same spring can have many different seat pressures depending on installed height, which could explain the different ratings on the same spring.

R.




Man... i used to know all this stuff... its been a looong time since i had my head in the cam books...

Anyways, so what you're saying is that as long as i can stay further than .060" from coil bind, i can shim the springs i have for a bit more seat pressure?

The 924-16 spring is a dual-spring. With an installed ht ov 1.900", and coil bind at 1.175", that gives me .725" to play with... minus .060", so .665"?

IF i install it at 1.800" (by my handy-dandy Comp catalog here), the 924-16 is now 137lbs... closer to the 150lbs Hughes springs seat at. That also brings the pressure at .500" lift to 311lbs. The Hughes springs are 325lbs at .500" lift. I assume this means my 'new' coil bind is .625"? Since the lift ov the Hughes cam is .518", that still gives me lots ov room.

Am i close? or is the math not so linear in all this...??? I'm just trying to understand the math now.