Yelo

I was looking up some old school cams this morning and thought it would be neat to post a comparo between two of them to show the differences that time has created:

Comp Cams 270H SBC cam
I ran this cam in a 1969 Nova SS with a 400cid motor, it had a pretty choppy idle and would spin out to about 6500rpms

Duration @.004: 270º/270º
Duration @.050: 224º/224º .470"/.470" 110lsa

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Crane Cams HR224 LS1 cam
This is a pretty standard grind now....most every manufacturer makes a 224º grind for the LSx motors and they're in everything from a 4.8 to 7.0's. MAX rpm's is about 6500

Duration @.004: 286º/280º
Duration @.050: 224º/224º .576"/.527" 113lsa

it's interesting to see the difference in .004 lift....with our roller-cammed motors there's ALOT more duration at lower lift. Max lift has also changed dramatically over the years....it was said in another post that .470"-.500" used to be considered alot of lift, now, I've got a "baby" cam and run .531" lift !!

jmproductions

Yeah that was one of the first things I noticed when I started getting into the LSx engines. Lift seems to be one of the areas where GM decided to make some significant improvements to increase power. A roller cam setup with .500 lift on a SBC only 10 years ago was considered to be pretty badass!

TurboGibbs

iTrader: (6)

The ramp rates on a roller cam can be much more aggressive than a flat tappet due to the roller "rolling" over a hill. imagine pushing a sled up a hill then strap some wheels to it and push. But, it is mainly due to the angle of the lobe against the sharp flat edge. Too steep and the slope will crash or dig into the sharp edge of the lifter. Racing teams, in classes where flat tappets are a must, will run mushroom lifters that have larger bases and must be installed from the bottom or bore the block to accept larger diameter lifters to help compensate and allow for a more agressive lobe. Some flat tappet lifters are crowned on the bottom surface as well to help but most racing classes don't allow such things. Older engine's heads were designed for flat tappet cams so the spring sizes and heights(valve lengths) were no longer or larger than needed to be since lift is limited on flat tappets due to the approach angle on the lobe. A longer duration camshaft can accept more lift due to having a wider base on the lobe and be able to to have a higher peak with the same angle. Typically what I have seen, contradicting the low lift durations you have in comparison, a flat tappet cam will have much more duration @.004" lift than a roller to widen the lobe base out as much as possible to get more lift capability. This also causes more overlap and a less streetable cam, especially for fuel injection and really for early fuel inj vehicles which had computers too slow to respond to the rapid a/f changes of a radical cam.
With the development of the gen3 engines, the heads, valve lengths, and valve springs have been designed to readily accept the high lift capabilities of a roller cam.
Just a little info for comparison, a 350ci 300hp engine in 1969 had .390 .410 lift and duration in the 190's advertised. This is the same cam they put in the 350 250hp truck engines for years with less compression. Of course if you rated that 300hp engine with todays ratings it would be something more like 225hp i'd imagine.

Full_Pull6.0HD

That's a good point you have brought up. before doing anything to my truck, my 1970 GTO was my project. Making the transition to newer engines took a little getting used to. I went through the same dilema when I bought my cam, the GTO has a comp 280 with like .480 lift or so. It is a handful to drive and keep idling in traffic, so when my cam for the truck was suggested, I thought it would be too much for a commuter. Not so though, more often than not it is difficult to tell there is a cam at all.

bluecajun5.3

iTrader: (31)

good info. that's something to really think about.
also if you look at it this way, the old style sbc's run 1.5, 1.52? ratio rockers and the lsx motors run 1.7 ratio rockers. don't know if that has anything to do with it though.

dirt track racer 81

iTrader: (45)

on my circle track car which is based off the sbc i run a comp 4/7 swap 292 300 duration .558 .549 lift 106 lsa

TurboGibbs

iTrader: (6)

with the higher ratio rockers the lobe can be less aggressive and still provide good lift and duration so the less aggressive lobe is easier on the lifters for longevity. Solid rollers have a high failure rate on the street due to their even higher lifts and lift rates and higher spring pressures. you have to spend $500+ on a set of solid roller lifters that will withstand an aggressive cam and daily driving. By aggressive I mean 250+ duration and .600+ lift. The size of the base circle of the cam plays a role as well on the lines of lifter load with aggressive cams.