I came across this in an article on Enginelabs.

"Jesel prefers to use larger diameter cams and larger cam lobes with lower rocker ratios. Higher rocker ratios increase the valve opening rates, but by using larger cams and lobes you can end up with similar opening rates while lowering the loads and stresses on the valve train." and "There is a noticeable difference when turning over a motor with the two different packages — small cam with high ratio rocker vs. big cam lobe with lower ratio rockers. It takes more rotational force to move the high rocker ratio package, and this required force (or drag) increases with rpm. It is our experience that the large lobe/low rocker ratio package provides a smoother, more stable valve train capable of more rpm and providing better durability."

Admittedly, he is talking engines with over 1" valve lift..

I have 3 engines with low ratio rockers, and while i am saving for a Mummert "hot rod in a box" i don't want to spend too much on parts for the 292 i am doing in the meantime. Cams are cheap, and and for less than 500 bucks i can do cam, lifters, valves, springs and collets.

i thought a larger cam may be the way to go while i'm saving for my box of 'get up and go go go'?




South Australia

I wouldn't want to pay for a cam and lifters twice, so if you do it, get the cam you plan to use with the other stuff. But be aware that it may require more clearance between the valve guide and retainer, which requires that the heads be removed for machining. Then the question is are they the heads you will use and should the money be spent on them so that the cam can be used, etc. Might the pistons require reliefs?
So, if it won't require a whole lot, go for it but if it requires a lot of work just to be able to use the cam, wait.

A better course of action may be to focus on items that are more easy to bolt on and can be used on the new engine like intake, headers, distributor, high ratio rockers, etc.


Lawrenceville, GA

A couple of comments:

Y Blocks have limited cam to crank clearance so bigger cam lobes and longer durations can lead to cam lobe hitting the rod cap.

Y Blocks have a VERY robust valve train. A 1.54 or 1.6 rocker is easily accommodated without undue stress. Increasing rocker ratio to gain lift is usually easier than a bigger lobe on the camshaft.

Do a search on the forum IIRC Ted Eaton did some low vs high ratio rocker comparisons during a dyno session

Here’s some more early morning rambling.

Large diameter cams have come to the forefront in the racing engines but those do require engine blocks that are machined specifically for them. The move to the larger diameter camshafts originated from the need for more stiffness due to the increase in valve spring pressures. The better accuracy of the lobes on the large diameter cams was a positive side effect. Loading at the lobe simply depends upon the rocker arm ratio and the valve springs being used.

For most engines, increasing the lift comes at the expense of reducing the camshaft base circle. The problem that arises for the Y engines is the amount that the lifter drops out of the hole as the lobe lift increases. As the base circle decreases, there is a subsequent drop of the lifter below the hole in which it resides. That is the limiting factor for lobe lift and to get even more lift at the valve, the rocker ratio then has to increase. The increase in rocker ratio then increases the loading at the camshaft as the leverage principle at the rocker then increases the valve spring pressure seen at the lobe.

Lorena, Texas (South of Waco)

Sinse we are talking cams Ted, do you see any advantage to use a 4 pattern cam in a y-block being that the manifold runner distance is not that much difference between cylinders? Did you change the cam grind in the Y engines that the exhaust temp was below normal? Never to old to learn.

Gary Ryan San Antonio.TX.

Ted, if you did a comparison on low v high ratio rockers, can you provide a link?

As i said in my original post, i am putting money aside for a Mummert hotrod-in-a-box complete engine kit,
but that will not be 'til later next year, also depending on Au$ v US$.

In the meantime i aim to build a lo-buck 292 with some go.

I have a lo mileage from recon truck engine C2AE with ECZ-C heads, +.030 pistons and +.010 mains and bigends.
It has a 63 dizzy and i will put my B manifold and holley 600 on it.
I was thinking along the lines of an isky .448 lift cam with new lifters and police springs with the 1.43 rockers.

.


South Australia

Due to the Y engines having intake runners that are closer to being equal in length versus others, four pattern camshafts will not see as much benefit on the Y’s based strictly on the runner lengths. On the engine that was seeing the low exhaust temperatures, the rod length was shortened 0.450” and the cam shaft lobe centers were increased an additional four degrees. These two changes gained over forty horsepower with everything else including the compression ratio remaining the same. I’ll attribute the increase in lobe centers being worth 90% of that gain and the reduction in rod length the other 10%.

Here’s the link to a recent thread also bringing up the multi pattern camshaft topic.

http://forums.y-blocksforever.com/FindPost83936.aspx

Lorena, Texas (South of Waco)

Here’s a link covering the thread that discusses horsepower changes in regards to rocker ratios. Those particular numbers were derived from iron cylinder head testing on the Y dyno mule. I’ll add that increasing the rocker ratio on the aluminum heads netted significantly higher gains as switching from 1.54 to 1.6 rockers on an aluminum headed Y engine saw a 12 HP gain.

http://forums.y-blocksforever.com/FindPost40649.aspx

Lorena, Texas (South of Waco)