ok with cams I understand the longer you stay at peak cam lift the better (within reson to the heads ) so lets say we have two
I know one way to get more lift is to get longer duration on the cam

would this be a way to get more lift, broaden the powerband?
these numbers are for the most part just thrown out here also

cam a is 240*@.050 with .510

cam 2 is 222*@.050 with a lift of .425

both of these cams lets say are rated at 1.5 lift rockers


now if on cam b you use a 1.8 rocker you would end up with the same (.510")

how much of a difference on peak power, how wide would the powerband be, were would the power be, and what sacrafice would I have to make to run cam 2 with the 1.8 rockers??

 

First problem I see is -------- Is this for a SBC? If so, where are you gonna find 1.8 rockers? What's your thinking here?


I guess the old cliche fits...... if it could be done, someone would be doing it already.

The largest I've seen are 1.7 for a SBC. They were Jesel (spelling) rockers.

I think I understand your thinking, but for what trouble it'd be to do it may not have a high enough payoff.

BTW, the cam with less duration is going to give you more low RPM torque than the other. How flat the torque curve will be all depends on the other characteristics of the engine. What type of intake manifold, what heads, what size headers, and what size carb/TB.

I don't know that I've helped a lot, but if you give more of a description of what other parts you're going to use, I'll punch them into DD2000 to give you a rough estimate.

 

i have a summit brand cam

224/224 at .5

here is my dyno screen capture.

 

Rx,

Your peak flow presumtions are, for the most part, correct. However, the ultimate goal of increasng the lift of a cam lobe, and thus the valve, is to increase the valve open or free area. There are other means to accomplish the same effect without increasing the valve lift. Increasing the diameter of a valve by only .030" increases the perimeter area by over 3%. To accomplish the same thing via the cam lobe requires a lift increase of about 0.016". By that, the same cam lobe with a 2.02" valve provides 9% more flow than a 1.94" valve. A 2.05" valve makes the increase more like 12½%. Increasing the diameter of a smaller valve (like an exhaust valve) from 1.50" to 1.60" inches increases flow area by over 15%, without changing the valve lift at all. Even an increase to a 1.55" valve increases open area by 7½%. On a smallish valve (like a 1.50" exhaust valve) the same open area increase of 15% would require a valve train lift increase of 0.065". That's pretty tough to do with a cam that's already at .480" or higher lifts and still run it reliably on the street.

You should at least consider changing the valve sizes as well as optimizing the cam profile.

 

thank you vader

I admit I'm not going to do this anytime soon but I would like to learn

what I am trying to do though is figure out how to get not just the peak flow up and really get the AVERAGE flow up without killing hurting daily driving too much if at all. that was the idea behind the cam/rocker thing. if you can run a cam that has the a really aggressive ramp ( roller cam of course ) to make the same amount of peak lift as a larger cam. would it make good power and still be streetable?
I know you have other things to worry about also though like head flow and such. running .500" of lift on a head that starts to reach stall flow at .400" your kinda killing yourself.
as another question how much would undercutting the valve's work or would kill how reliable they would be?



haven't seen much for 2.05 intake valves except for on one head.
the 1.8 rockers I have seen for a SBC and have even seen 2.0 ratio though I would have to look for them again

 

how could you make the cam stay at peak lift longer though?

thinking easily streetable cam lets say with a lift of around .430"-.480"

rather then have the cam go up and then right back down how could you peak it at it's peak lift area longer?


and what woudl that do (keeping all else the same: duration, lsa, lift, and such) for power, gas mileage and overall efficiency?

 

Roller cams stay at peak lift longer because the lobe shape cam be made very steep and radical.

What your talking about is the major downfall of poppet valves and cams ingeneral. But the best so far would be a roller cam with a very small lobe profile, and a huge ratio rocker arm. This way the cam would only lift the lifter say about .20" and the rocker would lift the valve .60" See what i'm saying? The valve will actually be open at a higher lift for much longer, because there is no ramp on the cam lobe. Its just bang, open, max lift, closed.

This is partially why LS1's have 1.7 rocker arms.

 

what would something like this do for efficiency though?
how would it effect the gas mileage and power output as well as the torque curve? again lets say it's keeping the same duration and same lift though?

 

It would make a more powerful efficient engine. An engine is simply just an air pump. If you limit the restrictions in and out you have a more efficient air pump.

 

thing is though you can put a cam with a longer duration in there and sure it might make more power and so forth but gas mileage is going to suck so in a way efficiency sucks


what would keeping the cam at peak lift do for gas mileage up or down?
and where would the torque curve be? the same mid range upper end low end?

 

as Vader states, Increasing the open area of the valve increases power for the same duration.

In theory the ideal valve would be like a camera shutter. Instantly open , Instanty closed, with no valve in the way.

Higher ratio rockers increase the speed at which the valve opens and closes and therefore is open longer at a point that facilitates air flow.

Flow numbers at max lift are not the most crucial numbers as the valve is only at max for a fraction of the valve event. The numbers in the .250 to .400 or average lift affect performance more. The higher ratio arms help get the valve into its average lift faster also.

This is one of the reasons vortec heads are so effective as their mid lift flow nimbers are better than most heads on the market even though their lift over .500 might be less.

Currently in NASCAR engine builders use 1.9 and 2.0 rockers, and I have read that some are trying to push to 2.1 .

The only downfall to high ratio rockers is an increased pressure on the cam and lifters. If a valve spring at max lift is rated at 300 lbs with a 1.5 rocker it is exerting 450lbs at the cam. With a 2.0 it would be exerting 600lbs. Which would cause excellerated wear on said parts. Which is why NASCAR builder Nitride or ceramic coat lifters and cam lobes to increase logevity.

 

larger valves aren't always an option on some situations


also aware that peak flow numbers at max lift aren't the greatest factor you also have to account for that transition perdiod in there where the valve is climbing and falling.

but with a smaller cam and larger ratio rocker arms how would that move the powerband around and what would it do for gas mileage?