Coming Soon: Higher Ratio Rockers

[asylummotorsports]

Here are the numbers I got with a stock 3500/3400 cam (.2727 lobe)

Stock 1.6 = .436

1.7 = .463 lift

1.8 = .490 lift

So where do the stock springs become the problem?

I'm guessing pretty damn early!

Duration would increase marginally, but not enough to affect alot.

[SappySE107]

Stock lobe is .269, not .2727.

[3400-95-Modified]

Duration at zero lift obviously doesn't change... but .050 and higher yeah.

Ben, how much of a change is it? Do you have a calculation for that? I've been trying to find one but I can't find it easily without having to make a graph.

[SappySE107]

I don't know how to get into that kind of detail on the software to see a .050 duration difference from the rocker ratio change.

[3400-95-Modified]

Actually... you make a good point... just by saying you don't know how to dig in that far, I think we are looking too far into it.

IIRC from the days of when I was measuring cams on the race car, the .050 duration is simply a measurement directly from the lifter on the lobe at .050 lift NOT the valve; so therefore your "advertised" duration should/will stay the same... BUT the valve duration will go up some and technically you don't list the exact valve duration(when buying/selling a cam) so in the end, those are numbers we never look at anyways.

Am I crazy for thinking that way?

[torq455]

Duration won't increase any at the valve or the lobe. The valve isn't open any longer. The valve open/close event is actuated more quickly, and in a non-linear fashion. In the end, it still was open the same amount of time. The only way duration would increase is if there is rocker deflection with the stock rockers and the new ones don't deflect, especially with stiffer valve springs.

[asylummotorsports]

Stock lobe is .269, not .2727.

I was just going by the specs listed on here under Engine Specifications for the 3500.

I guess I read it incorrectly.

Thanx Ben.

[SappySE107]

No thats what it says, but its not what has been measured.

[3400-95-Modified]

Duration won't increase any at the valve or the lobe. The valve isn't open any longer. The valve open/close event is actuated more quickly, and in a non-linear fashion. In the end, it still was open the same amount of time. The only way duration would increase is if there is rocker deflection with the stock rockers and the new ones don't deflect, especially with stiffer valve springs.

Incorrect, the valve will reach .050 lift quicker than before with a different ratio so therefore the duration on the valve itself will change. It's just the fact that when we list cam specs we use valve lift which is rocker ratio dependent, and lobe duration which is not... But you still have the rocker ratio to take into consideration when determining the actually valve duration, its just not affected as drastically as the lift is.

I know its for SBC's but its still a good read...

Effect of Valve lift (done by using high lift rockers)

http://books.google.com/books?id=UlvzvjzQMsoC&pg=PA47&lpg=PA47&dq=is+duration+affected+when+rocker+ratio+is+changed&source=bl&ots=DEG9HeKMz6&sig=Km9X5D1dXqJUXxnoNHbjFMX-cJM&hl=en&ei=swG5SY_3A9-BtwfIjpSdBg&sa=X&oi=book_result&resnum=1&ct=result

[Rhedalert]

My birthday's in April too so hopefully I can put this on my wish list

The only thing I need to determine is if I'll have valve spring coil bind. My cam is basically all-duration and only a slight "bump" in lift from stock (.460 at the valve). If I go with 1.8 ratio rockers, I'll be at ~.518 lift. I'm running LS6 blue valve springs, BUT I also have those ISKY spring seats that are pretty thick. I need to mic the spares I have when I find them and compare them to regular LS6 seats. At what lift do the LS6 springs bind up on our heads when using the LS6 seats?

[3400-95-Modified]

.500 IIRC... but I could be wrong.

[alerored04]

It likes the 1.8/1.8 on the 1393, making it .594 lift. Thats fine with the 26986 springs.

1.8 rockers on a stock cam or near stock lift cam is fine with the LS6 springs.

^^^i would stick with 1.7s myself, but that is just me

Thanks both of you. Is higher lift always = to more performance? I will start doing some research of my own and see what I can come up with.

[Lilchief]

When are these rockers going to be on sale? Are they going to be full roller rockers.

[Azrael]

Thanks both of you. Is higher lift always = to more performance? I will start doing some research of my own and see what I can come up with.

It's a bit of a trade off. You do get more peak HP (more-so from the intake side) but you do lose torque on the low-end.

[torq455]

well that depends on your cam. a good street able cam, more lift will cause a gain across the board. once you start getting bigger and having that lopy idle, you may lose a little low end. mainly rockers don't change duration much if any, just lift.