My cam is a 214/224, .523/.535. I think its pretty small for my engine but I really don't want to do a cam change. According to my calculations with the 1.85 rockers I could move the lift up to .569/.582.. Do you think doing this would be worthwhile? What kind of gains could I expect. I have 918 springs, is there anything to watch out for? Thanks.

 

i gained 11/13 using the VHP/Crane 1.89 accelerated lift rockers on the wife's 99 formula with stock cam. here's the graphs

hp graph


tq peak is misleading due to spike at beginning of run. cursor shows gain.

 

Thats not bad. I think I'm not getting the most out of the ported heads (2.08 x 1.60) with such a small cam.

 

you'll also gain a degree or two of duration and overlap as well, keep that in mind.

 

that's valve duration and overlap. not cam. you are changing the valve movement. the duration and overlap are ground into the cam. all duration and overlap are measured at cam lobe lift. not valve lift. it's an 'effect'.

 

Right, but the net result is the same so in effect it makes no difference if I'm not mistaken.

One question I have to go along with the thread starter, is if 1.85 roller rockers for example increase duration and high end hp, would they also reduce low end tq in turn? Just below 3k or so?

 

i can say from driving the wife's car, i don't feel any loss in torque under 3k. i think it has helped. from stock in an auto, you start to feel a pull at 3200 rpms with stock converter. after the headers, the pull started at 2600 rpms. with the rockers, it now starts to pull at about 2200 rpms. drivability is better. throttle response is better as well. nothing dramatic.

 

Ok, cool. I ask because I realize the 216/220 is popular among other things, so that's all good if it helps at most RPMs also.

But, I can't help but ask, since when is the wife's anything good for any reasonable purposes?

 

i did rocker arms and gained 8-9 rwhp. the gains come on at about 4200 i believe.
i have a graph posted in the dyno section here. do a search.

 

Well, that actually sounds like a substantial gain for just a rocker swap. I would have put those on a low lift cam for less than $200 no problem, but over that is just too much cash for only 10 hp, really. I'm actually surprised the tq is not effected too low in RPMs, isn't that what lift is supposed to do maybe I'm wrong.

 

A good cam class is needed here. There is not enogh room on this forum for that.

Try looking at the effects of what happens when you put the high ratio rockers on. All valve events happen at the same place, (openings and closings) but the lift per degree at the valve is increased by the fact the pushrod cup is moved closer to the fulcrum. Overlap in degrees is the same but the valve is opened slightly higher during this period. Don't be afraid of overlap as it is needed to draw the new charge into the cylinder. It is the fast guys who have learned to work with this to get in effect a natural supercharger. The negative produced by the exhaust leaving pulls new intake charge in.

Watch your piston to valve clearance from -20 degrees over TDC (at overlap) and +20 past.

High rocker ratios also put a high strain on the pushrods. Think of them like a pencil. Grab it from both ends and bend. It snaps back. That is what happens to the pushrod on every lift. Get the best pushrod you can find because the higher ratio rockers put a higher strain on the pushrods and they bend more. The net effect is the lost lift during part of the valve movement.

Scaz

1.34 60' 10.39 126 I have to use stock rockers.

 

Good answer.. Thanks

 

the VHP/crane rocker kit comes with guideplates, screw-in-studs, posi locks, and pushrods. http://www.vincihighperformance.com/superwebdeals.HTML

 

I'd buy 8 rockers and put them on the intakes. Leave the exhaust alone.

Chris