What would adding 1.8 rockers gain on lift and duration?

My BB has a COmp 280 H in it with .520 lift I/E and 230 230 at .050?

How much lift or duration would 1.8s add? I could run 1/2 1.7s and 1/2 1.8s.

Just curious about doing this instead of a cam swap.

Divide the valve lift by the old rocker ratio then multiply by the new ratio. Advertised dur for a hydraulic cam is unchanged, .050" increases by about 5º, .200" by about 10-12º. Overlap in degrees is unchnged but because of the increased lift at overlap centerline, the overlap area is increased. This could lower vacuum a bit and give the cam a slightly more cammy sound.

Most of the time increasing the ratio works best on the intakes only. I'm not sure why, but many test and racer experience show this to be so.

yea it works out to be like 6% more lift and duration. So without actually doing the math it comes out something 550 lift 243 duration

Another good reason not to put them on the Exhaust, is your more likely to bend an exhaust than an intake valve. Especially if you can't check the clearances and just want to add them after the fact.

Doing the math, it comes out to be .551" lift (.520/1.7=.3059, .3059X1.8=.551")....
At .050", .050" cam lift X 1.7=.085" valve lift. And .085" valve lift / 1.8 rocker ratio = .04722, about 2° more at the crank.
I see about 232° at the .050" equivalent, and .551" valve lift.

UDHarold

So by doing this is there any extra things I need to do besides swap the old ones out and readjust the lifter preload? This would give be in a sense a slightly more aggressive cam.

I think I'll do this and then when I have more time swap cams after Chevelle-abration to the Voo doo cam I have my eye on.

Originally posted by Whittaker:
So by doing this is there any extra things I need to do besides swap the old ones out and readjust the lifter preload? You'll need to check for coil bind, retainer to valve guide clearance, and make sure the pushrods clear everything. Valve to piston clearance could be an issue, although it rarely is.

Please considering buying a good old Isky 280 Mega on either 108 or 110 centers b/c it is already at 280/232 and .565" lift!! But make sure like Pat said that the springs, rocker slots and retainers are OK....

Or Harold, does Lunati sell a match for the tall Isky??

pdq67

So would it be safe to say that when installing 1.8 rockers, it would have little or no effect on the piston-to-valve clearance?

I have been considering the idea of installing 1.8's on the intake only.

Right now with 1.7's my intake valve lift is .602" with .110" v-p clearance. I would still check it, but would I have any issues? (Springs will handle the additional lift)

Not usually a problem since the close contact is during the overlap period. By the time the added duration and lift takes place the piston has moved away from overlap.