I just received my Isky 274 mega cam, and was a little concerned about the numbers on the cam card. Unlike comp, crane, etc, Isky rated the seat to seat timing on this cam at .007 opening lift and .010 closing lift. What is up with that? Comp rates theirs at .006 on both sides of the lobe, while crane rates their at .0045. So by comp standards this would be somewhere around a 280 duration, and by crane standards it would be somewhere around a 284-288 http://www.camaros.net/forum/eek.gif The 58 degrees overlap that this cam supposedly has is pretty much meaningless if you compare it to other brands...as are the DCR numbers. I am still going to use it (installed 4 degrees advanced), but my compression is on the low end of what I think is acceptable for this size cam. Does Isky rate all of their cams this way?
FWIW, this is still a pretty agressive hydraulic cam going by the .050 numbers...226@.050 with .490 lift. It ought to sound pretty healthy.

Each cam company has their own way of rating duration. This is not realy that big a deal. You could measure it yourself now that you have it in hand. There is no set standard when it comes to specifying duration. Lift is fairly simple but duration specs are all over the place.

-Mark.

And the Isky cams are fairly aggressive but work very well, imho..

Like their 280 Mega is 232 vs most all others at 230. Plus, they are high lift, too.

You can compare their philosophy on cams down through the years if you can find some old cats, because they were one of the first to use modern LCA stuff as well as high lifts. I would compare their non-Mega cams to the Mega cams and you will see what I mean. They used to sell an RPM-300 cam that was old-fashioned but worked well.

Why don't you just ask them why they did it to see what they say.. And please get back and tell us what they say if you do..

pdq67

the set standard for duration is "duration at .050" thats why the only way to truly compare cam duration between manufacturers is at .050, since they all have thier own ways of listing things. as for isky cams, i have one of their solid rollers and i really like the power it makes, w/ a nice broad torque curve. in regards to installing it 4 degrees advanced, put it in straight up and check it w/ a degree wheel , i bet you'll find its very close to 4 advanced already. i've been told by people this was the case w/ most all isky cams (including isky) and mine was the same way when i checked it. hope this helps.

That is a strange way of doing advertised duration. I'd at least expect the same standard on both opening and closing points.

Isky always had a reputation for cams that acted a little bigger than the numbers. At least that's the way I've always thought of them.

Either way I doubt it will make much difference on your DCR numbers in reality. I know that compression technically cannot begin until that intake valve closes, but how much air can you squeeze through a valve that is open only .006" anyway? You know SOME pressure has to start building in the cylinder before that valve is fully closed . . .

Just my opinion.

Eric, my thoughts exactly...in the real world it probably will make an almost unoticeable difference in power. But, at the same time, I think this thing is going to idle rougher than I expected (which is ok as long as there is sufficient vac for my power brakes). I wish all the cam manufacturors would use a set figure for seat to seat timing. My primary experience has been with comp and crane, so I know pretty much what their cams will idle like for a given duration. I also have learned that you can't just base a cam decision on .050 numbers...the seat timing IS a meaningful number.

I too was looking at there cams and noticed a very nice solid grind. 240 at .05 duration and around .480 lift with the lash out. But I looked farther down and saw it only had 274 advertised duration. I cant use this cause my DCR would be too high, but rethinking it I would think it would have at least 288 advertised cause the 282S by comp is 4 degrees smaller at .05 and has a 282 advetised. Is it true you can knock about 6 degrees of a solid cam for lash? Eric 68 I noticed you are using the crane energizer rockers, are they holding up well? I ask cause I have heard you have to by the expensive ones to get real durability. I know you race um too! Thanks

Moe, the seat timing on a solid cam is even more mis-leading because most cam manufacturors rate their solids at something like .015 lift. After seeing how Isky rates their hydraulics who knows where they rate their solids at.

Travis,

You are right on about seat timing with solids. Comp uses .015" for adv duration (if I read my cam card right). In reality, since you set your valve lash to .022, you wind up with a cam that has considerably less duration at the seat then the numbers suggest.

I THINK my 294s in reality is about 288* at .006" and about 240* @ .050 lift at the seat. I can, of course set it a little tighter for more duration or a little looser for less - I can even set intake and exhaust differently for a dual pattern effect.

Moe, the Energizers have held up well, I have about 10,000 miles on them now and the fulcrum bearings have loosened a little bit since they were new, but not enough to make me adjust valve lash. The roller tips are still nice and round with no signs of galling or flatteneing out. If I had to guess, I'd say they'll be good for another 10k.

whoops, i just re-read the post and see i misread it, i thought you were confused about advertised duration, i see you were talking valve events, sorry. i have an isky solid roller, 250 at .05 duration, .610 lift w/ 1.6 rockers, and my "cam card" (its actually a sheet of paper w/ a bunch of cam specs on it, including mine.) list four different points of measuring valve events for the various cams on the sheet. .007, .017, .020,.022. each being the same on intake as exhaust. my cams advertised events are measured at .020. i dont know why they do it that way, but i do know isky cams are famous for making power, and i'm real happy with mine. good luck

[This message has been edited by 68rs406 (edited 10-07-2002).]

Glad I read this.

I was going to e-mail Isky and ask if they recommend advancing the cam. I went with a Z25 cam for a 355. I should get the block back in about a week, and am looking forward to it.