I will be the first to admit that I am completely cam illiterate. I'm gonna do some research on this stuff tonight cause I know I have some literature at home. But in the mean time, can anyone explain the difference between these two cams and tell me if there is a benefit of the LT4 over the L98 cam and for what reasons if any.

L98 Cam:
The duration at lash point in degrees (intake/exhaust) is 294/294; duration at .050" tappet lift (intake/exhaust) is 202/206; and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 403/415. Valve lash is zero/zero and lobe centerline is 115 degrees.

LT4 Cam:
The duration at lash point in degrees (intake/exhaust) is 279/287; duration at .050" tappet lift (intake/exhaust) is 218/228; and maximum lift with 1.6 rocker ratio (intake/exhaust) is 525/525. Valve lash is zero/zero and lobe centerline is 112 degrees.


Also, any comments on CompCam 1.6 roller rockers as opposed to the GMPP rockers ( https://www.spoperformanceparts.com/...=773&CATID=764 )? To me the GM parts are looking better, but if someone can comment otherwise?!?

 

I'll give it a crack. BTW, you don't have to be an "expert" to understand these terms.

Duration at lash point: sometimes a related term (advertised) is also used. You can usaully ignore this one cause the important one is:

Duration at .050" lift. This is key because unlike the last spec, where different manufacturers have their own way of measuring it, with this one, .050" duration means duration at .050" lift, no matter who made the cam. Anything under 210 is a torque cam on the intake. around 216 - 224 is a midrange cam, anything over 230 is a high rpm cam. Not that a 214 cam won't pull to 6000, but it is optimized for something like 2200-5000. Cam makers will sometimes run more duration on the exaust to help engines with weak exaust ports or a restrictive exaust system.

A cam will seem bigger in a smaller engine than a bigger engine. e.g., a cam with 218 might have a smooth idle in a 400, but be rough in a 283, and it's rpm range would be shifted higher than in the 400.

Max lift is the cam lobe lift multiplied by the rocker ratio. e.g. .25" at the lobe multiplied by 1.5 would be .375 at the valve. Theoretically. You won't actually get that.

Valve lash zero/zero: it's telling you it's a hydralic cam cause solids need to run lash, as they can't self adjust like a hydrauilic lifter can.

Lobe centerline: right after .050" duration, the most critical spec of the cam. Closer centers (106-108) mean more valve overlap, that is the time when both the exaust and intake valves are open. Overlap is beneficial at certain rpm's, cause the exiting exaust helps suck in the intake charge, but more overlap means a rattier idle. Centers 112-115 make for better idle. Wide centers also used on blower engines to prevent boost escaping during overlap.

The LT4 moves the optimum rpm range up in comparison to the L98 cam, mostly due to more duration. But if the rest of the combination isn't setup to work in that rpm range, it might run worse than the L98 cam. The intake, heads, exaust, torque converter, diff ratio, etc. would need to be matched to what the cam's intended rpm range.

Some guys will pop in a bigger cam, which starts to work at a higher rpm, but by the time the cam starts cooking, the heads, intake, etc, are packing it in, so not much benefit, if any, is seen. You get not much gain at higher rpm, cause the rest of the combination can't work up there, but you give up low rpm torque with the bigger cam. You get an engine that can't run up high, and is short on torque. Lose , lose situation.

Running a higher rpm cam with 2.73 gears and stock converter = dog.

 

Thanks, that helps me understand a couple things. Right now I've got a mildly modded plenum and a Vette stall...nothing drastic, but not stock. So I guess I need to know how this will work with my combo. I've got some other plans as well that I want to do in the spring, money depending of course. Right now the plans are to get headers, possibly have my stock heads ported.

 

not the lt4.

All the LT4 cam really is just 1.6 rockers on the base lt1 cam.