I keep getting asked the same ?s so I will try to explain the basic principals of cam design & selection. The cam is basically the heart of the engine and controls the power. It is also 1 of the least understood parts of the engine.
There are 4 parameters in the design of cams - duration, lift , overlap, & centerline.
1] duration - this is the most important aspect of the cam as it determines what rpm the cam works at , this is the # of degrees that the valve stays open measured in crankshaft rotation. When selecting a cam this is the first thing to consider determine what you use the engine for & be honest or you will be disappointed with the performance !!
This works as a guide & the numbers are approx as centerline, porting, roller cams etc. will vary the results a bit.
Advertised @.050 RPM
240 - 250* 200 - 210* idle - 4500
250 - 260* 210 - 220* idle - 5000
260 - 270* 220 - 230* 1300 - 5400
270 - 280* 230 - 240* 1500 - 5700
280 - 290* 240 - 250* 2200 - 6000
290 - 300* 250 - 260* 2700 - 6200
300 - 310* 260 - 270* 3000 - 6500
310 - 320* 270 - 280* 3500 - 7000+
The peak Hp will be reached approx 500 rpm before the max rpm & the peak torque will be reached approx 1500 rpm before max rpm, the other secret to making power is to match all the other components such as intakes, headers ,head work converters to work at the same rpm so the whole package works together, you will be disappointed if you match an intake rated for 4500 rpm max with a cam that starts working at 3500 rpm!!
2] lift - this is how far the valve is lifted from the seat, lift does not affect the rpm the engine works at but the more the better at a given duration , Mopar cams use a wider lifter so the valve can lift faster than other makes. UltraDyne , Hughes & Mopar all have cams designed to take advantage of the wider lifters Also the Mopar heads stop flowing more air or the valve becomes invisible to the air flow around .550 lift without port work.
3] overlap - this is the amount of degrees both of the valves are open at the same time & this is done to use the velocity of the exiting exhaust to help pull in the new air/ fuel mix this effect works better with higher rpm which is why the overlap increases with bigger cams, but the increase also hurts idle quailty & causes the lope when the engine is running. Larger headers will also hurt this effect by decreasing the velocity & resulting vacuum.
4] centerline - this is the least understood aspect of cam design & to over simplify the higher the # of degrees the longer & flatter the power band becomes [eg 115*] & the lower the # the shorter & more peaked the power band becomes [eg 106*] for example a 115 cam may give you 300 hp from 3500 - 5500 rpm with a peak of 375 hp where a 106* cam would give you 275 hp from 3500 -5500 rpm & a peak of 395 hp [these figures are arbitrarily made up] I prefer the long flat power band , it works well with the long mopar rods & gives pull everywhere but if you have ideal gearing & 5 speeds in the trans to decrease the rpm drop between shifts the car should run faster with a lower centerline cam.
Generally choosing a smaller cam will hurt you less than choosing a cam that is bigger than you need.
If you have more ??s , ask!!
