eLTwerker

I've played around with J-Rod's VE calculator quite a bit. How is it that the same camshaft can have different amounts of overlap and different valve events at different lift points? A cam will have a certain amount of overlap and the valves will open and close at said point. Why do these figures change just by measurements from higher or lower lift points? I don't get it!

SincalT/A

iTrader: (16)

two cams can have the same numbers @.050 lift on up but below like say @ .006 can be very diffrent causing the valves to overlap more or less.plus you can have the same exact camshaft and change rocker ratios in turn changing valve events also.

eLTwerker

So, how can the valve events calculator accurately give overlap @.050 with only those spec(which J-Rods calculator can and does do)? You could then put specs of two cams in @.050 and the VE calculator would show the same overlap. But if one of those cams has a smaller duration @.006 it would have a more aggressive ramp rate and likely more overlap. Just putting in the specs @.050 could be misleading.

I'm just wondering how reliable specs @.050 are. From what I've seen they can be very misleading.

SincalT/A

iTrader: (16)

the numbers are some what misleading.i havent seen this calculater but i would be willing to bet the peak hp numbers are fairly close given two identical cams @ .050 but the area under the curve is where agressive ramp rates really shine. more aggerssive ramp rates equal less overlap on identical cams @.050 which then equals more vacum more thottle respone more low rpm torque more low rpm hp basically more efficient cam.think of it this way if you could run square lobes on a cam that would be ideal for ohv engine.valvetrain limitations would suggest otherwise.

Sweetred95ta

iTrader: (2)

Exactly. The more aggressive ramps should peak a little (5-10 rwhp, depending on cam) higher, but you're exactly correct on the area under the curve.

SincalT/A

iTrader: (16)

added more info to the above post

eLTwerker

Wouldn't torque peak a little sooner due to less overlap?

SincalT/A

iTrader: (16)

that depends on the combination of engine you are dealing with give me a combination and i will give a educated geuss.

eLTwerker

I'm just talking all things possible being equal. Just looking for a broad generalization here. Take one car, install a cam and dyno. Same car, same cam but with wider LSA (less overlap). Torque would peak sooner, right?

SincalT/A

iTrader: (16)

on a wider lsa torque would peak earlier if the engine relied more on intake port velocity to fill combustion chamber.if the engine relies more exhauast scavaging to fill the chamber more overlap would be disired.there is also a optimal lsa for a given engine combination meaning you can change lsa so much either way and run into negative results.