mgags7

What exactly is it about the design of the cam lobe profile that moves the powerband around to certain rpm ranges?

My thinking so far is as follows: There is a certain point at which the lobe's design(lift) is going to "match" the flow characteristics of your induction/head/exhaust manifold the best, and that is where it will make good power.

My original thought was that high lift cams would do best in the very high end, but after seeing results of my crower3s (h22) their long duration makes power up top, yet not in the midrange, however, skunk2 stage2 cams make power in the midrange, and they're much shorter duration, higher lift cams.

discuss

mgags7

bump.....some kinda input would be nice

DonF

Why bother? Read the "cylinder head flow" thread. Theory is not acceptable, just what cam should I buy.

mgags7

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DonF &raquo;</TD></TR><TR><TD CLASS="quote">Why bother? Read the "cylinder head flow" thread. Theory is not acceptable, just what cam should I buy. </TD></TR></TABLE>

aww come on don.....damn these allmotor guys....

DonF

Well for starters, duration, overlap, scavange effect is related to port velocity, RPM's.

bluedlude

ive been wondering the same thing man. i would think that a long duration cam would raise the powerband up in the RPM's. and ive been reading some of my books and theres a couple of things about cam design in there. but i think that got me more confused than anything.

but continuing with my thought on the long duration cam. i think the long duration is more of a design factor when you consider driving at a specific RPM range. and im kinda interpreting that from a tidbit i picked up on here too.

if you know you are going to be revving at like 6K+ you would want a long duration cam. and i could try to be all technical, but i think of it kinda of like the rocker pad trying to keep up w/ the cam profile. if you have a steep ramp, you would have a harder time following the profile at a high RPM compared to a long duration.

remember Combustion Contraptions, cylinder head flow thread. just like that. if your head doesnt flow at low lift numbers, and you change to a long duration cam then you are effectively flowing less volume per degree of the cam. so a cam with shorter duration would be better suited for the head. but hey, these are my interpretations.

crx=si

compression also helps with long duration...long duration with high lift doesn't help compression on a stock motor

Combustion Contraption

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by crx=si &raquo;</TD></TR><TR><TD CLASS="quote">compression also helps with long duration</TD></TR></TABLE>

compression helps with everything for the most part.

in my opinion the most important aspect of long duration camshafts is how well the induction system can keep up. If the plenum, runners, port, valve angles support cylinder filling well after the piston has reached BDC on the intake stroke, you only have power to gain by delaying the closing of the intake valve. The trade off is that an induction system 'tuned' to deliver this effect will generally only do so in one part of the rev range. but if the guy really knows what he's doing, you can gain power everywhere with a properly designed inlet system.

Combustion Contraption

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bluedlude &raquo;</TD></TR><TR><TD CLASS="quote">i if your head doesnt flow at low lift numbers, and you change to a long duration cam then you are effectively flowing less volume per degree of the cam. so a cam with shorter duration would be better suited for the head. but hey, these are my interpretations.</TD></TR></TABLE>



if you cant fill the cylinder at the beginning of the stroke, youre gonna have a tough time filling it at the end.

mgags7

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Combustion Contraption &raquo;</TD></TR><TR><TD CLASS="quote">

compression helps with everything for the most part.

in my opinion the most important aspect of long duration camshafts is how well the induction system can keep up. If the plenum, runners, port, valve angles support cylinder filling well after the piston has reached BDC on the intake stroke, you only have power to gain by delaying the closing of the intake valve. The trade off is that an induction system 'tuned' to deliver this effect will generally only do so in one part of the rev range. but if the guy really knows what he's doing, you can gain power everywhere with a properly designed inlet system.</TD></TR></TABLE>

So this would be a good reason behind the fact that the crower3s didn't do much on my stock head/IM setup....which is understandable.

So is having a fast ramp speed good then? If the valve opens so fast the intake can't respond in time whats the point? I would imagine smaller ports with higher velocity would like fast ramp speeds, no?

bluedlude

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mgags7 &raquo;</TD></TR><TR><TD CLASS="quote">So is having a fast ramp speed good then? If the valve opens so fast the intake can't respond in time whats the point? I would imagine smaller ports with higher velocity would like fast ramp speeds, no?</TD></TR></TABLE>

but then again, you dont have to worry about that since the H22 has over 100% VE