You first need to compare the "@ .050" duration figures. The cam you now have is more like an RV/ factory Hi-po cam. Those duration figures are misleading. Do you want more cam, or less cam? Or in other words, do you want the engine to put out more power, farther up the rpm scale, or move the powerband lower down the scale ? The 280/.512 lift cam sounds like Comp Cams 280H, which is a lot hotter cam than what you have now, which will in effect move the power output farther up the rpm scale. The @.050 duration for this cam is 230* vs the cam you have now, which is likely in the neighborhood of a 214/224 @.050 I know this sounds wrong but that's what the "Advertised" figures (which is the 290/300 on your cam) vs the 280* for the Comp 280H translates to in the more important @.050 figure is. The duration and overlap affects output far more than the lift figures do. Overlap is the time in which both the intake and exhaust valves are open at the same time between top of the exhaust stroke and the begining of the intake stroke. Overlap is also controlled by the lobe separation angle. A wider angle results in less overlap, a narrower one creates more overlap. Overlap serves to create a scavenging effect in the upper rpms, flushing more exhaust out of the cylinder chamber. It also affects idle quality (more ovelap creates the "rumpity-rump" idle associated with Hi-po cams) I hope this helps you in deciding what cam you really want, you weren't real clear in what you meant by your thinking your cam wasn't really tailored to your needs.stirling33 said:I am currently running a cam with 290/300 Duration and .472/.496 Lift which I know is not a good set up for my application. If I went to a cam with 280ish Duration and .512 Lift, assuming I kept everything in my sig the same what kind of increase do you think I would see? I am also thinking of upgrading to a 650 DP carb if that matters.
His current cam sounds like the Ford Racing A312 and the 280/.512 is Comp Cam's 280H.SoCalCruising said:Assuming that your heads have more good quality flow at .512, then it may help. There is such low flow under 0.050" lift, most people talk about cam duration at that lift point. Can you supply duration for both cams at that lift? If the new cam has less advertaised lift, but more at .050", then you will likely see a noticeable improvement, some due to duration/lift and some due to higher dynamic compression, which I suspect would occur. Can yo also quote the LSA of each cam?
D.Hearne said:You first need to compare the "@ .050" duration figures. The cam you now have is more like an RV/ factory Hi-po cam. Those duration figures are misleading. Do you want more cam, or less cam? Or in other words, do you want the engine to put out more power, farther up the rpm scale, or move the powerband lower down the scale ? The 280/.512 lift cam sounds like Comp Cams 280H, which is a lot hotter cam than what you have now, which will in effect move the power output farther up the rpm scale. The @.050 duration for this cam is 230* vs the cam you have now, which is likely in the neighborhood of a 214/224 @.050 I know this sounds wrong but that's what the "Advertised" figures (which is the 290/300 on your cam) vs the 280* for the Comp 280H translates to in the more important @.050 figure is. The duration and overlap affects output far more than the lift figures do. Overlap is the time in which both the intake and exhaust valves are open at the same time between top of the exhaust stroke and the begining of the intake stroke. Overlap is also controlled by the lobe separation angle. A wider angle results in less overlap, a narrower one creates more overlap. Overlap serves to create a scavenging effect in the upper rpms, flushing more exhaust out of the cylinder chamber. It also affects idle quality (more ovelap creates the "rumpity-rump" idle associated with Hi-po cams) I hope this helps you in deciding what cam you really want, you weren't real clear in what you meant by your thinking your cam wasn't really tailored to your needs.
Not necessarily. Also depends on what GT40 heads he's got. Not everyone can swing the big dollar heads. Whichever one's he's got are at least 25 hp better than stock unported heads.mustangdave said:Not to dog your combo, but those heads are holding you back quite a bit too.
Vinyl66 said:From what I have seen, the Y303's (if that is what you have) need help on the exhaust side so that is why I specified a split duration cam.
You definitely do not need to go too big without knowing your compression ratio. Big cams like high compression. Low compression will favor a smaller cam with less overlap to help build cylinder pressure.
D.Hearne said:Change the cam. Do the carb, then see how it reacts. Then decide if you want more. What rear gears do you have now? If it's less than 3.50's, I'd look into a gear change before doing more engine mods. In my 68 Merc, I simply swapped chunks in it's 9" from 2.75's to 3.70's and knocked a full second off the 1/4 mile times. Got the 3.70 chunk from a parts car and really the only cash outlay was for a gasket and new copper washers for the chunk nuts to loose the second off the 1/4. Not bad for a 4200 lb car.
D.Hearne said:Find out your true static compression ratio before deciding.
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