Performance Increase

[stirling33]

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.

 

[88 Fox GT]

Probably not any more than 10rwhp.

 

[SoCalCruising]

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]

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.

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.

 

[D.Hearne]

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?

His current cam sounds like the Ford Racing A312 and the 280/.512 is Comp Cam's 280H.

 

[stirling33]

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.

Well I definitely want an increase in overall power. Right know with my current setup it dynoed at 300HP on the motor peaking at around 4500. I would like to get some more power and to have that power available farther up the rpm scale. This car is a street car but so I want the power to be available right away and obviously it won't need to run past 6k.

 

[Vinyl66]

You should look into Comp's Extreme Energy series cams. The XE268H specifically.
They have faster ramp rates than older designed cams. The 268 has 224 intake duration and 230 exhaust which I would think would work very well with your heads. It has .509 and .512 lift.

I had one in my car when I had the 302 in it and ran low 13's all day long with Twisted Wedge heads. It will allow you to rev to 6000 easily. It is a mean sounding cam compared to stock.

 

[D.Hearne]

The 280H has more duration "under the curve" than the XE268H. Duration at .050 is 230/230. It will definately move the powerband up. But I would also advise you to find out your true static comp ratio before choosing a cam. Too much cam with too much overlap and not enough compression and you'll end up with a dog out of the hole. The 280H's minimum comp ratio is 9 to 1, which with your combo, you could have more or less, depending on the chambers and piston compression height.

 

[mustangdave]

Not to dog your combo, but those heads are holding you back quite a bit too.

 

[D.Hearne]

Not to dog your combo, but those heads are holding you back quite a bit too.

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.

 

[Vinyl66]

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.

 

[stirling33]

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.

I do have the Y303's - so my next question is, would it be worth it to port out these heads to open them up, or just save the money and try and find some nice used set of AFR's or TW's?

 

[D.Hearne]

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.

 

[stirling33]

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.

I am currently running a 3.80 rear, so that is not an issue. So back to the cam debate it sounds like it's between the 280H and the XE268H. Any other opinions out there.

 

[D.Hearne]

Find out your true static compression ratio before deciding.

 

[stirling33]

Find out your true static compression ratio before deciding.

thanks for all the input......this will be my weekend project

 

[bnickel]

that ford racing cam he has is the same cam as the the speed pro one i run in my 351w. the .050 duration on that cam is a lot higher than what DHearne has suggested it is .224/.236 @ .050 NOT the .214/.224 suggested. if you go to a .230 duration cam you will gain some on the intake side and lose some on the exhaust and just like all ford heads the Y303 needs help on the exhaust side so you would be better off with a split duration cam like what you already have but with more lift. also the LCA on this cam is 114 which is pretty wide but it makes for a better idle which is one of the reasons i chose it. the cam you have is a decent cam but it's not an all out high performance cam. i'd say it's a little more than an RV cam though. it's roughly equal to a comp 280h magnum cam with just a little less lift.

edit: i also think the xe268 would be a good cam for you. but do still find out the static compression ratio before you decide. mine is about 9.5:1, 10:1 would work better with this cam but i'm ok where i am with it.