Did I screw Up? With my cam.

[concobra]

Big Boss

Making a cam shaft selection is complicated. May I offer some points of view.

1. Unless your combination of engine components and your driving style is exactly same as someone's other engine and driving style using their cam is useless to you.

2. Do you know your heads flow numbers? Any cam selection without this is at best a poor guess. If you haven't flowed your heads consider getting them flowed. Flowing them will yield data to help you define the maximum lift your heads will flow well, flow verses port size and cross section which determines lobe profile, effective RPM range of head flow verses cam timing, and approximate cylinder filling capablility.

3. Have you accurately measured your true compression? Static compression is only a measuring tool to determine dynamic compression. The relationship between dynamic compression (intake valve closing point) is much more important than your static number. This, with cylinder filling capabilities, determines Cold Cranking Pressure. And that determines how much cam and /or compression you can run with pump gas. There are some other effective points but those points may clutter this discussion.

Let's consider your current cam and compare this to your engine based on the information you supplied.

1. 9.5:1 is very low for this size of cam. Your Dynamic compression is 6.87:1 and your cold crank is 165 lbs. This will yeild a lazy engine with poor throttle response, poor vacuum, and inconsistent idle characteristics. If you are going to run this cam you really need to reconsider your compression ratio. A minimum of 10.5:1 will yeild a still conservative number of 7.56:1 and 189 lbs of cold crank with this cam in your engine.

2. Given the size of your engine 498 CID. Low riser heads, even if ported to their best, will not flow enough to take advantage of that many cubic inches. So actually using a large duration cam, like you have, will allow more cylinder filling time and help these heads.

3. This cam is using some older design lobes for Comp. Intake is lobe # 6012 and the exhaust is # 6013. These are slow opening and closing lobes and should help promote reasonably good velocity through the runners/ports.

4. You cannot compare hydraulic profiles to solids so don't confuse the two.

5. Keep in mind that a solid cams duration and lift are impacted by the amount of lash. Net lift is obvious but the reduction in duration is harder to qualify without the cam being degreed in the engine but the rule of thumb is for every .001 of lash you need to subtract .5 degree of duration. So your intake lobe is really 242 degrees @ .050 and that is not too big for your engine and driving style. Exhaust duration has much less effect on the engines manners.

6. Cam LDA of 108 is on the tighter side but tighter lobe angles usually produce better cylinder scavenging and with the low riser heads having a poor combustion chamber design and very poor exhaust flow this should help.

7. This cam will make power to somewhere between 5800 to 6000 rpm then sign off very quickly. But that is a good street RPM. Power will come on around 2700. It will clean out around 2200 RPM. This is a big engine and it can use this cam.

8. Driving manners. It will idle rough. Stop and go driving will be a pain. But after all it is in a Cobra and that is what the cars are all about. IF not buy a new vette.

9. Tight lobe center cams work better with open plenum manifolds. So if you going to keep this cam then something like a Offy port-o-sonic and maybe a older Holley Street master would work. The Edelbrock Victor is too big for the heads. Dual plane manifolds could be used if you cut down the divider so the total carb. sees all the of cylinders.

10. Carb at least an 850 cfm but I would run a 1000 cfm holley HP.

11. Last comment though redundant. If you do not increase your compression, change cams. If you do decide to stay and 9.5:1 and this is accurate then respond to this thread and we can discuss this. But, changing cams will only be a band-aid to making this engine run to it's maximum efficiency. It needs more compression.

Concobra