Did I screw Up? With my cam.

[concobra]

Hello RodKnock

That is a reasonable assumption on you part and in general makes good sence. Let me try to explain the variables.

There are three issues that present themselves here. 1. Very low static compression of 9.5:1. 2. Very large camshaft duration. 3. Cylinder filling ability. These three specifications work in a dynamic fashion to each other.

1. The low static compression of 9.5:1 yields a volume of 119.7 ccs at TDC on Big Boss' engine. This is a rather large area and will take a lot of ignition timing to get the flame pattern to fill this area during initial combustion. In addition the spark plug location on the original FE heads in way to one side which also contributes to poor flame travel. The more timing to move the flame across this area the better. So to speak.

2. Cam timing as it relates to static compression determines actual or Dynamic compression. Dynamic Compression is defined as the numerical number associated with the event when the intake valve closes and the cc displacement at this point verses the cc displacement with the piston at TDC. With the cam at 6 degrees advanced this number on Big Boss' engine calculates to 7:1. This is still a very low compression number as it relates to both performance engine building and toleration to detonation with 91 octane pump gas. Therefore using a lot of timing will help overcome this by creating more force against the piston which is the primary job of high compression. In other words we are cheating the engine into thinking it has more compression.

3. Cylinder filling. With all due respect to original low riser heads these do not have a good design and do not move alot of air/fuel mxture well on their own. That is why this cam helps to some event by having a lot of lobe duration to give the head ports time enough to fill the cylinders. Even with the cam's help the cylinder filling is not good. If you can't get it in you can't make big power. ( The old " An engine is nothing more than an air pump" theory holds true here)

Given these conditions is why I recommended these specifications to Big Boss.

Let me share one point as proof. My Current Cobra runs a solid roller with 256 degrees of intake duration, a static compression of 12.1:1, and a cylinder filling capacity of 105% percent as registered on the dyno. I run this thing on 91 octane all the time without any signs of detonation heard or as inspected on the piston tops or rod bearings. One consideration though. I keep the RPM above 3000 before ever flooring the gas pedal. But this should be normal practice with any usage of a performance / upper RPM engine.

Regarding your comment about being an expert. I am sure you know quite a bit and I truly enjoy a dialog about engines. I am not an expert either. I just enjoy engines. The only thing I am an expert in is making my wife mad when I spend too much on my own engine. (She is mad quite often.)

Concobra