Well after a lot of searching I have setteled on the 224/236 custom cam @116 lsa.My ? is when I was about to order it the guy asked me if I wanted the ex centerline ground straight up or at any given angle?And what springs would you suggest?Thanks fellas

 

Not trying to speak for rich or others, but this is what i've gathered....

Usually on a cam such as the 224/236, most blower grind versions of this cam do not run more than a 114 or 115 for blower apps (I'm assuming for optimized overlap reasons). Also, the PCM is set for 4* advanced, which is what most cam companies grind the LT cams on to begin with. CC306, 305, crane cams, etc are 4* advanced off the shelf to match the PCM calibrations.

HTHs and anyone feel free to correct me.

 

The confusion comes from the way an LT1 distributor (Optispark) is driven off the end of the cam. It is a common "hot rodders" practice to install a cam a few degrees advanced. When a big cam is used, this will tend to improve low end torque (at the expense of the high end). With a standard LT1 setup, if you don't install the cam "straight up", the ignition timing will be off in proportion the the amount that the cam is installed advanced or retarded. FWIW, the injector timing will also be off, but since this is just a couple of degrees that is of no significance. You can still install a cam in an LT1 advanced or retarded, but to do so you need an adjustable timing set and you must compensate in the PCM timing tables for the added advance (or reatrding) of the ignition timing. IOW, if you install the cam 4 degrees advanced, you must retard the ignition timing 4 degrees to get back to where you were.

Now, you can see why many LT1 cams have the advance "ground in". This means that the distributor drive pin is offset by (for example) 4 degrees relative to the cam lobes during the grinding process. If the cam is installed "straight up" in this situation, the valve timing (determined by the position of the lobes relative to the piston position) will be, in effect, 4 degrees advanced. Sorry if my explanation is muddy, it's easier to demonstrate with a cam sitting in front of you than to describe verbally. If you look at a cam card for an LT1 and see that the valve timing events are specified at the same "cam installed at" position as the LSA, the cam is ground "straight up". If the card reads something like "valve timing events for a cam installed on a 110 degree intake center line" and the cam has a 114 degree LSA there is 4 degrees (114-110) of advance ground into the cam.

I have experimented with a number of LT1 cams on blower cars. To be honest, there is very little difference on the dyno, or on the road or track, between retarding or advancing the cam cam a few degrees. My current recommendation for the 224/236 cam is a 116 LSA and a 112 degree intake center line (IOW, 4 degrees of advance ground in). This will give a very broad torque curve, nice idle, etc. If the car is more track oriented, narrowing the LSA to 115 or 114 degrees will provide a bit more peak hp at the expense of the low end. As the LSA is narrowed, the effect of any advance becomes less noticible.

Hope this helps.

Rich

 

Hey Rich thanks for the reply.Are there any advantages between going with a hydralic or solid roller?Before I forget which spring do you suggest the guy at CC suggested the 978.Is This the way to go?Thanks again

 

Not with HR lobes, like the ones under discussion. I think the CC #977 spring would work. I have used it with an installed height of 1.900".

Rich