340 Static Compression Numbers and Test Procedure
Doesn’t it mater how the cam was cut and how far advanced it was cut for? I don’t under the thinking of why cams are made with different degrees of timing in the first place and when they are how they need to be “offset” or taken into consideration when degreing the set up on the motor. You should definitely do a video!
Because all the lobes are on one stick. That's where you get lobe seperation angle (displacement). That is the angle between max lift on the intake and exhaust lobes of the same cylinder. As you move the timing events around, you must change the LSA. You can have 5 cams all with 280 degrees of seat to seat timing and all 5 of them can have a different LSA, depending on when you open and close the valves. And all will have different chacteristics.
ICL, or intake centerline is where max lift occurs relative to piston movement. If you have the same 280 cam and let's say it's ground on the Comp cams de facto 110 LSA (which can't be changed after the cam is ground) and Comp says put it in on a 106 ICL, that means you are timing the cam so that when the piston is 106 degrees ATDC the valve will be at max lift. If you install it at a 110 ICL, it is now what I call straight up and 4 degrees retarded from where Comp called for. That means the intake valve now opens 4 degrees LATER and it also closes 4 degrees LATER. Let's say you go hog wild and put the cam in on a 114 degree ICL. That means you are another 4 degrees retarded, and 8 degrees retarded from the cam card.
And again, the valve events are now occurring 8 degrees later than what the cam card called out. Retarding the cam delays the opening and closing of the intake valve. This usually reduces bottom end
torque for higher RPM power.
In your case, I'm guessing you either have the wrong cam, or it is significantly advanced. Just like retarding the cam, advancing the cam changes the valve events.
Let's say you go in 4 degrees ahead of the cam card and use a 102 degree ICL. You have now opened the intake valve 4 degrees SOONER. And you close the intake valve SOONER. This builds low RPM cylinder pressure. Which in you case is a bad thing.
Advancing the cam will always reduce intake piston to valve clearance and increase the exhaust valve clearance. This is because you are moving the valve events ahead (advancing them) so you will have more intake valve opening at and around TDC.
If you retard the cam, you will gain P/V clearance on the intake and lose it on the exhaust. This is because you are delaying the intake valve opening, and you'll have less intake valve opening at and around TDC.
You can also figure out what happens on the exhaust side by advancing and retarding cam timing.
BTW, it should be pointed out that cams ground with the de facto Comp call out of 4 degrees advance is mostly marketing hype. They did that because you can get lucky and maybe not need an offset key or bushing to get the cam timed. If you have a timing set with multiple key way options, this ground in advance is totally unnecessary. I guess the best scenario is you don't have a multiple key way option and you just "line up the dots" (I can't say how much I detest this, as degreeing a cam is very simple...I couldn't pass HS shop class if I couldn't do it on 3 different engines) then the 4 degrees advance ground into the cam would get the cam where the cam card called out.
It's all pretty simple stuff really. But it is important. When I look in a catalog and all the cams are ground on the same LSA I know that is a huge compromise.
The real reason why Comp chose the 110 LSA as the de facto LSA for most of their cams is simple economics. When a cam core is cast, the lobes are already there, in rough form. Getting a core for let's say a 105 LSA is much more difficult to find. Same goes for a 114 LSA. You can only move the lobes a few degrees either way or you run out of lobe to grind on.
If you use a 110 LSA on most everything, virtually every core you grab out of the bin will easily take a 110 LSA where a 105 or 114 may not fit on there.
Hope this makes sense.
