Thread: lunati or comp cam

Tweet

Originally Posted by blumule

i thought the exhaust side needed to be larger than the intake. also arent the durations more important than lift? if i decide on the lunati with the higher lift would i need to change my pushrods? I know i need to change my springs and lifters. Also what do the lsa numbers mean? lunati at 112 and comp at 110.

No, the exhaust duration does not necessarily need to be longer than the intake duration. Scroll down and read Iskenderian's Tech Tip 2003 here....
http://www.iskycams.com/techtips.php

I don't think you can say that one or the other, duration or lift, is more important than the other. They are both functions of camshaft design and both have to be considered when choosing a camshaft.

You won't necessarily have to change pushrods. What you want to do is mock up the assembly and check to see that the rocker is at the mid-point on the valve stem tip at half lift. Get yourself wrapped around this CompCams tutorial....
http://www.compcams.com/Products/CC-'Pushrods'-0.aspx

LSA is lobe separation angle. It is the result of adding the intake centerline and the exhaust centerline and then dividing by two. The centerline is the half-lift point of the lobe or valve. For instance, if the intake valve opens at 10 degrees before top dead center (BTDC) and closes at 40 degrees after bottom dead center (ABDC), then the duration of the intake lobe is 230 degrees (10 plus 180 plus 40). Half of 230 is 115, so if we start at 10 degrees BTDC, then halfway around to the max lift of the lobe (or valve) is 105 degrees ATDC. So, that is the intake centerline (max lift, halfway through the duration cycle for that lobe or valve), 105 degrees ATDC. Doing the same on the exhaust side and using the exhaust opening and closing points, you will come up with the number for the exhaust centerline. Let's say that the exhaust centerline is 119 degrees. Add the intake centerline, 105 degrees, to the exhaust centerline, 119 degrees, and come up with 224 degrees. Now divide that number by two and find a Lobe Separation Angle of 112 degrees.

The tighter the LSA (110/108/106/104/102), the more bottom end the cam will have and the less it will have on the top end. Power will build quickly and then peter out on the top. Tighter LSA will also give you a choppier idle and lower manifold vacuum. This is important to consider if you are using any vacuum-operated accessories such as power brakes.

The wider the LSA (112/114/116/118), the less bottom end the cam will have and the more it will pull at the top end of the range. Wider will also smooth out the idle and contribute to higher manifold vacuum.

110 to 112 is a good all around LSA. Some manufacturers, like Comp, will use mostly 110. Other manufacturers, like Iskenderian, will use mostly 112.