I get the theory. I just couldn't look at the numbers and predict how it's going act. Nor could I look at a combo and say, "Yep... U need this cam rite here".
I get the theory. I just couldn't look at the numbers and predict how it's going act. Nor could I look at a combo and say, "Yep... U need this cam rite here".
Simplistic way to look at is: If you have lots of overlap on a boosted engine, you end up blowing (or loosing) boost pressure out the exhaust, when you should be trying to fill the cylinder. The 86-93 5.0 had a 114* LSA. A 5.0 Ford Motorsport "B" cam had a LSA of 112* and thus a "poppity pop" idle. The 94/95 5.0 had a LSA of 115* and the ECU was a lot more sensitive to changes in overlap. Thus the "E" cam typically worked better on a 94/95 5.0 for drivability reasons. If the car is N/A and you want to make power at a higher RPM, you have to give it more LSA to make it so the cylinders will have time to fill at the higher RPM. So a typical LSA for a high winding small block would be in the 107-110* range depending on the rest of the engine build/car usage. Test at 11:30 P.M.
LSA (lobe separation angle) numbers can be interpreted like this: the higher the # the less overlap, the lower the # the more overlap. Overlap is defined as the # of degrees that both the intake and exhaust valves are open. The longer both valves are open at the same time, the more diluted the incoming air/fuel charge is at an idle, thus at an idle it tends to make for a rough "poppity pop". But at high rpm's you need the overlap to help get the cylinder filled. When the exhaust is being pushed out of the cylinder by the piston, if you start to open the intake valve, you can use that velocity to help start to pull in the air/fuel charge. That is a basic description, a whole lot more is going on than just that tho.
Exactly! This is why you will notice all motor and most nitrous cams with a 110 lsa and the blower/turbo stuff with a greater lsa 112,114, or in my case 116. LSA isn't the only thing that factors into a cam being lopey, obviously more duration (the longer you allow the valve events to happen) will contribute to the idle characteristics of the motor. Also consider valve lift and ramp rates (higher ramp rates with a solider roller vs a flat tappet for example) as they contribute to these same characters. Like @Bullitt347 said, there is a lot that goes on in cam shaft design and selection. You can literally spend hours researching camshaft design only to be more confused than when you first started. Overall I agree that the cam @madmike1157 has will have nice street manners and not be too killer sitting at a stop light while still being able to make copious amounts of unusable power!
I'm running a lumpy nitrous cam with my turbo. It works great if you ask me. Yeah, maybee I am missing a few ponys, but Its what is allowing me to hold the two halves of the stock block together.
Mike, are the stock mounts made from fairly heavy steel? If they are, you can always by polyurethane for windshields and fill the spaces in the rubber. Sounds hanky, but they get stiffer and you get a slightly nicer stop light experience.