Engine geniuses please!

[pimpmaro]

Ok... What I'm trying to do is learn how to build my own cam specs. I understand the basic concepts and aspects of a cam, but I'm trying to figure out if there are any mathematical formulas or theories behind choosing the proper lift and duration (as well as lsa) for a particular application and/or goal. Thanks guys!

[Volvord 784VC]

There is not an easy answer to your question. Cam specifications are determined through a series af variables that include: engine size; compression; intake type, flow & style; head port shape, size, volume; combustion chamber design; exhaust manifold (header) diameter & length; exhaust system size; vehicle weight; tire diameter, engine power range preference, vehicle purpose (road race, strip, street, ...); and many more ..... Also cam design and ramp speed plays a part, flat tappet, roller, solid, or hydrolic , the number of variables are huge.

Many of these variables can be defined through formula to determine how different cam profiles and designs will effect engine performance. But there is also a lot of "black magic", experience, and testing that really tunes a cam profile and maximise the potential. There are some excellent computer programs that will "crunch" the numbers for you and give you theoretical HP figures for various cam profiles

There is good information on many of the camshaft manufactures web sites, there are also some good SAE papers on camshaft design. I am in the process of finalizing the cam design for a new engine I am building for my car, just using the various profiles available from the various manufactures makes this a lengthy task.

Good luck

[pimpmaro]

I figured as much. I'm a student at Georgia Tech and haven't had the chance to go through internal combustion design yet. What I was interested in doing was taking the standard Comp XER lobe, and then designing a duration and lsa to taylor it to the powerband I'm looking for (i.e. centering it around my shift points the way my car is geared) and then from that point, trying to calculate the maximum lift I can have. It's a daunting task any way I look at it.

[Volvord 784VC]

Try playing with some of the computer simulation software like http://www.racenet.net/software/dyno2000.php this might be exactly what you are looking for.

[chevota]

No formulas that I know of other than what the cam mfg catalogs have. After absorbing as much info as possible, it still took about 10 or more different grinds to get a feel for what works. I must have changed the cam timing 50 times as well. I learned that I either like bigger cams, or cam mfgs like to be very conservative with their recommendations.

I like wider lobe centers because they still make power just as well, but idle/lowend and mileage are greatly improved. Intake centerline seems to be very important, spend the time to dial it in. I would set a 3.5” stroke crank at 110, a 3.75” at 108. Fast ramp speeds rock, look at the duration of the cam @ .006", .020", .050", .100", .200", .300" to get the real picture of what a cam is made of, two cams can have the same advertised specs but in reality be totally different. Duration #'s are far more important than lift, also high lift is very hard on the cam because you need much stronger springs to keep it together. Just enough spring pressure to do the job is best, and a well cut cam can use even less pressure than a generic cam.

Example, I use a Crower hyd cam with 525 lift and 248/252 @ .050 up to 7800rpm with a seat pressure of only about 100lbs. I also run .010" lash. The cam has very close intake/ex duration numbers because my ex flows very well, a typical head needs more ex duration. I live close to Crower so I get to stop by and look at their “Master Lobe List”, it shows all the lobes they’ve made with all the specs. You can pick which lobes you want and they’ll cut it, very cool….

Hope this helps in some way.

[pimpmaro]

Yeah that does help quite a bit. In particuar the engine I'm workin on is a 2002 LS1. Hyd lifters, non adjustable valvetrain so I don't have to worry about lash. 1.7 rockers. What a few of my friends are running is somethin like a 231/237 .595/.599 with a 113 lsa. I'm not sure of the ICL off the top of my head. What I'm particularly trying to figure out is stuff like, if I lower the lift to say .550/.550, how much could i increase duration without a P to V clearance problem? Or maybe even a larger reduction in lift. Also, thinking about lowering the LSA to maybe 110. I'm really foggy on my lobe centerlines and what the best dial in would be, for me it would be trial and error on the dyno. Springs aren't such a big deal since I plan on doing a spring swap with the cam. Something like a Comp 918 or maybe the 987s, but I'd have to get the seats machined for them. What I've gathered from what you've said is that I'd basically make more power if I widened the duration and used less lift. But that has to be only to a point...