How strokers affect how a cam "acts"
Ahhh the old "cubes eat duration" myth. They don't really. A lot of the engine builders/testers on here will tell you that. Read this:
I totally agree. When I started this thread it was because I kept reading that LSA doesn't effect idle quality when I KNOW it does. LSA has a larger effect on idle quality than duration does. I also wanted to dispell the notion that cubes "eat" duration--totally false as well. When I decide on cam timing events I take into consideration so many aspects of the build from the hard parts to the totally subjective aspects it would take a long time to put pen to paper. I do have a bit of a "system" but its more based on experience and it wouldn't translate to paper well at all. J.Rob
RAMM is a respected engine builder who does great work. As he mentions, cubes don't "eat" duration. So the idea of going two steps up just because you add 76 cubes? I wouldn't.
When picking a cam. Look at it for everything it does. Pick it based on valve events, duration, lift, type, LSA, etc. The bigger the duration/intake valve events, the higher static compression you need to get proper DCR. The tighter the LSA the narrower the powerband/more torquey it is. The higher the lift the more you have to worry about piston/valve clearence. Make sure the cam matches the heads. Why put in a cam that lifts to say .600 when your heads give up flow at .450? Etc etc. Then pick it based on what you want it to do. This is going in a big heavy ramcharger, with 4x4, for I assume offroading? Even if you aren't offroading. You're moving a vehicle that weights what, 5000lbs? That takes torque. Adding stroke will help add a ton of torque. But keeping the cam smaller will help as well. It's great to say "Oh I got a 500 horse stroker" but if it doesn't make torque till 3000 rpm, what good does that do you? It'll still be a dog off the line. I see you mention high rpm street use, but doing what?
Also 9:1 compression isn't nearly enough for either cam you mention. Here's DCR:
XE268R - Your dynamic compression ratio is 7.14:1. Your dynamic cranking pressure is 137.78 PSI.
XE274R - Your dynamic compression ratio is 6.98:1. Your dynamic cranking pressure is 133.72 PSI.
On good 91 pump gas you can "theoretically" run up to 8.5:1 DCR on iron heads. You want hot street use? Get that DCR up to 8:1 or better.
And as a good "rule of thumb", whenever you're looking at cams. Whatever one you like best. Pick one size down from it. People ALWAYS overestimate what cam they want. A slightly too small cam is always a lot more fun than a slightly too big cam.
