How does a cam hate an intake pressure level?

 

Physics

 

is it true to say a "boost cam" introduces overlap in a camshaft which causes the DCR (Dynamic Compression Ratio) to decrease allowing it to be much safer on the engine and also more ignition timing to be ran.

As an example, whats the point of having 15psi but your timing at 8 or 9 degrees with a stock cam. Compared to a diff cam where you can run 15psi and 14 or 15 degrees or timing.

Do I have this right?

 

Have you seen the range of cams labeled as "boost cams"? Its quite comical really. I am pretty confident whoever sells "boost cams" just labels them as such to convince the buyer to buy it whether it actually works well or not.

In general there are some patterns of cams that work well with superchargers, turbos, NA, or nitrous. If you want to call those particular ones "boost cams" is up to you. In general you want a long intake duration for all cams for more power. Supercharger wise you want a long exhaust duration with a late EVC. Turbo wise you will want shorter exhaust duration compared to a supercharger and a less overlap.

Spark timing is not your goal with a cam or power adder...power is. What do you care if it takes 10 degrees or 15 degrees to make the same number? A bigger cam will behave differently, but saying one is better than the other is not a fair statement without the context of what the goals are. If you want a stump puller and never go over 4000rpm and have to pass emissions and want grandma to drive the truck, theres nothing wrong with the stock cam. If your goals and expecatations are different then obviously there are better cam designs for you.

 

All the "turbo" cams i've seen are some iteration of equal int/exhaust with an LSA that puts the overlap at 0 or under. The ideal is that turbo setups, especially with LS's have a higher exhaust pressure than boost, so to avoid corrupting the intake charge you keep the exhaust out, by running no overlap.

seems like successful cams are 210~230 in/exh with a LSA 114~118 to keep the overlap at 0.

bigger cam will move your torque curve up allowing you to hold hp and higher rpms. You will make more power, but suffer (which is a relative term) tq down low.

keep in mind that hp = (rpm x tq) / 5252.

If you don't plan reving higher than 5k, the stock cam will do the trick. If you plan on trying to make more hp/ pound of boost a good way to do it is rev it up. simply reving the engine higher won't net extra hp if your tq falls off before 5k.

you should also see more hp per lb of boost with a bigger cam.

There are other benefits to a bigger cam because your increasing engine VE. typically cooler EGT's and better fuel mileage.

Most are limited to pump gas. So you might make 550whp on 20 psi on 93 with a stock cam. You could make 100 whp more with a cam and intake on 20 psi on 93. the idea is that you'll be limited on pump, so to make more power regardless of cam, you'd have to up boost and run meth, e85 and/or race gas.

 

Thanks for both of your responses.

when I say "boost" cam I am thinking of the isky triple 12 cam.