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Discussion Starter #1
hopefully someone can explain to me the importance of cams, or lack of importance of cams in turbo applications. i have read that they really don't do much for hp improvements, and the stock cams are good enough. can someone explain to me in detail the role of cams in fi apps?
 

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Here is a little something I found on dune-buggy.com. They had a descent writeup on what the difference between NA cams and FI cams. Here is is

Originally found at http://www.dune-buggy.com/turbo/enginebasics.htm
On naturally aspirated engines that run high RPMs, usually there is a lot of overlap because the air doesn't start moving instantly. By opening both valves at the same time, it gives the intake a head start and helps to flush out the cylinder of the exhaust. The exhaust by now is a column of air that is already headed out the pipe and helps pull in the intake charge. On turbo cars, this valve overlap will allow the increased cylinder and exhaust pressure to flow backward into the intake.

Some turbo cam grinds also wait with opening the intake valve until the piston is already headed down. This is because on a boosted engine the exhaust back pressure can be as high as 30 PSI. The intake pressure under boost is only 15 PSI and will be blown backward. By waiting until the piston has started downward, the cylinder pressure drops and the trick is to open the intake valve just as the cylinder pressure is crossing 15 PSI (in this example).

Good high performance cams for naturally aspirated engines will have a intake and exhaust duration of say 270, 280, or 288, 298 etc. Notice the exhaust event is longer than the intake. On turbo grinds, it is always shorter, say 270, 260 (intake, exhaust), or 275, 255.
So, armed with this knowledge we see that overlap is not good for a turbo application. Most cams are for NA setups like Ford Racing or Comp cams. Therefor you will want to avoid putting these cams into a turbo car if at all possible. Note though that with tunable cam gears you can tune out some of the overlap and still have a descent result. Just not a big enough result to justify buying the cams for that setup. If you already have the cams installed it's not a show stopper to just tune out the overlap and move on. If you don't already have these cams and you plan on going turbo do not buy them.
 

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Discussion Starter #3
i haven't already done cams but i do plan on going the turbo route. but i'm trying to build my engine up so i don't blow my ass up. just trying to get an idea of what i need inside.
 

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call ray at mcnews, he can set you up with some crower turbo cams!! thats what i did
 

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Discussion Starter #5
well i know that they make turbo cams, but i basically am asking for an explanation between turbo cams and n/a cams. osiris helped out a little but i need someone to dumb it down a little for me lol
 

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umm to the best of my knowledge

n/a cams have a lot of overlap because as the exhaust goes out, it pulls in the cooler air from the intake (physics)

turbo cams don't have overlap (when intake and exhaust are opened at the same time)

this way your boost doesn't go right out the cylinder
 

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Discussion Starter #7
then why have i been told that the stock cams are good enough? is it truly necessary to upgrade to turbo cams, or is it safer to because they are stronger or something?
 

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Good turbo cams DO have overlap.

It's basically like this:

If you have a small turbo(smaller T3, etc), you have a lot of backpressure and there's going to be a limit to the amount of power you're going to make.

Using a big cam with lots of lift, duration and overlap would be just as silly with s mild turbo motor as it would be for a mild NA motor. Stock-ish and mild cams generally don't need too much overlap to have good driveability...but it certainly doesn't hurt to have some. Want to make some easy power on a stock Zetec? Retard the exhaust cam (add overlap). It's no different with a turbo application.

If you have a big turbo (larger T3 turbine stuff, T-4, etc), high-flowing head...and you're looking to make big power, you use bigger cams. When you use bigger cams, overlap is ESSENTIAL to maintain good driveability. Backpressure isn't any different in a performance turbo application than it is in an NA application.

I'm not saying to go to some full-blown top-fuel cam, but the old line about "overlap is bad with a turbo motor" is nonsense. Without overlap, you end up with a motor that has about the same torque as a dremel tool...very peaky and weak-suck in the mid-range (say 2500-5000).

Very generally speaking...where you start with your motor (horsepower-wise) will determine where you end up when you add boost. Add 15 pounds of boost to a 150 horse motor and you get 300 -- add 15PSI to a 250 hrse motor and you get 500. There are some things that make it a little more complicated than that...but that's essentially the way it works.

One simple example if this would be this: If you need 15:1 compression to make the 250 horse, it's not going to work too well with a turbo.
 
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