header or not to header?

rpburnette said:

Anyway, I have a question for you. You talk about opening up the intake side, but how much needs to be done to really improve the flow. Will just a large intake tube and a new t/b do the trick or are you talking cams and heads. I have been thinking of getting blown and I want to get the supporting mods, but I want to get the right ones. I am not looking for every once of power, but I have been thinking of getting Bassani headers but if I need new heads and cams than I might just stick with the stock heads.

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A larger smoother intake tube, MAF and T/B is one way to improve intake flow. Another depending on the amount of air you're trying to move is to have the manifold and blower (assuming it's a positive displacement) ported. And yes a good port and polish of the heads and cams will do the same as well.

Is it all necessary??? It all depends on the amount of power you're trying to make and how restrictive your system is to start with. I have to admit, that the Kenne Bell components (blower and intake) are a very high item to start with, so unless you're trying to eek out ever little ounce of jam, porting these components probably isn't necessary. Bet were it a centrifugal, you can bet going to a high flow intake beyond the stock PI will net you some great gains.

The headers and other exhaust mods as already explained have the opposite effect. They will allow boost pressure to be relieved some, since the system is able to expel exhaust gasses more freely and less is being backed up within the system. This will only work to a certain extent on a stock engine, since the stock cams will only allow for so much cylinder fill and evacuation because of their relatively mild lift and duration. That being said...its this relatively mild lift and duration that keeps our cars idling smooth on the street and making good low end torque figures. I've know half a dozen people that have used blower cams in Positive Displacement blown cars that have lost a pile of low end torque and not gained a lot of top end in the process. PD blowers are very sensitive to cam changes….more so that Centrifugal blown cars. A set of cams that work well with a Centi car is often far overkill for a PD one. You have to keep in mind that PD blowers ram huge volumes of air into the system in one revolution of the pulley, in comparison to a Centi that needs several revolutions and more blower RPM to move that same volume of air. Boost is more gradual with the Centi and as such, cylinder fill and evacuation is more controlled. IMO, cams should probably be one of the last things on the list of a guy running a Kenne Bell, or other positive displacement charger after all of the other avenues (intake, exhaust, pulleys) have been addressed/exhausted.

rpburnette said:

Also, wouldn't lowering the boost pressure but retaining the same amount of power be better for the engine. So even if you got new headers and the boost dropped 1psi, but you still have the same power, couldn't you change the pulley, add 1psi and now you have more power at the same boost as before. Sorry for any repeated questions or info, just trying to learn.

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Exactly! Lower boost levles, while still making the same amount, or better power is what you're looking to achieve. Just because one makes a certain amount of boost, doesn't mean that they're moving the same volume of air. A smaller displacement engine, with a more restrictive intake system will see a lot higher numbers on the boost gauge than one with the larger displacement and more free flowing intake/exhaust system. This is why you often see small displacement imports running 16psi or so in order to run with a V8 that's making half that. Small displacement engines are more easily and quickly pressurized and as a result, boost levels rise more quickly and often to a higher extent. That same blower, spinning that same RPM on a larger displacement engine, now has twice the cylinder volume to fill and as such won't see nearly the same numbers on the boost gauge…..yet its still seeing the same volume of air.

Now, pulleying up after doing these mods is one way to make more power again. Discharge temperatures will now be lower, because a lesser volume of air on the intake side is being backed up within the system and more is being expelled on the exhaust end. The system is to an extent working more "efficiently" than it was before, but it only works this way as long as the blower is still running within it's efficiency range. You can only over spin a blower so much before it literally runs out of breath and a larger volume supercharger is needed to bring things to the next level and pick up the slack. Then you get to start all over again with the next model up.