So i have a friend that "knows a lot about engines". I say this because no matter what i say he will come up with some other thing to try to prove me wrong. To give you an idea of his knowledge of engines he doesn't know what block deck height is. Anyways we got into an argument the other day about what power adder is more efficient a turbo or a blower. He swears that a blower motor will out power a turbo motor any day. But I see lots of blower kits that are rated for 8psi and say 35% gain in power. But 7.5psi on a turbo is 50%. To me it seems like turbos are more efficient am i missing something?

It depends on the rest of the system, in general turbo's are more efficent, BUT results may vary according to how the rest of the engine is built.

It also depends on what type of blower you are talking about.

Turbo's take a lot less power to turn, but it depends on how it's set up

Turbos don't take any power to turn, it's all free from the exhaust. (Dragsters excluded) A turbo will have a larger power reservoir to draw from than a blower and won't rob the motor of power due to parasitic drag on the RA. Figure - roughly - around 20% of motor's horsepower is spent turning the screw so the blower starts at a power deficit and has to make all that power back up and more. You can only get a pulley so small to up the boost. The upside is that the power is always there, there no lag that is associated with a snail, you push the 'go' pedal, the blower pulley turns in relation to the crank pulley. The turbo 'lags' because of the time it takes to build enough exhaust velocity to spin the turbine. However once that power comes on, its all addition - not counting the extra heat generated by that 1600° lump of cast iron hanging off the motor.

The problem with turbos is that they are externally more complicated. Oil feed and returns to run, mucking with the exhaust, etc... whereas a typical modern supercharger is slapped on the intake manifold, squirt some more fuel, run another belt and you're done. I'm generalizing of course, but you get the idea.

Show me a practical supercharger that put the squeeze on the incoming air to the tune of 30psi without melting into a puddle of aluminum. A turbo can do this all day long with the supporting modifications.

Cliff notes - turbos are more efficient, generate more power, but typically provide power later in the RPM band, produce more heat and require a lot more room and plumbing than a blower. A blower provides power all the way through the RPM band, is simpler to install, but is less efficient, and unable to achieve high boost levels.

I'm a recovering turbo junkie, but I give it about 6 months once my new motor is running before I start looking to boost it!

well he is putting together a 406sbc that has stock heads, victor jr intake, 590lift 290dur and lsa 108 cam.(lsa seems too tight for a blower cam) and a centrifugal blower at 10psi (no intercooler). I guess this means i should build a turbo motor so we can duke it out at the track.

I can tell you that thing will be a turd. Waaay too much cam for those heads. The boost will help, but the heads will fall flat at 4500 rpm.

10 pounds and no intercooler? Heh. He can have fun with that setup.

No expert here, but I do have one of each (on different vehicles, of coarse). And I know that turbos do take power to make power, by making the exhaust push harder to get out of the engine... It's sort of the opposite of headers in my opinion, which will drain horsepower. So both blowers and turbo take power to make power, although I don't know the percentages, I'm sure they're out there in internet land! My 6-71 blown 350 is Way more fun to drive!... No "turbo lag"! So I vote BLOWER! IMHO!

I'm a turbo guy myself - generally more efficient from an energy standpoint, and they are completely load-related. light throttle conditions its like having a N/A engine. Boost is regulated by your right foot. With a blower, its always operating. Boost effort is regulated strictly by RPM.

Blowers typically have much heavier moving parts (especially roots type) and more bearings, and added friction from belts. The turbo is (IMHO) a far more sophisticated means of forced induction. The only real benefits I see to a blower are cost and simplicity. For everything else, the turbo is the "winner."

Of course, it also depends on the situation. In a drag race, power is power. You tune it to get X hp and since that always happens at WOT and redline, it matters very little how you get it. You either get there with 20psi from a blower or 17psi from a turbo, but for anywhere else but WOT, turbo is definitely my pick.

As usual some good info and some info that is flat our wrong. This topic has been neat to death over and over. These are two totally different animals actually three if you want to split up the rooots blower and the centrif. A centrif blower acts a lot like a turbo as far as the way they operate.

One thing turbo fans like to think is that the boost is free. That is not true, there is no such thing as free HP.

As far as compressing air the centrifs and turbos get the nod. Now you must understand that there is more to making power than just boost.
Moving air is the key (flow) and roots blower move air very well, they just aren't great compressors. Moving air and compressing air is two different things.

If you build each combo like they should be build, which is to take advantage of the type of power the engine makes then they will all perform similarly. Turbo engines make a lot of top end power, but they give some up down low. A roots blower makes rediculous power from idle on up, you must have a suspension that can use that power. A turbo car is easier to hook because they don't hit the tires as hard, but pull extremely hard once they are moving. This is why the nitrous, and blower cars typically leave the turbos cars at the line, but the turbo car run them down on the big end. Look at the MPH difference for the same ET with a turbo car vs a blown car. Turbos make HP, but give up torque. Once again it depends on what the car is used for and what the goal is.

Boost with either type of source is going to depend on your right foot. I can drive around all day with my blower and not make a single pound of boost. Like any other form of forced induction, the engine must have a load and wide open throttle to see the max boost. You have to remember boost is a measurement of back pressure in the manifold. You will only have boost if you are producing more air/fuel into the intake than the engine can use at the given time (RPM)

So i think over the next year or so (probably end up being two) I am gonna build two identical short blocks and turbo one and put a blower on one. Same heads, pistons, rods, and cam. I think the blower motor will put more torque lower in the rpm range but will give up power on the top end where the turbo will be screaming. I don't know what this kid is thinking with running that big of a cam, with stock heads and that intake and only gonna shift at 5500? I tried explaining the idea of "powerband" and that you need all the components of an engine to match to be most efficient but once again i am wrong. I give up on people. I believe it was Ron White who said, "You can't fix stupid". Lol oh yea no intercooler? i am gonna sit down and do the math and figure out how hot the air is gonna be going into the motor.

Is that why you see so many 'turbo funny cars'??

Turbos are the way to go. I know a guy with a twin turbo 455 He's putting down 600 ft*lbs @ 2800 rpm at the wheels! That's right with a roots 871.