TOTD Turbocharger or Supercharger?

[dguy]

mr dough tell me how you would put an intercooler on a 3800sc fiero.  this should be interesting.  just like the guy that said putting a 3800sc in a fiero gets ya 11's .

Well I'm not Mr. Dough, but since in a quick skim of the remaining diatribe which this thread has turned in to I didn't see anyone show you an example of an intercooled L67, I feel obligated to post this link.

Scroll about 1/3 to 1/2 way down the page, and start reading.  

[dguy]

On another note, as I have said on this forum before.  It’s almost imposable to piss me off; no one here has.  I’m just that kind of guy.  Cheers.

So Aaron, now that yet another thread you started has wandered off on a rather spirited tangent, care to share with those of us who are interested in the original topic what your preference is in blower styles, and why?  

[JAYGT]

wow that is a neat intercooler.  not the kind you could get at the junk yard for 50 bucks but still it exists.  i never would have thought you could cool that type of sc.   i guess you can get anything if you have money to burn.   i stand corrected.
 
i have a jdm 94 toyota supra twin turbo intercooler that i got shipped from japan.  i think it was 80$  from my guy.  also a twin turbo setup, blow off valve  and the big single ct26 turbos as well.  was going to go turbo around a year ago.

[aaron88]

I really don’t know too much about superchargers and turbochargers, but I may be able to offer some insight.  I know that there are three basic types of superchargers and one basic type of turbocharger.  I also know that it’s the application that determines what it is you should be looking for.  Plus it should also be noted that a turbocharger is a specific type of supercharger and not something different altogether.

The three main types of superchargers are roots, screw and centrifugal.  The roots type is a positive displacement s/c (supercharger) therefore is always compressing the same amount of air per rotation which is dependant on the engine rotation, therefore has the tendency to always produce the same boost pressure regardless of the engine rpm.  The screw type is also a positive displacement s/c, however the screw design allows this type to compress the air with less recirculation or turbulence than the roots type, resulting in a smaller heat gain per boosting psi.  With a centrifugal s/c you have the most number of options.  However when hooked up to a pulley has one major disadvantage.  It may not produce any boost until engine rpm rises over 2500 rpm.  It is however the lightest unit and allows for more options to cool the air.  It also has the most un-linear throttle response of the superchargers.

A turbocharger is a centrifugal type of s/c that has been doubled up with a second centrifugal s/c to run one unit on the exhaust and another in the air intake.  The net result is a slightly more efficient system of boosting your intake than the conventional belt driven s/c.  This efficiency comes with one slight disadvantage, there will be a small lag in the throttle response.  This lag depending on how much you want to spend can be almost nothing.

Now down to the part that people may care about.  Lets say that we are to compare the three units at lets say 8 lb of boost on the same motor (lets omit the different cam grinds for now).  So you have an 8 psi pulley on your roots s/c, and an 8 psi pulley on your screw type s/c, and a turbocharger that produces 8 psi at maximum engine power rpm.  The result is going to be this; the turbocharger will produce the most power, the screw type the next and the roots the least amount of power.

So why does anyone bother with pulley type superchargers?  Because there are many other factors to take into account.  Ease of installation, cost and availability are a few of the largest factors, but the largest factor is likely the type of throttle response desired.

Car manufactures prefer to put on positive type s/c because they offer more predictability to the driver and fewer options to increase boost.  With a turbocharger the amount of boost increases with the engine rpm therefore creating an element of unpredictability to the engine life and driving response.  Large companies don’t like surprises.  But the demand is there, so what they do is use a very small amount of boost so that the driver that will likely present a problem will also likely modify the units and therefore void his warranty or any manufacture responsibility for mishaps.  Driver gets the car he wants and auto manufacture gets to sell more cars without having to worry about the consequences.  So everyone is happy, except the guy that gets his house driven through by Mr. Dilwad running a turbocharger and nitrous without learning how to drive first.

Anyway, lets say that you wanted to build a drag strip racing car.  I would recommend using a screw type supercharger.  Although you may loose some power over turbo you will also make your power in less time,  and as we all know, your launch off the line can be more important that a few extra ponies.

Now lets say you wanted to race a car over a longer distance than a ¼ mile.  I would recommend using a turbocharger.  It is lighter and more efficient, which is always a good combination when racing.  Also when on the track, turbo lag is much less of factor, and in many cases not a factor at all.  You simply learn to hit the throttle a fraction of a second sooner.

But if you were to ask me what my preference is.  That is a different story all together.  I have no interest in drag racing, but my preference is for the screw type supercharger.  Although the efficiency is less, I also find the engineering more sound.

This is getting long.  So I’ll stop before people stop reading my posts.  I can just see many people reading the first few lines and then skipping down the last few.  Are you the type that skips right to the desert?


Aaron

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[dguy]

The three main types of superchargers are roots, screw and centrifugal.

<much other interesting info snipped>

Have you ever come across any diagrams or photographs of the internals of the roots and/or screw types?  I've seen more centrifugals than I can count, but seem to have no luck with the other two.  Then again I had never heard of a screw-type s/c until reading your post this morning, so I haven't yet looked.  

This is getting long.  So I’ll stop before people stop reading my posts.  I can just see many people reading the first few lines and then skipping down the last few.  Are you the type that skips right to the desert?

All depends upon what the main course looks like.  ...and I like the way you cook.  

[FieroDough]

if they always have the same psi (roots, what eatons is based one) why is a smaller pulley give you more psi? I know the eaton superchargers have a pressure valve that can be adjusted by vacuum or computer.

cheers!
Eric

[GoFast85]

Does that mean that I can adjust the boost on my eaton series 11 by a computer adjustment?

[aaron88]

"if they always have the same psi (roots, what eatons is based one) why is a smaller pulley give you more psi? "

(End Quote)


Lets say that the pulley on your s/c runs directly off your crank and that the crank pulley is twice the size of your s/c pulley.  Just for the ease of calculation lets also say that it’s the circumference of these pulleys that are in relation to each other.  So for every one rpm of the motor you would get your s/c pulley to turn twice.  Now lets say you decided to put a pulley on the supercharger that was twice as small as the one above.  Now you would have the s/c pulley turning 4 times for every one turn of the motor.  Does this answer your question?

Aaron

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[aaron88]

Have you ever come across any diagrams or photographs of the internals of the roots and/or screw types?

(End Quote)

[aaron88]

Screw s/c

[aaron88]

Centrifugal

[aaron88]

These three are only the basic styles of s/c.  There are literally an infinite number of variations that could do the same thing, and an endless number of combinations to upgrade and virtually an endless amount of time and money that could be put into a s/c.

[dguy]

Fascinating stuff...  thanks for the follow-up!