Can someone give me the FI for Dummies explanation of why a turbo generall makes more torque at a given hp level than an SC?

I know most SC impeller speeds are related to eninge rpm, but would that not be the same for a turbo as well? They are both shoving air into the plenum, and the turbo will generally shove hotter air, but I am having a hard time wrapping my brain around why turbo torque numbers seem higher and in much lower rpm.

 

SCs often have parasitic hp loss because it uses power to make power. Turbos are powered by exhaust gases.

 

It's very simple. A turbo is able to hit it's maximum boost sooner.

Like you said, an SC is RPM dependent. It will only hit it's full boost at or near Redline.

 

The turbo runs off exhaust and can spin much faster sooner, smaller turbo's spool faster than larger ones, large ones make more power. The SC runs off the motor so you have to be spinning the motor up to the higher rpms to get the effect of HP and torque. SC seem to be a bit more reliable but can also make big power. There both good.

 

So basically the turbo hits its full boost earlier and then as rpms climb and turbo spins faster any extra boost would be released by wastegate or be negated as the heat of intake air climbs vs> SC which just climbs the whole time without wastegate until max rpm?

 

Pretty much. There's no wastegate on an SC tho. On an SC you decide max boost by changing the size of the pulley.

UD.

 

Correct

[quote]released by wastegate or be negated as the heat of intake air climbs

Nah, not right.

The wastegate is a mechanism to bypass exhaust gas and hence not create the excess boost in the first place.

As for the heat of the intake charge.... not really relevant. Gas heats as it is compressed. This is the same for turbo and SC. Too much is made of the idea of a turbo being exhaust driven and hence hot and this being thermally transferred to the charge air. The charge air is moving so fast the main contributor to it's heat is compression.

 

yes and no


Yes superchargers have parasitic loss since it is directly coupled to the crank.

HOWEVER

Turbos also cause a parasitic loss by being in the exhaust path.


In order to get a set amount of mass flow / pressure there is a need for work to be done on the incoming air charger.


This work must come from some place be it crank power or exhaust gas flow / pressure.


Why to turbos makes more TQ then a SC(CT,VT,KW)?

Simple look at where each type of FI mass flow profile.