boost
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Joined: Dec 2010
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From: or
Year: 1988
Model: Cherokee
Engine: i6 4.0l
Back yard mechanics don't always know how to properly set up a turbo.
Turbo lag doesn't mean it robs power. Turbo lag means it doesn't start adding its extra power unil the turbo kicks in. Since the exhaust is already there turbos are considered free power. S'chargers take power directly from the engine's crank, which is considered parasitic loss.
The SC doesn't ever overcome the fuel loss restriction. The s'charger is always spinning, always forcing air into the motor. More air demands more fuel. Turbo's are different as they don't spool (spin and force extra air) until the motor is under load. Therefore they actually increase MPG where s'chargers use more.
Its fact, and has been discussed at great length in this forum alone.
Turbo lag doesn't mean it robs power. Turbo lag means it doesn't start adding its extra power unil the turbo kicks in. Since the exhaust is already there turbos are considered free power. S'chargers take power directly from the engine's crank, which is considered parasitic loss.
The SC doesn't ever overcome the fuel loss restriction. The s'charger is always spinning, always forcing air into the motor. More air demands more fuel. Turbo's are different as they don't spool (spin and force extra air) until the motor is under load. Therefore they actually increase MPG where s'chargers use more.
Its fact, and has been discussed at great length in this forum alone.
the turbo is always spinning as long as the engine is running...
turbos have parasitic losses... its obviously less than a s/c... but they still do...
sc's parasitic loss comes from the power robbed by mechanically spinning the compressor
turbo's parasitic loss comes from the power robbed by restricting the exhaust into a small hole to spin the compressor
and the turbo lag is the effect of the turbo robbing A LOT of power before it starts to spool... the turbo is a HUGE restriction on the exhaust... because of the huge restriction on exhaust leaving the motor, it is restricting how much air it can pull in...
Last edited by JeepingDan; Jan 8, 2011 at 12:36 PM.
Member
Joined: Dec 2010
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From: or
Year: 1988
Model: Cherokee
Engine: i6 4.0l
no i think maybe you should. this is the relevant passage to this discussion. and is exactly what i said in my first post.
the reason people gain mpg in their s/c car over how it was NA is just this:
less throttle to move
less throttle to climb hills
lower rpm while accelerating/going up hills/etc...
even if there is no boost pressure... the s/c will still be pushing more air into the engine that it would normally be sucking in by itself... resulting in better power at lower rpms, and less throttle
same basic reason a silverado gets better fuel mileage than a cherokee while making much more power and torque and having a bigger engine... it drives around at very low rpm... it climbs hills at a low rpm... it accelerates with very little throttle and at low rpm... it does't have to shift down to climb most hills... etc...
do you honestly think if you could keep your heep in overdrive up hills instead of shifting down it wouldn't get better fuel mileage?????
the reason people gain mpg in their s/c car over how it was NA is just this:
less throttle to move
less throttle to climb hills
lower rpm while accelerating/going up hills/etc...
even if there is no boost pressure... the s/c will still be pushing more air into the engine that it would normally be sucking in by itself... resulting in better power at lower rpms, and less throttle
same basic reason a silverado gets better fuel mileage than a cherokee while making much more power and torque and having a bigger engine... it drives around at very low rpm... it climbs hills at a low rpm... it accelerates with very little throttle and at low rpm... it does't have to shift down to climb most hills... etc...
do you honestly think if you could keep your heep in overdrive up hills instead of shifting down it wouldn't get better fuel mileage?????
Low RPM can also equal fuel savings
Supercharged engines are able to make good power at the low end of the RPM (revolutions per minute) range. For any given speed your car is traveling, your will burn less fuel at low RPM as opposed to high RPM, as the engine needs more fuel to spin faster. Cars will often have transmissions with five and six speeds or more to maximize this effect. It's not uncommon for vehicles so equipped to cruise at highway speeds with the engine RPM barely over engine idle speed.
Supercharged engines are able to make good power at the low end of the RPM (revolutions per minute) range. For any given speed your car is traveling, your will burn less fuel at low RPM as opposed to high RPM, as the engine needs more fuel to spin faster. Cars will often have transmissions with five and six speeds or more to maximize this effect. It's not uncommon for vehicles so equipped to cruise at highway speeds with the engine RPM barely over engine idle speed.
Last edited by spiceman; Jan 7, 2011 at 07:09 PM.
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Joined: Dec 2010
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From: or
Year: 1988
Model: Cherokee
Engine: i6 4.0l
this is off vortech's website
What will a Vortech supercharger system do to my mileage?
When the supercharger system is installed as purchased, mileage often times improves due to the increased engine efficiency. If you tend to drive with a "heavy foot," your mileage may suffer.
When the supercharger system is installed as purchased, mileage often times improves due to the increased engine efficiency. If you tend to drive with a "heavy foot," your mileage may suffer.
Seasoned Member
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From: Michigan
Year: 1998
Model: Cherokee
Engine: 4.0
You said:
same basic reason a silverado gets better fuel mileage than a cherokee while making much more power and torque and having a bigger engine... it drives around at very low rpm... it climbs hills at a low rpm... it accelerates with very little throttle and at low rpm... it does't have to shift down to climb most hills... etc...
Drives around at a low RPM? Could explain that?
same basic reason a silverado gets better fuel mileage than a cherokee while making much more power and torque and having a bigger engine... it drives around at very low rpm... it climbs hills at a low rpm... it accelerates with very little throttle and at low rpm... it does't have to shift down to climb most hills... etc...
Drives around at a low RPM? Could explain that?
CF Veteran
Joined: Nov 2010
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From: North Carolina
Year: 1999
Model: Cherokee
Engine: Gas
You said:
same basic reason a silverado gets better fuel mileage than a cherokee while making much more power and torque and having a bigger engine... it drives around at very low rpm... it climbs hills at a low rpm... it accelerates with very little throttle and at low rpm... it does't have to shift down to climb most hills... etc...
Drives around at a low RPM? Could explain that?
same basic reason a silverado gets better fuel mileage than a cherokee while making much more power and torque and having a bigger engine... it drives around at very low rpm... it climbs hills at a low rpm... it accelerates with very little throttle and at low rpm... it does't have to shift down to climb most hills... etc...
Drives around at a low RPM? Could explain that?
FuelEconomy.gov says;
94 Cherokee 4x4 I6 Auto gets 14 City 18 Highway.
94 Silverado 4x4 5.7 V8 gets 11 City 16 Highway.
Member
Joined: Dec 2010
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From: or
Year: 1988
Model: Cherokee
Engine: i6 4.0l
Seasoned Member
Joined: Nov 2010
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From: Michigan
Year: 1998
Model: Cherokee
Engine: 4.0
I looked at that too. I also compared a 1998 Grand Prix GT with a 3.8 and the same year same engine but with a Supercharger. The non-supercharged one gets more MPG.
Member
Joined: Dec 2010
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From: or
Year: 1988
Model: Cherokee
Engine: i6 4.0l
CF Veteran
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From: North Carolina
Year: 1999
Model: Cherokee
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Just thought of a good example. Government's fuel economy website states that the regular 3.8L Grand Prix from 2000 gets 17 and 27mpg.
The supercharged 3.8L Grand Prix gets 16 and 25mpg.
The supercharged 3.8L Grand Prix gets 16 and 25mpg.
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Joined: Dec 2010
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From: or
Year: 1988
Model: Cherokee
Engine: i6 4.0l
that comparison is not valid. we are talking about putting a supercharger on a engine that was built to be NA. and asking if that increases fuel mileage.
Seasoned Member
Joined: Nov 2010
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From: Michigan
Year: 1998
Model: Cherokee
Engine: 4.0
CF Veteran
Joined: Nov 2010
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From: North Carolina
Year: 1999
Model: Cherokee
Engine: Gas
Member
Joined: Dec 2010
Posts: 100
Likes: 1
From: or
Year: 1988
Model: Cherokee
Engine: i6 4.0l
the point is A BIGGER MORE EFFICIENT ENGINE IS GETTING BETTER FUEL MILEAGE THAN A SMALLER LESS EFFICIENT ENGINE.
adding a supercharger to a i6 4.0l will INCREASE ITS EFFICIENCY ON AND OFF BOOST.
the extra efficiency added by the supercharger overcomes any parasitic loss to spin it. OR ELSE THERE WOULD BE NO POINT OF PUTTING THE THING ON THERE.
Last edited by JeepingDan; Jan 8, 2011 at 12:39 PM.