At a previous job I worked for a company that made motorsport/tuner related products.
They had an agency for Eaton superchargers.
I remember someone claiming that a supercharger could increase your fuel economy.
On one had I can see that more power would mean smaller throttle position for the same highway speed (theoretically).
But on the other hand there's more mechanical drag/loss of turning a supercharger.
Anyone got any hard evidence one way or another?
There's a thread on here somewhere that talks about a custom made car that had about 600 whp in a Dodge Stratus with a Mitsubiushi (sp?) 3.0L and a higher geared tranny. He actually got a bit better mileage out of the car at cruise than before the modification.
If a car has forced induction coupled with higher cruising gears, it can get better mileage. It's also becoming popular for OEM vehicles to be turbocharged and fitted with a smaller engine for economy. Basically if you can make enough hp at very low revs by forced induction, you come out ahead.
You just have to keep your foot out of it
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Quote:
Originally Posted by jamesqf
I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
Last edited by ShadeTreeMech; 11-15-2010 at 07:16 AM..
Forced induction allows the use of a smaller displacement engine, which under non boosted situations would allow higher BSFC operation because the normal loads would be higher than the normal loads on a larger displacement engine.
When you use taller gearing you get better mileage for much the same reason, lower rpm and higher load, even if the displacement is the same.
Ford is doing that with their ecoboost engines, so it has become mainstream.
Better transmission gearing and more speeds in the newest cars as well as dual clutch automatics get better mileage, but in reality the new 6 speed dual clutch transmissions are not automatics, but automated manuals.
If you supercharge and engine you can get more air and fuel into the combustion chamber. That will only give you better mileage if you use fewer total engine revolutions per mile to travel, since if the supercharger will use more fuel per revolution if you use any boost.
It can definitely work, if it build enough low end torque to push very tall gears. It also has the benefit of making efficient vehicles that aren't total slugs when you punch it to merge, which lots of drivers appreciate.
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Call me crazy, but I actually try for mpg with this Jeep:
Typical driving: Back in Rochester for school, driving is 60 - 70% city
So in a similar vein, a bigger motor with more torque & tall diff gears would get better mileage?
I'm using the stroker kits for V8's as a point of reference.
I'd suggest reading the thread ShadeTreeMech posted. It'll clear things up. I can pretty much guarantee a bigger engine will decrease mileage as will a stroker kit. Taller gears definitely will improve mileage.
The problem with SC is you have pretty high crank drag from SC, unless you build in clutch and bypass but then your not getting any benefit at cruising speeds.
Turbo is the way to go your using free exhaust power to turn turbo. Even with same engine size you an get slight mpg boost but most times is best to lower engine size by like 25-30% to get real good mpg increase .
Turbo is the way to go your using free exhaust power to turn turbo. Even with same engine size you an get slight mpg boost but most times is best to lower engine size by like 25-30% to get real good mpg increase.
...as well as the static compression ratio, from typical 10-11:1 down to around 9:1 or so.
...and let the blower "relief" value dynamically 'control' the actual working compression ratio.
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