smokeshow

iTrader: (16)

More power = more fuel. Period. A higher power (peak power, mind you) to weight ratio does NOT mean better fuel economy. Otherwise, we'd all be driving around with 632 big blocks, would we not? According to that theory, anyway...

Now higher average power, meaning power under the curve, will net you better fuel economy. Out of boost the turbo isn't making more power. If anything at all, it is creating pumping losses on both the intake and exhaust side due to the turbo being a restriction on both ends. The losses are minimal, but they are certainly not gains.

baSICK5.0

iTrader: (1)

True. But with this logic the parasitic drag of your Superchargers resistance to turn and the restriction in air flow due to your Turbocharger should really kill your engine and net you like 3 mpg.....BUT WAIT...WHILE IT DOES DEMAND MORE FUEL, IT INCREASES THE POWER AND MOVES THE VEHICLE EASIER BECAUSE OF THE ADDED POWER. THE INCREASE IN POWER AND CHANGE IN WHEN/WHERE THE ENGINE MAKES POWER MAY BE GREATER THAN THE PROPORTIONAL ADDITION OF FUEL, THUS NETTING MORE MPG EVEN THOUGH ITS USING MORE FUEL THAN N/A.

IDK I dont know nothin. I dont have a supertruck with quadboosted trunk mounted turboNOSers and greddy type SRTZXK4 blow mehoff valves.

lownslo

iTrader: (3)

truthfully bud, a turbo will not gain any mpg. the tune might help you but realistically you can't gain any power out of boost with a turbo, on top of that you can't prove that It would. Its similar to an Electric supercharger, if your K&n flow xxx cfm freely and you buy a super charger (electric) that flows xxx-xx cfm then you are restricting the air flow. You then take into consideration the weight added and not only the restriction of the turbo not making positive manifold absolute pressure, but the restriction of the exhaust exiting the chambers..... it causes a flow issue while the turbo is out of boost. Can you gain mpg with a turbo, sure......can you lose mpg with a turbo, sure.......can you prove either.....no!

baSICK5.0

iTrader: (1)

Im not saying you can build power out of boost. But why cant this happen like so:

take a 4.8 ecsb. Motor isnt great for towing the heavy truck around. You must use x% throttle to drive from 0 - 55 mph in 1 mile.

Install a turbo on that same truck. the engine make more power and YES uses more fuel at WOT and at the same % of throttle than before the install BUT It doesnt take X% to get the same results in performance as before. it only take y%. Less % of throttle, and possibly less fuel once the factors are all laid out.


What Im saying may not mean a dang thing but Im just thinking that if a turbo is very carefully seleced for the application and is efficient the power/speed increase capabilities vs fuel increase wont be a 1:1 ratio thus not 100% gonna get less mpg.

My idea is that you can gain more say 50% more power and use 25% less throttle while only adding say 25% more fuel. idk

who says the 50% more power demands 50% more fuel?

baSICK5.0

iTrader: (1)

also just curious what kind of power increase did you see and how much mpg loss?

cjg454ss

iTrader: (27)

a turbo does not have to be in boost to be helping an engine, 5inhg vacuum is better than 15inhg vacuum. you dont need 5psi of boost to say a turbo is helping. also if you can drive around the truck under 2k rpms just say where before you were at 3k rpms but now have increase the low end torque to move the vehicle...you will help mpg. ...and dont start with that . PERIOD bull$hit.

baSICK5.0

iTrader: (1)

This is my logic as well.


lol at the PERIOD.

lownslo

iTrader: (3)

i started with a 5.3 stock, 17.2 avg
went to 6.0 with ls6 cam and yellow springs, 15.4 avg
turbo on 7 psi, 14.2 avg
stock made 278/289
6.0 made 301/347
7 psi made 480/504 on safe tune
10psi made 513/567

there is a direct relation here. I see your logic and while yes staying out of boost will net better fuel mileage, you can't possibly put in all the factors. An cjg you are incorrect, 15 inhg of vac is better than 5 inhg. You want to stay as far away from boost as possible to increase the chance of better fuel mileage. It takes less throttle to get to zero on the boost gauge than before, so staying in vacuum is harder and the fuel comes in sooner with a turbo......there is so much here that factors into this, I don't even feel like typing cause its a never ending debate......

I will say the truck is more responsive down low and cruising along but, the fuel it needs to meet the demands of the turbo are far greater than when stock. My truck gets decent mileage on the highway due to the vac staying so low but stop and go has been affected greatly.

so don't buy any FI to increase fuel mileage........

smokeshow

iTrader: (16)

What you are not taking into consideration is that mileage is not simply a linear function of RPM. You have to consider engine load. If you were at 15inHg before and you suddenly increase to 5inHg manifold pressure, it does not mean it is more efficient. It means there is more load on the engine, therefore making the throttle open more and consuming more fuel in the process.

If you were to graph power vs engine efficiency in terms of fuel economy, you'd notice that it is definitely a negative exponential graph. The more power you make, the more that graph is going to quickly become less efficient. So, if your truck makes as much power at 2000rpms with a turbo as it did at 3000rpms without one, even assuming the same engine load, you'll still consume more fuel at 2000rpms with a turbo.

Does that make sense?

JoeyGC5

iTrader: (24)

My 2005 2500HD crewcab on 35's is very fun with KB's MP70 kit. Tows very well, gas mileage is as best as can be, and I've had 0 issues with the turbo kit in 14k miles.