hey guys this might seem like a dumb question for some of you but i'm new to this whole thing so i'm gonna ask. Being that a turbo charger gives you more power by introducing more air into the combustion chamber, will it give me more gas mileage? Or will the ecu have to be adjusted so that the fuel input is increased as well? If the latter is the case, and I drive the car easy for the most part will my gas mileage stay the same or go down? And if down or up by how much approximately?

 

well, you can't slap a turbo kit on the car without dealing with the fuel management somehow.

I'm gonna tell you, no, right off hand.

If you want better mileage, drive slower. If you want more power, go forced induction.

 

When you are doing 75 mph on the highway, yes, and when you step into it, no, all in al, it will probably average outabout the same as before. I have had twins for over a year now, and I average around 300 to 325 miles on a tank of gas.
One more note...You are sure to have alot more fun driving your car!!!!!!!!!!!!!
and that alone, should be the reason for going F. I. Enjoy!!!!!!!!!!!!!!!!!

 

at cruise it's not going to give better mileage than stock....why would it? chances are likely you're running larger injectors to compensate for more air in the engine=more fuel=worse mileage.

 

I lost about 5 mpg since going turbo a year and a half ago. Went from an average of 26 mpg to 21 mpg. Of course, it is very hard to keep my foot out of it, a lot harder than before TT. I think it would only have been a 2 -3 mpg drop if I could drive normally.

 

In a normal cruise situation with the management system tuned properly you would have similar fuel mileage. The turbo system will not require additional fuel below 103.5 kpa (in a vacuum situation). This is the area of mapping in the ECU you will be driving in most of the time.




I hope this helps my friend.
Chris Macellaro

 

I'm getting a consistant 13.5 mpg with N.A.

 

If you're serious, then there is something very wrong with your car. I don't get less than 16 mpg in all city driving, using my gas pedal like an on/off switch...

...and that's with my mods!

 

+1

 

26 miles to the gallon???wtf i only get 20

 

Just cruising alone I had wayyyyyy better gas mileage Turbo'd than n/a.. On a trip from my house in West Atlanta to Charlotte, NC the nav said I averaged about 35mpg.. I would think it was incorrect if I didnt make the entire trip on a 3/4 tank of gas. I do not think I ever hit full boost on that trip though, when I drove aggessively that gas mileage went down to 10mpg.

 

AS N/A i'm averiaging 28.2 - 28.7 on criuse when I drive to places like San Jose, Los Angeles, Santa Cruz It also has to do with roads flat. When I do the twisties, mountains, etc. I'm only getting 19.2 - 19.8 mpg. This is current. Before the NISMO Headers, Exhaust, and CAI, I was around 24.5 - 25.6 on plain stock. I am also going FI before end of this year, as I have the APS TT sitting in the garage now. I agree as long as you don't put the foot in it, gas mileage will be good as before, but each time you step on it, then it's like a tiny little leak in the tank. But then, why would we not step on it, that's what FI is all about anyway. Enjoy it, I know I will.

 

Installing a turbo kit is in no way going to inprove mpg significantly. Like said, at cruising speeds, it should remain the same. Remember, because of boost, you will be adding more fuel than you did when N/A at all times.

 

You can get close, but never better. Even if the engine's C/R was the same, the turbo's put considerable backpressure on the system which hurts your power. The power you need to cruise at a given mph will require more work off boost due to this backpressure than it would have stock N/A. With the additional weight added by the system the mileage will also be slightly worse. Also, the high fuel pressure and/or injectors means part throttle will be richer than with smaller injectors no matter how good the tune. As an example, 750cc injectors can't be as efficient at part throttle as smaller 333cc injectors. The smaller injectors can better handle the less fuel injected for part throttle cruise. These are all answers to the same question asked in Corky Bell's book on turbo's.
Will

 

I'm sorry, but there's absolutely NO WAY that it's possible to get better mileage with turbo than n/a, period. It just will not happen. I don't care how you drive. Even when I'm at my best, I'm doing 25mpg tops, on the highway at gentle cruise.

 

Is that 5AT or 6MT?
I am barely getting above 15 in city driving on 5AT.

 

The reason you think you're getting better mileage with the onboard computer is because some of the systems (I know BMW's is like this) measure fuel injector pressure (as in load). The system is tuned to the stock injectors. For example if the stocks were 200cc (easy number) and you need 50cc of flow to cruise at 70mph, the computer would know you are getting x mpg because it's tuned to know that 25% fuel load=50cc and it divides it by speed, etc. But if you upgrade to 400cc injectors, and you're cruising at 70mph, you still need 50cc of flow, but the computer only knows you're using 12.5% of the load, so it thinks you're using 25cc of fuel and getting much better mileage.

Does that make sense?

 

Bottom line is this: It takes more fuel and oxygen to make more horsepower, and only oxygen is free. As described so eloquently above, even if you keep your foot out of it, you're still likely to get worse mileage with FI. And even when you're not standing on it, ANY aggressive driving will kill gas mileage because your A/F will likely be at ~12:1 whereas your OEM was considerably higher under the same conditions. You have to pay if you want to play.

 

I get about the same. City driving sucks though.

 

Hello!

You are speaking about a very small amount of degradation of Volumetric Efficiency with the pressure ratio drop across the engine due to a possible restriction that the turbo off boost may or may not cause. In my experience I have found only on very restrictive and inefficient set-ups have a very negligible drop in VE due to the turbo inlet posing a restriction. With most of the current systems out for these cars this is not a problem and I would not worry about this issue my friend.


This is the reason for closed loop to trim pulse width. Although using a large injector such as the 750 cc/min you have stated on a completely stock ECU would be far out of the realm of closed loop correction. Most piggy-back and Standalone ECU's on the market allow for trimming and scaling injectors and pulse width. Again with a proper system/injector selection/tuning you can have similar fuel mileage as the factory realized. As long as other major modifications that effect VE have not been made. The average bolt on turbo kit if tuned properly will not affect economy as said above.


Cruise Horse Power is again negligibly changed. In my experience most vehicles need very little power to actually run down the road once up to speed. Steady state most modern vehicles fall into the 15 -50 hp range needed to maintain speed steady state.


All due respect to Mr. Bell and no disrespect meant. Mr. Bell's book has some good theories and practical equations. In my line of work and business I am afforded the opportunity to test tuning theories and mathematical equations on actual working examples of these situation/engines. I have been fortunate to be able to apply what I have heard and learned from others and have been able to find what works.


Have a great day sir.
Chris Macellaro