So this past year I slapped on a vortech V-3 system with a haltech full standalone EMS and DW850cc injectors with a walbro 255lph pump, had the car tuned making 420whp 365wtq, trying to figure out as to why I am only getting 8mpg out of the car??? It does not appear to be leaking any fuel anywhere not out of the tank and not in the engine bay....I can't seem to figure out as to why I have such terrible gas mileage....anybody have any thoughts on my situation?

 

I'm planing to go SC, with the same configuration, so I'm interested too!

 

What are you doing/using to measure the MPG?

 

I am taking the amount of miles I am driving (just under 100 miles) and then dividing the gallons that I am putting in (approx 12 gallons per time) to measure MPG.

 

I suspect you are getting the poor gas mileage because you have a supercharger making 420 horsepower.

 

Lots of city streets with idling at red lights?

 

Are you at 100% throttle all the time? What's your af/r at boost and cruising speeds?

 

I'm averging 8-10 miles on my Vortech...on e85...

 

My vortech is making 426 and with a heavy foot I get 17mpg, so no it's all how you drive and how your gears are set up. Why do you think corvettes with over 400 hp make close to 30 mpg.

 

Your injectors are overkill and maybe you're running rich. Who did the tune.

 

Sounds reasonable to me. Also depends on if you're doing a lot of city driving and acceleration.

 

The Corvettes of which you speak are undoubtedly stock. Put a supercharger on the Corvette and see how the mileage drops.

 

I had a C5 Corvette (stock) with a an A&A vortech S/C kit on it....made 500whp....@ 7lbs of boost

Got about 14 city, 25 hwy......biggest problem was traction.

I suspect its your tune......(whats your AFR through the RPM range?)

I recently grabbed a 350Z and would love to add FI, but....just haven't seen a good recipe yet.

 

Poor Tuning!

I get 26-28 Hwy @ well over 500whp

 

What he said. Yes, SC will decrease mpg but not at that rate.

 

I had the car tuned at PFSupercars, hardly ever in WOT anymore not much city driving at all up by me either yes my injectors may be a little big but the gas mileage should not have dropped that much, I mean I drove the car back from MD to NY 500+ miles the day it was tuned and made it back with only having to fill up once and now I am filling up every other day.....so the tune should be fine changed out the plugs made sure everything is good just not understanding why I am having this problem now....

 

Important question: What AFRs do you see on your trips to work?

You say the tune should be fine, but without monitoring your AFRs you don't know for sure. There are many factors that could effect your tune or cause the computer to think your car is lean and add more fuel when it isn't needed. The haltech will control the injectors so having larger injectors is not a bad thing as long as your ecu can manage them properly. The haltech has a very robust o2 control/fuel compensation table system that will add fuel based on certain parameters. You need to log your drive and see what your AFRs are. If you are running rich then you can troubleshoot the correction tables.

it took me several weeks after initial tuning to fine tune the haltech tables to get my AFRs where I wanted them while cruising which lead to consistent AFRs and better gas mileage.

 

Damn some day i want to learn to tune like you!

 

^ so do the Nissan tuners as thats almost 20% better than stock.

If he pulled the plugs, if the car was running that rich, then the plugs would be black. I get better than 8mpg on E85. To burn that much fuel, your car would run like **** as well.

 

If he's getting 8mpg and the back of car isn't covered with black soot(rich), then he's leaking fuel.