Advanced Engineering Tech - i want high hp(700+rwhp) and decent mileage

i got me a g8. i love the car and plan to mod the hell out of it. the basics along with a good sized turbo. this car will be bad ass eventualy.

my goals are to keep very near stock driveability, stock mileage when driving easy and at least high 10's in the 1/4.

here is the problem. this thing is a freeking pig. my stock mileage is very low. i am seeing 14mpg with mostly around town driving and not beating on it much at all. sticker says 15/24 but it turns out very few people are geting over 21mpg even on the highway with easy driving.

my new goal is the same as my old goal but now i want to signifacantly improve the mileage over stock. stock set up is a l76 wich i guess is some kind of bastard ls2/ls3 set up? it also has a 6l80e tranny and the car weighs 4000lbs.

since i plan on boosting it i could stand to loose a few cubes. maybe destroke the 6.0 with a 4.8 crank? anyone know where that would put the displacement? next idea is just drop a 4.8 in there, did they ever make an aluminum 4.8? if not then maybe an aluminum 5.3 with a 4.8 crank to make an aluminum 4.8. keep the cam on the mild side and run a ton of boost. duel fuel it so i can run 87 octane most of the time but still be ok when it gets into the high boost.

hell i got 13-14mpg in my stock 4wd silverado and 13-14mpg in my stock tahoe both with similur driving mostly in town as this g8. :confused:.

What RPM's does that car turn when going 70? what are the current trans ratios and final ratio?

1st Gear Ratio
4.027

2nd Gear Ratio
2.364

3rd Gear Ratio
1.532

4th Gear Ratio
1.152

5th Gear Ratio
0.852

6th Gear Ratio
0.667

2.92 rear gear.

calc tools says 1850 on the rpms. i dont know for sure without hiting the road.

I really don't think losing cubes would justify its self. My LR4 Sierra gets the same thing as one of my customer's 2wd Silverado SS truck (which is equipped with an LQ9 of course), maybe 1 or 2 mpg better if we're both stretched out on the intersate. I average about 18-19 with mainly country road/highway driving. I would think that a stiffer gear might help your city mileage. Maybe a 3.73 or even a 4.10? Taking the load off of the engine would undoubtedly help city, but of course you lose your highway mileage. Have you checked it on an interstate trip?

have you looked into getting a tune in the car?people are picking up quite a bit power wise,not sure about mpg wise.My friends stock 04 gto picked up 40rwhp and gained mpg cause the stock tune is very agressively done for IAT's.

Call Ron and Mike at Vengeance Racing..Speaking from experience if anyone can make you a high HP car with great MPG and excellent street manners it is them! :thumb: They have done a few G8's already. Agree with the tune... good tune will help with your goals as well! Just my0.2.

a couple turbos and 2.73's may get you there

i have no highway mileage numbers yet.

my first mod will be hp tuners. the shifting on this thing is horiable. i have a great local tuner and know a thing or two myself. i am not expecting much mileage out of the tune but the driveability has to get way better. thing is often confused as to when to shift up/down tm is out of hand.

i wont be doing any displacement drops anytime soon. might be something to try if i ever hurt the stock motor.

there are a few key areas you can look at

1. engine efficiency, can you operate in a more efficient (BSFC) portion of the map (gears)
2. Road load, items such as tires (compound, width, etc..)
3. Aero load, lowering, smaller mirrors
4. Friction, Driveline friction, FEAD friction (decrease belt tension/underdrive pulley)
5. Mass, weight reduction is a huge benefit.. for example lotus elise does 0-60 in 4.7 seconds and gets 43.5 mpg..
6. Transmission, that converter is eating up energy and not allowing your engine to operate in the most efficient zone (low rpm,high BMEP). Work on the converter lockup strategy
7. calibration strategy, trans shift points, DFCO, lean cruise, etc..

There are many ways to increase fuel economy, but GM decided the mix between durability, performance, and fuel economy..

don't sacrifice the cubes. just get a turbocharger and turn down the boost when you want to drive economically.

smaller cubes and higher boost should get u better mpg. How much wont be know till it built. Its a very heavy car which hurts the mpg.

My GTO 6liter get 26 mpg at 80mph interstate. But its a 11.1 compression and tunes to runs lean when putting along 6speed helps alot. When in city or im in boost at all that Mpg goes down fast. 750rwhp at 15 psi babying it i might get around 15mpg city

If your worry about Mpg while driving city. A big heavy V8 car is not what you want.

Interesting concept. High HP family street car that gets good MPG. Keep posting any mods with results. Very interested in your results.

I would bet, just by installing the turbo, and IF you can keep your foot out of it, the VE would go up, and it would pick up a little just from the turbo. It would be interesting to see. The HP tuners should net you some. Did you get a used one or new? Mileage? It might improve as the engine gets broken in???
I ended up passing on the G8, just didn't want to strap myself down with that much of a payment.
I picked up a 09 Malibu on the GM discount for cheap, it has a 2.4L Ecotec, and is begging for a turbo. I have a ton of room on this one. Maybe by fall I will start on it.

parish8 when you pick a project you want a challenge don't you lol. good luck on it and keep us posted i'm sorry i don't have any useful in site for you.

I would think power to weight ratio should be looked at. Maybe a bigger engine that work's less hard to move the weight wouldnt eat as much gas?