Bimmerman

First post.

Can anyone recommend a setup to get highest mpg possible the motor will go into a 2700lb BMW e30( stock 121hp) all the labor will be done in house I'm wondering which motor will give me the best mpg 4.8,5.3, or 6.0. stock hp will be a 3x improvement so hp isnt a concern.

jetech

The 4.8l being the smallest will provide the most economy for your build

Keith

Don't forget about the 5.7. Check out this guy's video.

LS1Formulation

iTrader: (13)

There's a balance between engine displacement and car weight/drag when it comes to getting good MPG. If your engine is too small, you end up pushing the throttle down more to get the power you need and end up using more fuel. I wouldn't use a 4.8 for this reason. An aluminum 5.3 would be the only choice I'd consider. My Formula, when stock, got 30 MPG on the highway with a 5.7 and a T-56. Your trans and gear ratios come into play for this as well. My T-56 has a .50 6th gear and the engine only turned about 1300-1400 RPM at highway speeds, using a 3.42 gear. Build your engine for great part throttle torque and your MPGs should increase. If wanting to stab an engine in bone stock, I'd look for an L33 5.3 liter. The price increase to get ahold of a 5.7 isn't worth it. I'd only use one if I could score it cheap.

wretched73

6.2 LS3 with dry sump oiling

Y2K_Frenzy

I agree with what you’re saying about small motors & heavy cars, but his only weighs 2,700 lbs. So I think almost anything would suffice as long as he has realistic expectations of 20 some odd mpg’s combined city/highway being “good,” and not 30-40. I think you also hit the nail on the head regarding the transmission ratios and rear end. If I wasn’t trying to go fast I think I’d put the cheapest and lowest mile motor in that I could afford and call it a day. Stock cam and all. If I was trying to get the break MPG records I probaby wouldn’t be V8 swapping it.

68Formula

The 1st generation Blazer S10s were a great example of how too little displacement can make mileage worse. The 2.8L V6 got terrible gas mileage, and when they went to the 4.3L, it actually improved. I even had a friend with an early version that did his own swap when the 2.8L died, and his mpg improved as well. Same deal with the iron duke 4 cylinder Camaros vs. their 2.8L V6 counterparts.

That being said, I wouldn't flinch @ a 4.8L pushing 2700lbs. It's not going to have to work hard to accelerate that little of weight. But, the aluminum block L33 5.3L idea has some merit in regards to mpg for a few reasons:

• Better F/R balance comparing to the original BMW motor
• Less mass to haul around
• 9.9 compression

Add underdrive pulley system, drop in a Summit 8727R1 200/205 113+4, set of 1 5/8 long tube headers and good flowing exhaust. With a proper tune it'd be more efficient than stock and probably have ~375hp (400hp with a NNBS intake and 90mm throttle body, but that wouldn't measurably change mpg in either direction).

Next level would be to get a PCM with the OS capable of enabling lean-cruise.

TrendSetter

As someone that built an aluminum 4.8 for fuel economy a long time ago, I would do an aluminum 5.3.

Bimmerman

Thanks for the replies guys. This seems like it be the most cost efficient way to achieve my goal , I'll mate it to ZF 8hp and hopefully i can get 30mpg+ . The guy that made the 40mpg corvette seems to have it figured out with running his ls1 lean. 30 mpg plus should be doable with the L33 8hp trans and the right tune