Piston Slap: The Making of the BMW M3 "Big Tank" Edition

John writes:

I own an E92 M3 and it’s my huckleberry, except for one thing—with a gas tank capacity of about 16 gallons, road range is a measly 300 miles between fills. And when I drive, I want to drive.

Every other car I have owned has been able to do 400 miles on a single tank in highway driving with the exception of my STi, which only did 330 before rapid maneuvers caused temporary starvation.

So my question is this: is it possible to fit a larger gas tank to my car—say one of about 20 gallons or so? If so, what are the positives and negatives of this, and where would I get one?

Sajeev replies:

Back in the day, GM had you covered. Anyone remember the 36.5 gallon “ Big Tank” option Chevrolet offered for the Corvette in the early 60s? Back here in Bimmer world, you have two opportunities for installing a 20-gallon tank in your M3. Only one is guaranteed to work.

I have never seen the underside of an E92, but I do recall the M3’s rear mufflers being pretty gigantic. Which means you remove them, run tiny mufflers (like Dynomax bullets) and route both pipes on one side. (Get some ear plugs too.) Only then will a 20-gallon fuel cell fit. Maybe.

If that’s out of the question, how in love are you with your trunk? That’s the only sure location for an E92 with a big gas tank. If either way is feasible, getting the tank is easy: any race shop stocks these fuel cells. Dimensions are readily available too. There are plenty of E92s set up for race purposes, and you will emulate their wiring/fuel pump/safety setups for your car. Not exactly easy, but it’ll be easier than you think.

P.S.: Doing an LS-X powertrain swap with the F-body’s 6-speed transmission (with that insanely tall top gear) might get you to the magic 400 mile mark. Think about it: that powertrain means you can idle at 55-ish MPH. That, and the V8 M3 will be disgustingly fast and light. So, again, LS-X swaps are still made of WIN.

[Send your technical queries to mehta@ttac.com]