Longer Stroke?

[MadisonMPG]

Originally Posted by TheEnemy

AMC 258, I had the stroke wrong, its 3.895.

Its for an old CJ7 primarily for off road use, I'm trying to build good performance for the low end, and still keep an eye on fuel economy.

wat

[beatr911]

The roller valve train is a popular mod for reducing friction, it certainly wouldn't hurt mileage iether. Piston and head ceramic and friction reducing coatings seem like a good idea for a high output engine. Helps control heat issues. They have DIY products these days so the cost may not be too bad. I'd try it if I was rebuilding.

Be sure to play with cam timing. I advanced my Ford 2.3 OHC cam 9* and got a very noticeable boost in low-end torque. Easy and relatively cheap. Shortly after, I went to bigger and heavier wheels/tires so I can't isolate the cam timing change mileage effects.

[wagonman76]

My experience is that the longer stroke does help. I noticed this over 10 years ago, long before trying to hypermile.

The only difference between the 2.8 and 3.1 MPFI engines is the stroke. Same everything else. With all else equal on the car, they run off the same ECM and chip.

I have had several A-body wagons and sedans with these engines and in every case the 3.1 has a lot more torque and gets better mpg than the 2.8. All had the same trans with 3.33 final drive. Miles on the engine did not matter. The 3.1 can climb most any grade in OD and seems to move along effortlessly. It feels like a workhorse, like a diesel. The 2.8 is pretty much hopeless in that department.

[beatr911]

Don't know if they have low tension rings or single ring pistons for an engine your size. The only reason I mentioned it was that the MPG optimized Metro XFi uses single ring pistons. One sealing ring and one oil control ring vs. the usual two sealing rings and one oil control ring. Total Seal I hear makes "gapless" rings which may be a help.

I love dual purpose vehicles that do it efficiently. Some day I hope to have a fun autocross/track day car that gets 40+ mpg on the street. I applaud you for considering good mpg with good off-road capability, it shouldn't be mutually exclusive.

[TheEnemy]

Maddison: Lower fuel consumption = more play time, and I have yet to find a gas station, let alone a working gas station on any trails.

Waggonman: That may have as much if not more to do with the whole engine tuning. Similarly Chrysler has a 3.8l V6, a 3.3l flex fuel V6, and a 4.0l V6 that they put in the town and country minivan. The 3.8 puts out nearly as much HP as the 4.0, but at a higher RPM. The 4.0 also gets 1mpg better city and 2mpg better highway mileage. The 3.3 when running gas is supposed to get the same city mpg, and 1 less highway compaired to the 4.0. Possably because it is a little underpowered for highway speeds. Unfortunately Chrysler decided to put the 3.8 into the current line of Wranglers, off roaders have been complaining about its lack of power at lower RPM's.

Beatr: The engine has 158k hard miles on it, its due for if not past due for a rebuild. Are those the rings that circle twice kind of like keyrings, if so I have been considering those, they should seal as good if not better than a double or tripple conventional ring, with the added bonuses of not having the time consuming task of setting the gap on the rings, and not increasing the gap as the engine wears.

Several of the local Auto-X guys report peak MPG in the low to mid 30's, and they are generally not easy going on the skinny pedal. It shouln't be too hard to get one into the high 30's or low 40's and still perform decent on the track.

[wagonman76]

I love dual purpose vehicles that do it efficiently. Some day I hope to have a fun autocross/track day car that gets 40+ mpg on the street. I applaud you for considering good mpg with good off-road capability, it shouldn't be mutually exclusive.

Me too. I used to use my old 6000 wagon to tow my 5x8 enclosed utility trailer, quite often too. It actually towed it better on the highway than my Trans Sport van with 3800 does. I also used it to move back and forth from college, I could fit my hideabed loveseat in the back along with a ton of other things. The back would also perfectly fit a twin bed mattress and I would go camping with it. It was a monster in the snow. I could clean it out and take the whole family places. I took it down seasonal roads and 2-tracks sometimes. I still have the car, I designed a small plow for it have been using it to plow my driveway since 2005. Hands down the best car I ever had.

Waggonman: That may have as much if not more to do with the whole engine tuning.

When I swapped the Celebrity from a 2.8 to a 3.1, I didn't retune it or anything. Just bolt in and go. Went from 29 mpg to 32 mpg on downstate trips.

[Bicycle Bob]

A stroke change that does not need new pistons or rods will have very little effect except on compression. Long strokes don't directly affect torque, etc, but they allow relatively less valve area, so the available power band is lower. For a low-speed, high efficiency engine, the camshaft is the one to change.