power to mileage

[shawnxj]

ok so i've done a little searching around and i see mileage numbers all over the place. i recently rebuilt my 88 renix block and it runs pretty good but i'm contemplating either stroking the renix block or switching over to a obII h.o. block and stroking it. basically what i want is good power and better gas mileage with more tunability. would going with an obII setup work for the tunability or should i go the painless fuel management route? now i already have a 450 hp 350 in my truck for when i just wanna do stupid things and don't need anything outrageous in my jeep but i would like to see somewhere in the 250 hp 300 ftlb area and still get around 20 mpg. also keep in mind i'm running 5.5" of lift with 35's and 4.88 gears on an aw4/242.

are my desires even possible? what's the most power i can make and still keep the mpg in the 20 range? how much harder would it be to get to mid 20's like i saw some of your guys doing in the couple searches i made?

[1bolt]

hmmm the 5 inch lift, 35's and AW4 are going to make your chances of getting 20mpg pretty slim I imagine.

With 3.5 lift 33's (only 10.5 inches wide) 4.56's and AW4, all synthetic fluids, I've gotten 20mpg on occasion long freeway trips exclusively (4.6L with an RV cam) but normal driving it is much closer to 17-18 mpg.

My wifes stock 97 XJ with a scan gauge installed only manages a little over 20 MPG on the freeway as well. usually averages around 19mpg in normal driving... That's honest averaged MPG not your typical tall tale MPG. Like: Yeah i filled up with 10 gallons (really 12) and went about 300 miles (really 260) I've got mileage spread sheets for every vehicle I have for as long as I own it. I put the real mileage in and the exact gallons, and I fill up at the same pump when possible.

The main issue with Jeeps fuel economy wise really is aerodynamics they are bricks plain and simple. The 4 banger only gets a MPG or two better in the same vehicles.

[lafrad]

well, depending on where you drive, a stroker can help with mileage... more torque to hold a gear, instead of shifting, helps QUITE a bit.

Also, dial that compression ratio up far as you can go on your fuel of choice, and there is extra MPG.

20 mpg with a lift and aggressive gears/tires? well... lets just stick with: mileage will probably be *better* with a stroker. no number guarantees

Now, about how to run the engine.


Stay away from OBD if you can. get the new block, optimized head, exhaust.... all the physical, engine parts... get a nice after market PCM with sequential fuel injection and the ability to control spark (if you can swing it, go for the distributor less stuff... it just plain runs better). After market lets you FULLY tune the engine, and that will give you great MPG AND power/drivability... OBDII will just limit you to how a stock OBDII vehicle behaves.

[shawnxj]

thanks for the replies.

now for aftermarket computers who should i be looking at? i know painless has 1 and so does edelbrock and holley if you buy their fuel injection kits

[Shark]

thanks for the replies.

now for aftermarket computers who should i be looking at? i know painless has 1 and so does edelbrock and holley if you buy their fuel injection kits

pardon my ignorance but why go though the troulbe and expense of an aftermarket computer instead of just a MAP adjuster?

[RAPTORFAN85]

pardon my ignorance but why go though the troulbe and expense of an aftermarket computer instead of just a MAP adjuster?

With an aftermarket computer you get more controlability (if thats a word) then with just a MAP adjuster. The MAP adjuster changes the values over the whole RPM range. A system like the Apexi for example can change the AFR at certain points in the RPM range. Say that you had a lean spot at 2500-3500 RPM, you could dial in more fuel just in that RPM range, not over the whole RPM range like a MAP adjuster would do...

[lafrad]

well, in closed loop mode, no matter WHAT computer you use... you will have the same fuel consumption per RPM per MAP pressure.

Where a standalone is nice, is having a custom timing map. That can give you MUCH better mileage if you can optimize timing in your high-vac cruising areas.