Gas mileage J-10 build ideas

What I'm thinking about is building an engine around 200 inches and putting a small turbo on it for gas mileage in a J-10. Low compression (8:1 would be fine), 5-6 psi (no more than 10 max, and don't really want that much), all boosted out by 3000-4000 rpm. So a four cylinder turbo will be fine, and also have little to no lag. I just want 4.0L power (around 200 NET hp @ 3500-4000 rpm -- that would be about 265 GROSS hp, off a crank dyno with no accessories) with a smaller displacement. With the turbo increasing power and torque this should mean having good power and burning less gas.

Right now I'm exploring using a 3" stroke 199 crank in a late model 232/258 or 4.0L block. Need the 71+ block for good transmission selection. The pre 71 block has a 1/8" shorter deck height. The 199 has shorter rods than the 232. When the deck height was raised in 71 to allow for the longer stroke needed for the 258 the same 199 and 232 rods were used -- the 199 rods were used for the 71-79 232 and the previous 232 rods were used for the new 258. Bore remained 3.75". I might just have to keep the 232 displacement to keep costs down, or use a 4.0L block. Don't really want to spend a lot on custom pistons. I plan on using a blow-through turbo and 390 cfm Holley carb on a Offy DP intake, not EFI.

The idea is sort of like the Ford T-bird turbo coupe -- 2.5L four with the performance of a 5.0L V8 model (1985 model 2.5L turbo = 150hp @ 4400/240-lbs.ft. @ 3,400 RPM; 5.0L V-8 = 150hp @ 3,200 rpm/270-lbs.ft.@ 2,000 rpm).

I've got a Ford turbo 2.3L with five speed in the back now --- maybe I should just drop that in the J-10? The main difference will be when torque peaks and comes in -- much higher rpm than the 258 or a 3.3-3.5L I-6. A stock 83 258 peaks at 110 hp @ 3000 rpm, 205 ft/lbs @ 1800 rpm -- 1400 rpm less for hp, 1600 rpm less for torque. Some of that can be made up with gearing though. The five speed should have a lower first gear, and I'll be using 4.10 gears with only 30" tires. XJs used 4.10s with the 2.5L -- @ 2500 rpm with 4.10s 54 mph in 4th, 78 mph in OD using 30" tires. That's more like it!  Might be doable...

I wonder what 4x4 trans I could use -- Jeep CJ T-5?? The AX15 won't bolt to the T-5 bell housing, but I don't know what the input shaft length on the Ford 2.3L T-5 is (it's from a Merkur XR4Ti). Don't want to go 2WD, but I probably have enough length with the long bed pickup to do a divorced t-case... Will have to research Ford 4x4 trannys.

Read and tell me what you think! I first considered the 258 with a small turbo, but that won't help the gas mileage much. Should a little since overall engine efficiency should come up a bit, and the engine won't work as hard with the turbo, but a smaller displacement with the turbo is really the best way to go.

The four actually burns no more gas than the six even though it's turning a bit more. Two fewer cylinders sucking it all in. On the flip side it's not really burning much (if any) less either. For a decent comparison, the 2.3L turbo coupe with five speed was rated 16 mpg city, 24 mpg highway, 19 combined. The 302 T-bird with AOD was rated the same. Auto 2.3L turbo was 15/21/17. This is from http://www.fueleconomy.gov/feg/bymake/ford1988.shtml.

The 4.10 gears in my truck is the killer. I thought I had 3.55, they were stock, but this old farm truck was ordered with a 258, three speed manual, and 4.10s! The four will like the 4.10s a lot better than the 258, even with a five speed OD trans replacing the three speed. If I keep a 232/244/258 I'll be using an AX15 from a Cherokee -- 0.79 OD. That puts me at 55 mph@ 2000 rpm in 5th, 2540 rpm @ 70 mph. So 70 would be about the top cruising speed. A 31" tire brings rpm down to 2460 @ 70, a better choice. 33s down to 2310 rpm... but don't really want real big tires. Might have to get some Grand Wagoneer axles, 3.31 and 3.55 gears more common. A Mazda M50D was used in Rangers and has the same OD ratio. A 0.70 OD sure would be better, drops 300 rpm! But the four would need it...

So what do you think you would do? Street truck, light hauling, want decent gas mileage -- 20 mpg+ highway cruising (60-70 mph). J-10, prefer to keep the 4.10 axles. Engine is the main thing now, pretty fixed on a five speed manual (seems like the obvious choice anyway). Tire size is changeable. 232 turbo? 258 NA? give the 2.3L turbo a whirl??

Since I haven't built an engine yet, just have the frame done, I've been thinking a lot about this. Maybe the only way practical way to keep the 4.10 axles and get decent gas mileage is to use the 2.3L turbo motor, since I don't really want real big tires. A 232 wouldn't be turning excessively at 2500 rpm/70 mph, but wouldn't do a lot for gas mileage. 3.31 or 3.55 gears and smaller tires would be a better combination. With 3.55 gears and 30" tires 2500 rpm would be 80 mph, 2200 @ 70 mph. But then 60 mph would only be 1884 rpm... with a good torque cam and no load that would be about the slowest you could go in OD. 55 mph in 4th (1:1) would be 2186 rpm... not bad at all. 3.31 would be a bit too high -- OD would be useless under 70 mph  (85 @ 2500 in OD, 2050 @ 70; 55 @ 2039 in 4th). I'm still considering 2000 rpm the best steady cruise speed though a torque cam will cruise at a bit under, as low as 1700 rpm. Pushing a big brick down the road/through the air will load an engine pretty heavily as 1700 rpm though. At 2000 rpm it's well into the torque band and not working real hard. 3.73 gears were popular in Grand Wagoneers, but the minor change (2310 @ 70 in OD vs. 2500 w/4.10) may not make it worth the effort. Still, 200 rpm might make a noticeable difference on long distance cruising without taking much from the low end. The AX15 has a 3.83 first gear though, pretty low (total gear reduction in first with 3.73 gears is 15.29:1 -- 15.70:1 w/4.10). My 83 J-10 had a T-176 w/3.82:1 first but only 2.73 gears (10.43:1 total). Had to slip the clutch to take off with no load, but the engine was about worn out. Not enough first gear, and 4th was about like an OD trans.

I think I'll keep the 4.10 axles for now no matter what engine I decide to go with (trans will be a manual five speed no matter what). I can always change the axles later at little cost as long as it's a common Wagoneer ratio. The only thing is the Wagoneer used axles that are about 4" narrower than the J-truck in the rear, 5.5" narrower in front. Swapping complete axles would be a problem. 2" wheel spacers are $70-$85 a pair, 2.5" around $90/pair. Cheaper than swapping ring and pinion though.

I'm using this as a sounding board, just in case you didn't notice! I'm open to any ideas. Cost will be a consideration, but I can find most of what I'll need from the local salvage yards. There's a Jeep shop about 45 minutes away that might like to have those 4.10 axles and should have some 3.55s they'd swap (entire axle assemblies, not just gears).

Well, I just found out that the Merkur 2.3L turbo five speed motor puts out more than the T-bird Turbo Coupe motor -- 170-175 hp (depending on website) vs. 150 hp with 12-14 psi boost. I won't be running a cat converter...

Merkur specs:

ENGINE

Type - turbocharged 4-in-line, iron block and head

Bore x stroke - 3.78 x 3.13 in. 96.0 x 79.4mm

Displacement - 140 cu in. 2300cc

Engine-control system - Ford EEC IV

Emissions controls - 3-way catalytic converter, feedback fuel-air-ratio, EGR

Turbocharger - AiResearch T3

Maximum boost pressure - 15.0 psi

Valve gear - belt driven single overhead cam, hydraulic lifters

Power (SAE net) - 170 bhp @ 5200 rpm

Torque (SAE net) - 195 lbs-ft @ 3800 rpm

DRIVETRAIN

Transmission - 5-speed

Final-drive ratio - 3.64:1 limited slip

Gear Ratio Mph/1000 rpm Max. test speed I 3.36 5.5 34 mph (6200 rpm) II 1.81 10.2 63 mph (6200 rpm) III 1.26 14.7 91 mph (6200 rpm) IV 1.00 18.5 115 mph (6200 rpm) V 0.83 22.3 129 mph (6200 rpm)

XR4ti Curb weight - 2920 lbs, Jeep J-10 curb weight - 3770 lbs. So there's a 850 lb difference. The 4.10 vs. 3.64 gears should make that up (I do realize the XR4ti used about a 25" diameter tire though...).

With 4.10 gears and 30-33" tires (haven't decided tire size yet) I'd be running in the 2500-3000 rpm range with the four rather than the 2000-2500 with a six while cruising. Shouldn't make much difference one way or the other. Should still be able to tow 5000 lbs.

The only draw-back so far is from a Popular Mechanics long term owners report:
"Real-world fuel mileage lived up to EPA estimates -- in fact, beat them slightly. However, as a Massachusetts mechanic observed, "They boast of good mileage, but you have to use premium fuel at a premium price. What's the advantage?" "  Well, I could go with a bit less boost (and power) and maybe run regular, not sure how the ECM would like that though. Oh, they were reporting 30 mpg on the highway, 20 mpg city, and 24 mpg average. I wouldn't think I could get that, but drop 4 mpg from all of those and I'd be a happy camper -- provided it will still pull 5000 lbs without being in low range. Not being able to use OD and having to slow to 55-60 fully loaded would be okay though. That might be the hang-up -- the Cherokee (no turbo though!) is only rated at 2000 lbs towing capacity with the 2.5L/five speed combo. I can get by with less than 5000, would like to pull a light car trailer with  something like an American on it, but don't have to. If it would pull a car on a tow dolly that would be sufficient. I have the brakes to stop it, that's for sure!

Having to put premium fuel in isn't that bad. There's a 0.27-0.30 difference here -- that's only an extra gallon of regular every 12-13 gallons of premium. What's that, about the same as getting 1 mpg less? I can live with that!  

Edited by farna - Apr/30/2012 at 1:16pm

Don't forget that truck is as aerodynamic as a brick...
Won't matter from a standing start, but will on a highway, towing or not.

I think an AX15 has about a 3.8 first gear, or perhaps an S10 T5 gearset or amc T5 gearset ?

Get you up on boost quicker, the AMC set is 4-1 first and I think the Gm S-10 is around 3:9-1.

I'd go AX15. use the matching flywheel and you are all ready should you decide efi may be better later.