Question: SBC Fuel Economy...

[snowbored]

OK, I got a new gastank to replace the one with a hole, did a complete tuneup, including installing a Pertronix Flame Thrower HEI coil setup and Taylor plug wires, adjusted my timing, etc, and I'm still getting 10 MPG. I am HEI carburated, and have a NP203, turning new 32-11.5 BFG Mud Terrains. It seems like most of you get 15 MPG at least. Does the 203 really eat up that much? I can live with 10 MPG, I'm just worried that I am missing something that is wrong. I have replaced fluid in TH350 with Redline's stuff, replaced the fluid in my diffs, and rebuilt the knuckles. The tranny and diffs looked fine. I am going to replace the fuel lines and fuel pump (I want a spare for when I'm in the middle of no-where, and might as well throw the new one on and use the old one as the spare).

Another SBC question, did you guys replace the fuel lines all the way to the tank? I'm redoing the lines, and wonder if I only need to go to the aluminum ones, or if replace them and should go all the way back. Also, are you guys running the tank pressurized still or did you go with a vented gas cap? Thanks for any advice.

 

[Downey]

You do have a few things going against you:
(a) Alot of the 15-20 mpg you here is on FJ40's. My guess is your FJ60 is not going to see that kind of milage.
(b) You didn't say what your SBC is, a 305 is going to get better mpg than a 350.
(c) Your carbureted, good luck with that!!!!!
(d) Your running a TH350, no overdrive gear!!!!
(e) Your running 32" tires, and possibly no lower gear ratio to make those tires spin a little easier.

 

[2damslow]

Mine gets about 13 with the Holley pro-jection. Carbed, I only got about 10 or 11.

I understand that I can get more if I have the O2 sensor, but i just have the open loop injection right now.

I used to have a suburban with a two barrel road demon. That thing had tons of power and got about 14mpg.

 

[inkpot]

Howdy! Should be able to do a little better.What cam, carb, exhuast, compression, displacement, etc? John

 

[Texx]

Honestly, with my old 350 FJ60, your mileage is about right. You might even gain a mile or two by switching to 33" tires. Your 350 is screaming at highway speeds, the best way to get more mileage is to lower RPM.

 

[kitb]

carbed gm 350, with a ranger o.d. 33 inch tires= 12mpg
running on lpg I get 10 mpg

 

[RockDoc]

3FE, A440F, driving ~70 mph on the highway I get ~15 mpg (US gallon)

 

[cfdlighthouse]

tired 2f weber progressive...33inch swampers i got 16mpg on my last trip running 65....might not have the power of the sbc but damn 10mpg.....at these gas prices...ouch

 

[TURNMEOVER]

tbi 350 sbc in a 40 with 16 mpg. and she is heavy.

 

[snowbored]

Thanks for all the replies. I guess I will stop fusing with the engine until I can swap out the NP203, and maybe the TH350, and/or watch CL for a fuel injection setup. For inkpot, it's just a GM 350 crate motor, Edelbrock manifold and carb of undetermined models (to be honest, the carb is running better than my tuning could do, so I haven't wanted to be tempted to mess with it), nice dual exhausts without cats (sounds awesome). Manifolds not headers. No idea on the cam either. Not plain stock, but not enough to idle horribly. I guess I should have mentioned that it's more than 50% in town driving, add to that the 1mpg at least hit from the NP203, so that seems about right to me with the numbers you've all posted. I just wanted to make sure the mileage didn't indicate I have some issue I'm not seeing. Now I can move away form Chevy stuff to cruiser stuff. Thanks again.

 

[lehiguy]

Ok, there may be something not quite right with your state of tune. It sounds like there are some things about which you're not quite sure, like what cam or even which heads for that matter, and you don't have an overdrive in that tranny, so that's working against you. What gears are you running and what size tire? The worst I ever got with my 350 was around 10 MPG, pulling a crazy load into a vicious head wind. The last Moab trip I got 17 going down, 16 coming back. That's a carburated (Rochester) 350 turning 35" tires with 4.56 gears and she's spring over, so it is the proverbial barn door. What carb do you have? is it a Holley, Rochester, Carter/Edelbrock??? What about your timing advance curve? With some carefull tuning you should be able to pick up several MPG, but you have to know from where you are starting to know where you are going. For the record, I just switched to FI, but my carb and distributor were so well tuned, I have NOT seen any increase in milage yet. With further tuning, I hope to, but the old school stuff can work very, very well if you set it up right, and it can be repaired or tweaked with very little effort. There is some beauty in that.

 

[snowbored]

The engine is an early 90s Target Master crate motor, it looks to be the same heads. The carb is an Edelbrock 1405. The manifold says Edelbrock in the front, and Performer by the distributor. New Taylor 8mm wires. Pertronix Flame thrower coil and HEI internals. Timing was set at 2 before I did the tuneup. It's now at 12. Vacuum advance is at 12, for mechanical I followed this pages info: HEI Tuning Secrets. I have no clue on the cam, it's not enough that it idles horrible, but it is something more than stock. I haven't touched the carb as I don't want to screw it up. Plug are ACDelco 45s, .45 gap. The exhaust smells normal.

 

[Elbert]

I dont' think with a carb setup and old school 3 speed you are going to get much over 10 mpg or so.

 

[snowbored]

Thanks guys. Elbert, that sounds true. I'd just though no hole in the fuel tank and a tune up would net me something in mileage. If I take lehiguy's 16 MPG, factor the difference of NV4500 to TH350, NP241 to NP203, higher HP engine (more efficient) to mine, I think I'm doing OK at 10, which I'm fine with for now. Now I can move on to the fun cruiser stuff that I got this rig for To bad it took more $$$ to get to that point than I planned (but that's always the case, right?).

 

[Elbert]

Yes... $$ is always an issue with the LC mods. Just for a reference my 92 K1500 with TBI 5.7 does good to get 15 mpg on the hiway. I'm still working on the tuning (ECM) on my FJ60 so I don't have any realistic numbers to share. If you have a carb, a three speed trans, agressive tires and 4wheel drive, gas milage just is not going to be that good. I would make sure and get the truck tuned up, change the plugs and get it running good and then forget about fuel economy.

A LC or for that matter any serious SUV (4 wheel drive) old school machine is just naturally a gas hog.


I'm still trying to get my machine running right...once that happens I plan to just drive it here and there and have fun. I certainly don't drive this thing to work....since my commute is 60miles one way.

You may be able to gain some MPG by a good tune up, making sure your timing is right, and your rich/lean is correct on the carb. Outside of that you have a box that you are pushing down the road..

 

[lehiguy]

I have played with all different types of carbs and I like Rochesters the best for driveability, tunability and milage. These can be leaned in one spot and fattened up in another. The high vacuum cruise mixture is separately adjustable from the low vacuum mixture and you can change when that enrichment occurs. The secondaries are huge for horsepower, the primaries are relatively small and make for terrific low end torque and milage. The float is central and it's small, so they don't flood, and ther are millions of these in wrecking yards everywhere you look. Once you get one of these tuned and the distributor advance curve dialed in, it think 12 or 13 is certainly achievable for your setup and I think you will find that it will have a bit more spunk as well. I'm betting that your heads may be a low compression, small valve variety, that hurts both performance and milage. Vortecs are the affordable powerhouse head to have but they require a different intake. If you look around you may find an old-school tuner who can help. I know a guy in Salt Lake City who will hook up all the instruments, put you on the dyno, tune the carb and the distributor for maximum efficiency. I'm sure he's not the only guy in America still doing this. All this depends of course, on how much cabbage is spilling out of your wallet. One thing that you can do for free, is check the vacuum advance piece on the distributor, these will fail from time to time and leave you with a vacuum leak and no advance. Also, an older HEI may suffer from the years of abuse by not advancing mechanically. Take off your dist. cap and see of the rotor rotates freely. It should snap back into place with gusto. If it doesn't, take the ditributor out, remove the gear from the bottom, disassemble the mechanism on top and pull out the shaft. Clean it up paying special attention to the area where the shaft passes through the upper bushing and where the mechanical advance rotates. Whenever I started to see my milage taper off, it was always my tired distributor getting gummed up and not doing its job.

 

[PPFJ60]

If you want to maximize your fuel economy on the road then the best solution would be a Honda Civic. Mine gets 40 to 44. The Honda Civic is not much good off road or in snow but my SOA FJ60 with 36" swampers, TBI 383 V8 handles that with no problem. I get 13 to 14.5 on the hwy with FJ60 and about 9 to 10 in low range off road. The best transmission for this setup is the 700R4 with the lower first gear and the overdrive. I just picked up an NP203 to add to my FJ60 so I will dual transfer cases.

 

[snowbored]

Thanks again guys. I'm not looking to get gobs of MPGs, I was just taught that one good way to know if you have issues is if you are getting poor fuel economy (versus just getting poor in general from having a big truck ). It looks like I'm getting about right, so I'm happy. I'll look into re-carbing or going fuel injection once I actually get some stuff done to make this a family camping rig, I don't want the wife asking why I didn't just get a GTO if I'm just gonna play with the engine forever. In the past my dad could just listen and smell the exhaust, and know everything going on with the thing, but I live to far from him now, and it seems like old school guys are getting fewer and farther between. Now I'm realizing how much I leaned on him for help, and how much of the enjoyment was doing it with him. But that's part of why I got this setup for me and my son and daughter (she seems more into it than him) to work on together.

 

[lehiguy]

I forgot to mention that your Edelbrock carb is fairly tunable also in much the same way as the Rochester. I ran one of these for a time, it never got the milage or worked as well off road as the Rochester, but it ran strong. Try a local performance parts store for the jetting kit they sell, or perhaps Summit racing or Jegs. These will have some guide lines about how to change the calibration to achieve a small percentage leaner or richer in a certain part of the metering curve. That will help to maximize, or at the very least verify what settings you have. It's easy to do, and then you can know for sure where you stand.