How low can you lug a carbureted motor?

manual overdrive trans

 

I managed 41 mpg out of my old Mustang. 302 with a T5, 3.73 gears in a 7.5" rear. The engine was not stock. Not really wild, just a well thought out, lightweight good running thrown together 5.0. It ran a hydraulic roller that spec'd out at 239-232 at .050" and .544-.512 lift. IT was a turbo cam that was originally in my old '74 Maverick when it was turbocharged. I cruised between 68-74 mph at 2200 give or take. When I say lightweight internals, we're talking super light pistons (403g each), lightened pins (87g), ti valves, light pushrods, alloy damper, light clutch, etc. I spent lots of time planning it...and it ran well. Fun car. I want another one.

THe 2.3 turbo deal...yes they are good engines but they aren't as fuel efficient as you'd think. I managed 37 out of my Merkur but keep in mind that a Merkur is much lighter than a Mustang and has better aerodynamics. Not to mention that to get that 37, I was turning the engine off and coasting down long hills, killing the motor at long stop lights, etc. I did see 44 mpg once but I am not 100% positive that it wasn't an error in calculations. My SVO never got better than 24 but it had a open plenum intake, Holset HE351CW turbo, custom cam, which all meant NO low end torque (below 3500). The thing to remember with those is FLAT GROUND. If you are driving up/down any hills, it will go into boost which kills MPG, especially with the stock turbo (either a T3 .63 or a T3 .48 which is actually worse in that sense).

 

41 mpg with a 302 CID V8 and 3.73:1 rear gears, you really need to work for Ford Motor Company. Most of the Hybrids on the road today aren't getting 41 mpg. You could be a multi millionaire.

 

I am running a 302 with a 4 speed O/D manual tranny and I am running somewhere around 1500 to 1600 RPMs at 60 MPH, I'll have to double check on my way home but I am pretty sure that it runs 1700 - 1800 at 70-75mph definetely no higher than 1800rpms at 70mph. My rear gears right now are 3.00:1 with a Lock Right Locker. I generally get around 20mpg if I keep my foot off the floorboard and shift at a decent speed.

 

To expand on what Paul had to say ... be concerned about the torque converter. If run at too low an RPM and it is below the stall speed, you can potentially burn the transmission up because the convertor will be slipping all the time. I don't know what would be involved at adapting a lock-up convertor in this instance ... probably could be done, and would avoid the overheating ... no idea how it would affect drivebility.

 

Something else I forgot to mention. I have a vacuum gauge in my car, and I drive by it when I want to get good economy. Your driving habits are also a huge part of fuel economy.

 

Yup. That's the ultimate solution. If I can find a 4 door with either a 250 or a 302 and with a 3 speed manual I'll be all over it. From what I've heard here on the forum my chances aren't too good. I will keep my eyes open.

paulie

 

Think I read on the Forum that all the controls for the lockup converter for an AOD are contained in the converter. Now I'm wondering if I could use an AOD lockup converter in my stock 302 C4. Guess I'd need the big bell and flex plate. Anyone tried that?

 

Very good point. I'm looking to get an old car for my wife that gets pretty good mileage, so I won't be able to control the driving habits part of the equation very well. I'll mention it to her.

paulie

 

The AOD lock-up converter gets its lock-up with a clutch and band in the transmission. The input and lock-up splines will IN NO WAY work in a C4.

The C5 used a cetrifugal clutch to lock the converter but it proved useless and trying to find a locking converter for the C5 is hopeless - you can still find converters but they don't lock anymore.

 

Point well taken about running a non-lockup converter at too low of an rpm, but I was thinking about an AOD with lockup converter.

paulie

 

What info would you need? I don't have a car yet. I am looking for one, a 4 door. Let's see, it will be my wife's car. Engine will be stock type rebuild. I'll make some improvements for efficiency's sake. Electronic ignition, small tube headers etc. It will be a daily driver. 90% in town driving. I'd like it to do well on the highway at 70 mph, too. She's not a speed demon, but I doubt she'll watch a vacuum gauge if I hook one up. Performance is not what I'm looking for; just mpg, given that I'll start with a 250 or a 302.

what would you do?

paulie

 

Buy her a Kia?

 

Negative on that transmission, Buck Rogers. I can't hear you.

My wife is not a suburban soccer mom. She grew up on a farm. Thank goodness.

paulie

 

Honestly with that statement I would just use a warmed over stock motor with a c4 and the stock 2.73-3.00 gear ratio. It might be counter productive putting a heavier transmission that wastes more horsepower like an AOD does just to have it sitting in traffic. If you keep your car tuned well you will still achieve decent fuel economy on the highway just as long as you dont get your rpm's too high.

But if you want a really all around fuel efficent car you might look at something newer, heck the new hybrid fusions recently got 80+ mpg in a 1500 mile test and most of that was city driving back east.