Anyone Build 302's for MPG? And General Wagon Economy

[turbo2256b]

But with a wide-ratio 5-speed you can run stupid-high rear gears and practically idle on the interstate, while still having reasonable takeoff ability from stand-still.

A stupid high gear would depend on an engine build, a stock engine does well with high gears running around 1800 rpm. A built engine might do better with lower gearing on the highway as the power curve comes in at a higher rpm and possibly do better in economy. I have built quite a few engines based on just improving volumetric efficiency which usually increases power and economy.

[MrMarquis]

You have a good 5-speed already tho... Too bad it's the wrong bolt pattern for a 4.6 engine. Then again I wouldn't go hacking and slashing into a nice whale just for hypermiling purposes - now if the slushbox went poof then all bets are off

This is the plan. I don't know much about the new transmissions and how long they are expected to last; but if and when it dies, it's all free game.

[gadget73]

Something to consider about wide ratio transmissions is the broadness of the engine's torque band. If its not wide enough to mate up with the RPM change caused by each shift, you're likely worse off.


A properly maintained automatic should be good for at least 150k, and probably upwards of 200k unless its just a shitty transmission. The 4R70/75 should have most of the bugs worked out by now. I wouldn't expect one to die early at this point. They've been working on the design since 1980, its pretty mature at this point. Probably about time to kill it off now that its reliable

[DerekTheGreat]

What Thain said. Before I learned about power bands and the importance of torque down low I'd throw my four banger ranger in fifth any time I was cruising steady. I couldn't figure out why I was getting mileage in the middle teens. So the only change I made was running it in fourth and my mileage went into the low twenties, not to mention the engine sounded much happier. Can't believe I did that...

[His Royal Ghostliness]

A stupid high gear would depend on an engine build, a stock engine does well with high gears running around 1800 rpm. A built engine might do better with lower gearing on the highway as the power curve comes in at a higher rpm and possibly do better in economy. I have built quite a few engines based on just improving volumetric efficiency which usually increases power and economy.

Of course. My experience has been that generally "truckifying" an engine with RV cams for low-end torque tends to produce quite good fuel economy when driven at lower engine speeds. This is where a stupid-high rear gears would come handy. This in regards to highway cruising, city driving is obviously way different.

Something to consider about wide ratio transmissions is the broadness of the engine's torque band. If its not wide enough to mate up with the RPM change caused by each shift, you're likely worse off.

Yup, there is that. But honestly unless you're towing heavy (this is a car we're talking about so not very likely) torque band width isn't all that important - as long as she doesn't drop to idle after an upshift (like a Cummins with a wide-ratio 4-speed behind it) she will continue to pick up speed, may be slow for a short while till the powerband kicks in but she'll still accelerate. And this being MPG driving, acceleration will probably not be of high concerns to the driver, slow and steady gets the job done there.

What Thain said. Before I learned about power bands and the importance of torque down low I'd throw my four banger ranger in fifth any time I was cruising steady. I couldn't figure out why I was getting mileage in the middle teens. So the only change I made was running it in fourth and my mileage went into the low twenties, not to mention the engine sounded much happier. Can't believe I did that...

A vacuum gauge comes real handy when it comes to that. Manifold vacuum is what you wanna look at. When I drove my old truck by the vacuum gauge and not the tachometer, I was able to consistently squeeze 20 mpg out of it. Still had enough power to spin 33s across an entire intersection, with at least one upshift in the process

[gadget73]

ah yes, the old "econ-o-meter". Hell, that became a standard feature in the late 70s in some things. It does work, even with an EFI motor it can tell you stuff.

[His Royal Ghostliness]

Heck mine was never that fancy, just your standard shop equipment type just left laying on the floor where I can see it. May have had a ziptie to kinda keep it in place, but I doubt it Does work indeed, just gotta know what your engine is capable of - that particular engine IIRC could only pull 15-16 at most if any amount of throttle was applied, but really as long as vacuum was above 12 the power valves would stay shut and fairly little fuel was being used. Now I kinda wanna know what a typical SEFI 302 runs at when babied...

[knucklehead0202]

If I ever build a v8 for fuel economy i'll put a shotgun in my mouth and pull the trigger with my toe. That said, a decently-built, mild small block should be able to attain reasonable mileage. Not stupid prius mileage, but over 20 is not unreasonable. Mod motors are notably better on gas than the small blocks though, that is for sure.

[DerekTheGreat]

^^^This.
At gas stations people always say things like "Nice car!" which are then followed up with "What kind of MPG's does it get?" I keep track for my own records but I've started telling people things along the lines of, "I don't know, I just put gas in it when it's empty." or "Life is too short to drive boring cars."

I think mod motors are a tad better due to less displacement, more power and better aerodynamics when compared to boxes. If anyone has ever put one in a box I'd be interested to hear about their MPG's and I'd wager their MPG's are significantly less in the box.

[turbo2256b]

tHE ENGINE BEFORE THIS ONE NOW IN cREAMY when ask about economy most would freak as it did better than there econobox.

[sly]

I want to put a 3.7L V6 in a box (that 300HP job from the moostang/F150) or an ecoboost and see how that would do. Would probably need to cut some coils off the front springs though.

[gadget73]

I think mod motors are a tad better due to less displacement, more power and better aerodynamics when compared to boxes. If anyone has ever put one in a box I'd be interested to hear about their MPG's and I'd wager their MPG's are significantly less in the box.

I know of the opposite swap, a 5.0 into a roundy. No idea what he gets for mileage though. The square body does fairly shit things for efficiency, no doubt about that. I get 3-4 mpg better with the Mark VII, and its pushing similar weight with a high mileage engine. I could probably put the driveline out of the Towncar into the Mark and get that same 3-4 mpg improvement.

[jaywish]

I am following this resurrected thread with great interest. A build with mpg and power is what I am working towards. I know the two are usually opposed to one another but I am trying to figure how to get decent HP/torque and still get very good economy. By decent I think at least 250+hp and 25mph highway would be good target. I was getting 22 to 23 highway taking it easy. (63/64 in a 55) (71/72 in a 65).

The idea of a supercharger is very appealing it would most assuredly get more than 250hp. I don't know what happens with a supercharger and an economy cam when you ask the car to fly. Not saying I would put in a strict economy cam in the car but I am wondering if that combo would totally fubar it up or would it juice up the top end where a lower end power cam is usually crap.

Understand I am gathering data. Thus far I think, 302, cast crank, flat/dished forged pistons with molly rings, gt40 or gt40P heads, balanced rotating assembly & frp headers car already has 2.25" duals. Don't have a cam choice or know supercharged or just explorer intake. I have no plans to dump the AOD at this point, maybe someday but this is more than enough for now.

I think this will probably happen in my dd that I want to last a long time, maybe the rest of my driving life. So it needs to be done right. I want effortless cruising, and hill climbing along with some Yee-ha action from time to time. I know "you can't always get what you want, but if you try sometimes..."

[ootdega]

Not sure I'd classify ten miles over the speed limit as "taking it easy."

[jaywish]

I did say I would like to have the Yee-haw on demand.

To me a steady speed where I regularly get passed by some other drivers to be taking it easy. I am not talking about hyper-mileing here just nice easy cruising. Watching the traffic ahead and behind, planning your moves including passing slower traffic without abrupt speed changes which you need to think about if you keep right except to pass. Not slowing more than a bit for hills and not getting into passing gear unless entering the highway or you need it to get out of some crappy situation which you couldn't plan your way out of.

Of course it is always god for the car to clean the carbon out from time to time (cough, cough).