MPG out of a T18/T19 or NP435

[70StockRed]

Black Friday is next week, so while she gets the day for shopping I am taking the next day to hit the junk yards.

Anyways, just getting going on this build and am excited! I had a 65 Mustang with 200 inline 6 a few years back and loved it.

I recently picked up a 70 F100 shortbed with a C6 behind a tired 300. It starts shaking and screaming on the freeway around 55. It came with a front disc brake conversion, power steering (thompson pump), and an A/C unit. My goal is to make a good daily driver out of it with at least 20 MPG and able to do 75 to 80 on the freeway. I plan to start by putting in a T18 or NP435, then swap the engine to a 240 and gear the back end to 2.75 to 3.00. Is this just wishful thinking even with the proper tuning?

Is there a better manual trans to put in it? Is the M5OD going to suit me better? I like the idea of the 4 speeds because they have the reputation of being easy to work on and can last for years. The Mazda 5 speed has some mixed reviews though most are good. Is it fairly straight forward to rebuild? I won't be doing much pulling or hauling with it. Helping friends move here and there will probably be the most of it.

Any thoughts will be great appreciated. I am still learning the ins and outs with this truck and want to build it good and pass it down to the kids.

Respectfully,
Linwood

[Red Mercury]

Without knowing what you have up your sleeve for the 240 engine swap, you might be disappointed. I have 2 stock 1967 F100's with 3-speed transmissions. They both had 3.70 gears and 240 engines from the factory. I have swapped in a 3.00 set and a 3.25 set. At highway speed, it won't matter which transmission is used since the top gear ratio is 1:1 for the T18/NP435/3-speed manual. The stock 240 does not have enough power to drive the 3.00 or 3.25 gears. Don't get me wrong, it is drivable, but there is no power for passing or climbing hills and the engine labours to get up to speed. Gas mileage improved slightly, maybe 15-16 MPG at best. There is a reason that Ford put 3.70 gears in the trucks with 240 engines from the factory. It was the best match in terms of drivability. Now if you plan on doing some performance upgrades to the engine you might be on to something.........

[motzingg]

I've got the 240/3sp/3.7 gear combo and its got plenty of pep at 60 where the engine is turning like 3,something rpm. It never looses speed on hills and can accelerate on the on ramp with modern cars just fine.

i'd say 3.5 or maybe even 3.3 might be do-able but the 3.0's are gonna really suck.

The other thing is that the 4 speeds have crappy ratios, 1 is granny, 2, 3 and 4 are all close and either your 2/3 or your 3/4 is going to be a huge jump depending on what tranny, i cant remember the ratios off the top of my head. If you put tall gears in it you'll have your 'overdrive' in fourth gear that you want, but you'll be wound out sideways in third, and you'll dog it going 1-2 where you need the 'get me through this stop light before i get t-boned' kinda acceleration.


I'm decided on the M5R2 for those reasons... 5 gears with 'road' gearing give you the 3-4-5 at good ratios. Plus you can keep your 3.70's or go up or down depending on your power curve. I'm gonna try it with the 3.7's and maybe try 3.5's if i have the power to pull it. Either way the m5r2 is designed for a light truck at 'modern' highway speeds and not 55mph speed limit.

i'm getting used to winding the piss out of my 240. it doesn't seem to mind going 60 or 65 for 20 minutes each way during my commute and fuel consumption probably isn't affected much from the 2000-3000 rpm range, as the torque curve is pretty flat through there for this engine. It really bugged me at first, but the guys on 'fordsix' forums all say that motor can sing at 4 grand all day long without missing a beat.

One thing that really is killing you though, is that slushbox.. C6 having no lockup converter, especially if it is worn out and slipping in the clutches, will really trash your fuel economy 2-3 mpg.



the one thing you cant beat is physics, and bumpsides are giant f'n bricks going down the road, pushing it past 65 is going to kill your fuel economy whether you've got a big-block or a hamster in a cage. Air drag goes up with velocity cubed, if you've ever ridden a motorcycle going from 60 mph to 80 mph goes from a pleasant sunday drive to a punishing hurricane.

I'm just retraining my brain to go 65 and enjoying it. It takes me less than a minute more on my 20 mile morning commute, and even on long trips, it works out to one half-hour pee break every 200 miles.

[guhfluh]

If you get the right T-19, the gears are pretty evenly spaced and would work better with a low ratio rear gear. It's the 4.xx ratio first from the 86 or so diesel or 460. I believe it's called a wide ratio version. Otherwise, like motzig said they're all 1:1 in top gear and have a huge spread between gears. The 240 also doesn't mind high rpms like he said, because of its short stroke and that's where it makes its power/torque. The 300 likes less revs and more low end torque. Either motor needs intake/carb/exhaust mods to wake them up. My f250 came with a 240 , 3.73 gears and T-18. It got 13mpg at best and I had to drive wide open to barely keep up with traffic. The 300 with an intake, 4bbl Holley and efi exhaust will actually beat traffic now. The new overdrive 4spd trans has the same gear splits as the T-18 did and a horrible 2-3 shift rpm drop, but it does have overdrive. I'm also getting much better fuel mileage. I think I can get 20mpg after I'm done tweaking the carb and ignition and driving 65mph.

I think the M5OD is an ok trans for a truck that isn't going to make a lot of power or tow a lot. It's light duty, otherwise it has good gear ratios for a driver. I don't like that you have to use a hydraulic master and slave, but if done right, it will be much better than the mechanical linkage setup.

I would keep the 300 and just modify it and then drop in an AOD trans in place of the C6 instead of swapping to a manual and re gearing. Then you can play with the gears after, but 3.70 with OD should be pretty nice.

[caseyj10]

If mileage is the goal then an OD tranny is a no brainer. get the M5R2 out of the 80s-90s f150s.

[guhfluh]

If mileage is the goal then an OD tranny is a no brainer. get the AOD out of the 80s-90s f150s.

[motzingg]

i don't have personal experience with the AOD's, but being a lockup OD auto, they are probably a c-hair away from the M5r2 fuel economy wise, especially if you are doing your driving at highway speeds. Plus converting all the control stuff, hacking in a clutch pedal box, getting rid of your column shifter... ugh... sounds like a ton more work. besides your old lady or your kids might like the auto better. I'm normally a big fan of manual, but for daily driving work the auto has some advantages, especially if its a good one that has been gone through by a shop with a shift kit or something like that.

i've read a lot and talked to a lot of people with the M5R2's and the big reliability issue they all say is the bearings getting run dry because the plastic fill plug gets crusty over 20 yrs of being exposed to oil, and leaks. Most of the people i've heard trash talking it either ran it dry, did something really dumb like pulling a stump, or are just repeating internet BS heresay.

The word on the street is, get one from a running (crashed) truck. check the trans for signs of gear oil leakage. if there is oil in the trans when you get it, and it isn't covered in crusty grime originating at the fill plug... you're probably in good shape. I would probably stick my finger up the fill hole and wipe around, see how much metal you feel.

lots of folks run these behind 300+ hp 302's so they can handle the power no problem. There has been some discussion of them getting hot while towing and that being a possible cause of bearing failure, but I think running synthetic oil would be a pretty good safeguard against that if you plan on beating it... which i plan on.

plus synth gear oil doesn't smell like cat piss.. for me that alone is worth the price of admission!

[guhfluh]

^^^Agreed exactly.

With the fluid, just do your research. Full synthetic is always better than Dino oil in my opinion, but you need to research which ones are good with yellow metals, fiber, etc. that the intended trans may have. Viscosity is critical as well.

For the AOD, I have come to like John Deer Hygard Low Viscosity. Many racers swear by it and it is very good for steel on steel wear with Zinc as well as good grip with not too many friction modifiers. I use it in both my Dodge built transmissions.

[70StockRed]

Thank you everyone for the replies. guhfluh, I see your post on the fordsix thread as well. I think I am going to take your advice on keeping the 300 in the truck. Will save me some money to go with what I already have as well. If I can get close to the 20mpg mark with that and a 4 speed, I should be satisfied with the results.

The main reason I bought the truck was for the ease of being able to work on and maintain it myself. I just sold my Infiniti QX4 because I got so sick of not being able to fix it when something went wrong. This last week the starter went out on my F100. It took me 40 minutes and $40 to have it switched out and running again. And that was will travel time to the parts store. My buddy at work couldn't believe it. Not to mention I did it with two hand wrenches and left the ratchets in the case. This is a big reason I am thinking that the older 4 speed will fit my build better.

As for the rear end gears. Would something as low as 2.5 work? I think those are car gears but as a daily driver, I will be driving the truck as a car most of the time anyways. If I get to where I need better working gears I can put the old ones in again.

[70StockRed]

Picked up a T18 out of an 84 F350 over the weekend.

As anyone put in anything lower than a 2.75 rear end gear ratio? I see a couple of 2.50 ring and pinions on eBay. Would that be too high mated behind the 300 and the T18?

Respectfully,
Linwood

[motzingg]

consensus amongst people who have driven them seems to be that 2.75 is all the taller you want to go.

that 'lazy JW' guy built a 'high mileage' setup specifically and he has had some good posts (or you could email him) about the 'point of diminishing return' for MPG with tall gears.

at some point you'll be shifting 3/4 all the time and lugging full throttle in 4th which will hurt your mileage more than it helps.

what i'm doing, is getting the trans sorted out first, then i'll drive it for awhile and see if i want to go taller.

the specific fuel economy of an engine is going to follow the torque curve very closely, the cool thing about the 300-6 is that the torque curve is pretty flat from 1500-3000 rpm, meaning that the fuel economy at 1800 rpms isn't going to be that much better than the fuel economy at 2700 rpm. I let my very haggard 240 run out to 3100 @ 70 mph regularly with the 3 speed and 3.7 gears. The engine doesn't seem to mind at all, and its probably not hurting my economy much, although i don't regularly drive that fast, nothing starts smoking or catches fire when i do.

If you are running 3.0 gears you'll be doing 2500 rpm (this all assumes a 28" 'stock' tire) at 70, and with 2.75 gears you'll be doing 2300 rpm. I think the stock engine will have a hard time pulling anything taller on the highway with enough power left over to pass or pull a trailer. That means you have to down shift and now you're turning 3000 + rpm again. It took me awhile to get over my prejudice against revving the crap out of a 50 year old tractor motor, but lots of old timers who ran these things in heavy trucks with low low gears say the big sixes can and will spin 4k plus rpms all day long without missing a beat. In fact, some of the guys who have more experience with the forged-crank HD motors said the main reason for going to a forged crank was so it could rev out higher (same with the free-er flowing exhaust) instead of for higher torque capacity.

I know from a lot of experience towing large stuff with underpowered vehicles, you are better off keeping it in 1:1 and letting the engine go a few 100 rpm higher than shifting back and forth between OD and 1:1. My minivan does 2-3 mpg better towing a boat when it is left in '3rd' instead of shifting back and forth in OD.

Unless your C-4 has major problems, the highway behavior will be the same for auto vs. manual 4-speed. My suggestion (assuming everything else on the truck can take it) is to wind it out to 70, 75 mph and get yourself used to the sweet song of a screamin' six. After a few 5-10 minute bursts of shredding it on the highway without anything blowing up, i got more comfortable and learned to love the bomb, so to speak.

[sampjenningd]

Without knowing what you have up your sleeve for the 240 engine swap, you might be disappointed. I have 2 stock 1967 F100's with 3-speed transmissions. They both had 3.70 gears and 240 engines from the factory. I have swapped in a 3.00 set and a 3.25 set. At highway speed, it won't matter which transmission is used since the top gear ratio is 1:1 for the T18/NP435/3-speed manual. The stock 240 does not have enough power to drive the 3.00 or 3.25 gears. Don't get me wrong, it is drivable, but there is no power for passing or climbing hills and the engine labours to get up to speed. Gas mileage improved slightly, maybe 15-16 MPG at best. There is a reason that Ford put 3.70 gears in the trucks with 240 engines from the factory. It was the best match in terms of drivability. Now if you plan on doing some performance upgrades to the engine you might be on to something.........

This I can confirm.

My 100 has ENOUGH power on the highway... had her up to 70 with no issue, but if you want to be passing people with the 240 inline 6, you'd better have some sort of nitrous kit installed!

0-60 in whenever I damn well feel like it, get off my backside!

Also, stock 3SPD manual, I get ~15. These trucks have all the aerodynamics of a somewhat streamlined brick.


What I will say is that with stock gears, stock everything, I was able to pull a 3,000lb Uhaul trailer full of my crap across the state, up and down hills, through cities and on highways. The 240 is such a darling. If I could marry a motor, my wife would be lonely.