I have a 89 F-250 with a 351, C6, 4:10's and 33" tires. I have noticed that I am getting bad gas milage (7.5 MPG). My first question is with the 33" tires how much will that screw up the speedo and odometer? My second question is how hard would it be to swap in a E40D tranny?
Thanks in advance,
Stew

 

i got a 89 f150 351 c-6 with 3.55's and it gets 7.5-8. and i think it gets like 9-10 if i run exxon. how many rpm's are you running at 70?? i am running 3300. i just drive it... i put a fuel filter, cap and rotor, plugs and wires and didn't pick up any milege. thought it might help but it didn't. i think the aod has electronic controls??? maybe. i dunno, but tranny swap it pretty easy if you get the driveshaft for the same truck as yours to go with it. i just pulled my c-6 and rebuilt it and put it back in today. i didnt have a tranny jack, but i had a 20 foot long piece of 3x8 oak board and a block for a fulcrum. i like that better than a tranny jack anyways. i don't have a nice concrete garage or driveway tho. just dirt. so that works good for me. if you let the motor and tranny hang down far as it will go, you can get an impact in there easier than anything. worked for me anyways.

 

i forgot to mention the flywheel. you may have to get a flywheel for a 351 to a aod. for your year model. if its not the right one, it may vibrate real bad and throw all your bearings out. i did it to a 454, put a 350 flywheel on it and it vibrate real bad and threw all my bearings. bad day!

 

The E4OD is computer controlled, it means changing computers and some wiring....maybe more. If anything, I'd switch to an AOD I guess....but I don't like automatics heh. The AOD is not computer controlled, so it should swap over.

7.5MPG is probably because of the 4.10/33s/no OD/off speedo....and probably a tired motor. All of those are factors....the speedo is probably you're biggest. Ya can't get an accurate MPG if you don't have accurate mileage...

 

Speedo/odo will be off about 5% going from stock tires to 33's. Don't feel bad, I have an F350 with 351 & C6 and run it with 33's and 4.56's. I save alot of gas by driving slower on the highway.

 

mustangGT221 is correct about the E4OD being computer controlled. Although I haven't had the need to purchase a controler I have spoke with a fellow from Beauman Controls (might've misspelled) about tranny components. This company offers what you might need.

As for fuel economy my 1990 F250 XLT LARIOT 4x4 is currently getting 9-10mpg on winter gasoline. The all time high average w/topper and a road trip w/mild weather is 13mpg. I sure wish I could get back up to it. The truck has a 5.8L eng., E4OD tranny, 4.10s, K&N air filter, JBA stainless/ceramic coated shorty headers w/smog hookups, and a Gibson 3" S.Steel exhaust w/single outlet. If you have the time, I think the swap is do-able but pricey.

 

I forgot to mention, but I've had this truck since 1991. It does'nt matter much if I drive 55 or 75, loaded or empty, up hill, down hill, down south, or out west. The addition of headers and air filter just dropped rpms to 2000 at 60mph instead of about 2200-2300rpm in od. At 75mph, I'm at about 2500-2600rpm now. The tires do affect the speedo and I am currently back to running a stock size 16" rim instead of 16.5 and 12.50x33s. It's a heck of alot easier to park now.

 

Millrat, how did air filter and exhaust change the engine rpm's for any given vehicle speed??? You must have been operating in a different tranny gear, since engine rpms can only change in relation to vehicle speed by changing axle ratio, tire diameter, or tranny gear....

 

I wish I had the answer for you, but I don't. I have driven this truck and monitored vacuum and rpm forever. When I have made a change or modification I have compared it to previous observations. My travels are daily driver and trips, aswell as off road. The exhaust and air induction were the most recent improvements last year. The fuel milage was no change or negligible. However I did note a seat of the pants change in performance and the change in rpms at traveled speeds. The vacuum seems constant. When I drive I set the cruise and monitor rpm, I know when I'm on a level run, grade up or down. I use the tach as a generic measure of what load the engine is experiencing. Theory would be that the engine is breathing or producing slightly more power at a constant moderate throttle. "making more power at a given rpm" perhaps because the ecu expects certain perameters and adjusts the timing/fuel curves accordingly. I don't really know. My quest has always been observable recordable changes. I spent a coin or two and I can say that you can't expect results as advertised, such as increased fuel economy etc..., to be remarkable. My fuel economy did'nt change, I like the sound and response when I lay into the foot feed but the only observable change has been the tach. As for future changes I have considered a spacer plate for the throttle body and an insulator for the upper intake.

Theory and common sense say that a spacer plate is a waste of money since the truck is fuel injected, ie,. no gain in velocity of incoming air/fuel charge since the throttle body only controls air. However, if you increase the volume of the intake by adding the insulator gasket and a spacer plate for the throttle body you will increase low end torque.

The design of the upper intake is such that the front cylinders are starved for air since the incomming air takes the path of least resistance, a straight line back. Maybe their efficiency was increased by better scavengig of the cylinders. Perhaps if I add a throttle body spacer a change in the dynamics will increase the of volume of air to the front cylinders by creating turbulence. Adding a spacer to the upper intake which increases volume would therefore lean out the air fuel ratio. Remember that in an SD system (speed density) air/fuel ratios are based on tables created for specific barometric pressure, engine coolant temp. air intake temp, throttle position , etc. If you have a better explanation let me have it. I am only an enthusiast, when I can afford it, I bolt on parts and then I try to figure out if I was a sucker, since education is expensive that is what I chalk it up to. Thanks for the question cuz it make me think and search for the answer rather than accept the status quo.

My next pursuit is tunning.