I am just curious as to what other people's 400's and 351M's run like in the performance and milage area. i have a 79 f-150 supercab 4x4 with a 400, a c-6, 4.10 gears, "trac-lock", and 33x12.5 inch tires. i recently completely rebuilt the engine. its bored .040 over and has new everything. even more recently i found i had two cracked heads so i put in a new set, without the egr stuff, which i lightly ported and polished. it also has an edelbrock performer intake, a quadrajet, performance coil and wires, a high flow air filter, and somewhat free flowing exhaust (no cats and a glass-pack). the vaccum gage reads a steady 16 psi at idle and im running the timing at about 15 btdc. everything is fairly smooth but i just dont feel like i have the off-the-line torque that it should. dont get me wrong...its gotta be hard turning TWO big tires through a t-case and a big tranny...but it is a large v-8, with some mild performance stuff on it...is it too much to ask for to be able to break em loose off the line? (which it cant do by the way...maybe a very faint squeal is about all i can ever get out of it). does anyone else out there have the same basic set up and if so...what does your truck run like. also what kind of gas milage do you guys get? i know i cant ask for much being a big heavy truck with lower gears...but im thinking (when im easy on the throttle)i should be getting at least ten right? well im getting anywhere from 5-9 mpg right now. my friend in his 70 chevy was getting 15 mpg on the highway with a 350, 4.10's, and the same exact carb im running right now...and it had some ***** too. anyway, just thought id see if anyone out there has a good running 351M\400 to compare mine to and see if i need to work on something. thanks in advance for the help.

 

I get 10 to 13 MPG out of my 351M. It's in a 79 F-250 4x4,with 33s. The engine was rebuilt quite a while ago it has about 100,000 on the rebuild. It has basically the same set-up as yours except I'm running a comp-cams 268,a 1406 edel carb and mine has 3.54 gears. You are not far off with the kind of mileage you are getting, the Quadrajet has never been known for great gas mileage. Did you degree your cam or put in timing gears with the keyways to put it in at straight up,advanced or retarded? This can make a difference too. Also, sometimes the ring will slip on the harmonic balancer making the timing marks all wrong. I would try pushing the timing up until it starts to spike on a hard pull then back it off just a bit until it quits spiking. My mileage went up about 2 mpg when I set up my timing.

 

Hello 79supercab4x4, I own a 1978 Bronco with the 400 in it, c6 tranny, np205 transfer case, trac-loc rear end with 3.50 gears. I rebuilt the motor about 30,000 miles ago and it is bone stock, except for its bored .60 over, 2 barrel carb. stock intake manifold, stock exhaust manifolds with dual exhaust and flowmasters, 32x11.50x15 BFG AT's. The timing is set at 8 degrees B.T.D.C. When i "get on it" off the line, the tires will bearly brake on the pavement, unless its been raining. Off-Road, and they dont seem to be spinning very much then either. I think its got alot to do with the trac-lok rear end, it seems to want to keep both tires locked unless im in a bad bind. The only time i every noticed the tires brake loose, is when it just starts to rain and turn a corner, then punch it. And it only brakes for a second. Do you notice both tires wanting to spin on your truck? Or is there something wrong with mine? Well, thats my 2 cents, have a good one. Rob

 

thanks for the replys guys. before i read this i had just got done tuning my carb and timing and have it running a lot faster (dont know on the milage yet). ya when i rebuilt it i didnt need to degree the cam in sicne all you do is line up the marks on the timing gears and throw it in there. i just tuned the timing by sound and it runs pretty good now. for 78, ya its the same with my truck turning both the tires all the time. thats the whole idea of the trac lock after tuning i took it out for a spin and could break both tires loose off the line easily for a few seconds so im happy in that respect. it sounds to me like theres something wrong with your bronco though...even though its totally stock, its a lot lighter than my truck is. im surprised it doesnt have any off-the-line, tire spinning torque. even when my engine was bone stock, on the wet pavement i could stomp the gas and keep the tires spinning all the way to third gear...and thats with the 33's and trac lock. and if i ever go around a wet corner and punch it, it can get dangerous (but VERY fun) maybe its all in the gearing? ...well, thanks for the info guys, its been helpful.

 

Just thought I would throw in my 2 pennies on the Bronco vs Truck thing. I had a Bronco that seamed pretty low on power the only thing you have to remember is a Bronco has a couple hundred pound topper on the back these aren't built light also the Bronco I had was equipped with a stabilizer bar on the back that would help plant the tires. The Bronco is also a much shorter wheel base which puts more wieght on the rear wheels. I definately agree the gears make a big difference too.

 

Ya, i almost mentioned the weight distribution thing in my reply but then i thought about it and remebered....even though, respectively, theres more on the back in the bronco, theres still a lot less weight on those two tires then on my two tires. its a supercab with a 5th wheel trailer hitch, and three gas tanks in the back, so that alone shoudl make up for the topper. also u gotta remember that under very hard acceleration, a LOT of the weight is shifted to the back tires anyway. good points, but i still think its wierd that the tires just barely "break" on a wet turn. with a posi and a 400, your rear end should be all over the road on a wet pavement. i have a friend who owned a 400 bronco (with a 4 speed though) and he says it was one of the fastest vehicles hes ever owned...hes never owned a hot rod or anything but he says it was really fast well as everyone here puts it, "thats just my two cents". is there anyone else out there who has similar vehicles. if so let us know what they run like. thanks

 

I have a 78 Bronco, 351M, 4-sp, 2-v Holly, all stock. When I first got it, there was a "flat spot" when I accelerated around 1500-2000 rpm. I changed dist. springs to a lighter set; made advance come on sooner. After that it ran great. Gets about 12 mpg around town, best of 16 on a vacation trip once. Wouldn't trade it for anything. Don "Nothing lasts forever except natural stone and old Ford trucks."(W. Nelson)

 

I just recently purchased a 79 Bronco. It has a 400 mated to a 4-speed. It gets about 11-12 mpg, either on the highway or in town. It is stock as far as I can tell. Right now it has all the power I need and doesn't burn ANY oil, but I'll probably sink some money into it anyways.

 

I've got a 77' Ford F-150 4x4 with 12.5x33's, a 400, c-6, np-205, 3.57's (as far as I can tell, 50 teeth on ring gear, 14 on the pinion). I built it up about 20,000 ago. Bored over .060, flat tops, an RV performance cam (351's and 400's are known for their their large torque production at low RPM's, so I worked with it), edelbrock performer intake, holley 650 carb, stock distributor & coil, timed by ear, and titanium seats in the shaved heads (for higher octane unleaded fuels because compression was boosted a bit with the flat tops and in the 70's leaded gas was still popular I guess so the valve seats on ford's weaken with our unleaded fuels today causing the seats to be eaten up). I can squeal the rears all the way throught the intersection on dry pavement (I had the front drive shaft off 1 time, otherwise it is all time 4 wheel drive). It is fun to drive in the rain and snow because all 4 break loose, beats mustangs and camaros up to about 45 mph, and beats most cars getting up to speed off the intersection while hauling the race car trailer (you don't even have to put the pedal down all the way. The torque is unbelieveable, it sits you back in the seat, but so is the gas milage, if your romping on it it goes down to 4-7 m.p.g.. Normal highway driving is right around 10 m.p.g.. I have never owned a truck which can cause front driveshafts (constant velocity joints) to clunk from romping on the pedal, and no--the front end bushings and t-case are not loose or worn and the truck has no suspension lift!

Fun in Minnesota!

 

My 400 has a stock cam, Performer intake, and Edelbrock 600 carb, and headers. 3.5" gear and 35" tires, and its a 4 speed. I have no problem at all spinning my tires in 1st gear, and can usually get them to spin in 2nd. In granny gear you can't even floor it, cuase there is so much torque. In the rain I have to be careful, or the truck will fishtail all over the road, in any gear (floor in in high gear and the back tires will spin in the wet.) Off road I have to be in 4wd, or I am spinning tires almost continually, unless idleing (no gas pedal pressure at all.)

I would say check the timing, too, the balancer has spun on mine, and the marks on it bear no relationship to actual timing at all. I just advance it 'til it pings on acceleration, then back off 'til it stops.


fordmando
78 F-150 4x4 400 4 on floor
86 Nissan 300ZX
George

 

Oh, and I get at least 12 mpg, sometimes as high as 15 on the freeway.

fordmando
78 F-150 4x4 400 4 on floor
86 Nissan 300ZX
George

 

Yea for the old Ford trucks. My son and I built up a 79 F-150 4X4 short bed truck last winter. We had the engine work done at a local speed shop pretty near the Hot Rod article. It's a 400M with everything done to it. Performer intake, 650 double pumper Holley, Cleveland valves, Comp Cams custom grind cam,Ohio pistons (9.7), align bored,balanced, cc'd heads, bored .30 over,intake ports matched,Headers,MSD billet distributor, MSD ignition and wires,aluminum water pump, Holley fuel pump, Stock fan blades. This thing sounds absolutely BADD ##### (loping), when it idles. It too has stock gearing, 3:50 limited slip with a C-6 tranny. Mashing it off the line gets the 35-10.50X15 BFG tires spinning for about 30 feet.
Lots of torque but no rpm's due to the long stroke of this engine. Makes this old man feel like a young kid again.

 

 

I have a '81 F-150 long box, with a '77(i think) 400 swapped in. I don't know everything about it but, I think it is stock. It has about 80,000 miles in my truck, and I don't know how many from before. It got new distributer, wires, plugs, this summer. The stock carb was also rebuilt stock. It had dual exaust before, but a few years back it was switched to dual into muffler single out. No cat on it. Not sure of the gears, or if trac-lok or not. Tires are stock 235 75 R15's. I can't break them loose on dry pavement unless around a corner, and then not very much at all. If I get on it off the line when it is raining, I can get them to break loose for a while. I recently noticed after driving for my 70 mile trip to college, when I stop and leave it in gear at the stop lights, it doesn't idle very good. It kind of surges between 500-600 rpm. Any ideas? There has to be something wrong here, Right?

John

 

I have a 351M in a 78 F-250 with 4:11's and 33's. The engine is a stock rebuild with only about 4K on it. It has a lot of low end torque. I can't keep from spinning the tires when I start out, but it is a longbed and is very light in the back. If I fill up at the gas pump, drive on the highway, and fill up again, I get 16 MPG. Around town, I've been averaging 9 to 9.5 MPG. This is in Colorado. I had the timing at 14 deg initial, and it would advance mechanically to about 33. Last night, I advanced the timing to 16 initial, and hooked up the distributor vacuum advance to the full vacum port on the stock Motorcraft 2bbl carb. One of the threads on this forum suggested that for an increase in mileage. From testing it last night, it seems like that lowered the full throttle acceleration a little bit. Only time will tell about the mileage. I always have the old settings to go back to I guess. I can't get it to ping by advancing the timing. It just starts missing. Haw far can you advance it? It seems like there's a too far point. For some reason, it doesn't ping. I've also owned a 400M in a '79 Bronco. It got a flat 10 MPG. It ran pretty well until I got a very bad rebuild on it, and it never ran the same. Very bad.

Jeff