Hey guys...first post here from Nashville AR....been a lurker for a while. I have a 1977 F150 XLT Lariet LWB 2WD. It has a 400, C6, 9" rear end. I'm getting around 8-9mpg...30 mile round trip a day...its eating my lunch. Long story short...the 400's mains are starting to go and it is going to need to be pulled soon. I would like to know with this setup...everything I will need to do the 400/C6 to 300/C6 swap. I could go C4 but would rather just find a smally C6 to go with the 300 so I would have to move tranny crossmember or change driveshaft...This is what I know so far is needed...

*300 inline six
*small block C6...either casing to switch internals or another tranny
*Engine mounts and Towers

I'm guessing the small block C6 should bolt right in....what about throttle hook up...kickdown cable for tranny...fan shroud...things of that nature. I'm not in a huge hurry...running ALOT of Lucas...so the mains will be okay for a while...lol. Been back and forth SOO many times whether to go through the 400...I have a 351M also I could work into the picture...or if I'm going to the trouble of taking the engine out...why not spend the time and money to put the 300 in...double my fuel economy when I get it setup right....and have more low end torque...I putt around anyways so speed is not an issue. I'm an agri (FFA) advisor and own a peach orchard...this truck is a work truck....to and from school....and working around the peach orchard. I have researched this alot...just wanting to get the in depth pieces of information that I'm missing from the ones that have done this before or know of it being done. I also thought about trying to put some 3.08's or maybe a hair higher in with the 400 and try it out...but i'm afraid it wouldn't help too much. The highway is what is killing me...if I keep her under 50mph its not so bad. I also like the longevity factor in the 300. Again thanks for all your help and look forward to hearing responses and opinions...will post pics of truck soon.

 

What rear end gear do you now have? What rpm @ 60mph? Stock tire size? It sounds like it may have pretty low gears if it's winding up by 50, so a gear change may get you further than you think.
Are you going to be rebuilding the 300 or just swapping one in? If either way you have to rebuild, then you would have to decide wether the cost of the swap is justified by the +4mpg or so (300 17-19mpg vs 400s 12-14mpg both fresh with a reasonable gear). If you plan on keeping it for a while the swap would definitely pay for itself in time.
Also, you won't have more tq with the 300 over the 400. The 400 had the longest stroke ford ever made. The 300 is still very tqy and super durable though. My last 300 went 250k before I sold it, started at 18-20mpgs (EFI) when new and ended up at 9-10mpgs by the time I let it go. Still reliable, but tired.
Just some thoughts.

As far as the swap goes, I've never done this swap so I can't tell you specifics. You are on the right track though with mounts, and bellhousing though. A heads up when looking for towers/mounts, ones for FE motors from earlier years also fit the 300.

BTW, Welcome to FTE!

 

I think the rears are 3.50. I'm not for sure...the plate says 13J for the axle. I have not been able to find that number...tried on fordification.com but could find it. I am also running 31/10.50's on the rear. They were free...lol...but do help. I'm not taching out...but it just does alot better under 50. I do plan on keeping the truck...I love the ol' girl. I think it would pay off...not only with mpg...but engine longevity and ease of service. I would just like to have all my parts together before I attempt the swap...I would assume the C6 linkages and all would still work fine. I'm wondering about the throttle hook up...kickdown cable...and radiator...read the radiator would be fine, but wondering about the shroud. Hoping some folks that have seen or done this will chime in soon. I'm pretty decided on the swap the more I think about it. I even contemplated just selling the truck and getting one with the 300 already in it. But its hard to find a lwb, 2wd, f150, 300 and c6...I wanna keep my c6...I have the 6050lbs GVWR chassis setup and really like it. With the C6 and 300 it would be tough as nails. I was thinking 3.08 rearend, 31" tires, c6, and 300 would get close to 18 or 19 mpg with the way I drive. bumping up from 8-10 would a NICE step up...I drove it 50 miles yesterday. Again...great to be here and thanks for ALL your help.
Anyone have any pictures of say 75-78's with 300's in them...2WD. Pics of the engine bay...or maybe pics of swapped in 300's? would love to be able to study some pics and see how the throttle and such tie in.
What about ignition? I have the Duraspark ignition...I have read that will not work with the 300...is this true?

 

Here are a few pics of her. Have alot to do but for 700 bucks I can't hardly complain.

























I really like the fact that its still pretty well original...down to the 1977 first year aluminum truck wheels...have the centers for them...just not on it.

 

cool trk man i have the twin to urs but mine has a 302 in it.the main thing ur gonna need is frame mounts the accelorator cable n bracket u can still use ur radiator just turn it under the motor n add another hose to it i run a bigblock rad in all my trks everything else is self explanitory

 

thanks! do you have pics of your truck? what do you mean turn the radiator under the motor?

 

i meant turn the bottom rad hose just under the engine use a peice of pipe to connect another hose to it n over to the rad ive been runnin mine like this for 7yrs now w no problems or u might b able to find a long flexable hose to do the same thing but all i had at the time was what i used so if it aint broke dont fix it ryt lol

 

ill try to put a pic on here tommarrow

 

Your sure right about that!! Would love to see some pics of my trucks sis. What kind of price should I be looking for...found a supposedly running 300 and C6 today for 650 on craigslist...I think I can do better than that. What do you guys think?

anyone know what 13J axle ratio is?? still not able to find it.

 

I think your going to spend more time and effort than the return will justify, but it's yours to do. A 300-6 with a high geared rear in a heavy 8 ft pickup is gonna work hard?

Having said that, if it were mine (it ain't) I'ld pull the 351M or 400, slap in some rod and main bearings, have a valve job done on the heads if needed keep my AC and maybe convert to R-134 and then if I still didn't know the rear gear, I'ld jack her up and spin the wheel on one side two complete revolutions by hand counting drive shaft revolutions. If she's smokin', I'ld consider a set of rings, etc .... but if it's just bearings you think .... mine has never used oil but I had to put bearings in at 75 thousand miles. I did it laying on my back, motor in truck, never touched pistons. That was 1992.

Then I'ld find me a 9" hogshead with a set of 3.00 gears or maybe higher for those flat Arkansas roads and ride.

I've seen 14-15 on my heavier 4x4 with 3.50 gears and 351M ..... but you get only 8-9 ? Something's not right. If that truck has the original Ford Motor Craft 2 bbl carb, I'ld say good chance the power valve is leaking, maybe the accelerator pump as well. My step daddy had one like your's, was a 351M 2bbl and it sucked gas worse than my '77 4x4. One day I noticed it looked like a puff of black smoke, so I pulled the carb and tore into it and sure enough, it needed overhauling. Made a big difference in mileage.

 

I would be tickled if I could get up to 14 or 15 with it...I drive at 55 or less...it has a holly 4brl on it. Not a double pump...525cfm I believe..was on it before I got it...just has an adaptor. I never pull anything...and when I do its not much...normally a 16' trailer with some scrap on it or something from the orchard. Does use oil..but does not smoke...its out of the crankcase vents...Probably valve guides leaking...no smoke from tail pipe...may need rings...If I keep it I'll pull the engine and look it over. I do wonder if the benefits are worth the time and money. I know a longer stroked 400 "should" do a bit better putting around like I do than a 351m. I'm probably going to jack one wheel up...but I figured someone might know what that axle code was...I look it up and never find that certain code...that has me bumfuzzled. I had first though to pull the engine put mains and rod bearings in it...maybe a cam and lifters...do the cam bearing trick for oil psi...and call it a day...but the 300 is an entrieging engine. decisions decisions....lol
I wonder how many have sat trying to figure out what to do in an instance like this? lol

 

Get the rod and main bearings back right and slip in a Melling high volume oil pump and you won't have to worry about doing any tricks with cam bearings.

Sounds like some body wanted that "WHAAAA sound" and didn't want the expense of an intake.

A good stock carb on that 2 bbl intake ...
... OR ...
... a rebuild of what you have (carry some extra pump diaphrams and while you have it open, do the anti back fire check valve mod on the Holly) and a real Performer intake would help.

Also, use a vacume pump and check to make sure the vacume advance is still working on the distributor and check the vac hose to make sure it's getting a vac signal .... I like intake manifold vacume for mileage but sometimes you'll hear plinking and have to go back to ported vacume signal.

That truck will get better than 8-9 mpg.

 

I kind of thought it would...I have a 351m sitting in the shop with a performer on it...dual plane...was thinking about putting it on then started the whole straight six deal. lol. Why do you like manifold vacuum better?? Its ported right now. Already put a pump diaphram in it as it was leaking...lol.

what will anti back fire check valve mod do?? I'm not a holly guy. Actaully I'm more of diesel guy...another reason the inline 6 intrigued me...they'll run forever...fewer moving parts and such, anyways. The more I think the more I may keep the 400. I'd like to also put a better cam...well at least not a "retarded cam and chain set". Something from idle to 4500 or something. I've researched them some. I like what Crane has to offer. I just do not want to put money in something that I'm still going to get 9 or 10 mpg and never drive over 55...drives me nuts. I know it can do better than that. Wish I had a tach on it.

 

take u a 300 six put an alum intake ,header,&a cam u will have a motor close to 300 hp w about 450 ftlbs of torque then u have a good work trk and a cool cruiser

 

First thing to do is go through the carb. Pull that intake off the 351 and put it on your current engine. Holley carbs have a bad habit of destroying power valves when they backfire. This will give you horrible fuel mileage. The check valve seals off that passage when a backfire occurs. Look up the list # on the carb to find out what size it is. Have you looked for the tag on your rear diff.? That tag should tell you the gear ratio. Also, you can go to your local auto parts store and order a timing set for a 1970 fullsize car with the 400. That will help your cam timing. Throw on a set of headers and dual exhaust. Had one I got 16 mpg with on the highway. Also get yourself a vacuum gauge and figure out where you run at cruise. Change your power valve to be a couple points below that cruise #. Just a few thoughts. Loved my 400.