I put a 351W long block from a 90' F-250 (plow truck) in my 96' F-150, just using the 96' upper intake, exhaust manifolds, valve covers, and ignition. It works just fine, has stock heads but was overbored 0.060", I bumped the valve timing 2*, and the base ignition timing is at 13*. I consistently get 16.5 or 17 mpg on the highway, 31 miles to work each way with one slow down to 40 through a small town. Stock tires and consistent maintenance does the trick for me.

Just saying, that era of 351W should work just fine if it has good spark, fuel, and compression. Check on those 3 items first.
Is the cat plugged? I've heard of the air pump never shutting off and over heating the first cat till it melts, doesn't always plug completely and will act like a major dog of a truck but still go down the road at whatever speed.

 

One thing I noticed that nobody really touched on was axle gearing. Do you happen to know what the axle ratio is in the rear end (and front if 4x4)? In these years Ford was notorious for running super tall gears in a lot of their trucks, especially 1/2 tons. Both of my six cylinder (manual trans) powered F150s had highway gears, the 84 had 3.08s and the 96 had 2.73s. In stock trim both trucks were slow, underpowered, and hard on fuel. Since then I have regeared both, the 84 now has 4.10s and the 96 has 3.55s. The both have more get up and go off the line and don't seem near as sluggish when hauling or towing. And fuel economy, well if it hasn't stayed the same I would dare say it has gotten better.
You mentioned your "new" F250 has the E4OD trans, they seem to be a good tough piece but they do rob a fair amount of power. Not only that but the shift characteristics of the E4OD is completely retarded. I would suggest going to a "lock up delay" kit and maybe adding a shift kit to firm things up a bit. A friend of mine had a lock up delay kit installed in his 95 F350 Powerstroke, he said it made a huge difference in performance... the truck wasn't so doggy going up through the gears.
Hope this helps a bit.
John

 

you need to calculate your CR. Keep in a couple points under 10.0:1 or you'll be running 91 octane all the time.

I asked about axle gears on the first page and nobody answered me.

 

I can't calculate the compression without knowing the deck clearance @ TDC, cc of the valve reliefs and the dish of the pistons (if any). If I know the cc of E7TE heads and the stock compression I can work it backwards. Plus, if the E7's are ~60cc then it's pointless anyway. I think I could get by on 89 Octane with between 9.5 and 10:1 with the closed chambers and some good chamber polishing. A well polished chamber can be worth almost a full point in compression in terms of octane requirement.

 

E7TE heads are rated to have 64cc chambers and stock CR on a 5.8 with these heads is listed as 8.8:1. In reality the head chambers vary between 62cc and 64cc but that doesn't have a hugh impact.

 

So, do you think swapping a set of C9 351W heads would be feasible? They flow slightly better in stock form and with a mild pocket port would be a fair improvement. They should also give a slight bump in CR and I'm gonna go out on a limb and say the older chamber design may also offer an advantage in terms of quench (could be wrong).

I guess the question(s) is/are will the water jackets and intake bolt holes match up and will the difference in rocker arm design create issues? Since the late model 302/351W used the same heads, would the pushrod length be the same?

I know a set of iron GT40 heads would be better & easier, but I have several sets of good '69 351W heads collecting dust. FYI: If you haven't already seen it, there's a cool head flow chart on Allfordmustangs.......

Ford Mustang: Mustang Tech: Engine: Ford Head Information Center

 

I believe I remember bringing this up when I was doing some research during my 351w rebuild and the consensus was that the 69 heads would be better than the E7's but they would have taken more work at the machine shop to get them ready to bolt up... thus they were not financially feasable for me. But that's b/c I didn't own a set.

And correct me if I'm wrong but did the 69/70 heads have hardened seats in them???? That might be some extra $$$ at the machine shop.

I'd think with a P&P on the E7's with some 1.7 rockers and you'd be breathing just as good at the C9's... Obviously the GT40's are the popular option around here for cheap HP, but I'd say go for the C9 heads! I don't know many if any guys around here that are running them and I know back in the day those heads were the "cats meow!" I go with them just to be a little more origional than others and I can't speak for everyone but I'd love to see some dyno numbers with those heads!

Sorry can't help with p-rod length and other specific questions...

 

No, they don't have hardened seats (good call). I was thinking of the bump in compression to around 9.25:1. I drive the truck a lot, so hardened seats would be a requirement. I do have a complete '69 4V 351W engine that has been completely rebuilt with hardened seats, a factory 4V intake (rare) and a mild Comp 260H cam. I was kinda looking for an early '80s F150 shortbox to drop it in. With everything in mind, I agree that you'd be as well off to start with the E7's, mild pocket port and have them milled. Which brings us right back to just buying a good used set of GT40s and have the best over-all scenario.

 

The E7 vs GT40 debate is one that I was making myself and I think... IF I'm not mistaken we decided that GT40's would be outside the capabilities for the SD computer that is in the 87-94.5 gas trucks.

I just noticed you have a 91 which will have SD (speed density) computer. SD basically means your computer will calculate the amount air your motor needs from a predetermined chart... Instead of a MAF system that will use a air sensor to give your motor what it needs. MAF systems respond way better to cams, intakes, heads, etc... Than the SD system does. Making major modifiaction to the motor itself will require you to either convert the truck to MAF or go backward in time to a carb...


just fyi...

 

Not entirely, there are at least a couple guys here with those heads and the Crane cam on an SD 5.8 and it runs fine from all reports.

 

oh... darn it then!! I do remember some controversy on one of my posts about whether the gt40s would work with sd or not when I was doing my 351w rebuild....

I wish I had known the gt40's would've worked! Grrrrrr..............

 

My truck's actually a '97, but it is still SD since it's a F250HD. I'll probably never convert it to MAF. The SD is simple, reliable and works very well for a daily driver.
It kinda gets a bad rep due to some limitations, but it does respond to minor mods and at WOT it doesn't matter anyway. I do, however, like the flash tuning potential of the newer OBD-II.

 

I'm pretty sure all the 97 F250 gassers should have been MAF... SD stopped in 94-95 almost completely!

Maybe a PO put a SD motor in it on you...

 

Nope. all F250-350's were SD up until 98 when they changed body styles. Unless you had a Cali truck, then it may have been MAF.

But i'm one of those people who went ahead and used the GT40 heads, a good cam, 1.7RR and headers and i do not have any problems with the motor at all. Idles like stock, and will put you back in your seat. Its a torquey little small block, thats for sure

 

maybe I need to P&P some gt40's for the 351w! Good to know...

I would have thought that since Ford when to MAF in 1/2 tons they would have done the same in 3/4 and 1 tons... But I guess this is Ford we are talking about! They like to do screwy s***!