Transmission and t-case limitations- motor swap (kinda)

Folks, need to pick some brains about an idea that I got earlier today.

I have a 1993 Ford f250 with the 351w and a ZF-S5 M/T paired with a 4.10 rar.

Im going to be swapping the heads out for GT40 heads, along with the intake and a new exhaust. Depending on motor health I may add a supercharger.

I had the brilliant (or dumb) idea of taking the 1995 Ford SVT Lightning motor (also a 351w, but it produced 240hp and 340ftlp or torque) and rebuilding that and swapping it. Given it would have the GT40 heads and roller cams.

But my question lies in this: lets say I rebuild it to give a touch more power AND supercharge it. The small block tranny is rated to hold 420 ft-lbs of torque with a ratio of 5.2:1 (1st) and 0.76:1 (5th). Im worried that the transmission can’t hold this if I overdo it. Ive heard (with no confirmation) that the big block Zf-s5 could hold 470ft-lbs of torque. That may be for the 7.3psd (or idi year depending)

Can the bell housing be swapped to mate the two? Or can I switch the guts over? Or???

Also: transfer case for 4x4 (already have on the truck stock), i have no idea what I may need if I swap transmissions, or if the t-case is different from the big block motors (460 and 7.3).

Would I need to rob a 460 of its tranny and t-case to make this work?

Just put a c6 behind that engine

Hard pass bud. I hate auto transmissions. And a C6 only has 3 gears…

With that amount of torque, 2 gears would be enough.:grin:

With a one ton 4x4 truck, what you need it torque, not horsepower. If you find a 460 to take the transmission off, just put the motor and all in.

460 has a different tranny, well bell housing anyway. Not sure if you can swap those. I think when it went into ‘96 all the ZF tranny’s went to a 470ft-lb rating.

Besides, Here a 460 and 7.3 parts truck will cost you the same… $8000+ maybe 6 with a blown motor. Might as well rebuild a 351w which can make power if you want it to. And its a solid unit, 460’s are good, but they fall off after awhile. Or just get beat to death, or timing slips and I hate timing.

Old mopar, I could, but doing 35 at 5000rpm makes no sense. Having 5 gears to cycle is great. Makes cruising even with a trailer easy.

The reason I won’t motor swap to a 7.3, is because in a couple years or less ill be retiring the old gal to cruising and doing light chores. No more towing, ok maybe a redneck plow and road leveler but whatever.

Do all those extra gears add speed beyond what the 3 speed produces? I don’t think it works that way. I don’t think they offer a double overdrive 5 speed.

Funnily enough, I did something similar with my 1995 Bronco. It had the 351W/E4OD combo. I found a wrecked 1995 Lightning. And I bought the heads and intake manifold off of it for a song. Luckily both my engine and the Lightning’s engine were mass-air so, compatibility hiccups were minimal. If you just swap the heads, you will need the Lightning exhaust manifolds. The factory manifolds from the F-250’s engine will not work, the exhaust ports on the GT-40 heads are shaped differently than the ones on the stock E7 heads.

As far as I know the transfer case is the same ( BW 1356) for all F-Series and Broncos up until 1996ish. So the F-150/250/350 all used the same one. As far as the transmission goes. It’s rated for 420 ft/lb at 26k GVWR, so it’s not quite as bad as it first seems. And a worked over supercharged 351W is going to be making a bit more than 470 lb/ft of torque anyway. I don’t think swapping a stock S5-47 is going to buy you much more capability, at least not to the point where it would be cost effective.


More gears = less RPM’s. Easier on the motor, enables a higher speed. You’ll eventually tach out, and as we all know, OBS Fords aren’t huge rev fans.

For 80mph in 5th (.76:1) i run right about 3k rpm, and I don’t like going any faster even though semi’s pass me from time to time. Im usually the slow poke and run 70 to drop RPM’s and ease up on the motor. 3rd in a C6 is 1:1, which is my 4th gear. That’d be ohhh 3500rpm at 80. Pretty taxing and that sucks fuel.

Also, my truck is a M/T as is, I would have to swap a lot more for an auto tranny that offers no benefits.

Fair point. I should note im not going to run much boost. Enough to take up a little slop and make hills a touch easier.

Are there any other M/T’s that would fit that can handle more power, with decent reliability?

These are 302 heads, not 351W heads. The valves are too small for the big motor. Choose an aftermarket head with bigger valves and ports.

If you want a cheaper alternative than supercharging and then having to worry about the transmission, go bigger. Rebuild the engine with a stroker crank kit ($2000). That gives 408 cubic inches for BIG, broad torque. Plenty of grunt to get your attention. The block prep and the crank kit are cheaper than a supercharger. Heck, a ready-to-go long block is $5500 from Summit rated at 425 hp and it should run on pump regular. It doesn’t list torque but it must be greater than 450 ft-lbs.

The trans and T-case you have is plenty strong enough to take all that assuming it is all in good condition. And, of course, you don’t need to worry about bolt pattern.

+1 to @Mustangman. Remember, there is no replacement for displacement.

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Yes they are 302 heads, however the 351 can accept them. The GT40 heads have varying combustion chamber sizes, I believe the biggest was 65cc off the explorer. They do work, there is another thread about just doing that and it does make a difference at elevation. Let me find the link.

Im not super set on a super so that may be a good option. All I want is a decent bit more power because I live at 9k feet in elevation. Swapping heads and allowing the motor to breathe plus a redo after 26 long years of use, will be a huge jump from what its at now.

Ill have to look into that stroker kit, dang good idea. Heck i’d be doing cartwheels if I pushed 400ftlbs put of the motor.

My point is… the GT40 heads don’t flow enough for a 351. The valves are small 1.85 inch intake and 1.54 exhaust on the GT40 Cobra or Explorer heads. That means peak power at, oh, 5200 rpm or so on a 351. Any good aftermarket heads will come with 2.02 intake and 1.6 exhaust valves and produce more torque and peak HP. Since you are at 9000 ft elevation, 10:1 compression with aluminum heads should run well on pump regular as long as the cam isn’t super conservative - short duration.

But a 4 inch stroke crank… THAT will just put the cherry on top!

Just a heads up, my truck is EFI and tachs out at 6k rpms. I don’t need high RPM power. I need the power band to stay in a similar range to what I have now, 2300-2900rpm.

That being said, what heads would you recommend?

This looks to be pretty close to what you want…

185cc intake port aluminum AFR heads making 500 ft-lbs So something around 170cc on a 351 and something closer to 185-190 cc for a stroker motor.

Edelbrock Performer aluminum heads would work great on the 351 and Performer RPM’s for a 408.

The problem you will have, if you are keeping the factory fuel injection, is nearly any modification you make will require re-calibration of the ECU. Likely needing some chassis dyno time. And I don’t know what can be done with the 1993 ECU - re-flash, chipped or what? - to make those recalibrations.

The do this sort of stuff in Hot Rod magazines, for example this 505 hp 351W/GT40 combo from a 2014 article. Some of the photos and illustrations appear to be missing, but the text still might be of interest.

The only experience I have with the 351W engine is that one time I was d riving a Ford Galaxy equipped with that engine & the water pump failed when I was out in the middle of nowhere in Colorado, and the only mechanic available happened to be across the street from a cowboy barn dance in process. I have to say that barn dance was some experience.

Ohhh that is of great interest. Test 2 setup may be what i lean towards. That’d be more than enough power for my use in the truck.

If I decide I need more, ill scrap together funds for a 7.3psd and really push some power.

That is a race engine;
Starting with a bone-stock 351W truck engine, we bored the block 0.020-inch over, fitted KB flat-top pistons to the stock crank and rods, installed a Crane hydraulic roller cam, and reassembled the engine with GT40 cylinder heads. That combination was good for 391 hp at 5,900 rpm and 405 lb-ft at 4,300 rpm. After that, we dropped Trick Flow’s 11R cylinder heads on the same short-block and made 505 hp at 6,700 rpm and 451 lb-ft at 5,200 rpm.

Those engine speeds and torque curve are unsuitable for towing.

Power loss at 9,000’ elevation is very noticeable, a supercharger will bring the performance down to sea level and then some however is it worth the effort? If you want to keep the same truck, perhaps. A used turbo diesel truck might be had for the cost of the modifications to this truck.