302 to 351 or not?

351W Swap In A Fox Body Mustang
VRISTANG

Note: This discussion focuses on EFI conversions as this is the most common route taken.

Engine Mounts-
Stock 5.0 mounts will bolt up to the 351w. Aftermarket alternatives include solid mounts and polyurethane mounts. Convertible Engine mounts are supposedly reinforced / stronger. Another alternative is lowering engine mounts from HP Motorsports. These are solid and lower the motor ¾”. Lowering engine mounts will reduce clearance between the oil pan and k-member. This presents clearance issues with some aftermarket pans and stock k-members, but should be ok for the FRPP pan.

Heads-
302 heads are the same as the 351w heads with the exception of the head bolt diameter. 302 heads have a 7/16” head bolt hole and the 351w has a ½” head bolt. Opening the holes can be done by hand or sent out to a machine shop.

Exhaust Headers-
Stock 302 headers will bolt up the head of a 351w (since the heads are basically the same), but will not mate up to the mid-pipe due to the extra width of the 351w. There are many aftermarket suppliers of 351w Fox Body headers including MAC, FRPP, Kooks, Hooker, and Hedman.

Intake Manifold-
Since the lifter valley of the taller 351w is wider than the 302, a new lower intake is required. Aftermarket suppliers of 351w intakes are numerous. Some 351w lowers will bolt up to standard 302 upper intakes, which can help reduce conversion costs. Be cautious with intake height if you are trying to clear a stock hood. Another option is to cut down the upper intake (This is easier on the plastic box upper from Comp Cams. This will cause clearance issues between the TB and valve cover if the upper is trimmed more than ¾”).

Oil Pan-
The 351w is wider so a new oil pan is required. The lowest cost option is probably the FRPP 351w pan for Fox Body applications. Aftermarket companies have standard volume, high volume, drag race , and road race pans available. A pan specific pickup tube and dipstick will also be necessary.

Oil pump-
The 351w oil pump is different from the 302 (mostly external). These are readily available in standard volume, high volume, and high pressure models.

Distributor-
The taller 351w does require a longer distributor. This can found from several stock Ford factory applications, mostly pickup trucks/vans. Some aftermarket suppliers do have electronic/TFI distributors available, such as MSD and Accel. Be sure that the cam drive gear is appropriate for your application. Roller cams require a steel dist. gear.

Engine Management-
Any stock 302 computer will handle a 351w. The EEC-IV will be fine until the combination gets more dramatic with larger injectors, heads, intake, and cam. Aftermarket plug in style chips are not going to offer ideal performance. The best solution is to invest in a chassis dyno tune or an EEC-IV computer tuning system.

Flywheel/Flexplate & Starter
The counter weight of the 5.0 is 50oz. The 351w counterweight is 28oz. You can reuse a 5.0 flywheel if you have it rebalanced at a machine shop. This is probably the easiest and most cost effective alternative. If purchasing new parts just make sure that the flywheel weight and starter tooth count are correct.

Harmonic Damper-
Again this must be matched to the counterweight of the 351w. Another consideration here is getting the crank pulley to line up with the rest of the serpentine belt system. FRPP does have a damper available specifically for this application.

Fuel Injector Rails-
The stock 302 rails will not be wide enough to fit the wider 351w lower intake. If the flex line in the front and rear of the stock rails is removed and replaced with longer sections of high pressure fuel line the stock rails will work just fine.

Fuel Injectors-
Proper injector size will depend on the application.

AC/PS-
This is the only stock 5.0 accessory bracket that requires modification. The stock AC pump and Power Steering pump will bolt up if a ford bracket is used. Without AC (PS only) the FRPP part number is M-8511-A351. For both AC and PS applications the FRPP number is M-8511-B351.

Emissions-
The crossover tube from a 302 can be used if it is cut and a section of high temp hose is used. The 302 air pump will bolt up correctly, and there should be no issues with the air injection system. The EGR should mount up properly, but this will vary with intake manifold selection. Routing of EGR hoses may need to be modified.

Hood-
The easy way to do it is get a taller cowl hood to replace the stock hood. This offers the aggressive look that many are looking for. If desired though, the 351w can clear the stock hood. Clearance will depend on engine mounts and intake manifold selection. If necessary some of the bracing on the underside of the hood can be cut away.

Items Not Affected By The Conversion

Transmission- Just be sure to use the correct input shaft bearing in the crank.
Bellhousing-
Valve Covers
Water Pump
Altenator
Clutch
Timing Cover
Radiator
Timing Chain

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I have that saved on my computer. Great write up. I intend on doing a 408 eventually, in a different project car though, not mine.

Your reply (of 2 years ago) was very helpful. I want to put a stroked and supercharged 351W into a '94-'95 Stang. I think I know most of the answers, but my main concern now is whether such a converted car can pass emissions in NY. There's no inspection of engine parts here - at least for a pre-OBD2 car. But there is a tailpipe sniffer and a preset dyno run. Any thoughts?

I haven't rebuilt my 302 or even worried about it because once it pukes, a 351w is going in its place. However, i would try my damnedest to get a roller motor (i *think* they were '92+ 351W but i'm guessing). This way any current 302 cam will slip right in and you won't have to screw with breaking in flat tappet cams and adjusting rockers. You can also get more aggressive cam profiles with a roller. You could go with a retrofit kit, but the small circle base cams are more expensive and limited in specs because of their small size (mainly limited in lift).

(and holy crap i just realized how old this thread is...lol)