what's needed to drop a 351 in a fox?

cenok is family

15 Year Member
Jun 25, 2003
Norman, Ok
I think i have to get the correct motor mounts...are there any other special parts needed to put one in my 87 gt? i figure i'll have to get a cowl hood too. will my transmission, flywheel and clutch all bolt up to the 351? also i just got a set of long tubes for my 302; will i be able to use them with a 351? thanks for the help
  • Sponsors (?)

I think i have to get the correct motor mounts...are there any other special parts needed to put one in my 87 gt? i figure i'll have to get a cowl hood too. will my transmission, flywheel and clutch all bolt up to the 351? also i just got a set of long tubes for my 302; will i be able to use them with a 351? thanks for the help

The motor mounts are the same, depending on a few things, you may need a cowl hood. Your tranny will bolt up, but you will need a 28oz flywheel. Your headers will bolt up, but you will have to do alot of bashing on your body to get them to fit.

You will also need a double hump 351 oil pan, 351 EFI dizzy, 351 intake, and a set of swap headers.
use convertable motor mounts out of a fox, your tranny should bolt up, not sure on that one.

Your headers wont work, you will need 351 swap headers for the fox body.

Depends on the intake manifold as to if a hood will work or not, but if its any performance wise, youll prob need a new hood, or cut a hole in the factory one
E7s will work on a 351w, but they will seriously choke the power. A hci is good on a 302, but a hci is great on a 351w.

I am using 'captured' 'vert' mounts, Lightning lower, and comp cams box upper. I still had to trim about .700" off the upper intake.
I did clear the stock hood though.

Here is everything I have been able to find on the swap...

Updated 12-26-06


302 to 351W Swap in a Fox Body Mustang



This FAQ was written for converting a T-5 5.0 efi Mustang to a T-5 351w efi Mustang. The conversion will be slightly different if starting with a 2.3l or carbureted Mustang OR converting to a carbureted 351w. Converting transmissions is beyond the scope of this document.

Background Info-

The major disadvantage of the 302 is its lack of strength at high power levels. Most will agree that at ~500hp the factory 302 block will try to split in half. For many the solution to this is an aftermarket 302 block, which can be expensive.

Another alternative is to swap in a 351w block. The 351w is supported by the aftermarket nearly as well as the 302, but can handle much more power than the 302. Some common safe power numbers given for the 351w are usually in the 600-700hp range. There are 2 basic production blocks available; the 69-70 blocks had a deck height of 9.480”, and the 71 up blocks had a deck height of 9.503.” This is compared to the 302 deck height of 8.200”.

351w Casting Numbers

The casting numbers are on the passenger side near the starter location. You will have to turn the block upside down, or use a mirror to see them.

The year will be designated by the first 2 digits of the casting number.

The first digit is the decade and will be a letter. C=1960's, D=1970's, E=1980's, and so on. The second digit will be a number and specifies the year of the decade. Some examples follow:




For more info on how to identify various Ford engine blocks check out the following link…


Getting Into the Nitty-Gritty

The 351w Engine Block -

69-70 - High Nickel content and thicker main webs (These are the only Production Ford 9.480" Deck Height 351w blocks)

71-74 - Reduced Nickel content thinner main webs (71-up had 9.503" Deck Height)

75-91 - Reduced main web thickness

92-On - Lifter Bores were lengthened to accept roller lifters

There were some 351w Mexican blocks as well. The early versions of which are desirable due to their beefier castings and higher nickel contents. A Mexican block can be identified by the useless looking knobs cast into the block on either side of the timing cover, and an “Hencho en Mexico” cast into the lifter valley. Mexican blocks were supposedly used on some US vehicles, but they are a fairly rare find.

Camshaft and Lifters-

The specs of the cam will depend mostly on what your goals are for the motor. Cam spec selection is way beyond the scope of this FAQ. What you want to watch out for is selecting the correct base circle for the lifter combination and using the stock 302 HO firing order (since you are most likely reusing the stock 302 computer).

69-91 351w blocks -
Roller Lifter Option 1) Standard Base Circle Cam / Aftermarket Linked Bar Hydraulic Roller Lifters
Roller Lifter Option 2) Small Base Circle Cam / 302 HO Roller Lifters

92 & Later 351w blocks -
The Standard Base Circle Cam can be used with 302 HO Roller Lifters.
A Small Base Circle Cam is not needed in these blocks.
(The 92 and later "roller" blocks will have a F4TE casted into the block near the starter)

If using solid lifters (either flat tappet or roller) then a standard base circle cam can be used on any year 351w block.

If in doubt, ask the company you plan on purchasing the cam from (or better yet a reputable engine builder) what would be appropriate for your application. They will need to know what year the block is and what lifters you plan on running. Additionally it may be helpful to have your rocker ratio available, and what piston you will be using if not stock.

NOTE: Small Base Circle Cams are known to be less than ideal, as they are weaker. There are not as many cam profiles available for the Small Base Circle Cams, so your Off the Shelf Cam selection will be severely limited. If possible, it is recommended to avoid the Small Base Circle Cams.

Firing Orders-

Early 289 & 302 1-5-4-2-6-3-7-8

302HO & 351w 1-3-7-2-6-5-4-8 (this is all 83-93 Mustangs, and all 5.0 Explorers)


Again, there are far too many options available to cover here. Check with the cam manufacturer on what length pushrod you will need. Or even better, you can use a pushrod length checker and measure them yourself.

Roller Lifters-

The stock 302 lifters can be swapped over to the 351w (see the cam discussion above) with a little machining/grinding and a reduced base circle cam.

First the spider will require 2 holes to be drilled in the main valley. These holes will be drilled over the cam bearings, so great care should be taken not to damage the camshaft or bearings. Risk can be minimized by removing the camshaft, and drilling the holes before the cam bearings are installed. Some grinding may need to be done to allow the factory 302 dogbones to sit flush on the 351w block as well. A Dremel is adequate to get the job done. Be patient and work slow; it is easier to remove material than put it back. Of course it would be best to do this work before having the block cleaned and prepped for assembly. Ford Hydraulic Roller lifter (for both the 302 and 351w) part number is M-6500-302.

If all of this does not sound appealing to you then maybe some of the aftermarket roller lifters will be a better option. These tend to be fairly expensive however. Look for lifter pairs that have a link bar, connecting each pair of lifters.

Rocker Arms-

This will depend on the heads you select. All of the same rules that apply to selecting rockers for a 302 still apply to the 351w. Options to consider are Pedestal vs. Stud Mount, Roller vs. Non-Roller, and Brand.

Engine Mounts-
Stock 5.0 mounts will bolt up to the 351w. Aftermarket alternatives include solid mounts and polyurethane mounts. Convertible Engine mounts are rumored to be stronger & shorter. Another alternative is a set of lowering engine mounts from either Year One, Moroso, or HP Motorsports (HPM). These are solid and lower the motor ~¾”. Lowering engine mounts are useful for gaining hood clearance, but will also reduce clearance between the oil pan and stock k-member. This presents clearance issues with some aftermarket pans and stock k-members, but should be ok for the FRPP pan. The use of an aftermarket tubular k-member may help improve clearance with aftermarket oil pans.

Un-Confirmed –

From 87-90 the convertible Mustang had the “captured” mount design, while the Hardtops had the standard design. The captured style mounts are said to be ½” to 1” lower, and to be stronger.

In 90 and later Mustangs, ALL were equipped with the captured design.

Aftermarket Prothane mounts are said to mimic the design of the early Hardtops. While the Energy mounts are said to mimic the convertible “captured” mounts. So, Energy Engine Mounts should be the same height as the 87-90 convertible “captured” motor mounts

302 heads are basically 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, if done with care. It would be best to send this work to a machine shop however. Keep in mind however, that even ported E7 heads are considered to be restrictive on a modified 302. Putting E7 heads on a 351w will limit the potential of the motor. Look to the Aftermarket companies like AFR, TrickFlow, Edelbrock, Holley, and Canfield. Most of these heads will make more power out of the box, than an E7 with full port work.

Exhaust Headers-
Stock 302 headers will bolt up to the head of a 351w (since the heads are basically the same), but will not mate up to the factory 302 mid-pipe due to the extra width of the 351w, and may even make contact with the transmission tunnel. There are many aftermarket suppliers of 351w Fox Body Swap headers including MAC, FRPP, Kooks, Hooker, and Hedman. The Ford shorty headers are p/n M-9430-A58.

Here is a discussion on fitment issues with LT headers - http://www.corral.net/forums/showthread.php?t=875671

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. Most of these companies offer a 351w lower intake that will bolt up to their 302 upper intakes, which many Mustang owners may already have. Being able to reuse your current upper intake can present a significant $ savings.

NOTE: It is often rumored that the stock Mustang upper will bolt up to a stock 351w EFI truck lower. No such combination has actually been found to work though.

However -

As of December of '06 there is a new product available for adapting a truck 351w EFI lower intake, to a Fox Mustang Upper intake. The adapter can be found through B.C. Broncos at http://www.bcbroncos.com/store/. Here is a link directly to the adapter http://bcbroncos.com/store/product_info.php?products_id=1176&osCsid=9fd34cb5d813d8838e446ddda9faf1de.

Be cautious with intake height if you are trying to clear a stock hood. If the above mentioned drop motor mounts are not used then, another option for gaining hood clearance, is to cut down the upper intake. This is easier on the plastic box upper from Comp Cams, as the aluminum intakes will require cutting/welding followed by machining to square up the mating surface.

Shortening the upper intake will cause clearance issues between the TB and valve cover if the upper is trimmed more than ~¾”. Keep in mind that TrickFlow and many other aftermarket head companies have raised the valve cover flange up to .300” which will limit how much you can trim from the upper intake. Of course the use of tall aftermarket valve covers will be somewhat restricted as well. If you do plan on cutting the upper intake, be sure to do a full mock up with all parts that will be installed later. The part numbers for the Ford 351w Cobra/Lightning manifold are as follows; Upper M-9424-D50 / Lower M-9461-D58.

Oil Pan-
The 351w oil pan rails are wider so a new oil pan is required. The lowest cost option is probably the FRPP 351w pan for Fox Body applications (M-6675-A58). 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. If using a main girdle and/or windage tray, be sure to select an oil pan that will clear these added components. If you can find them, the 351w equipped Crown Victoria and Grand Marquis had an oil pan that will fit in your Fox Body Mustang.

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.

Oil Pump Driveshaft-

It is advisable to utilize a heavy duty oil pump driveshaft. The cost is minimal considering the importance.

If you find that the heavy duty oil pump driveshaft does not allow the distributor to fully seat, then the best solution is to trim about .250” off the bottom of the distributor. This happens because Ford changed the dimensions of the distributor, but most aftermarket companies (like ARP) didn’t change the dimensions of the oil pump driveshaft to match.

The taller 351w does require a longer distributor. This can found from several stock Ford factory efi 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. As mentioned in the ‘Oil Pump Driveshaft’ section there is a potential for interference between the distributor and pump driveshaft. The best solution is to trim about .250” from the distributor.

Engine Management-
Any stock 302 computer will handle a mild to moderate 351w swap. The EEC-IV will be fine 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, such as a TwEECer.

Flywheel/Flexplate & Starter
The counter weight of the 5.0 is 50oz. The 351w counterweight is 28oz. You can reuse your 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 for the other components you already have. Ford flywheel M-6375-A302.

Harmonic Damper-
Again this must be matched to the 28oz. counterweight of the 351w. Another consideration here is getting the crank pulley to line up with the rest of the serpentine belt system. Many aftermarket dampers will come with an appropriate spacer for this application. FRPP does have a damper available specifically for this application (Damper M-6316-C351, and spacer M-8510-A351 or -B351 or -C351)


Thanks to r.barn, who has contributed the following links regarding the Ford spacers…



Fuel Injector Rails-
The stock 302 rails will not be wide enough to fit the wider 351w lower intake. However, 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. Simply cut out the stock flex line and replace it with high pressure fuel line, available from any parts store. A couple of hose clamps will secure the hose in place. It is also important to make sure the hose does not rub on anything.

Fuel Injectors-
Proper injector size will depend on the application. A mostly stock 351w will be ok with 19lb injectors, but with the addition of an intake & Throttle Body (with stock heads/cam) will most likely require 24lb injectors.

Fuel Pump-

A 190lph pump is recommended for mildly modified Mustangs. If an all stock 351w is being swapped in, then the stock fuel pump may be adequate. It should be noted that due to the re-circulating nature of the Mustang fuel system, installing a pump that is too large is not an issue. If in doubt, go with a larger fuel pump.

Heater Core Hoses-

The stock 302 routed the heater core coolant through metal tubes on the passenger side of the lower intake manifold. These metal tubes may or may not bolt up to the 351w lower intake. Either the tubes can be replaced with tubes from another application (junkyard parts), or heater hose can be used to replace the metal tubing. Just be careful that the hose will not bind or rub anywhere, especially the throttle linkage.

This is the only stock 5.0 accessory bracket that requires modification. The original AC pump and Power Steering pump can be reused if an FRPP bracket is used. If using Power Steering only (without A/C), the FRPP part number is M-8511-A351. For both AC and PS applications the FRPP number is M-8511-B351.

Most emissions equipment can be swapped over, and will be required if the car is to pass emissions testing. The smog pump will present few challenges, as the 302 pump bracket will bolt directly to the 351w. Mostly of the difficulty with the air pump will come when ensuring clearance between the headers and pump hoses.

The EGR setup will vary depending on the application. The stock 302 routed the EGR gasses through the lower/upper intake. With some creativity the AIR passages on smog legal heads can be used for EGR, in fact several factory applications used a similar crossover pipe, which routed the exhaust gasses from the heads up to the EGR valve. These crossover pipes can be found on 351w equipped trucks and vans.


Some State Inspections Agencies (California) will require the use of the Emissions equipment that was used on the factory application the motor was sourced from. If you pull your 351w from an F150, you may be required to install the smog pump, EGR, etc. from the F150.

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/modification. If necessary some of the bracing on the underside of the hood can be cut away, and the insulation mat can be removed. In general at least 3/4" will probably need to be trimmed off the height of the new 351w motor, but this will vary greatly with each combination. The reduced height can be achieved with lowering engine mounts (as mentioned under the engine mount section), or by shortening the intake manifold (as mentioned in the intake manifold section). There will be some mock-up needed for each application.


Spark Plug Wires

Some Vacuum hoses may need to be lengthened or shortened

Accessory drive belt length will most likely change (Measure for best results)

Items Not Affected By the Conversion-

Transmission - Be sure to use the correct input shaft bearing in the crank
Valve Covers

Belt Tensioner
Water Pump
Timing Cover
Radiator and hoses

Timing Chain

Oil Filter (the 351w uses the same part number)

Head Gaskets (same part numbers apply)

Desirable Upgrades-

3 core Radiator and Electric fan

Subframe Connectors

Tubular K-member (if clearance issues are feared)

Z-spec T-5 (or other high power upgrade)

Torque box Reinforcements

2.5” or larger exhaust

1 5/8 headers should be considered a minimum with 1 ¾ being ideal.