5.8 conversion - MustangForums.com

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Old 03-13-2006, 10:41 AM   #1
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Default 5.8 conversion

What does it take to do a 5.0 to 5.8 conversion? Are the 5.8 reliable as or better than the 5.0 block? Thanks
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Old 03-13-2006, 11:22 AM   #2
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Default RE: 5.8 conversion

a 351 and a 302 are pretty much the same motor, the deck hight on the 351 is just taller, so you can stroke the motor more. a 351 is a great motor it is the 302's big brother. I have never done the 5.8 swap but i am looking at doing it in the next few years. from what i read it does not take a whole lot. Now if you are planning on running a s/c or a turbo than a 351 is a great place to start, you can leave the motor a 351 and get more power than if you ran a 347, and it will be twice as reliable.
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Old 03-13-2006, 11:34 AM   #3
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Default RE: 5.8 conversion

The 351W is a Windsor class engine. It is made on the same factory line as our beloved 5.0. However, the 351 posseses several qualities that make it a desirable block for an engine buildup. The advantages of using a 351W vs a 5.0 (302):

Obviously, you get an extra 49 cubic inches of displacement. As the saying goes, there is no replacement for displacement. Second, the webbing in the lower half of the block is thicker, making the block stronger. Third, the crank has bigger main and rods journals, making the cranks more durable than their 302 counterparts.

FACTS: What you need to know/consider when you swap a 351W into a Fox3 platform chassis:

The 351 block is very similar to the 302. That means that almost all parts swap between a 302 and a 351. This includes: Heads, cam, lifters, timing chain, timing chain cover, water pump, engine mounts, and all sorts of other stuff. The bellhousing bolt pattern is the same as a 302, so all trannies that bolt to a 302 will bolt to a 351. However, there are some differences in the 351 that necessitate new parts:

1) The oil pan is different. Motorsports carries one. You can also get an oil pan of of an early eighties LTD Crown Vic. If you go the junkyard route, remember you also need a oil pan pickup tube, and a special main bolt that the pickup attaches to. The FMS pan is a pretty good deal, and if you shop around, you can get one for under $100, which comes with the dipstick, bolt, and pickup tube.

2) The internal balance of a 351W is the same as pre-81 302's (28.2 oz). The 5.0 HO has a 50 oz. unbalance, which means you cannot use the flexplate/flywheel or the harmanic balancer off of an HO engine. You have to get the correct pieces from a dealer/junkyard.

3) The deck height is higher, which means you need a different intake, since the 351W intake is wider. A 5.0 Upper will bolt to a 351W lower.

4) Also, a higher deck height means that the accessory bracket will need to be replaced. FMS sells the new bracket for about $50.

5) The higher deck height means the headers sit up higher than in a 302 powered Mustang. A special set is required for a 351.

6) A 351W will in all likelyhood not clear the stock hood. You will need a cowl hood for your car.

7) The distributor has a fatter shaft. You can obtain one from a 351W powered FI truck (if you are using FI) or any late 70's/early 80's car using the 351W and a Duraspark system if you are going to build a non-efi car.

Those are the major differences. As you can see, for about $1000 you can put a 351W in your Mustang. This is cheaper than a stroker, plus you wind up with a more reliable engine.

Tips: There are several things to look out for to ensure that your swap to a 351W is easier and more successful. They are as follows:

1) A high volume oil pump WILL NOT clear the FMS pan. If you want to run an HV pump, you must either modify the pan, or buy a Canton or similar pan, for many dollars more. The modifications just include cutting down the front drain bolt, and welding on a corner to the pan to clear the pump housing.

2) Get new motor mounts. If your mounts are questionable already, the additional weight of the 351W will make them fail in a hurry. I recommend the 87-93 convertable mounts, which will work in any 79-93 Mustang.


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Old 03-13-2006, 12:36 PM   #4
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Default RE: 5.8 conversion

can we make this a sticky so we dont get asked this same question every other day?
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Old 04-21-2006, 04:53 AM   #5
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Default RE: 5.8 conversion

I have a question about something not addressed in your great paste from fast351.com: the firing order on a 351W is different (1-3-7-2-6-5-4-8) than a 302 (1-5-4-2-6-3-7-8). If you want to be carbureted, all you have to do motor-wise is swap the wires on the cap and voila! BIG question, though. Didn't FoMoCo change the firing order in later 351's? If so, to what?

HOWEVER, if you want to keep your sequential EFI setup, how does one match up the firing order to the injection pulse? You can still swap the firing order on the cap, and it will run, but it won't make NEARLY as much power as it could/should. It's easy to figure out why.

The fix, then, is a different ECM that will in the correct order "fire" the appropriate injector, right? I'm SURE there's an aftermarket conversion kit/package out there, isn't there? OR...what OEM ECM's would be compatible with whatever EEC module your Mustang happens to run? OR can you reprogram your existing computer to pulse the injectors in the right order?

This something that a swapper keeping EFI needs to know, 'cause I'm thinking of the same dang swap, but I want to iron out the sequential fuel injection issue before I put both feet in, because I want the drivability/tunability/power-making ability of EFI.

SOMEBODY'S got to be all over that, because it's just too easy otherwise - all those cubes, longer stroke, torque, thicker block webbings, stronger all around rotating assembly (on and on it goes!) and all you REALLY need is a wider lower intake, different headers (maybe) maybe a new oil pan, new accessory bracket (that's a new one to me) and a hood. C'mon, that's a cinch!
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Old 04-22-2006, 08:35 PM   #6
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Default RE: 5.8 conversion

it seems as though the 82 and later 302 HO engines have the same firing order as the 351W (1-3-7-2-6-5-4-8). I am verifying this, and if it's true (and I think it is), then EFI is not an issue. I'll check back later.
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Old 06-25-2006, 05:02 AM   #7
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Default RE: 5.8 conversion

yea yea i have said this many many times the 351w and 302w in are cars has the same firing order
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Old 07-11-2006, 06:32 PM   #8
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Default RE: 5.8 conversion

ok so I have an 86 mustang. I also have a stock 351w I pulled out of a bronco I bought. My question is, will this stock 351w fit right into my 86 mustang??(note: my 86 mustang engine bay is completely empty, everything was taking out.)
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Old 07-11-2006, 06:36 PM   #9
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Default RE: 5.8 conversion

ORIGINAL: groundpounder

it seems as though the 82 and later 302 HO engines have the same firing order as the 351W (1-3-7-2-6-5-4-8). I am verifying this, and if it's true (and I think it is), then EFI is not an issue. I'll check back later.
They do, the 5.0 H.O. has the same firing order, the non-H.O. 5.0s do not.
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Old 07-12-2006, 04:37 AM   #10
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Default RE: 5.8 conversion

Here is the info I have on the 351w swap in a T5 Fox Mustang.
From my site - http://www.freewebs.com/vristang/fox351wswapfaq.htm

Let me know if you guys have any comments.

302 to 351W Swap In A Fox Body Mustang

Note: 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.

Another alternative is to swap in a 351w block. There are 2 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” The 69-70 blocks also had thicker main webs and higher nickel content, making them significantly stronger. From 70 to 74 the 351w maintained the higher nickel content, but lost some of the material in the main webs. Another small reduction in the main web thickness occurred in 75, along with another reduction in Nickel content (supposedly), but after that the block remained basically unchanged until it ended production. From 1994 on, all 351w blocks were equipped with roller cams/lifters.

Getting Into the Nitty Gritty

Firing Order-
See the cam discussion below.

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 deck height and lifter combination, and using the stock 302 HO firing order (since you are most likely reusing the stock 302 computer). Probably the best thing you can do is ask the company you plan on purchasing the cam from, 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.
Here is some unverified info on Ford 302 & 351w 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 with a little machining and grinding. 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 bearing is installed. Some grinding will 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 assy. 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 supposedly reinforced & stronger. Another alternative is lowering engine mounts from HP Motorsports. 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.

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, if done with care. It would be best to send this work to a machine shop however.

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 factory 302 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. The Ford shorty headers are p/n M-9430-A58.

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 the 302 upper intakes, which many Mustang owners may already have. Being able to reuse your current upper intake can present a significant $ savings.

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 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 my 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 manifold are as follows; Upper M-9424-D50 / Lower M-9461-D58.

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 (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 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. If a high volume oil pump is to be used, it is recommended that a high volume oil pan be used as well (most aftermarket HV pans seem to be 7qt).

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 t
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