Chris Hemer
February 1, 2008
Photos By: From the 5.0 Mustang archives

Horsepower makes heat, so even if the 351W you plan to install is next to stock and your original radiator is in good condition, it's likely you're going to need a bigger, better radiator. Again, how much cooling you will need is directly proportional to the amount of horsepower you'll be making.

U.S. Radiator in Los Angeles, California [(323) 778-5390], is a great source for copper/brass radiators, while Fluidyne in Mooresville, North Carolina [(888) FLUIDYNE], or Griffin in Townville, South Carolina [(864) 845-5000], can set you up with the correct aluminum radiator for your application. Using a new or aftermarket water pump is also a good idea.

Rather than bore or confuse you with all the legalese involved with engine swapping, suffice it to say that swapping a 351W into your '86-'95 should be legal in California--or states adopting its emissions guidelines--provided you don't defeat or remove any of the factory emissions equipment. This includes, but is not limited to, the smog pump, the engine-control computer, the original cat H-pipe, and so on.

However, modification is always a touchy subject--even with a 302--so it's important that you carefully map out what you are considering before you do it. Then try to determine if (A) it's legal or (B) it will pass California's rigorous Inspection and Maintenance (IM) program, commonly known among enthusiasts as a "smog test."

Keep in mind that just because the part(s) you plan to install carry an E.O. (executive order) number, it doesn't necessarily mean the car will pass IM. Parts are certified independently, except in the case of certified power packages, so when various emissions-legal parts are mixed and matched, the engine may not pass. Under current guidelines, the owner of the car must do whatever it takes to make the engine pass when it has been modified, regardless of cost. In other words, don't get too carried away when you build your 351W--or any engine for that matter--because you may be forced to dispense with the big injectors, cam, and after- market computer in order to get your car to pass.

In summation, the wisest decision is to contact a referee station in your area, tell them what you have planned, and find out if it's legal. It will save you a lot of time and expense later.

Not surprisingly, the 351W weighs more than the 302--an additional 100 pounds when you're comparing apples to apples. If you're replacing your 302 with a 351W of like configuration (i.e., both have iron heads), the added weight won't adversely affect the handling of your car, and it will drop front ride height only an additional 1/4 inch, according to our experts. However, if you want to gain the muscle and lose the fat, you can use aluminum heads, a tubular K-member, an aluminum radiator, a fiberglass or carbon-fiber hood, and move the battery to the trunk (or any one of the above). These mods will make any weight difference imperceptible.