What is a 5.0 HO?
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This is just a quick posting that might help clear up confusion for folks saddled with stock standard-output 5.0 engines like our cars came with. Many knowledgeable enthusiasts seem to think they're exactly the same as Mustang engines, whereas (to my knowledge) the main shared parts are the block, crank, rods, and (I think) the lower intake manifold. Obviously the accessory drives and such are different, but those don't exactly make or break horsepower ratings. These are just the differences I can think of off the top of my head - I strongly suggest visiting a great site called Coolcats.net to read technical info from a more tech-savvy enthusiast than I am.
Pistons (dished vs. flattop)
-- Not much to say here, except that dishes tend to lower compression ratio, perhaps as low as 8.5:1 depending on who you ask. Also, the HO's 9:1 slugs were super-durable TRW forgings that can take huge nitrous hits, etc., while I've seen no evidence that the dished slugs weren't plain cast aluminum. HO's got hypereutectic pistons in 1994 and 1995.
Heads (E6SE vs. E7TE)
-- Reading about cylinder heads has suggested that the E6 was a high-swirl design introduced for (as the casting number implies) the 1986 model year with the view of reducing emissions. Subsequent Mustang (and truck) motors used the better-flowing E7TE casting that was still able to meet emissions requirements. My '87 standard-output motor came saddled with E6 heads, and I think they were used for the remainder of factory 5.0 installations in Thunderbirds and Crown Vics. For the best bang for the buck, get F7ZZ "GT-40P" Explorer heads, but be prepared to make sure your headers work with the funky spark plug angle. Regular GT-40 iron heads have been, in my experience, really hard to find, and it is said that a ported E7 can make about as much power at a similar total cost.
Cam
-- The stock HO cams used from 1986 to 1993 were really pretty nice, and not only gave a great torque curve from the factory but are said to be good for 10-second runs with the right combination. They also use the 351W firing order, though I've not been able to learn why. According to my Haynes manual, 1978 to 1984 non-HO engines used flat-tappet cams with 0.2375/0.2474 lobe lift, which equates to .380/.396 at the valve with 1.6:1 rockers. Since I have a good used non-HO roller cam at home, I'll have to measure it when I get a chance for a more fair comparison. Roller HO cams were more in the neighborhood of .450 lift, but if you're reading this, you can also use Google to find the exact specs for the year you're interested in. Obviously, the shorter and narrower non-HO profiles were suitable for good idle and torque characteristics as well as the bigger cars' 4000-rpm effective redline (auto-trans Mustangs got a higher 5000-rpm governor).
Upper intake manifold
-- Again, not many hard numbers off the top of my head, but the HO manifolds certainly featured less restrictive passages. However, the smaller E6 pieces were probably better for the lower revs seen in luxury cars.
Throttle body
-- Not much to say. 60mm for the HO, 50mm for everyone else.
Fuel injectors
-- Same deal. 19 lb/hr for HO, 14 for the rest of us.
Really ugly cast-iron exhaust manifolds
-- Mustangs got ugly but reliable tubular headers that, while restrictive compared to aftermarket offerings, flow much better than your even uglier cast-iron units. They're also really cheap to acquire and super-easy to install, as you can still get a socket onto all 8 bolts and there's plenty of room for regular hardware-store Grade 8 hardware. Note that your stock cat pipes won't bolt up to headers, though a few key bits from the Walker catalog can minimize the number of additional changes necessary. Most Mustang H- and X-pipes do basically fit the Panther chassis, and provide an easy solution for relocating the O2 sensors, though they require more changes further downstream. Also, off-road pipes are illegal in many states and LOUD.
2" single or dual exhaust (vs. 2.25" duals)
-- A sewer-pipe exhaust system never won any races by itself, but logically it seems a little odd for a 5-liter engine to use the same size single exhaust as GM's 2.5L Tech 4. Mustangs got 2.25" duals from the factory, though stock Crown Vic 2" duals are easier to install on a Panther-body and are probably plenty if your engine is stock.
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Power ratings
Sources vary, but production '86-'93 HO motors are generally said to make between 200 and 225hp and about 300 lb-ft torque. Standard-output motors are said to make between 150 and 170hp and about 280 lb-ft torque.
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Page 1: Intro
Page 2: Engine details
Page 3: Suspension and General History
Page 4: What is a 5.0 HO?
