The Explorer 4.6 is an all aluminum engine based off the Romeo engines in Mustang GT's (windsor blocks stopped production a few years ago). The Explorer aluminum 4.6 is actually stronger then the blocks in the 96-01 GT's and Cobras (03' Cobras are iron with forged internals), a major difference is the thicker and stronger webbing on Explorer blocks that was sort of lacking on the 4.6 used in gt's/cobras. A lot of Mustang guys are snatching up 4.6 Explorer crate engines b/c of the stronger and more efficient design of the Explorer block. The engine itself can handle 800rwhp reliably, there are guys on the Mustang boards who have done it.
I'm pretty sure the Explorer crank is a 6 bolt and I've been told the heads are the same or very close to GT engines, a few people who have swapped blocks have said the cams are the same but I don't think so as I've spoken to SHM before when a friend was ordering Sean Hyland Motorsports parts for his 01' Cobra and they said the cams are not the same, I'm pretty sure they wouldn't stuff GT cams in their b/c the Explorer engine has a lot more low end torque then GT's.
As for times, my neighbor's 02' 4.6 Explorer thats 2wd w/ 3.73 rear, ran the 1/4 at 15.7 at around 88mph completley stock. The 4.6 responds awsome to mods, he now has an intake and dual exhaust and now runs the quarter in the 15.4-15.5 range at 89-90mph or so, the 5 speed auto keeps the 4.6 in it's powerband the whole time, just stall the convertor and you'll be in the meat of the powerband on launch and when it shifts. Pulls friggen hard up in the revs, I was suprised at how high it was trapping with only 2 mods.
I'll attest to that as I've driven his at the track when he took his highly modded S4 there (R.I.P.). Also, I've ran 16.1 at 85-86mph stalling the convertor in our 00' 2wd 5.0 Mountaineer, and when I've raced him on the street, his Explorer beat me off the line and pulls right away, now he demolishes me with only an intake and exhaust.
Hehehe, wait untill he pulls next to me after this summer if I decide to go with a 4.6 Mountaineer and drop an 03' Cobra engine in, 03' engines are only going for about 7500 now compared to 12-14k before, maybe it'll drop a little more come summer. So far, it appears it'll be an easy swap with only a few changes on Mounting brakets and other things. The new 5 speed tranny is also rated to hold over 400hp and tq reliably but I think I'll have it shipped off to Lentech for them to strengthen. Also have to find out how much the IRS can handle on the Explorers as it's not a beefy setup like 03' Cobras, and I'm not sure how a live axle would be able to bolt of to the rear of an 03'
EDIT - found a good link on the Explorer block, pretty much the same of what I was saying, but it shows the difference between the mustang/explorer blocks, you can see how the webbing and material is much stronger on Explorer engines like I was saying.
http://www.mustangweekly.com/2003/January/Block/block-1.asp
