Terry Mcgean: Mustangs with Ford's Special Service Package did indeed use steel wheels prior to the '87 model year, but the correct ones for an '86 measure the same 15x7 inches as the later 10-hole aluminum wheels. The cop steelies were unique to SSP Mustangs and appear to use the centersection from the more common 14-inch steel wheels of the period (used on Thunderbirds and Fox-platform LTDs with full wheel-covers) in a 15x7-inch stepped rim. The center caps are plastic and are also unique to police 'Stangs. The center and rim are fully welded, unlike typical passenger car steel wheels that are only welded at four or five points. They are most likely a little heavier than the 10-hole wheels, but if you want absolute correctness, the steelies are what you need. This stuff is most likely discontinued from Ford, and even used Mustang parts sources seem not to have them anymore. Check the Web; there are several sites devoted to SSP Mustangs with hard-core members who can probably help. We found a variety of images of SSP Mustangs at members.fortunecity.com/copcarsite.
Hot Cam Scrutinized
Steven Telkes, Saddle Brook, NJ: What are the specs of the GM Performance Parts PN 24502586 camshaft? I'd like to know duration at 0.050 and 0.006 tappet lift, plus the intake centerline.
Terry Mcgean: That's better known as the LT4 HOT cam, a hydraulic roller offered as an over-the-counter upgrade for the factory LT4 engine but applicable to any Chevy factory roller small-block. The specs are 279/287 degrees advertised, 218/228 degrees duration at 0.050-inch lift, and 0.525/0.525-inch lift when used with 1.6:1 rockers as the factory did with LT4 engines; with traditional Chevy 1.5:1 rockers, lift works out to 0.492/ 0.492. The lobe separation angle is 112 on the HOT cam as opposed to 115 on the production LT4 stick. According to GM Performance, the intake centerline is 109 degrees, and duration at 0.006 is 272/281 degrees.
More Info
GM Performance Parts
800/577-6888
gmgoodwrench.com
Speedy Bearings
Hank Earlian, Glendale, CA: I've heard of shops that build 455 Pontiacs by putting a 455 crank into a 400 block. They say it's better than a regular 455 because the main bearings are smaller. I always thought the factory made big-blocks more heavy-duty by making the bearings larger. So why would I want smaller bearings?
David Freiburger: When you say "larger bearings," you're talking about larger diameter. In the old days it was thought that the greater diameter provided greater surface area and therefore contributed to bearing life thanks to reduced surface loading (because the same pressure over more surface equals less pounds per square inch). However, larger-diameter bearings also have greater bearing speed, which means more friction and less oil life. Why? Consider the Pontiac 400's main-journal diameter of 3.00 inches compared to the 455's 3.25 inches. While the id of the bearings is slightly larger, we'll use those numbers for simplicity. The circumference of the 400 mains is about 7.07 inches versus 8.30 for the 455. Therefore, any given point on the surface of the crank journal must travel only 7.07 inches per engine revolution with the 3.00-inch mains, but it must go 8.30 inches per revolution with the 3.25-inch mains. Since the bigger bearing has a greater distance to travel in a given amount of time (6,000 rpm is 6,000 rpm regardless of main-journal diameter), then the speed of the crank surface in relation to the bearing surface must be faster. Since 6,000 rpm is 100 revolutions per second, that means difference in the speeds of the two bearing sizes is 58.92 feet per second (400 mains) versus 69.17 fps (455 mains). Slower speeds mean less friction and more power, and have even shown longer bearing life. That's why Nascar engines use tiny 1.888-inch Honda rod bearings in their V-8s.