Tom Wilson
November 1, 2010

And value is just what the fresh engine will bring to your used 'Stang. If you do the job right, this kind of upgrade should bring years more enjoyment to your classic Mustang.

On The Dyno
The last two miles our 198,062-mile stock engine made were on GTR's chassis dyno. It put out an excellent 207 hp to the tire. Helping factors were underdrive pulleys and precious little internal engine friction. It was, you might say, well broken in.

Don't let the power fool you, however. The old engine burned oil like a steamship smokestack-when it wasn't pouring out of the front crank seal and oil level sender-plus the oil pressure was dangerously low and wavering with rpm. It was surely ready to spin a bearing. Moreover, it was with one part per million from passing its next smog test.

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Our new X302 bumped the needle to 270 hp tuned with 13 degrees of initial timing and the fuel ratio leaned to 12.6:1. That seems under-achieving compared to the advertised 340 hp, but not really. Ford rates these engines with a carburetor, short-runner intake manifold, and long-tube headers. At the tire, 340 flywheel horsepower would be 289 rwhp, and you still need to subtract a bunch for the long-tube headers and short-runner intake.

Looking at it the other way, Ricardo says he typically sees 280 rwhp for a street-legal "head, intake, and cam" 5.0 such as ours. Swapping back to our underdrive pulleys would put an additional 10 hp on the clock, plus a couple more for a K&N air filter and cold air intake, and maybe a touch less fuel for 282 rwhp. (We have a paper filter and stock rubber inlet hose.) Either way, that puts our X302 right where it belongs, and it will only get better with more break-in miles.

Speaking of break-in-our X302 had just 603 miles on it when dyno'd. We're sticking with mineral oil until 3,000 miles. That's Ricardo's normal recommendation before switching to synthetic.

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Even at these most conservative numbers, our X302 gained 63 hp over our original stocker-you could say it really gained 73 hp if you account for the underdrive pulleys. Even better, we were expecting to decisively lose bottom-end torque, but really didn't lose that much. The numbers wander back and forth between the two engines below 3,300 rpm, and you can squeak the numbers by playing with ignition timing, so we're calling it nearly a draw to that point as the area under the torque curve about evens out.

Above 3,300 rpm the X302 simply soars away from the old 5.0 in both power and torque. All said, great results for a crate engine that's less expensive than rebuilding the old engine!

Baseline Baseline X302 Difference
RPM POWER TORQUE POWER TORQUE POWER TORQUE
2,500 117 247 110 252 -7 5
3,000 148 259 135 253 -13 -6
3,500 176 264 168 267 -8 3
4,000 197 259 206 285 9 26
4,500 205 240 237 290 32 50
5,000 205 216 260 285 55 69
5,500 n/a n/a 260 258 n/a n/a

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