Feeding the cast-iron intake...
Feeding the cast-iron intake on the Hi-Po 289 was an Autolite 4100 series four-barrel carburetor. The unit on the Hi-Po engine utilized the larger 1.12 venturis and was said to flow 600 cfm (480 cfm for the smaller 1.08 venturi models). Our used 4100 came from a seller on eBay.
The original Hi-Po did receive a special set of cylinder heads, but not one that necessarily provided a power advantage. The Hi-Po 289 heads offered a few desirable features, including screw-in rocker studs (no guide plates), cast-in valvespring bosses, and slotted pushrod guide holes (something shared with nearly all pre-'66 heads) that eliminated the need for either guide plates or rail rockers. These features make the Hi-Po heads both desirable and expensive, but any of the more common pre-'66 heads can be converted to Hi-Po use by drilling and tapping for screw-in studs and upgrading the valvespring package (there is no need to cut spring cups). Since all 289 heads flow the same and given the expense of original Hi-Po heads, we chose to build a replica set using '66 C60Z castings that already featured the slotted pushrod holes. The heads were treated to surfacing and a fresh valve job using the factory 1.78/1.45-inch valve sizes. Having been surfaced at least twice in their long life, our heads ended up with 52cc combustion chambers (right on the minimum service limit).
The Hi-Po 289 relied on a...
The Hi-Po 289 relied on a set of cast-iron exhaust manifolds that were specific to that engine. Our reproductions came from Tony Branda Performance. The cast exhaust manifolds were run with a set of 2.5-inch exhaust pipes on the engine dyno (no mufflers).
A few other important components were specific to the Hi-Po 289, including the cast-iron four-barrel intake manifold, cast-iron exhaust manifolds, and Autolite 4100 carburetor (with the larger 1.12 venturis). Good luck finding any of these in your local wrecking yard, but they are available from various sources. We purchased our intake and carburetor in running condition (though the carb came with a rebuild kit), while the cast-iron exhaust manifolds were on loan from Tony Branda Performance. If you need something for your Shelby or Hi-Po Mustang, give them a shout-they probably have it in stock. Tony Branda also supplied some of our Shelby components, including a set of cast-aluminum valve covers and matching aluminum Cobra oil pan.
We finished up the Hi-Po 289 with a 2.5-inch open exhaust, an MSD distributor with the ignition timing locked, and a Meziere electric water pump. Prior to start-up, the new Elgin Hi-Po cam was liberally coated with moly-based assembly lube, treated to a quart of Lucas high-zinc break-in lubricant, and finally prelubed using a drill motor to ensure adequate oiling to all rockers. After a computer-controlled break-in procedure and some ignition and carb tuning, we were rewarded with peak numbers of 275 hp at 5,700 rpm and 288 lb. ft. at 4,300 rpm. These numbers are as close as you'll likely get to Ford's power rating of 271 hp for the Hi-Po.
Run in '65 trim (but with...
Run in '65 trim (but with modern valve covers), our Hi-Po 289 produced peak numbers of 275 hp at 5,700 rpm and 288 lb. ft. of torque at 4,300 rpm. Though hardly considered a torque monster, torque production from the little 289 exceeded 275 lb. ft. from 3,400 rpm to 5,000 rpm.
Now that we had established that Ford was telling the truth about their Hi-Po, the ball was bounced into Shelby's court. This was the moment of truth, so off came the cast-iron exhaust manifolds and on went the tri-Y headers. Like the manifolds, the headers were run with simple collector extensions and no mufflers. Next to go was the Autolite carburetor and cast-iron four-barrel intake manifold. These were replaced by a reproduction Shelby aluminum intake (worth replacing the heavy cast-ion manifold on weight savings alone) and Holley carburetor. Unfortunately, we did not have access to an original 715-cfm Holley, so we utilized a more common 750 Holley instead. Truth be told, both were more than sufficient for the little 289 and both could be tuned to perfection.
With our Shelby mods installed, we yanked the hammer once more and were immediately rewarded with over 300 hp and 310 lb. ft. of torque. The Shelby version checked in at 303 hp at 5,800 rpm and 311 lb. ft. of torque, again just a whisker away from the 306hp rating offered by Shelby. Apparently, those Shelby guys knew what they were doing-not surprising since you don't win FIA championships (against Ferrari no less) without knowing a thing or two about making horsepower.
Mr. Shelby, we never doubted you for a minute!
For dyno use, we employed...
For dyno use, we employed an MSD distributor and Digital 7 ignition amplifier. Probably overkill for our stock Hi-Po, the ignition eliminated any concern for misfires or variations in the timing curve.
With the Hi-Po numbers in...
With the Hi-Po numbers in hand, we removed the factory cast-iron intake manifold and replaced it with a reproduction Shelby aluminum high-rise intake borrowed from Dr. Js Performance. Also note that we installed the reproduction Shelby cast-aluminum valve covers from Tony Branda Performance.
Off came the factory Hi-Po...
Off came the factory Hi-Po cast-iron exhaust manifolds and on went the Shelby tri-Y headers. Like the stock manifolds, the tri-Y headers were run with 2.5-inch collector extensions and no mufflers.