The 430 HP 392 ran like a “raped ape”. Great motor for the Superformance. Light weight and huge torque.  Conclusion: “Borderline excessive” – but wonderful. Ford did it right. Low end streetability is almost to the limit, especially with the single plane manifold, but not a great problem. With the Superformance stock 3.73 rear end gears and 3.27 first gear of the Tremec TKO transmission, first gear is a matter of controlling wheel spin. Fourth and fifth gear are the real problem. Before I blew the engine I had replaced the rear with a 3.27, a quantum improvement over the 3.73.

The 427 is like a “raped ape on steroids”. This should appeal to most of the male Superformance owners, that feel that “Too much is just enough” (absolutely nothing wrong with that). There is nothing that will come close to you with this combination. The combo is 80 lbs less weight on the front end and 100 more horsepower and torque than a comparable 392. Yikes!!! Hang on and enjoy the ride. The tried and true 460 pumps out gobs of torque, but its heavy front end weight only contributes to excessive wheel spin. If you want to hook up and go, the heavy 460 is not the way to go, although it is the cheapest. The all-aluminum 427 is nimble and quick. You won’t believe the difference until you try it.

Specifications

The 392 has a 4.030” bore and a 3.85” stoke. The Competition cam FW XE282HR-12 has a duration of 232 degrees (intake) and 240 degrees (exhaust) with a 112 degree lobe separation. Lift is 0.565” intake and 0.574” exhaust at.050 inch valve lift.

The 427 has a 4.125” bore with a 4.000” stroke, due to its Siamese cylinder bores. The custom cam has a duration of 236 degrees (intake) and a 244 degrees (exhaust) with a 108 degree lobe separation. Lift is 0.608” intake and 0.613” exhaust at.050 valve lift. The cam specs appear to be similar to the 392. The 427 idles rougher, even with the duel plane manifold (the 392 had a single plane manifold), but that may be taken care of with additional adjustments. The rough idle and excessive richness may be taken care of by a better initial timing.

How is the 427 to drive?

The acid test is street driving. When you put your foot into it the car responds like you kicked a keg of dynamite!!!, as it literally explodes into action!!! Initially, the 427, as delivered, seemed to have a slight problem below 2000 rpm compared to the original 392. To counter this I replaced the supplied HP 750 carb with the 650 double pumper that was the original carb I used on the 392 and it seemed to improve it a little. I was concerned about low-end driveabilty. That was my main concern, as I realized that 99.9% of my driving was not full throttle, but street driving. Better to compromise a few horsepower on top end for the majority of my driving. I am still working on that. RDI suggested that the initial advance curve was not enough and were more than willing to workout the problem with me to correct this problem to perfect the street driving.

RDI suggests that I tailor the initial ignition timing to about 20 BTC or more, and leave the total advance to 30 degrees at 3000 rpm. Rich idle seems to be the main concern. It was suggested that the initial timing be advanced. This is a minor point, but one that will have to be dealt with. RDI is more than willing to work this out. Preston Miller seems to be more than willing to be helpful.

Notice in the above image that I have used the largest K&N filter possible with the “Extreme” filter top. This combination was not available on the single-plane or “Air-Gap” Edelbrock manifold with my 392, as hood interference was a problem. The duel plane manifold may sacrifice up to 5% top end power, but gives you that 5% back in the range in which we mostly drive. A far, far better compromise. Also, flow characteristics of air cleaners change from the day they are installed. One hundred percent flow on day one may be less a few months down the road. I took the approach that I knew the air cleaner would become less efficient with time so had a much larger one installed to begin with. Even at 80% efficiency it was better than the older one at 100%. Why starve the engine with air? I have seen 460 motors with puny 8” air cleaners on them because of the increased engine height and limited hood clearance.

The Bottom Line

The all-aluminum 427 is in fact the “Ultimate Windsor”. The extra power is more than you could possibly imagine or ever need. It is almost perfectly streetable with the light weight front end. Even if you don’t care about the power, the reduced weight on the front end gives you the feeling of having a 260- 289” up front. The nimble handling is a huge plus. The 200+ extra horsepower over the original 1962 Cobra with 260 HP is incredible.

I would like to take the opportunity to thank both Dr. Stenhouse and Preston Miller, of RDI, in taking the time to work this problem out. Superformance, Inc, should be proud of the efforts put forth to come up with an ultimate Cobra worthy of the name.

Antoni Scott

Superformance SP 512

Post script: After some time with the  new engine, Tony switched for the custom cam back to the milder cam from the 392. He gave up some high end horsepower, which he seldom had the opportunity to use, to gain a good bit of low end drivability, which he uses every time he drives the car. Tony reports that it was a very worthwhile change from his perspective.