By Ro McGonegal.
Pictures by Moore Good Ink:
Long-time Mountain Motor engine master Jon Kaase (Racing Engines, Winder, Georgia) says, “The stock Boss 429 parts were a masterpiece for their time, but slightly weak and difficult to work on. We made every effort [with the Boss Nine] to fix anything that was troublesome or failure prone.”
At the end of 2007, Kaase decided to take “the plunge and build all new Boss 429 Ford retrofit heads and related parts. I was betting on the fact that there were other Boss fans and Ford enthusiasts out there that wanted these new parts as badly as I did. Although they’ve only been out for a short while, I’m happy to say that they have been well received and successful in whatever projects they have been used in.”
|Since build orders for the Boss 429 Mustang NASCAR homologation-specials ceased at 1,358 (859 were built in the spring of ’69; 499 more came to life as 1970 models later that summer), these units are rather scarce. Solving the cylinder block problem was easy. Kaase simply undertook the 429/460 big-block (in iron and aluminum) providing them with cylinder head oil drains in the correct location. The JKRE plan included using OE 460 head gaskets, so the deck surface of the Boss Nine heads is much thicker than the original dimension to provide the necessary clamping force. The Boss 429 was humorously under-rated at 375 horsepower while it probably made closer to 475 at the flywheel and without the parasitic drag of the accessories. The ports were huge, had poor low-speed velocity and didn’t begin to show their stuff until the tach was beyond 3,500rpm. Camshaft technology was light years behind the current form. Kaase knew that these two issues had to be addressed for a modern street-driven power plant that was originally created for the race track. |
To that end, he spent a lot of time rearranging the insides of the aluminum. Though the intake ports appear to be stock at the entry, they benefit from a revised short-turn radius and a revised approach to the valve seat. The floor of the exhaust port exit and the valve bowl under the seat were reduced in size. At all times, the quest was to make the Boss Nine heads appear like the OE castings.
Kaase modified the semi-hemi combustion chambers and relocated the spark plugs for resistance to detonation. Size of the combustion chambers has been reduced to 90cc so that flat-top pistons when fitted in a 460-inch engine will yield a compression ratio of 10.5:1. Further, the stock Boss 429 intake and exhaust manifolds fit the Boss Nine without modification. Moreover, the miracle of modern technology can produce camshafts with enough magic ground into them to puff up torque for low speed driving and provide a 750-800rpm idle, with duration that builds maximum cylinder pressure and different timing and lift for both valves.
The last area of contention, the wildly disparate rocker arm system, Kaase approached with his usual aplomb. He incorporated the rocker mounting saddle in the cylinder head casting, thus eliminating the mounting block, representing a savings of about $400 when purchasing the rocker arm set. These items are the produce of W.W. Engineering and are the very same that Kaase uses on his 820 cubic inch IHRA motors. The exhaust rocker arms, which have a ratio of 1.75:1, were designed to move the pushrods away from the block deck. In keeping with his “budget” approach to this project, Kaase uses Manley stainless steel intake and exhaust valves with BB Chevy-size 11/16-inch stems.
So what do you get when you apply Boss Nine heads to a 460-521ci short-block? How about an immediate increase of 50hp as compared to Kaase’s powerful P-51/SCJ heads? Swap these beauties on a 600ci version, and the output is 150 additional horsepower. And dig it ladies and gentlemen; all mechanical delicacies aside, you’d have to go a far piece to produce a wow-factor like the Boss Nine.
Check out the following outline for a behind-the-scene Boss Nine build.