Accufab offered this dual-75mm...
Accufab offered this dual-75mm throttle-body upgrade for the Ford GT, so why not install it on this GT500 motor?
What better place to start your search for a restriction than at the beginning of the inlet tract? The first component in the factory induction system was the air-filter box and mass air assembly. Ford saw fit to incorporate the mass air meter assembly into the top of the filter housing (obviously a cost cutting procedure). Until now, all of the testing had been run with the factory induction system, including the filter assembly, the rubber inlet tube, and the throttle body. During testing, the data logging indicated significant restriction present in the inlet tract, meaning there was most certainly power to be had by removing the restrictions. The first step was to attack the mass air meter. With nothing available from the aftermarket (while this was being tested), the guys at Kenne Bell simply took the cutters to the factory airbox. The cure was to remove the MAF assembly from the airbox and equip it with a free-flowing cone filter. Minor tuning was necessary due to the major change in the flow through the meter (to say nothing of the torque limiting features), but Ken Christley had the GT500 ready for dyno runs in no time flat. The MAF mods improved the power output significantly, upping the power peak from 664 hp and 677 lb-ft to 706 hp and 684 lb-ft. The MAF revision allowed more airflow to the motor, and as such, the peak boost pressure increased from 16.1 psi to 16.9 psi. The modification also dropped the vacuum present in the inlet system by nearly 2 inches.
While the 700hp mark came and went, we were still concerned about the presence of nearly 3 inches of vacuum in the inlet tract. While additional gains will likely be realized with a larger mass air meter (are you listening aftermarket?), Kenne Bell turned its attention to the next system in line, namely the rubber inlet tube and stock throttle body. Replacing the rubber inlet tube was a simple matter of swapping it out for the larger (free-flowing) unit on the Ford GT motor. The swap also required the use of the larger dual 75mm Ford GT throttle body available from Accufab.
 Making the throttle-body swap...  Making the throttle-body swap difficult were the drive-by-wire electronics (Ford GT throttle bodies featured manual cable operation). Kenne Bell and Accufab simply adapted the drive-by-wire electronics to the manual GT throttle body-problem solved. |  In addition to the Accufab...  In addition to the Accufab GT throttle body, Kenne Bell also employed the rubber air inlet. |  The combination of the new...  The combination of the new Accufab throttle body and rubber inlet elbow produced exceptional power gains. Despite no change in pulley size, the boost jumped from 16.9 psi to 18.5 psi and the power from 706 hp to 793 hp. A later run exceeded the 800hp mark, all with simple bolt-ons. |
The one hitch to the throttle body upgrade was that the Ford GT relied on a conventional (cable-operated) throttle, where the GT500 uses drive-by-wire. No sweat, the guys at Accufab and Kenne Bell simply combined the Ford GT throttle body with the electronics from the GT500 and-voil-instant dual-75mm GT500 throttle body. The company was clever enough to machine the inlet manifold (between the throttle body and supercharger) to accept both the smaller factory GT500 throttle body and the larger dual-75mm Ford GT unit. This was accomplished with a simple adapter plate.
This is perhaps the largest gain we have ever measured from a not-so-simple throttle-body swap. After making sure the ECU was happy with the new hybrid throttle body, the motor was run once again. With 23 degrees of timing and an air/fuel mixture of 11.5:1, the GT500 motor responded with an amazing 793 hp and 737 lb-ft of torque. The vacuum in the inlet tract was down by nearly 2 inches (leaving just over 1 inch still present), and the boost jumped from 16.9 psi to 18.5 psi. Inlet restrictions restrict airflow and boost production, which is why we saw such a huge gain in power from this throttle-body swap.
It should be noted that you will not see a gain of nearly 90 hp from a throttle-body upgrade on a stock motor, and may in fact see nothing at all, since the throttle body represented little or no restriction at the stock power level. The gains offered by the throttle-body upgrade will increase with the potential power level. On a 500hp motor, you will see less of a gain than on a 600hp motor. The same goes for a 700hp motor and (like ours) an 800hp motor. This motor did manage to exceed 800 rwhp on a slightly colder run. Oh, the power of simple bolt-ons.
Kenne Bell SC GT500-2.75 vs. 2.50 Blower Pulley
After installing the Kenne Bell supercharger in "Mods for GT500 Mods, Part 2," we were naturally curious about cranking up the boost. Unlike the factory Eaton supercharger, it was possible to easily replace the blower pulleys on the Kenne Bell blower. Stepping down from a 2.75-inch blower pulley to a 2.50-inch pulley resulted in a significant power gain. Torque production was up by 36 lb-ft (from 641 lb-ft to 677 lb-ft), but the peak power gain was less significant (from 656 hp to 664 hp). Since the power gains diminished with engine speed, we suspected there was a restriction elsewhere in the motor.