Here ya go. Manifold only change on a dyno.
The first order of business was to establish a baseline. As indicated, we installed the factory timing curve using the F.A.S.T. system and to our surprise, the supercharged crate motor thumped out some pretty impressive numbers. How does 483 hp and 427 lb-ft of torque sound? We all know that the Cobra motor is rated at 390 hp and 390 lb-ft of torque. Where did the extra 90 hp come from you ask? First off, we suspect the supercharged Cobra motors are underrated by Ford. Every one we have tested on the chassis dyno has produced much more than the 390hp flywheel rating would suggest. It is also important to understand that the rating from Ford is an SAE number derived with a full exhaust including cats, full inlet system (silencer, mass air and all inlet tubing) and full accessories.
Regardless of the rating, our test motor now produced 483 hp and 427 lb-ft of torque at a peak boost reading of 8.8 psi. As is the case with these supercharged Cobra motors, the boost curve provided by the Eaton supercharger dropped off with engine speed. This drop off in boost pressure would become much more severe as we increased the drive ratio on the blower.
After establishing a baseline, we decided that the first modification would be to tune the existing combination. Using the F.A.S.T. engine management system, Tom Habryzk from Westech dialed in a new timing curve that supplied 23 degrees of total timing everywhere (from 3,000 to 6,500 rpm). In stock trim, the WOT timing was as low as 13-14 degrees according to the gang at Kenne Bell. Increasing the ignition timing had a dramatic effect on the power curve. Since the supercharged engine was already equipped with 23 degrees of ignition timing from 6,000-6,500 rpm from the factory, there was very little difference in peak power but boy howdy did the power improve down low. The extra timing improved the torque production by as much as 40 lb-ft. No changes were made to the air/fuel mixture, which was kept constant at 11.8:1. We know that the factory air/fuel mixture can be considerably richer than this, having witnessed many Cobras running in the 10s on the chassis dyno. The difference would likely have been even greater had we elected to run the factory air/fuel curves as well on our baseline. No wonder the new Cobras respond so well to custom chips.
The next performance modification on our "Mods for 4V Mods" list was a set of 1 3/4-inch (primary) Flow Tech (Hooker) headers. Keeping the ignition timing at a steady 23 degrees and the air/fuel ratio at a constant 11.8:1, the long-tube headers and 18-inch collector extensions allowed our supercharged test mule to exceed 500 hp for the first time. The headers upped the peak power to 501 hp, while the torque peak was up slightly to 461 lb-ft. Interestingly enough, the boost pressure actually dropped with the installation of the headers. The reason for this is that the exhaust scavenging helped improve the efficiency of the engine. Improving the (pumping) efficiency of the motor will result in a decrease in boost (or back) pressure. Installation of (the right) cams, ported cylinder heads or increasing the displacement of the motor will all result in an increase in power combined with a drop in boost pressure. Please don't be mislead into thinking that we should now increase the boost pressure to compensate for the drop. The real test of the effectiveness of the headers is to install them with no other change.
so make me a set please
