...and a restrictor was installed...
...and a restrictor was installed in the thermostat housing to slow water flow for maximum heat transfer.
In Pull 1, we learned that the 598 was lean and in need of larger jetting. We started with 0.90 jets in the primaries and secondaries. Based on air/fuel ratio and brake specific fuel consumption (BSFC) numbers, McAfee concluded we needed to step up to 0.92 jets in the primaries. Benton Jackson, MCE Engines fuel system specialist, took care of this in short order. Ignition timing is conservative at 32 degrees BTDC to eliminate any chance of detonation and engine damage. McAfee's regimen includes step pulls in order for the engine to stabilize before rpm increases.
Dyno Pull 2
Holley 1,150-cfm Dominator
(PN 0-80673)
Jetting: 0.92/0.90
Ignition Timing: 32 Degrees BTDC at 3,500 rpm
Step pull in 500-rpm increments beginning at 4,000 rpm
| RPM |
HP |
TQ |
| 4,000 |
503.9 |
661.6 |
| 4,500 |
690.4 |
805.8 |
| 5,000 |
784.1 |
823.6 |
| 5,500 |
838.3 |
800.5 |
| 6,000 |
878.9 |
769.3 |
| 6,500 |
909.8 |
735.1 |
On the second pull, we were still too lean. McAfee increased jet size one step at a time again as a measure of fine-tuning. "Quantum leaps in jet sizes only add to the confusion of tuning," McAfee tells us, "at one jet size at a time, you know back to back from one pull to the next whether you're rich or lean without having to backtrack." The 0.92 primary jets did add 14.4 hp and 21.0 lb-ft of torque. McAfee elected to go up a jet size in the secondaries to 0.93 to see what happens next.
The velocity stack increases...
The velocity stack increases airflow velocity to aid power production, and it also measures the airflow going in. The ventilation hood overhead provides cool air, which also contributes to power. Of course these aren't real-world conditions. A dragstrip on a hot summer day is very different than a dyno cell. You may also need to change jet sizing and ignition timing when you go to the 'strip because conditions (temperature, humidity, and barometric pressure) can change dramatically.
With the engine fired and...
With the engine fired and warming up, Jackson checks ignition timing at 3,500 rpm. Timing was at 32 degrees BTDC, to minimize risk of detonation.
Fuel pressure and float levels...
Fuel pressure and float levels are checked. McAfee has specified the need for a minimum of 4.0 psi of fuel pressure at wide-open throttle. Static fuel pressure is approximately 6-8 psi at idle. The objective is to have plenty of fuel pressure and volume in both bowls at wide-open throttle.
McAfee (left) and Jim Grubbs...
McAfee (left) and Jim Grubbs of JGM Performance run the engine in while Jackson continues to make final tweaks.
Fuel system specialist Benton...
Fuel system specialist Benton Jackson of MCE Engines swaps primary jets between pulls. We started out with 0.90 jets in all four corners, which were too small. We needed larger jetting, which McAfee took one jet size at a time to simplify tuning. When you go one jet size at a time, McAfee tells us, it enables you to know exactly what happened with each jet swap.
Jackson installs 0.92 jets...
Jackson installs 0.92 jets in the primaries. We're staying with 0.90s in the secondaries as a measure of finite tuning.
This Wilson carburetor spacer...
This Wilson carburetor spacer was employed to increase velocity between carburetor and intake plenum. This usually results in improved torque and sometimes horsepower. Dyno numbers will say one thing, but depending upon what you shoehorn the engine into, track numbers may be more telling of whether or not the improvement was in the right area.
After the first run in and...
After the first run in and dyno pull, McAfee added CamGuard as added insurance for both durability and power robbing friction. CamGuard is an anti-corrosion, anti-friction additive that, with time and mileage, protects street and racing engines alike. CamGuard is available from MCE Engines.
Marvin McAfee of MCE Engines...
Marvin McAfee of MCE Engines has built a lot of bullets in his time, and while conservatively tested, his T-Rex 598 hit above the mark that was set for the engine build. With a larger carburetor and portwork to the cylinder heads, this Ford Racing big-block is certainly capable of much more. Not that 915 hp is lacking in any way.
Dyno Pull 3
Holley 1,150-cfm Dominator
(PN 0-80673)
Jetting: 0.92/0.93
Ignition Timing: 32 Degrees BTDC at 3,500 rpm
Step pull in 500-rpm increments beginning at 4,000 rpm
| RPM |
HP |
TQ |
| 4,000 |
521.5 |
684.5 |
| 4,500 |
698.1 |
814.8 |
| 5,000 |
787.4 |
827.1 |
| 5,500 |
848.1 |
809.9 |
| 6,000 |
883.4 |
773.3 |
| 6,500 |
915.7 |
739.9 |
In the wake of our third and final pull due to time constraints, our 598 T-Rex produced 915.7 hp and 827.1 lb-ft of torque. We are thrilled these numbers surpass McAfee's expectations. However, we're convinced that with more dyno time, this engine would be courting the 1,000hp mark. And if you run out of dyno time, you can always continue your testing once the engine is in the car and at the track. Keeping good records will go a long way in documenting the changes and performance or your engine.