Agent 87, Part III

In the last episode of Agent 87, we left our intrepid heroes wanting more. CHP’s Ed Taylor–built, 390hp Agent 87 355ci engine had found its way into Patrick Peterson’s ‘65 El Camino. After two sessions at the dragstrip, we managed to push this rather hefty cruiser to run a corrected 13.13/103-mph pass at Los Angeles Country Raceway (LACR). This was the El Camino’s way of teasing us, because we wanted a 12.

So we went home, put our tuner caps on, and decided to look a little closer at how the car ran. It was obvious from watching the El Camino on the starting line that it was lazy despite its 2,000-stall B&M torque converter and 4.10 gears. It was time for more torque.

If you remember our story on tuning by cylinder pressure (“The Tune ‘n’ Tweak,” May ’01), we needed more timing at low engine speeds. This additional timing below 3,000 rpm would help build additional cylinder pressure lost from the combination of a relatively big cam and low static-compression ratio. This would make more torque and improve the e.t.—at least that was the theory. Our original curve offered 12 degrees of initial timing with 36 degrees total, giving 24 degrees of mechanical advance in the distributor. At first, we tried the lightest advance springs that Pertronix offers, but that really didn’t bring the curve in any quicker. This also made the initial timing at idle very unstable. We also experimented with different advance weights with disappointing results. We knew we had to take the distributor apart (see the “Distributor Blueprinting” sidebar) to limit the total advance.

The problem was that the distributor offered 24 degrees of mechanical advance. This only allowed 12 degrees of initial timing to produce our desired total of 36 degrees. To remedy this, we modified the distributor to limit its total advance. Most distributors use a pin and slot arrangement to determine the total amount of mechanical advance that is located under the mechanical advance mechanism on stock Chevy distributors. With the distributor apart, our pal Brett Benson welded up roughly one-third of the slot. We then ground the weld flat and polished the surface with a Standard Abrasives unitized wheel and reassembled the distributor.

Once the distributor was back in the engine, we found that we had limited the mechanical advance to a mere 14 degrees, requiring 22 degrees of initial timing to achieve 36 degrees of total advance (14 + 22 = 36 degrees). Checking the curve, our 36 degrees of total was now all in by 2,600 rpm using one light- and one medium-strength spring in the advance mechanism. The original curve required over 4,000 rpm to achieve maximum advance.

Clearly we had made a radical change in the curve at low rpm. For example, the original curve offered barely 25 degrees of advance at 3,000 rpm, while our modified curve now had 36 degrees of timing at 2,500 rpm. A quick test spin revealed the El Camino felt stronger between 1,500 and 3,000 rpm. We also performed a hot start test to see if all this initial timing would make our Agent 87 engine hard to start. Ironically, the engine now starts quicker than it did before and is much more throttle responsive. If necessary, we could grind part of the slot back open again, which would give us 3 or 4 degrees more mechanical if necessary. We also were afraid that with this aggressive timing curve, the engine might detonate at part throttle, but this has not been the case. That may change, however, when the dog days of summer arrive.

Ignition curves were not the only things we tried. The 625-cfm Road Demon carburetor is a vacuum-advance carb that uses a spring in the secondary diaphragm to determine when the secondary barrels open. The stiffer the spring, the longer it takes for the secondaries to open. Changing the spring in the stock vacuum-secondary pod is rather cumbersome, so we ordered a quick-change vacuum-secondary pod that would make spring changes easier at the track. We didn’t want to make any more changes to the car until we could take it back to LACR to test, since making too many changes at once can get confusing and we wouldn’t know which change had made the most improvement. We again took the El Camino up to LACR and mounted the Mickey Thompson E.T. Street tires and Center Line Triad wheels on the car to eliminate the tire-spin problem with the tires set at 18 psi.

On the first pass with the better ignition curve, the El Camino left noticeably harder, pulling a better 2.08-second 60-foot time, but we did not see any improvement on our original 13.13/103-mph benchmark. It seemed that now our problem was traction. Even with the M/T E.T. Street tires, the El Camino still spun the tires.

Pat pulled the El Camino back into the pits and we decided to try a fairly light spring to see if quicker-opening secondaries would net a lower e.t. The Road Demon comes with a fairly light spring right out of the box and the effort netted us no gain.

By this time, we had run out of track time. Once back home, we plugged an Auto Meter fuel pressure gauge into the fuel line and were greeted with barely 3 psi (normal is 5-½ to 6-½ psi), even at idle. We figured we had found the problem. We also decided to add an Air Lift air bag to the right side in an effort to preload the chassis and prevent tire spin on the right rear tire. Back at the track, the first run was disappointing. Rechecking all our tuning points, Patrick drove the El Camino to a corrected 13.07/102.11, which was a small e.t. improvement. Now we only needed 0.08 second and we’d be in the 12s. Unfortunately, we had time for only one last run at LACR’s Friday night Grudge Night. As a last resort, we cooled the engine down, put ice on the intake manifold, and made sure the electric fan was off before making the last run of the day. The cooler manifold had paid off before with a slight e.t. improvement, but this time it was no dice. The El Camino ran slower (there was about a 10 mph head wind that night), and we were forced to head home without our 12-second timeslip trophy.

We’re not finished with this first version of Agent 87. While this has been an incredibly successful effort, we still want that 12-second timeslip. But even before that happens, we’d like to thank Patrick and his dad Jim Peterson for donating their time and energy to make all this happen. There’s also another Agent 87 355ci small-block coming together that will feature Hi-Tech Swirl-Quench pistons and a set of 72cc aluminum TFS heads for more compression. We will use this newer Agent 87 engine to go in search of even more torque, more horsepower, and more fun, all on 87-octane fuel. We’re also considering a third Agent 87 engine that will push the boundaries of high compression on 87-octane fuel. Stay tuned for the next episode of the Further Adventures of Agent 87.

Agent 87, Part I

Agent 87, Part II