In a search for more power,...
In a search for more power, we eventually pulled off the heads and sent them to Porter Racing Heads in Vermont. Dwayne Porter polished up the exhaust ports and redid the valve job. Final flow numbers were 292 cfm on the intake and 220 cfm on the exhaust at 0.600 lift.
Tweaking The Combination
The Edelbrock heads were initially bolted on right out of the box, and they worked great with the motor making 550 hp at 5,700 rpm on the engine dyno. Once the motor was off the dyno and into the car, we started to tweak on it a bit and ended up swapping a number of parts around before hitting on the current combination.
One of the first things we tried once the car was up and running was an Edelbrock Performer RPM manifold. The thinking was since this was a street car, the extra torque from the dual plane design would be beneficial to us. in fact, that was exactly the case, as we noticed a fairly big jump in low-end torque when comparing the Performer RPM to a Victor 383. We're fairly certain the exhaust manifolds influenced this test, since they kept the motor from using all of the flow available with a race intake. Just like with the big cam test, the big intake manifold killed the low-end torque, but didn't make any more power on the top end.
We also spent some time testing a few different carburetors and found the Edelbrock 800-cfm units to be a great choice. We ran both the AVS and the AFB versions on this motor and saw identical power curves. According to our contact at Edelbrock, the AVS version received some internal improvements when the tooling was produced, so the AVS should provide a slight increase in performance. We didn't see a horsepower improvement, but we did find the AVS carb would make the same power as the AFB, while using one size smaller jets. that means the AVS version is a little more efficient of a design.
We overlaid our chassis dyno...
We overlaid our chassis dyno results with those from an '02 GTS Viper. Our 466 cranked out an additional 67 lb-ft of torque and 49 rwhp over the Viper. Who says you need headers to make power?
Test Results: Dyno And Track
It is a little tough to summarize the dyno testing that this combination has seen. In the last year alone, it has racked up more than 40 pulls on the chassis dyno. At one point, we had a standing date at the chassis dyno every Friday morning! The purpose of all of this testing was to sort through the choices on camshafts, intake manifolds, and carbs. Even with all of that testing, we still haven't fully explored rocker arm ratios, spark plug gaps, timing curves, and so on. When it comes to flogging a motor, lets just say that the win light probably goes to the guy who works the hardest.
But we can say the best dyno numbers posted to date were pulled down when running the MP .528 cam with the Performer RPM manifold and the Edelbrock AFB 800 carb. We rolled into the dyno shop one nice crisp morning, and the big 17-inch Goodyears spun the dyno up to 527 lb-ft of torque and 474 hp. Given a 15-percent powertrain loss for a manual transmission, we estimate the power at the flywheel to be in the neighborhood of 560 hp for that set of pulls. The car has spun the dyno up over 460 rwhp dozens of times, but that 474 is the best pull to date.
Taking this car to the dragstrip is a bit of a lesson in how hard it is to hook up a stick shift car on street tires when you have a ton of torque. Our first few passes resulted in huge wheel spin and low 13-second quarter-mile times at 113 mph. Based on the mph, we knew the car had plenty of power, but getting it hooked up has been a challenge. Of course, the car is set up for Pro Touring mode not drag racing, so it has big stiff torsion bars and low profile 17-inch tires. Neither of those really helps the traction situation at the drag strip.
We did compromise the pro-touring setup a bit by bolting on a set of BFG Drag Radials and that gave us enough traction to dip into the low 12s, but the car is still posting slow 60 foot times. No doubt if we bolted on some slicks and tweaked the suspension with some old drag racing tricks, we could see some high 11s at the track. But those suspension mods would ruin the handling of the car, so we'll just have to settle for having a 12-second car that can corner. Maybe at some point in the future, we'll work on the suspension some more and get it to a point where we can have our cake and eat it too.