Round II
With the 165 Comps clamped down and a fresh oil and filter change, our 347 was ready for round two of testing. Since we didn't even touch the distributor during the head swap the motor had no problems firing right up. Once the coolant temperature was at 180° and the dyno cell cooled to 67° (the same temperature used on all runs) we were ready to floor this mill.

It took no more than the first pull to realize the merits of the Competition porting package. The heads produced single digit gains up to 5300 rpms, but then really showed the benefits of the extra air flow with an average of 15 horsepower and 13 lb-ft of torque to 6500 rpms. Peak flywheel horsepower improved to 456 from 440 with the standard 165 head. That's a pretty significant change considering the runner volumes are identical between both sets of heads. Often times a swap to a better flowing head results in a loss in low-end torque and horsepower - a direct result of poor low rpm velocity through the runner. Clearly the additional CNC work on the Competition 165 has no downsides.

Timing The 10.5:1 compression 347 performed best at 34 degrees of timing, regardless of which 165 head was on the motor. 36 lost a couple horsepower at a few points while 38 lost as much as 8 horsepower across the board.	Spacer This four-hole 1.5" tapered Wilson Manifold spacer was thrown on near the end of our testing. Surprisingly it was worth a consistent 5-7 horsepower and torque across the rpm band. This pushed our motor above the 460 horsepower mark.
Carb Size While the cfm's may seem inadequate for a 347, the Demon 650 made more power across the board than our tried and true Jet modified 750cfm double-pumper. We had to jet the Demon up to 79 primary and 86 secondary.	Exhaust Gas Temperature Montoring exhaust gas temperature in each header primary provided visibility on air/fuel delivery to each cylinder. The single plane intake showed hotter temps (leaner) in cylinders 1 and 8.

Fine Tuning
With a few more hours of dyno time left we focussed on extracting out as much horsepower as possible through tuning. We had already explored leaner and richer air-fuel mixtures via jetting the Speed Demon 650. Barry Grant delivers the mechanical-secondary 650 with 73/79 jetting in the primary and secondary metering blocks respectively. This calibration proved to be dangerously lean for our motor. As a result we crept up on jetting in 2 step increments until we obtained a power loss, then stepped back jetting until maximum power was obtained. Our final jetting was was 79/86, a huge jump from the out-of-box calibration. Along with air-fuel ratios we relied on EGT and BSFC numbers to ensure we weren't treading on lean ground. Dave's experience with Speed Demons is they tend to make best power with BFSC numbers in the .420-.440 lb/hph range. Also interesting to note is that the better flowing Comp heads made best power with the same jetting (79/86) as the standard 165 head. It's always a good sign when you make more power with less fuel consumption.

With the Speed Demon dialed in, we threw on a Wilson Manifolds four-hole "tapered" spacer. The underside of this 1.5" tall spacer features a conical taper similar to an orange juicer. Wilson claims this increases air flow into the carburetor and also serves to improve air/fuel mixture. Our testing showed the spacer to be worth as much as 7 horsepower and 10 lb-ft across the board. These gains came with no other changes and we saw a consistent rise in the calculated Volumetric Efficiency of the motor (see Table 1).

Is 475 Horsepower Possible?
Here you've got a fairly straight forward recipe using off-the-shelf parts. No porting, no custom cam, just a host of parts from your favorite speed shop and a stout bottom end from a good machine shop. Bolt it together and you've got an easy 460 horsepower and 430 lb-ft of torque. In a five-speed car this should translate to around 390 horsepower to the wheels based on a 15% drive train loss. So what can we do to get a bona fide 400 hitting the ground? Well it may not take more than an intake manifold. The gains with the four-hole spacer suggest to us that the single plane intake was the wrong choice for this motor. A Stealth or RPM Air-Gap is likely to produce more average power for this motor considering our under 6500 rpm peak. In fact Dave showed us test results from a recent engine dyno session where an Air-Gap produced 20 horse across the board over a Victor Jr. While this goes against our typical line of thinking that single planes perform better, we can't help but take notice of these results. The next step for us will be to drop this motor in a car and compare manifolds, both at the track and on the chassis dyno.

Chart 1: AFR 165 Standard vs. AFR 165 Competition     AFR 165 Competition Peak HP: 456@6000 TQ: 423@4200 AFR 165 Standard Peak HP: 440@6200 TQ: 419@4200

Table 1: AFR 165 Standard vs. AFR 165 Competition   Horsepower Torque RPM Std. Comp +/- Std. Comp +/- 3500 284.7 289.9 +4.2 415.3 422.8 +7.5 3700 291.7 296.1 +4.4 414.1 420.3 +6.2 3900 307.9 311.6 +3.7 414.7 419.7 +5 4100 326.2 330.6 +4.4 417.8 422.8 +5 4300 342.6 346.6 +4 418.4 423.4 +5 4500 357.4 360.1 +2.7 417.2 420.3 +3.1 4700 372.8 375 +2.2 416.6 419 +2.4 4900 388.6 391.5 +2.9 416.6 419.7 +3.1 5100 403.9 408.7 +4.8 415.9 420.9 +5 5300 417.2 426 +8.8 413.5 422.2 +8.7 5500 427.8 439.5 +11.7 408.5 419.7 +11.2 5700 433.9 449.4 +15.1 399.8 414.1 +14.3 5900 438.6 454 +15.4 390.4 404.1 +13.7 6100 439.8 455.6 +15.8 378.6 392.3 +13.7 6300 440 454.9 +14.9 366.8 379.3 +12.5 6500 437.1 452.4 +15.3 353.1 365.6 +12.5

Chart 2: AFR 165 Comp + Wilson Manifold Spacer     AFR 165 No Spacer Peak HP: 460@6000 TQ: 432@3500 AFR 165 With Spacer Peak HP: 456@6200 TQ: 423@4200

Table 2: AFR 165 Comp + Wilson Manifold Spacer   Horsepower Torque VolEff% RPM No Spacer With Spacer +/- No Spacer With Spacer +/- No Spacer With Spacer 3500 289.9 294.5 +4.6 422.8 432.1 +9.3 103.7 106.1 3700 296.1 301.3 +5.2 420.3 427.8 +7.5 102.8 104.6 3900 311.6 318.1 +6.5 419.7 428.4 +8.7 100.2 101.6 4100 330.6 335.4 +4.8 422.8 429.6 +6.8 99.5 101.1 4300 346.6 350.2 +3.6 423.4 427.8 +4.4 99.8 101.6 4500 360.1 365.4 +5.3 420.3 426.5 +6.2 99.0 100.8 4700 375 382.8 +7.8 419 427.8 +8.8 98.6 100.4 4900 391.5 399.1 +7.6 419.7 427.8 +8.1 98.0 99.7 5100 408.7 416.0 +7.3 420.9 428.4 +7.5 97.5 98.9 5300 426 432.9 +6.9 422.2 429.0 +6.8 97.1 98.9 5500 439.5 446.6 +7.1 419.7 426.5 +6.8 96.7 98.5 5700 449.4 456.1 +6.7 414.1 420.3 +6.2 96.1 97.6 5900 454 459.6 +5.6 404.1 409.1 +5.0 94.7 96.4 6100 455.6 460.3 +4.7 392.3 396.7 +4.4 93.3 95.0 6300 454.9 460.1 +5.2 379.3 383.6 +6.3 92.0 93.7 6500 452.4 457.1 +4.7 365.6 369.3 +3.7 90.9 92.6