Sorry I'm so late to this party, been buried in getting ready for PRI, among other things. It was actually a rather frustrating dyno session because we were fighting a problem with the engine for most of the afternoon. We couldn't get it to start. Repeated checks for spark and fuel showed that we had both, but despite that the engine just wouldn't fire. Mike had already run it just this way on the engine stand, so it was a real puzzle. One issue was that I didn't have a complete cable to run from the MSD to the plug in Mike's distributor, and I think that may have been the culprit in the end, because the connectors I put on the end of the cable, to plug into the MSD plug on the distributor, may have only been making intermittent contact. Of course I checked them a half dozen times, so I just don't know; we got spark at the plug when we checked it. Go figure. We swapped MSDs, coils, and finally installed one of my MSD distributors and my plug wires. Still no joy. Towards the end of the afternoon I called Kevin, and he came over with another MSD, an MSD tester, a coil, and the cable that I didn't have. The tester indicated that my MSD and my coil were working properly, but we still didn't have any luck. Then we figured out that we goofed when we installed my distributor and got the distributor in 180 degrees off; Mike was the one that finally figured that out. When we got that right about 4:00 the engine fired right up. We swapped back to Mike's distributor and wires, and then they worked fine too. So we were finally able to do some testing. I'm still not sure what was wrong, but again I suspect that cable that we were using at first.
We went through the usual tuning routine and optimized timing and jetting, and after 10 dyno pulls we knew what the engine would do. But after looking at this data again tonight, I think that something else may be going on that is limiting the high RPM power. There are two dyno pull graphs below, the first one to 6000 RPM and the second one to 5800. After about 5300 this engine stops climbing. During the dyno session I thought this might be electrical noise on the signals, because sometimes they show up like that, but I noticed looking at the data tonight that the HP graph is discontinuous, tracking a different line after 5300 RPM. The way the graphs look, I'd suspect possibly valvesprings that are not up to the drill, the hydraulic roller lifters pumping up, or more likely an ignition problem, maybe with spark scatter in the distributor or something. The choppy appearance of the graph is a giveaway that the engine isn't happy past about 5300 RPM:
These graphs look just like the graphs from my 428CJ dyno mule, which had flat tappet hydraulic lifters that were the culprit limiting valvetrain control after 5300 RPM. See my book for a comparison between hydraulic and solid lifters, and you will see about the same thing with the flat tappent hydraulics. But I think an ignition issue may be more likely...
I don't think the issue is exhaust related. The dyno has a pressure sensor in the exhaust system, and after conducting experiments with the exhaust connected vs. open headers, I've never seen a HP difference until the pressure in the exhaust system gets close to 1 psi. In this case, the peak exhaust system pressure recorded was 0.366 psi on pull #9. Also, for anyone interested in the correction factor, due to the cold weather the correction factor was very close to zero, only about 2.1%. At the end of pull 9 inlet air temperature was 55 degrees, barometric pressure was 29.27, and vapor pressure was 0.12.
Vacuum at wide open throttle was up to 1.3" at the end of the pull, and there is usually power to be had if you see vacuum levels over 1", so I think a bigger carb would be a good investment.
The reason I think the primary suspect is ignition is that the engine is continuing to pull air at the higher engine speeds. In most cases, if you look at the engine's air consumption (the gold line in the graph below) it will track very closely with the horsepower level. The graph below shows that despite the HP falling off, the engine is continuing to use more air. When a valvespring or lifter problem exists,
usually you will see the air curve start to get choppy like the horsepower level. There are cases where a valvetrain issue will not show that characteristic, but in most cases it will. Its too bad that we burned all that time on the dyno trying to get the engine to start, because it would have been interesting to identify this issue, and then try to correct it with a different distributor. Kevin's test equipment indicated that the MSD and coil were working correctly up to the 7000 RPM limiter set in the MSD, so if it is electrical, its got to be the distributor, wires, or plugs.
Oh well, water under the bridge at this point. Its a strong engine for sure, and it was a real pleasure to have Mike and his friend Andy here for the day, and thank goodness Kevin came along with some parts that seemed to solve the problem.
