914-6 finally gets it's dyno runs, The dyno raises more questions Options

[RogerPihlaja]

So, I finally found a chassis dyno that was willing to run my 1970 914-6. The 3.0 liter 911 SC engine had about 1000 break-in miles on it. The attached file has 3 hp & torque curves from 3 dyno pulls superimposed. A 6300 rpm redline was observed. As you can see, the engine is still pulling hard at 6300 rpm and would produce more power if it were spun faster. I have heard 3.0 liter 911 SC engines are safe to rev to 7000 rpm; but, I wanted to get confirmation before I tried it. The engine has a Clewett Engineering engine management system with MAP fuel injection, coil at plug electronic ignition, wide range oxygen sensor closed loop, 1-5/8" ID Billy Boat headers, and a twin outlet sport muffler. The valves, springs, pistons, connecting rods, and crankshaft are stock. There is a mild cam from WEBCAM (Grind #40) in it.

I was somewhat surprised at the shape of the torque vs rpm curve. The dip in the torque curve between about 2600 - 3600 rpm reminds me of the bad old days of emission controls with carburetors. The [Air]/[Fuel] ratio would often go lean just off idle resulting in a flat spot in engine response and driveability around town. Do I need to remap the fuel flow for more fuel in that rpm region? Or, what else might be causing this dip in torque? Also, the flat shape of the torque "curve" surprised me. Isn't there supposed to be more of a peak? This isn't some "tractor" engine?

By the way, the engine sounds great on the dyno! I have a video file with audio; but, it's ~31 mbytes. If someone has a way to deal with a big file on the website, please let me know and I'd be glad to share it.  TooSlo86_Racing_Dyno_Chart.pdf ( 599.22k ) Number of downloads: 97

[PlaysWithCars]

Sounds like you need to find someone that can tune the FI/engine management system. The stock file is usually just to get the engine running and set a baseline. It's never going to run to it's potential with a stock tune.

(IMG:style_emoticons/default/agree.gif) I'm suspicious that you have too rich AFR and too conservative ignition timing. I'd be looking real close at ignition timing curve as the biggest culprit. Even if the dyno doesn't have AFR capability, you should be able to monitor and log most of this through your engine management system(s).