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

[jd74914]

Interested in more details as well. Did you just put the Clewit kit on and hit a dyno with it's base map? This looks like the results of a super conservative base tune, ie: the kind provided by the manufacturer to get your car to start and drive on the road or to a dyno. Usually these have very conservative ignition timing and are quite rich. The expectation from the manufacturer is that you're going to tune it, though Clewit doesn't make that too clear on their website.

Is this the kit you're using?
https://www.clewett.com/index.php?main_page...products_id=491

It has the O2 sensor shown, was this installed? With an Elite ECU you have the ability to data log so you can record what's actually going in.

Note: You don't really need a 911 guy to tune, most competent tuners familiar with Haltech software/peculiarities would be fine. With data logging you might even have good luck with driving around and a remote tuner analyzing the data and sending you updated files.