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924RACR
Joined: 29 Jul 2001 Posts: 8803 Location: Royal Oak, MI, USA
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Posted: Fri Apr 27, 2007 12:42 am Post subject: Dyno tuning report |
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I finally got the racecar on the dyno the other day, here's the run-down:
First two baseline readings were down about 5 hp/ft-lbs from the previous day's readings; perhaps the dyno software hasn't quite learned enough about compensating for humidity. Certainly there were no changes made to the car or tuning.
The repeatability of the dyno is certainly excellent! Back-to-back runs really overlay well. Note - when we reported numbers yesterday, they were from a peak that is actually a bit of a phantom, not a legit reading (due to the engine missing at high revs/loads - more on that later). I need to get the graph outputs from Kendall (dyno owner), but as I recall we were just brushing 100 ft-lbs of torque towards the end - between about 95-100 from around 3000-5000rpm on the final run.
So after playing around with mixture and spark - we picked up about 5ft-lbs across the curve, about what we'd expected to from this type of tuning. We also tried a 4-degree offset cam key to advance the cam, see what that'd give us; didn't have much impact, very small/modest shift in the power curve (like maybe 50 rpm, it seemed?).
First we leaned out the mixture (in spite of it running already a bit lean mid-range; this got us a bit of power - though it didn't make much impact on the O2 sensor readings, they stayed lean throughout. Then we added 3 more degrees of spark advance for a total of 42deg - that also got us a little more, but now the engine really started to break up in the 5500-5800 range. Then we put in the cam key, readjusted the spark timing back - no real gain, just the slight power peak shift as noted.
Finally we tried to eliminate the misfire at 5500. While it had gotten better or worse as we'd moved around spark timing or bumped mixture, it never quite went away. We deduced that it was occurring on the low-tension side, and so replaced the distributor pickup wire with a newly-created wire (shielded twisted pair). This immediately improved idle, much smoother, now within 100rpm rather than 300-500 rpm variations. When we ran a pull, however, there was little impact on power, surprisingly enough. Likewise, we still suffer from the misfire.
However, we then brought the mixture, which at this point was still substantially leaner than our starting point, back richer again - this started bumping the power curve up further. Returning pretty much to our original mixture setting (which was determined experimentally, on-track) resulted in the net gain (along with the ignition timing change) of the 5ft-lbs or so noted above.
Where to go from here? Well, that's plenty of advance; the engine should be able to take it, but it would be nice to confirm. This would best be achieved by running again on the dyno with a knock sensor hooked up - I believe Kendall has the option to do this. Hopefully the old 924 engine won't cause it to misdetect due to raw noise and vibration!
We also still are fighting the misfire. While the car was up on the dyno lift, I did notice that the front exhaust joint from the header downpipe to the main exhaust section appears to be leaking a bit. It's possible that this is enough to throw things off; this would possibly also account for the O2 readings, all the way back at the tailpipe, to be off so much. So I will be ordering up a band clamp to better secure that joint, and we shall see what that does - should be in time for Race 1. The other possible culprit is the Hall effect sensor in the distributor itself; I'll probably order up one of those in the meantime as well, to swap in. _________________ Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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Min
Joined: 04 Nov 2002 Posts: 2368 Location: Vernon, British Columbia, Canada
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Posted: Fri Apr 27, 2007 1:14 am Post subject: |
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Your running 42 degree's total advance? .... My ignition curve max's at 35 at WOT, maybe I can get some decent power gains from upping the timing? hrm. Very nice report. BTW, my knock sensor reads solid knock after 4k rpm or so due to engine noise.
Min _________________ Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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924RACR
Joined: 29 Jul 2001 Posts: 8803 Location: Royal Oak, MI, USA
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Posted: Fri Apr 27, 2007 2:36 am Post subject: |
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Correct, 42 total, no vacuum, mechanical only. 93 octane fuel, 9.5:1 CR.
I don't think it'd be a great idea to run a street car that hot. No idea about durability, starting, driveability. _________________ Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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924RACR
Joined: 29 Jul 2001 Posts: 8803 Location: Royal Oak, MI, USA
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Posted: Fri Apr 27, 2007 3:10 am Post subject: |
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Some additional comments. They say you need to be prepared and have a plan for testing different things when you hit the dyno - boy are they ever right!!! Now I've got exhaust changes I'd like to try, and ignition (want to put a solid number on the difference between my Permatune CD box and stock ignition, if any at all). May eventually get around to trying a different header.
Another note - boy am I glad my car cools real well! Minimizes down-time between runs, when I want to just bump timing a degree, etc, it's very nice. Already sorted out any hot-running issues long ago, had no worries, but it was real nice when I could make a good hard pull, drop it to idle, then idle for a couple minutes, right back down to the first line no worries.
Great place to debug stuff... _________________ Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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Min
Joined: 04 Nov 2002 Posts: 2368 Location: Vernon, British Columbia, Canada
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Posted: Fri Apr 27, 2007 3:21 am Post subject: |
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924RACR wrote: | Correct, 42 total, no vacuum, mechanical only. 93 octane fuel, 9.5:1 CR.
I don't think it'd be a great idea to run a street car that hot. No idea about durability, starting, driveability. |
Ya, keep in mind I've got a fully programmable ignition curve. So I can keep starting at 10 degree's so it starts easy and then program the curve to anything I want, If your running 42 degree's, I might be able to get away with running a bit more advance then as well, which is nice to know, since I'm being pretty conservative with it atm.
Min _________________ Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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924RACR
Joined: 29 Jul 2001 Posts: 8803 Location: Royal Oak, MI, USA
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Posted: Fri Apr 27, 2007 4:47 am Post subject: |
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Ah, that extra adjustability does help!
Pics and a little video (sorry, no sound) will be available later, for all you 924 freaks... _________________ Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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endwrench
Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana
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Posted: Fri Apr 27, 2007 5:56 am Post subject: |
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Great report! Lots to go over and gleem. Thanks!!
Are you getting 100lbs at he wheels or corrected?
Todd _________________ '79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!.... |
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924RACR
Joined: 29 Jul 2001 Posts: 8803 Location: Royal Oak, MI, USA
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Posted: Fri Apr 27, 2007 6:01 am Post subject: |
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As promised:
We were just getting up to 100ft-lbs at the wheels, 101hp at 5600rpm. _________________ Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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