How to hold 3000 RPM to check timing?
08-23-2013, 01:22 PM
#16
Drifting
08-23-2013, 01:48 PM
#18
Rennlist Member
Thread Starter
I am also at 8 degrees at idle. With vacuum advance disconnected, I am supposed to get 20 degrees at 3000 RPM. Max should be 24-28 degrees at 5000 RPM with vacuum advance active. This is straight factory settings. I would like to add 4-5 degrees to all of this and increase my octane to 93 to provide knock insurance. I know my gas mileage will suffer, but I am wondering if it will be safe. 1984 USA L-jet, no knock sensors.
Thanks,
Dave
Thanks,
Dave
08-23-2013, 02:41 PM
#19
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I remember wrong. I was adjusting to 28 degrees at 3000 with both vacuums disconnected, and this made approx 8 degrees on idle WITH vacuum connected afterwords. I'm running 98 octane all the time.
08-23-2013, 04:39 PM
#20
Former Sponsor
I was thinking: Can I advance the timing 3-4 degrees at idle, and run premium gas, to improve performance? For my car the WSM says 4-8* BTC at idle with vacuum hose removed. This gives 20*BTC at 3000 RPM. If I set idle timing to 10* BTDC I assume the 3000 RPM will go to 24* or so. I would reset the idle speed to 650 RPM, and have a little more pep? Mileage would suffer a little, but my drives don't put on that many miles. Any thoughts?
Thanks,
Dave
Thanks,
Dave
I always run premium fuel in all my 928's. The additional $.10-$.15 of cost is a completely moot point, when "regular" unleaded fuel is $3.75-$4.00 a gallon.
I increase timing until they ping or have some other performance issue. If required, the spring pressure on the injection "flapper" can be loosened to get some extra fuel. Pretty easy to add 10 degrees of timing.
These engines hate 14.7 to 1. Try disconnecting the O2 sensor, fit a wide band, and shoot for a "cruise mixture" that is richer....gets rid of the "surge" issues that are so common.
With minimal effort/cost you can transform these engines into something completely different than stock.
08-23-2013, 04:45 PM
#21
Former Sponsor
The throttle on my car is down under the very hot spider and I don't se a way I can reach in there and hold it open, Greg. I cannot rely upon my wife to do this, so I may use one of those bar clamps set up to spread rather than clamp, and press between seat and gas pedal.
Thanks,
Dave
Thanks,
Dave
I forget that not everyone has my hands that have 45 years of working on cars "conditioned" into them.
I pull back my hands when I smell them burning....the pain response is slower.
"Mechanic's Wear" sells nice heat resistant gloves....virtually available anywhere.
08-23-2013, 05:20 PM
#23
Rennlist Member
Greg - I have a US 4.7. What AFR do you run under cruise/load? When I bought my 928 I was more used to turbo cars and tuned typically AFR to 11:1 +/- , but assumed (incorrectly?) that NA cars should run 14.7. My car was having that surge issue so I did disconnected the O2 and set the AFR manually to around 14 under cruise. What AFR do you recommend at cruise or under load on the 4.7?
08-24-2013, 09:49 PM
#26
Drifting
I've found that the "late" US 2 valve engine love timing and the performance increases significantly.
I always run premium fuel in all my 928's. The additional $.10-$.15 of cost is a completely moot point, when "regular" unleaded fuel is $3.75-$4.00 a gallon.
I increase timing until they ping or have some other performance issue. If required, the spring pressure on the injection "flapper" can be loosened to get some extra fuel. Pretty easy to add 10 degrees of timing.
These engines hate 14.7 to 1. Try disconnecting the O2 sensor, fit a wide band, and shoot for a "cruise mixture" that is richer....gets rid of the "surge" issues that are so common.
With minimal effort/cost you can transform these engines into something completely different than stock.
I always run premium fuel in all my 928's. The additional $.10-$.15 of cost is a completely moot point, when "regular" unleaded fuel is $3.75-$4.00 a gallon.
I increase timing until they ping or have some other performance issue. If required, the spring pressure on the injection "flapper" can be loosened to get some extra fuel. Pretty easy to add 10 degrees of timing.
These engines hate 14.7 to 1. Try disconnecting the O2 sensor, fit a wide band, and shoot for a "cruise mixture" that is richer....gets rid of the "surge" issues that are so common.
With minimal effort/cost you can transform these engines into something completely different than stock.
08-24-2013, 09:58 PM
#27
Rennlist Member
Thread Starter
I was thinking about Matt's AFM tune-up when Greg wrote this. I set my idle advance to 10* BTC. I can easily use premium fuel. The pep is noticeable.
Dave
Dave
