Checking timing and knock retard
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,469
Likes: 6
From: Winchester Ontario
Checking timing and knock retard
I am hearing of people running higher timing and liking the results. I am at a timing of 6 degrees right now. How would I know that 10 degrees would help me at all? I do not have any scanner, but my mechanic has a Snap On engine diagnostic tool, would that work?
When adjusting the timing, what should I look for on the scanner? Knock counts, total timing?
And as for reading the A/F ratio, I heard that just by reading the millivolts isn't an exact science, but what are the appropriate ranges I'm looking for?
I think someone said that 900 mV or so is around 12.8? Since I run nitrous (although bottle is empty now) what kind of A/F ratio should I be looking for...12.5?
Heh, lots of questions, but this is the place for answers.
When adjusting the timing, what should I look for on the scanner? Knock counts, total timing?
And as for reading the A/F ratio, I heard that just by reading the millivolts isn't an exact science, but what are the appropriate ranges I'm looking for?
I think someone said that 900 mV or so is around 12.8? Since I run nitrous (although bottle is empty now) what kind of A/F ratio should I be looking for...12.5?
Heh, lots of questions, but this is the place for answers.
Melting Slicks
Joined: Jul 2003
Posts: 3,227
Likes: 50
From: Pomfret, CT
Finalist 2020 C4 of the Year - Unmodified
Re: Checking timing and knock retard (black_89_vette)
Bob (Robertpel9) and I just bumped his up to 10 degrees last night on his 91 L98. He said he felt a DRASTIC improvement. I do not know anything about the scanners and such, but what you want to do is make sure that the car does not detonate (ping) at WOT (wide open throttle). You could use a scanner or engine diagnostic machine to tell you what your knock count is to make sure that you are in fact not detonating.
-Rick
-Rick
Safety Car
Joined: Nov 2001
Posts: 3,753
Likes: 191
From: Orange County California
Re: Checking timing and knock retard (1990CORVETTE)
You don't want metal coming together basically. You want the spark to come right before the piston reaches the top for maximum power. If that is too far off you can force the piston down before it is done coming up and that is a bad thing. When we rotated the distributor to 10* you could actually hear the engine like where it was vs bofore. It got very smooth. I think this is a "mod" definitely worth playing with. I don't want to exaggerate so i would give a percentage but i can safely say the car feels like a totally different engine was put in. Now i swapped gears too so a lot has changed but i would recommend playing with it. So far its been worth it for me. :cheers:
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Checking timing and knock retard (black_89_vette)
Using the scan tool is indeed the best way to set timing to the max safe value. Advance timing 2deg at a time and make a few WOT runs. You are looking for the point where the scanner shows a few knock counts and some timing retard near max RPM at WOT. When you reach this pint back off timing 1 or 2 deg, till you no longer see any knock count changes and no timing retard.
My A/F at WOT is 12.6:1 (from dyno pulls) and the O2 sensor shows about 920mV, decreasing slightly near the traps due to the ram-air intake. This should work well for a N/A L98 but I'm not sure a bout a NOS engine; I'm sure you'd rather be rich than lean there.
My A/F at WOT is 12.6:1 (from dyno pulls) and the O2 sensor shows about 920mV, decreasing slightly near the traps due to the ram-air intake. This should work well for a N/A L98 but I'm not sure a bout a NOS engine; I'm sure you'd rather be rich than lean there.
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,469
Likes: 6
From: Winchester Ontario
Re: Checking timing and knock retard (65Z01)
Advance timing 2deg at a time and make a few WOT runs. You are looking for the point where the scanner shows a few knock counts and some timing retard near max RPM at WOT. When you reach this pint back off timing 1 or 2 deg, till you no longer see any knock count changes and no timing retard.
WHen I took it to Agostino Racing to get it dynoed, the guy had it in 4th gear around 2500 RPM and then stomped on it for the dyno run, he pulled out of it by 3500 RPM saying it sounded like it was detonating like crazy. He said it sounded like it had an insanely high compression ratio. On paper, the CR should be around 9.3-9.5 and I use 91 octane gas. I have since bought new plugs and replaced faulty plug wires with Taylor Spiro Pro 8mm and NGK TR6.
I had my mechanic check the timing the day before and he said it was at 6 degrees. This is making me wonder why my car was "detonating" at only 6 degrees and how some can run it up to 10. Why would this be happening, and what should I be looking for?
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Safety Car
Joined: Nov 2001
Posts: 3,753
Likes: 191
From: Orange County California
Re: Checking timing and knock retard (drvette85)
i am at 10 now and let me tell you IT ROCKS. I dont want any more power at this point. I have to learn how to get this power to the pavement:) :eek: