I was able to advance my ignition timing to 15 degrees BTDC under boost and it does not knock at 18 psi, 12.2 AFR, and 93 octane with 10% ethanol. The power just felt a bit flat with the timing at 11 or 12 BTDC, and even at 15 degrees BTDC it does not feel that impressive. I have the timing fixed at 15 degrees BTDC right now with the vacuum line removed from the boost retard module on the distributor. If I spike to 20+psi it will knock but it will carry 16-18 psi to redline without knock.

The performance mods on the car are Trionic Red Top injectors, 3 bar FPR, LH fuel chip that I tuned myself, stock downpipe with a 2.5" exhaust and no cat, modified APC box, a K&N air filter that sits behind the stock intercooler, 85 exhaust cam and NA intake cam, 90' block and head.

I did a cylinder leakage test a few weeks ago at 100psi and none of the cylinders leaked any more than 5%. From what I read you shouldn't worry about cylinder leakage unless it gets up to 15-20%. The cam timing looks good, and there are 15 chain rollers between the marks. I checked the compression a few months ago when I was having starting issues with Megasquirt (started fine on the stock system), only had about 100psi on all cylinders but it was even between all of them. The engine was cold when I tested it and I have a feeling the fuel washed the oil from the cylinders from cranking. I added oil to the cylinders and the compression went up to 125psi. Is it possible that an engine can pass a cylinder leakage test, but do poorly on a compression test? Also if the engine has poor compression would that prevent it from knocking under 18psi of boost even if the timing was advanced to say 15 degrees BTDC?

posted by 96.253.216...

• No knock despite 18 psi and 15 degrees advanced, 85Aero, Tue, 2 Mar 2010 17:54:31 <-- Viewing This Message
  • Re: No knock despite 18 psi and 15 degrees advanced, Simon S, Wed, 3 Mar 2010 08:55:10
    • And plugs..., Simon S, Wed, 3 Mar 2010 08:57:13
      • See first response...., DrewP, Wed, 3 Mar 2010 09:31:29
        • Re: See first response...., Simon S, Wed, 3 Mar 2010 12:36:45
          • Not to be a stickler, DrewP, Wed, 3 Mar 2010 13:37:05
            • Re: Not to be a stickler, 85Aero, Wed, 3 Mar 2010 17:21:20
            • Re: Not to be a stickler, Simon S, Wed, 3 Mar 2010 17:12:34
            • I think we can all agree..., Steven Pfaff, Wed, 3 Mar 2010 14:23:56
  • Re: No knock despite 18 psi and 15 degrees advanced, Steven Pfaff, Tue, 2 Mar 2010 18:56:47
    • Re: No knock despite 18 psi and 15 degrees advanced, 85Aero, Tue, 2 Mar 2010 19:52:40
      • Re: No knock despite 18 psi and 15 degrees advanced, Steven Pfaff, Tue, 2 Mar 2010 21:09:36
        • Re: No knock despite 18 psi and 15 degrees advanced, 85Aero, Tue, 2 Mar 2010 22:01:14
          • Re: No knock despite 18 psi and 15 degrees advanced, Steven Pfaff, Wed, 3 Mar 2010 08:15:25
            • Re: No knock despite 18 psi and 15 degrees advanced, Simon S, Wed, 3 Mar 2010 08:51:56
              • Re: No knock despite 18 psi and 15 degrees advanced, Steven Pfaff, Wed, 3 Mar 2010 09:33:28
          • Re: Engine should be warm for compression test..., Street, Wed, 3 Mar 2010 00:38:30
    • and how are you detecting/measureing knock? nm, Steven Pfaff, Tue, 2 Mar 2010 18:58:19

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