| you really need to do to ensure that your car is prepared to go to the dyno - it will help to determine where the source of the problem is at. My 6 P's FAQ is the best place to start. You have checked a few of the things, but there are still many more, and you should also eliminate the PRVR system which can cause leanness problems just like you are having. The 6 P's: Proper Preparation Prevents Piss Poor Performance
[ http://twinturbo.net/net/viewmsg.aspx?forum=technical&msg_id=813994 ] Additionally, ensure that your exhaust doesn't have any leaks in it - this throws off the measured A/F towards the lean side. To answer your questions, changing the timing has very little effect on the A/F, especially only 3 degrees worth. The A/F is independent of ignition timing and in all the cars I have tuned, making changes as much as 10-13 degrees of timing had no perceptible effect on the A/F. This is because the A/F is dependent on your ratio of air to fuel, not on when you are firing the plug. As for the boost being lower, that's odd too. I'm under the impression that you have boost jets in the car (no boost controller) and this simple mechanical system would not be affected by ignition timing changes. SOME electronic boost controllers will be - those that do not use a feedback control will do exactly what you are seeing (there's a long explanation for that, email me if you'd like to know, I'm not going into that here). Since you have a fuel issue, the fuel pressure test in my 6 P's post and the PRVR inspection/elimination are where I suspect you'll find your problem. If you do have low fuel pressure and have an old fuel filter, change your filter - they aren't that expensive, and then retest. The AshSPEC stage3 program is solid and on a car where everything is working correctly, your A/F will be dead on at 11:1 from 4500RPM (peak torque) and up. I tune cars to 11.5:1 for pump fuel on the dyno which is ideal, but catering to the fact that not all cars are equal and many have issues, that extra half-point of A/F is simply for safety. When I am tuning a car on the dyno, I start with my appropriate 'StageX' program for that car's particulars and from the 1st pull I can tell you a lot about any problems it has, if any. This is because I know the program I used as the base-program is properly configured for a car that has no issues. Just as you are finding, the dyno actually functionally serves as a diagnostic tool - the fact it gives you the power and torque numbers to post on the internet is secondary to the main purpose of the equipment. With that in mind, let me ask you a question: When was the last time you saw a dynochart of a Z where no tuning was done and where the A/F and output were where they were supposed to be? It is very rare. The answer gives you an idea of how many cars out there have problems. What really amazes me is that we dont see more engine failures. I have been wanting to put together a comprehensive post (which I hope will VTF) about preparing a car for the dyno based on all of my experience in tuning. There is a TON of stuff that I know people aren't doing or even aware of and it would only serve the community to have it. I will likely be putting that together pretty soon. Let me know how your testing goes and if you have any questions - I would like to hear from you whether or not you find a problem.. agpowers@bellsouth.net
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[ agpowers@bellsouth.net ] Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the tailor.
Albert Einstein
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