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jimberg · 07-13-2001, 03:30 PM

Clint,

Did you just completely ignore what I wrote?

I wasn't trying to rain on your parade or anything, it's just the reality of the way things work.

In a nutshell, YOU CANNOT ADJUST FUEL PRESSURE AND EXPECT IMPROVEMENTS. If anyone has their doubts about this, you just proved it. The computer has a preset air/fuel ratio that it will maintain. PERIOD.

You can see that to some degree in your own dyno numbers. Look at results 3 vs. 4. You let the engine cool off, which theoretically should help get more air into your cylinders. But look at the A/F ratio - It got richer, not leaner as you would expect. The computer was already adapting to the change in fuel pressure. By the time you drove it home and to the track, the computer recalculated the adjustment tables and started applying them.

Adjusting fuel pressure only allows you to tweak the amount of fuel available for the computer to use. If you only have 19# injectors and running too lean at WOT, you can boost the pressure to allow more fuel to be delivered. That's about all that adjustable fuel pressure regulators can really do for you.

All is not lost, though. You now know that your best air/fuel ratio is 11.8:1 at 5300 and 12.7:1 at 4000. You can tell a chip vender (like JMS) that and they should be able to modify the computer's air/fuel target.

The guys at the dyno shop should have told you this before you even went in. I would have liked to see results from boosted timing, too.

Now get on the phone and order that chip.

------------------
351W 89 Mustang GT Convertible

[This message has been edited by jimberg (edited 07-13-2001).]

07-13-2001, 03:30 PM	#18
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Clint, Did you just completely ignore what I wrote? I wasn't trying to rain on your parade or anything, it's just the reality of the way things work. In a nutshell, YOU CANNOT ADJUST FUEL PRESSURE AND EXPECT IMPROVEMENTS. If anyone has their doubts about this, you just proved it. The computer has a preset air/fuel ratio that it will maintain. PERIOD. You can see that to some degree in your own dyno numbers. Look at results 3 vs. 4. You let the engine cool off, which theoretically should help get more air into your cylinders. But look at the A/F ratio - It got richer, not leaner as you would expect. The computer was already adapting to the change in fuel pressure. By the time you drove it home and to the track, the computer recalculated the adjustment tables and started applying them. Adjusting fuel pressure only allows you to tweak the amount of fuel available for the computer to use. If you only have 19# injectors and running too lean at WOT, you can boost the pressure to allow more fuel to be delivered. That's about all that adjustable fuel pressure regulators can really do for you. All is not lost, though. You now know that your best air/fuel ratio is 11.8:1 at 5300 and 12.7:1 at 4000. You can tell a chip vender (like JMS) that and they should be able to modify the computer's air/fuel target. The guys at the dyno shop should have told you this before you even went in. I would have liked to see results from boosted timing, too. Now get on the phone and order that chip. ------------------ 351W 89 Mustang GT Convertible [This message has been edited by jimberg (edited 07-13-2001).]