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Got Boost?
 
IMONBOOST's Avatar
 
Join Date: May 2001
Location: San Juan, Puerto Rico
Posts: 373
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Issued tuning mixture vs boost?

Since I purchased the turbo 3.6, first thing I did was install a Wideband Zeitronix and then a turbologic ball-bleeding manual boost controller. I set the boost to 13.5psi max and the car was running amaizing but leaner than I would like it to run, about 12.7 AFR at top rpm on third (did not dare to test fourth gear).

So I adjusted the mixture screw about 1/4 of a turn clockwise (richer). Now, the car apparently idles on open loop pretty steady at 12.8 AFR because I don't see the AFRs beign forced to 14.5 like it used to on idle. When crusing, the AFRs do still pull to 14.5. Now when on WOT, the car feels significantly slower and the peak boost on third droped to around 11 psi and the AFR at redline is about 12.0. So AFRs look good but car is slower loosing some boost.

My understanding of this is that before I was benefiting (faster) from the leaner condition at the expense of killing the engine.

Is my reasoning correct, can I then work with the mixture and manual boost controller to get the 13.5 psi but staying below 12.2 AFRs on redline?
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Old 07-31-2010, 05:47 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
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Join Date: Jan 2004
Location: Sacramento
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My CIS goals are about 13/1 in open loop just off idle before boost if possible and in the mid to high 11's at TQ peak (4500-5000rpm ) on boost where risk of detonation is highest. If it goes into the mid 12's (up to 13/1) at red line and it is not being pushed on the track to red line over long durations, that is probably about the best it is going to get with the stock WUR/CIS.

I would guess that when you set the CO richer there is a good chance that when the WUR boost enrichment is triggered you are going into the 10's on you AFR's. If so that will hurt your mid range power.

If you are ruining the stock K27-7200 turbo it is just to small for the 3.6 if boost is increased or other mods are made.

On my modified 91T it could only hold boost to about .9 bar at HP peak even with the EBC set at 1 bar. On your 3.6 that would be maybe about .8 bar. Thus, when you turn up the boost you might get a more boost and power in the early part of the power band but the turbo will hit a celling.

If it is a street car I could live with 13/1 at red line if I am in the high 11's at TQ peak or about 12/1 at HP peak.

This assumes your injectors are clean and balanced.

Another way to get more fuel is to shim the fuel pressure reg on the fuel distributor. This should add fuel progressively with increases in air flow and dose not need to effect your idle AFR's as it can be adjusted around. It will increase your cruse AFR's a bit. This assumes your fuel pumps are up to the task.

There are other things you can do like an adustable WUR, RPM-boost clamp, or Digital WUR.

The best.
Old 08-01-2010, 08:29 AM
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Join Date: May 2001
Location: San Juan, Puerto Rico
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Your target sounds thay way my car was set previous to the quarter adjustment, except I was reading the high 11s momentarily and most of the rpm range in the low to mid 12s. I decided to richen up percisely because the previous owner did not use the car frequently so there is the posibility of bad flowing injectors. I guess I am taking a lazy route and should just take the injectors out.

Great reponse thanks..
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-Ayrton Senna-
Old 08-01-2010, 08:59 AM
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