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MBC issues (long)
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Posted by Dean (more from Dean) on Wed, 15 May 2002 09:29:42 Share Post by Email
In Reply to: MBC, David M, Tue, 14 May 2002 22:53:42
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This is easy.

There are folks with ECUs that will map fuel to over 20 PSI with the T5 ECU without changes to the injectors or fuel pressures.

The folks with extensive mods and Viggens do not have exhaust gas temerature issues, so your mild tuning with a MBC will not have any problems. Note also that Abbott sells modfied ECU's without insisting that the OEM restrictive exhaust system be replaced or that the intake be modifed, which means even more heat.

The ECU is setup to map fuel until it does a fuel cut. It is that simple. The ECU adapts to your individual fuel pressure, MAP sensor, volumetric efficiency etc. It then calculates open loop on boost enrichment based on teh adaption to the various other variables based the guidance of the O2 sensor during off-boost running.

Actually, this works so well that the MAP signal can be altered to reduce the signal and the ECU will then re adapt and then the fuel cut is at a higher pressure.


So with all of the other folks who have gone before you, you have naught to worry about. Standard cautions about low restriction intake and exhaust mods being recommended, and an engine that is not in good mechanical condition should not be boosted. Use Mobil 1 etc etc.

I run a guage, only because nay sayers got on my case about my not having one. But one is not needed. With or without you increase the pressrure until you find the fuel cuts, then simply back the pressure off a bit.

I get around 15 psi of boost in all gears. But if you locate the pressure tap at the turbo compressor presure tap hose barb, you will get a significant boost roll off with higher CFM's (rpms). If you locate the pressure tap to after the IC core, then this is greatly reduced. From your reading you know that there are some yin/yangs about this issue.

As for parmeters to the ECU, the issue is knocking. The system will not knock if things are in good order. This is never reported. The ECU will control knock via timing and enrichment, which is also the case with many other modern turbo charged makes these days. You should run higher octane pump gas and keep injectors clean to get proper mixing and keep combustion chamber deposits reduced with Techron Concentrate.

Two years ago when I came to the BB with news that I had installed a MBC, all of the chicken littles came out screaming. And the folks who spent $800US with Abbott mods were indignant and some were quite hostile. But these days folks see that the ECU mods have distinct advantages over the MBCs. So if you want even more power and a less hairy 1st gear, you can spend the money on a modified ECU. If you like wild response, you can, as some have done, run with a MBC and a modified ECU.

Do the MBC, the vehicle will be much faster as the turbo will spool up much faster as it is then no longer held back by the ECU and the bleed valve characteristic of the BPC valve. The increase in responsiveness is the greatest benefit. You will have to un-learn the bury the throttle and wait techique and develop a much more agile throttle techique. Oh the burdens of power......

posted by 208.24.179...
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