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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Old 11-02-2009, 09:18 PM   #1
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tuned ecu vs MBC+A

This thread isnt gonna be what you think it is. Basically i was just wondering if you will always get a boost taper with a tuned ecu. I currently have a MBC+A and it holds boost very solid threw out the gear almost never tapers unless the IC is heat soaked. But when i see vids of people with tuned ECU stage 2-3 whatever, i see alot of taper, like ill see the boost gauge spike to like 20psi and taper all the way down to like 14psi as it goes threw the gear. Do all tuned ECUs taper down or can they hold boost threw out the gear, or does it just all depend on HW.
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Old 11-02-2009, 10:35 PM   #2
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Most tunes should take into account the fact that the stock turbo just isn't going to do any good running much boost at the end of the rev range. It simply just cannot push enough air to make it efficient on high pressure ratios up on the rev range.

As the back-pressure increases you only run a risk of breaking things trying keep up boost. Boost does not equal power.

Tuned ECUs still have the knock detection enabled so if they encounter knocks they will drop down the requested air amounts to safer levels, on manual control you don't get this. So there are no fail safes with MBCs, if you don't monitor your AFR and use headsets to listen to your knocks on high pulls you are running a high risk of breaking shit.

This topic has been discussed quite a lot already.
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Old 11-03-2009, 05:24 AM   #3
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MBC'd cars have the ability to add fuel, and retard timing if knock pesents itself.
assuming you have a viggen IC, you will run out of turbo WELL before you run out of fuel.

That being said, my old 9-3 ALWAYS tapered down to 13psi after about 4200RPM with the 3" exhaust, and t25

with the stock ECU, it would spike to 15psi, and drop to 13
with the tuned ECU, it would spike, and drop.
finally, I decided to just run the tuned ECU, and MBC.
seemed to be the best route.
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Old 11-03-2009, 05:46 AM   #4
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Boost does not equal HP/TQ.

I would take a tune any day over a MBC.
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Old 11-03-2009, 05:58 AM   #5
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'eh
I dyno'd before, and after the ECU, and I actually lost HP going from a HOT [email protected] 15psi(with 17psi overboost) to SQR ECU @ 19psi.

I'm not sold on tuned ECUs; Although it's the only option with T7's
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Old 11-03-2009, 06:05 AM   #6
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I currently have a Stage 2 tune on my ECU. But, the BPC went out on my T5 car. So I have been running a MBC set to the right PSI in it's place. Haven't had any issues. However, I do plan to try to get a T7 BPC (T7 units cost less and manage boost better) functional on my T5 car to remove the MBC and gain back some of those fail safes and get solid tune for healthy AFR across the RPM range.
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Old 11-03-2009, 06:24 AM   #7
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Originally Posted by 2legit2quit View Post
Do all tuned ECUs taper down or can they hold boost threw out the gear, or does it just all depend on HW.
When you mash the gas pedal you send a boost request to the ECU. Tuned ECUs simply have higher values throughout the RPM range @ a given throttle position. Whether or not the engine can maintain those requested boost values depends on the amount of hot gas the exhaust can get rid of (hence the 3" downpipe) and on the air/fuel mixture.

In a nutshell, yes, you can have an ECU tuned to "request" higher boost and less taper throughout the RPM range... whether it actually delivers is up to the ability of the hardware to support the request.

( I think this sort of makes sense.)

On my tune I didn't like the initial torque spike at low RPMs, and eventual drop in power as revs progressed, so I had the values altered to request less boost at low RPMs and more at higher RPMs.

At lower RPMs, during WOT, the BPC valve needs to be working perfectly to control the boost spikes (not so much spikes... but sudden boost that you get at a low RPM in a low gear).

At higher RPMs the knock detection comes into play more, as this is when you are gonna notice the A/F wanting to lean out.

If you have a strong, healthy, well maintained engine, then an MBC should be fine as long as you don't set it to some silly boost value. Like 25 psi on a stock engine. I personally would rather have the protection of a fully working APC system.
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Old 11-03-2009, 07:33 AM   #8
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Originally Posted by g96nt View Post
'eh
I dyno'd before, and after the ECU, and I actually lost HP going from a HOT [email protected] 15psi(with 17psi overboost) to SQR ECU @ 19psi.

I'm not sold on tuned ECUs; Although it's the only option with T7's

Statements like that is what worries me i dont wanna spend money on a tune (granted stevehayes is rather cheap) and lose power and lose that quick non tapered boost the MBC gives me. BUT i truely would love all the saftey of the Tuned ecu since my cars at 160xxx and would like to last me a few more years. I keep the engine / car well maintaned.

Alright so basically i just need to make a choice. Its eiher you get the Tuned Ecu where you might sacrifice some power and get taper but you get all the saftey beifits and are pretty much worry free.

And with the MBC+A you get solid boost in all gears at all revs, but limited to fuel cut off, Might get dangerous EGTs and no knock protection.
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Last edited by 2legit2quit; 11-03-2009 at 07:40 AM.
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Old 11-03-2009, 07:37 AM   #9
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^ Do it yourself for free. Problem solved. You can tailor the boost anyway you like.

Think of your gearbox.
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Old 11-03-2009, 07:41 AM   #10
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You could always ask Steve to set the torque request beyond the limits of the turbo, and have the boost-onset VERY low.(would pretty much be full-boost, ALL the time)
run the bigger FPR, for good measure, push the rev-limiter to 7200, and push fuel-cut to 28psi. In the upper RPM, he could be a little more aggressive with timing(assuming you have a good (better than Viggen) FMIC)

You'd pretty much have an ECU set to make the most of the stock t25.
I wouldn't expect more than 240WHP on it, though.

Mine was good-enough for 102, or 103 traps(full weight), and was perfectly fine on pump 93, every day of the New England year.
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Old 11-03-2009, 07:55 AM   #11
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Quote:
Originally Posted by 2legit2quit View Post
Statements like that is what worries me i dont wanna spend money on a tune (granted stevehayes is rather cheap) and lose power and lose that quick non tapered boost the MBC gives me. BUT i truely would love all the saftey of the Tuned ecu since my cars at 160xxx and would like to last me a few more years. I keep the engine / car well maintaned.

Alright so basically i just need to make a choice. Its eiher you get the Tuned Ecu where you might sacrifice some power and get taper but you get all the saftey beifits and are pretty much worry free.
Alot of it is how good the tune is. You will be limited to around 15psi on the stock ECU with a MBC because of fuel cutoff. I am a firm believer that when playing with the cars engine management, you should do it right rather than go the cheap way out. Not only is it much safer to go with a tuned ECU (which are very cheap now-a-days, no reason not to IMO) but you can get more power out of your setup than you could with a MBC.
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