how much boost on stock motronic - no add ons?

Discussion pertaining to positive pressure E28s.
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charofire
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Joined: Dec 27, 2008 7:56 PM

how much boost on stock motronic - no add ons?

Post by charofire »

While trying to convince my friend to consider using megasquirt recently, he felt he could run up to 6psi of boost safely on his 1985 535i without adding a timing regard chip or larger injectors. He's running an old kkk27 on a b35 1.3 setup. I told him it was foolish but perhaps I am wrong and maybe some users have put in a colder spark plug set and run 6psi safely on stock injectors?
demetk
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Re: how much boost on stock motronic - no add ons?

Post by demetk »

I'm running 8 psi of boost on a stock m1.3 system - stock injectors, AFM, 179 ECU. The only additional things I added is a RRPR and an extra cold start injector. So yeah, it's doable without a standalone.
tschultz
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Re: how much boost on stock motronic - no add ons?

Post by tschultz »

Why not get the timing chip for a bit of safety?

I'm running M1.0, RRFPR, 24lb injectors, TCD chip at 7psi. The old turbo was 10/11psi but I am still working up to it with my new TCD turbo.

5psi is pretty low boost pressure for M30B34.
Shadow
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Re: how much boost on stock motronic - no add ons?

Post by Shadow »

How much is the begi and chip? Might be better to just a plug and play megasquirt.
charofire
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Re: how much boost on stock motronic - no add ons?

Post by charofire »

That's why I ran megasquirt :D . There are actually microsquirt options now that will run an inline 6 just fine. https://www.diyautotune.com/product/mic ... g-harness/

One idea he was exploring was to use a 745i AFM with 24lb injectors, and a RRFR.
Grocerygetter
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Location: Massachusetts

Re: how much boost on stock motronic - no add ons?

Post by Grocerygetter »

How did this turn out? I’m looking to do the same with my 84 533i
marc79euro645
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Re: how much boost on stock motronic - no add ons?

Post by marc79euro645 »

I tried the begi route first, and wasn't really pleased. I think the afm I had was the biggest problem. Then I went MS which was a lot of reading. I didn't get a pulse signal for 3 weeks. I was really on my own. If you are committed to it, MS is the way to go. Nowadays, most towns have a tuner that can help if you have problems.
good luck
russc
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Re: how much boost on stock motronic - no add ons?

Post by russc »

Actually, Motronics 1.0(E28 M30b34) will take unlimited boost, if you tune the inj. sizing constant properly. M1.0 ignores the AFM signal on WOT, so its just a matter of retuneing the mid and WOT map. Thats actually very easy, Ive done it many times.

RussC
Spaz!
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Re: how much boost on stock motronic - no add ons?

Post by Spaz! »

I am curious about this too. I have an 85 535i that I am considering boosting a little to maintain power through a wide temp and altitude range. I have a war chip that needs a home and if it and a small turbo would do the trick that would be great.
Tiit
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Re: how much boost on stock motronic - no add ons?

Post by Tiit »

How exactly can M1.0 be tuned? Blank chip, chip chip writer, PC and software?
Ok guys I understand that M1.0 and M1.3 can take low boost safely. But how many of you actually have run turbo setup RELIABLY for a long term? To me, it seems like, once I go turbo, it's good bye for daily commute. It'll be a constant hassle and fiddling.
Tiit
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Re: how much boost on stock motronic - no add ons?

Post by Tiit »

How exactly can M1.0 be tuned? Blank chip, chip chip writer, PC and software?
Ok guys I understand that M1.0 and M1.3 can take low boost safely. But how many of you actually have run turbo setup RELIABLY for a long term? To me, it seems like, once I go turbo, it's good bye for daily commute. It'll be a constant hassle and fiddling.
tschultz
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Re: how much boost on stock motronic - no add ons?

Post by tschultz »

I used the TCD chip and drove it that was for not quite a year. Somebody has to be able to burn a chip for you.

My frustration was that based on temperature and a difference in injectors, the motronic would compensate for more fuel that needed in the cooler weather. For some reason motronic also didn't like my aem's narrowband signal, so I ran without o2 sensor and cut the WOT signal so the engine ran off of the AFM and then RRFPR (BEGI 2021) in boost. Overall it worked OK, but I felt like I was always fiddling with getting it right and recall the engine running rich when cool weather moved in. Overall it ran good enough that I could daily it to work and such. I think I put 3000 miles on it that way. Early on, I was worried about burning up my cat or other problems with a less than perfect fuel mixture.

Due to my elevation and injector size, I was also richer in boost than I wanted to be, so at 5000+rpm, my mixture was hitting 10.8:1 and I could feel it bogging the engine. But it was set it and forget it from the aspect of no change to ignition timing, idle quality or otherwise.

After installing megasquirt, it was apparent there was losses in engine response with the AFM and lack of timing control.

Megasquirt has been just as much work and time--mostly in terms of starting/warmup, getting drivability form my timing map, especially at low RPM, as well as getting the mixtures and smoothness I wanted with temperature fluctuations. I also have barometric corrections real time and that has been a chore to tune since temperature changes usually as you change altitude. Overall it has been more work than I expected and I still have some fiddling and tuning years later.
Not many people I have read about care for their base map and o2 corrections to be really close to target, but I just wanted the car to start up, idle and feel like stock. It's close but still the AFM had a smoothness to it that the map signal can't seem to match in transition on/off throttle.

I told a friend that if you want to drive it and forget it, turbo e28 isn't for you with Motronic. Maybe it would work better with the stock M1.3 system?
mitch5
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Re: how much boost on stock motronic - no add ons?

Post by mitch5 »

Honestly i wouldn't even consider a stock e28 a drive and forget daily driver. Fixing a rough idle, acceleration bog or a no start requires learning how the entire motronic system or taking it to someone who does know it. Given the age of most electrical components on a motronic e28, almost everything starts becoming suspect for causing an issue. I will say that motrnic 1.3 is closer to a forget and drive system, with there being less things to fail.

While the megasquirt system is by no means drive and forget i think its always a better overall choice for an ECU(assuming its a quality assembled unit) on a turbo setup. The megasquirt uses less sensors and if you have a sensor go bad makes it very easy to troubleshoot via the tuning interface. The huge downside of megasquirt is theres no "tune" to go buy, which is why everyone has to go fiddle with their own tune. Knowing how tune an engine is the huge learning curve that scares most people off megasquirt.

The best setup would be a megasquirt tune that works for an exact setup like a tcd kit. Problem is that the amount of work it would take to create a tune that has a perfect idle and start at all conditions(temp,elvation) is something only oems do.
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