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Discussion Starter #1 (Edited)
Ok I sold? (awaiting pick up) my car but promised buyer I would do little tidy up fixes.

Sent my original injectors out to get tested and cleaned and have a question or 2 as buyer asked me???

I have the Dinan 3.9 but they have the smaller 3.6 injectors and I also believe regulator.

I know pressure and ecu can vary fuel delivery.

Anybody know exact numbers on 3.6 or 3.8 regulator itself?

Curious as to what people think about Dinan using the 3.6 injectors on a 3.9 with more mods vs the factory going larger on both the reg and injectors? on the stock 3.8??
 

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Interesting topic... The same injectors were used on the b36 and b38 for a while, so there must be some pulse margin left over unless the extra pressure delivers the difference. Also max fuelling per shot is at the torque point so that's going to be the sizing point. The original Bosch injector was rated by BMW at 270 cc at 3 bar (b36 regulation pressure), and the b38 at 290 cc at the same (though the regulator is actually 3.5 bar on that).

I have seen on other flow sites the Bosch injector being rated as low as 226 cc at 3 bar.

Personally, I think you want the smallest (and most modern) injector you can fit that will deliver the WOT fuelling - my thinking is that it will be more acurate across the smaller range so the trimming will be more accurate.
 

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Personally, I think you want the smallest (and most modern) injector you can fit that will deliver the WOT fuelling - my thinking is that it will be more acurate across the smaller range so the trimming will be more accurate.
Interesting, do you have any recommendations that would work on the S38?

My original injectors have covered some 250k kms and I am looking to upgrade them if worthwhile rather than just buying 6 new ones from BMW.

Thanks.

Lantz
 

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Hi uk, that's not correct.

Injector is sized for peak airflow at maximum enrichment which accounts for ambient, coolant, head temperature , low Ron fuels etc.

Volumetric efficiency peaks at the torque peak, but not injector pulse width.

Injectors should not be unnecessary oversized, as you say, although this has more to do with meeting modern emission legislation than anything else.

So estimating a crude 30% margin from bmw, 3.9 ltr is prob ok.

Changing injector size would also require informing the ecu of the change, possible ofcourse if you know the code.
 

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Interesting. I'll clarify. What I am concerned about is choosing an injector that cannot deliver the max fuel I need. That is at the torque point, I think, but I haven't looked at the fuelling tables. I'm not entirely certain why enrichment would be applied at WOT, but all I want to do avoid is running lean. For a system at constant pressure more pulse = more fuel, but I may be missing something. More modern cars can vary pressure but not these.

I have selected a flow matched set and they are due at my house tomorrow. What I intend to do is to run the car (when engine is boxed up) and check whether they get maxed out. I'm hesitant to declare what they are without testing as I wouldn't want to give anyone bad advice.
 

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Hi, maximum fuelling point is at max airflow I.e peak power.

Say peak torque is at 4000rpm and peak power is at 8000. Assuming volumetric efficiency is the same, which it isn't, the engine is pumping twice as much air and hence fuel at 8k vs 4k.

You only run richer than lamdba 1 for extra torque, which is around 0.9 lambda and then for component protection - valve bridge, exhaust valve and exhaust manifold.

Fuelling tables in the ecu are normalised for engine speed and load they do not directly represent injector duty cycle or pulse width.
 

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Hmmm, max fuel total, but not per shot. The torque is proportional to fuel, but power increases with speed (more shots).
 

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Discussion Starter #8
Mine are at RC right now and I will post whatever flow numbers they give me. Injectors are like torque converters it is impossible to get an exact answer it is trial and error.

Honestly it was tempting to try a different set but car is staying in CA and it passes smog as is and I didn't want to upset anything.

It is interesting that Dinan with more mods kept the smaller injectors.

Ill post em when I get em.
 

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Hmmm, max fuel total, but not per shot. The torque is proportional to fuel, but power increases with speed (more shots).
Correct but an injector is a volume flow device, as the engine is an air pump, more rev means more airflow and hence more fuel flow required to maintain the required AFR.

For a gasoline engine torque is proportional to BMEP not fuel. BMEP correlates to cylinder filling (Air) which in turn relates to volumetric efficiency.

For diesel applications there is a much stronger correlation between fuel and torque.
 

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Discussion Starter #10
OK, I am in CA but RC received yesterday and I have them back to me today? I am not 100% sure they are the same injectors though? The bodies are now silver where mine were black? Pintle? caps are blue and mine were tan. The tops are the exact numbers though. Who knows, but if they are mine damn they work fast.

OLD CC NEW CC

227.0 240.0

235.0 241.0

231.0 240.0

234.0 239.0

223.0 240.0

232.0 240.0


HORESPOWER AT 80% CYCLE

OLD NEW

.65 162.0 168.9
.55 191.4 199.6
.50 210.6 219.6

There is more info on the sheet if anybody wants I can scan and email. Or ask and I will look to see if it is here.
 
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