JB4 logging question: Target boost data unit convention

[ColonelAdama]

Correct, one of the big issues with the JB4. I was merely stating that kind of boost at that AFR is bold. That is why you always hear people saying more octane is better with a JB4. It's basically a crutch.

B58 DME is going to target mid 14s no matter what octane you put in there. In fact, if you raise octane too much with ethanol, your AFRs are gonna go up when you max trims.

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[i3igpete]

Car sees low boost - it adds timing too early

This kind of leads back to my related question about boost control levers. Can the DME advance spark past the "ideal" ignition table? Or is it retard-only?

Mid 14s is 100% normal for this car, even at 20+ psi.

Back in undergrad combustion class I remember they were talking about this new fangled thing called Direct injection. Stratified charge was one of the benefits, locally rich for anti-knock but overall stoich/lean for emissions. I wonder if BMW is using that.

 

[ColonelAdama]

This is one of my related questions about boost control levers. Can the DME Advance spark past the "ideal" ignition table? Or is it retard-only?



Back in undergrad combustion class I remember they were talking about this new fangled thing called Direct injection. Stratified charge was one of the benefits, locally rich for anti-knock but overall stoich/lean for emissions. I wonder if BMW is using that.

Not really sure about the DME ignition tables. I read a bit about stratified charge and it doesn't seem that its used under high load situations. Apparently its not great for exhaust particulates either, so its probably on its way out. As far as I can tell, the B58 doesn't use it.

 

[razorlab]

B58 DME is going to target mid 14s no matter what octane you put in there. In fact, if you raise octane too much with ethanol, your AFRs are gonna go up when you max trims.

That isn't what I said. Either way, I'm no longer arguing with people on this forum, so carry on with your piggybacks. I do suggest taking a look at the actual ECU tables and strategy though. It's very helpful to know what it's doing if you are going to trick things with a piggyback.

 

[i3igpete]

Yeah I thought about it for a little bit, in order to use it at high loads you basically need to oversize your injectors AND rail pressure in order to intentionally create (for lack of a better word) fuel puddling. The fact that everyone goes port injection tells me that the DI injectors are not oversized.

In any case I'll take a look at what the FF setting currently is the next time I drive the car

 

[i3igpete]

I do suggest taking a look at the actual ECU tables and strategy though.

Just wanted to bounce some ideas off of someone else on here to accelerate my learning. Based on what I see here, my IATs of ~90F/32C and coolant temp of 195f/90c is essentially using the second row of IAT timing retard, between the first and second column. Assuming the DME linear interpolates and does not stepwise lookup, this means I'm around ~0.15x of the ignition retard scaling factor.

Since these are normalized tables, do you know what the raw Factor is?

 

[razorlab]

Since these are normalized tables, do you know what the raw Factor is?

Are you asking about this table?

 

[i3igpete]

Not quite, I believe that's the raw ignition table as a function of load and rpm. the table I grabbed from the Visconti a91 thread had a table of timing retard as a function of water temperature and IAT. Which I'm trying to figure out is additive or multiplicative with the other retard factors.

 

[ColonelAdama]

That isn't what I said. Either way, I'm no longer arguing with people on this forum, so carry on with your piggybacks. I do suggest taking a look at the actual ECU tables and strategy though. It's very helpful to know what it's doing if you are going to trick things with a piggyback.

I genuinely would like to do this but don't know where to start. I think it could help me figure out the cause of my DME boost targets dropping out randomly despite good trims/AFRs.

Anyone run a ROM compare on MT vs AT cars?

 

[razorlab]

Not quite, I believe that's the raw ignition table, the table I grabbed from the Visconti a91 thread had a table of timing retard as a function of water temperature and IAT. Which I'm trying to figure out is additive or multiplicative with the other retard factors.

What I posted is the reference for the tables you showed. The table you showed is a lookup percentage of that table.

 

[razorlab]

I genuinely would like to do this but don't know where to start. I think it could help me figure out the cause of my DME boost targets dropping out randomly despite good trims/AFRs.

Anyone run a ROM compare on MT vs AT cars?

If you haven't seen this yet, it's helpful...

 

[i3igpete]

What I posted is the reference for the tables you showed. The table you showed is a lookup percentage of that table.

ah ha! got it, IAT timing pull is not a scalar value, it's a lookup on top of a lookup. so if i interpret your table correctly, that means IATs (by itself) will never contribute more than 10 deg of timing pull.

 

[ColonelAdama]

If you haven't seen this yet, it's helpful...

Excellent, thank you!

 

[razorlab]

ah ha! got it, IAT timing pull is not a scalar value, it's a lookup on top of a lookup. so if i interpret your table correctly, that means IATs (by itself) will never contribute more than 10 deg of timing pull.

There are also some other tables to make sure the EGT's don't go crazy with too much ignition retard.

 

[ColonelAdama]

Sure didn't take much reading to figure out what causes throttle cuts on MT JB4 cars. Makes me wonder if some of my maps would work better in Normal mode lol. I have never logged in normal mode.

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