Full exhausts: Dip in HP at low rpms

[Cloud]

full exhausts with or without hfc such as the akrapovic / rpi / gintani all have this dip.
Can this be solved with an ECU tune?

[mixja]

Of course it can - requires some time on the dyno and adjustment of fuel maps...

[MrHarris]

So the dip is purely due to incorrect AFR caused by the full exhaust system? Has nothing to do with similar designs by the various aftermarket tuning companies?

[Lemans_Blue_M]

Originally Posted by Cloud

full exhausts with or without hfc such as the akrapovic / rpi / gintani all have this dip.
Can this be solved with an ECU tune?

This is being worked on as we speak.

The problem is finding a 'sweet spot' where the power curve stays up consistently throughout the entire rev band. (without any power dips along the way)

That's extremely difficult to pull off, since we have such a wide power band to cover with the S65 engine.

The one effective way to do this, (although it's not very appealing) is to match the rest of the rpm band to the dip, which slightly lowers your power across the board.

I don't think anybody really finds that solution acceptable, especially the end user.

This 'dip' within a narrow rpm band may be something we just have to live with, in order to extract the maximum power out of these systems. This dip is starting to show up on several cars running high-flow exhaust systems, and no one seems to have a workable solution to it thus far.

It may just be a performance quirk in the overall makeup of this particular engine. (in it's unrestricted NA form)

Someone may eventually find a solution to this problem (without the unsavory compromises), but it's going to be pretty difficult to pull that off...

[mixja]

Originally Posted by Lemans_Blue_M

This is being worked on as we speak.

The problem is finding a 'sweet spot' where the power curve stays up consistently throughout the entire rev band. (without any power dips along the way)

That's extremely difficult to pull off, since we have such a wide power band to cover with the S65 engine.

The one effective way to do this, (although it's not very appealing) is to match the rest of the rpm band to the dip, which slightly lowers your power across the board.

I don't think anybody really finds that solution acceptable, especially the end user.

This 'dip' within a narrow rpm band may be something we just have to live with, in order to extract the maximum power out of these systems. This dip is starting to show up on several cars running high-flow exhaust systems, and no one seems to have a workable solution to it thus far.

It may just be a performance quirk in the overall makeup of this particular engine. (in it's unrestricted NA form)

Someone may eventually find a solution to this problem (without the unsavory compromises), but it's going to be pretty difficult to pull that off...

There is a slight hint of a dip even in stock form - full exhaust seems to amplify the dip...

I'm just guessing it is a lean condition based upon comments from others...in reality it might not be as simple as fuelling. Could be a reduction in VE with some fine tuning of valve timing required - on a dual VANOS system like BMWs that would likely take many hours of tuning and testing...

[Lemans_Blue_M]

Originally Posted by mixja

There is a slight hint of a dip even in stock form - full exhaust seems to amplify the dip...

I'm just guessing it is a lean condition based upon comments from others...in reality it might not be as simple as fuelling. Could be a reduction in VE with some fine tuning of valve timing required - on a dual VANOS system like BMWs that would likely take many hours of tuning and testing...

Yes, this is exactly what is happening.

The freeer cat back (or header back) exhaust systems out now, create much less backpressure than the very restrictive OE exhaust setup.

This creates more HP &TRQ, but it certainly does amplify the rpm dip in the upper rpm band as well.

Several BMW tuners are working to smooth out this dip, but it's not as simple as going into the stock ECU and making a minor software code revision.

If it were, this topic would be a non-issue right now.

In talking to one of these tuners recently, the problem is trying to make the dip less noticeable, without compromising the power output in another part of the rev band. There is a 'domino effect' in play, where you fix one issue, but you end up with 2 or 3 more compromises somewhere else.

It's like trying to piece together a giant jigsaw puzzle.

Only one solution or combination will work, without making a mess of other things along the way.

Curious to see if this can actually be sorted out, without taking a performance hit in the process.

Or maybe we will simply have to accept that this is an unavoidable characteristic of this naturally aspirated engine, that cannot be corrected to our satisfaction. (100%)

[stylinexpat]

I am sill waiting for a reply from ESS on this and they have not been able to fix this as of yet from what I last understood from them. I am sure they will chime in here when they have a fix for it.

[AMPowerJ]

So EVERY full exhaust system does this? Is it more a function of the aftermarket cat-back exhaust or removed cats or both? I have been leaning towards the Fabspeed HFC and X-Pipe with stock exhaust but I don't want this 'dip' in power.

[TLud]

The dip in power does register on the dyno for the stock system. The freer flowing exhaust seems to remove one bottleneck in the stock system. However, the power at the point in the rpm band where the dip occurs seems to be held back by something other than the exhaust. I seriously doubt that it's strictly a question of a/f ratio or timing or similar problem correctable with additonal tuning, although timing may play a role.

I remember the E46 ZHP had the same dip. LeMans Blue already pointed out how BMW handled the solution: lowering the rest of the rpm band so that the dip was less pronounced. The problem was likely caused by the different cams and timing in that car. The double VANOS system does make this a difficult problem to correct.

While the dip in the E46 ZHP was so annoying that I actually welcomed the BMW detuning, the dip in the modified E9X M3 seems even more troublesome because it occurs much lower in the rpm band. The dip will be much more pronounced there because the ratio of the drop to power output at that point will be much greater than it would if the same dip occured higher in the rpm band. Plus, down low is where this car is somewhat starved for power.

Hopefully, the dip can be mitigated somewhat with tuning, but I doubt it can be eliminated entirely.

[askiles]

I had my Akra system dynoed last week with ESS, and the dip is due to the AFR going crazy right there. The guess at the moment is that there is no so much air flowing in that RPM range with the more free flowing exhaust, that the computer is not compensating quick enough for it, causing a lean condition. We looked at the graphs of the AFR's VS the power band, and you can see this. ESS is going to take a look at this, and over the next few months work out a tune for these high flowing exhaust systems. It seems like something no one has tried to fix, so it will be nice for someone to do this. ESS is great like that.

-Andy

[vamosvanos]

Originally Posted by askiles

I had my Akra system dynoed last week with ESS, and the dip is due to the AFR going crazy right there. The guess at the moment is that there is no so much air flowing in that RPM range with the more free flowing exhaust, that the computer is not compensating quick enough for it, causing a lean condition. We looked at the graphs of the AFR's VS the power band, and you can see this. ESS is going to take a look at this, and over the next few months work out a tune for these high flowing exhaust systems. It seems like something no one has tried to fix, so it will be nice for someone to do this. ESS is great like that.

-Andy

+1. Once you remove your cats you'll experience this dip. I remember Farbyce of GMG advised me NOT to remove my cats on my 6 GT2 for that reason. My .02.

[sales@ESSTuning]

Originally Posted by askiles

I had my Akra system dynoed last week with ESS, and the dip is due to the AFR going crazy right there. The guess at the moment is that there is no so much air flowing in that RPM range with the more free flowing exhaust, that the computer is not compensating quick enough for it, causing a lean condition. We looked at the graphs of the AFR's VS the power band, and you can see this. ESS is going to take a look at this, and over the next few months work out a tune for these high flowing exhaust systems. It seems like something no one has tried to fix, so it will be nice for someone to do this. ESS is great like that.

-Andy

Once AJ gets back we will look at trying to resolve the issue if we can. Other then the dip in power in the lower RPM's the exhaust is very nice and makes good power.

[Lemans_Blue_M]

Originally Posted by askiles

I had my Akra system dynoed last week with ESS, and the dip is due to the AFR going crazy right there. The guess at the moment is that there is no so much air flowing in that RPM range with the more free flowing exhaust, that the computer is not compensating quick enough for it, causing a lean condition. We looked at the graphs of the AFR's VS the power band, and you can see this. ESS is going to take a look at this, and over the next few months work out a tune for these high flowing exhaust systems. It seems like something no one has tried to fix, so it will be nice for someone to do this. ESS is great like that.

-Andy

Well Andy, actually quite a few BMW performance software engineers have tried to fix this rpm power dip phenomenon over about a 10 year period. (on a few different BMW cars)

To date, none of them have been able to fix the problem without making the compromise I explained earlier.

So despite the fact that their is still no good solution to this problem, I can assure you it wasn't from a lack of trying.

Earlier this week, I was talking the the software engineer over at Dinan about the power dip that they were getting in the upper rpm band with their new M3 X-pipe. (just released a few days ago) They also have not been able to fix this problem either. He explained to me how complicated it would be to correctly 'fix' one isolated portion of the rev band...without throwing everything else off in the process. There are limits within software tables to tune the AFR's without upsetting the apple cart. (a delicate balance must be maintained)

Now consider that Dinan (unlike an independent aftermarket tuning shop) has a direct relationship with the BMW software engineers in Germany. (who wrote the original code) So more than any other tuner, they actually have access to the all tools necessary to fix this problem. (in theory) Not only do they have access to the un-encrypted original base code structure, but they also have access to the engineers as well. So they can dissect and understand the methodology of how and why the code was written in a certain manner.

I can't think of one other tuner (besides Dinan), who would have that kind of access.

That's a HUGE advantage in regards to solving a software tuning issue.

And even with all that help in their corner...they still couldn't fix the power dip they experienced during their dyno testing of this new X-pipe.

So as you can see Andy, this "little problem" is not going to be so easily solved without some type of innovative out-of-the-box solution.

The standard software tweaking approach has not been successful thus far.

It would cost quite a bit of of money (and R&D time) to figure this out, so I'm not sure how many more tuners are going to pour xxxxxxx amount of resources into a project that may or maynot bare fruit.

I certainly hope that ESS can look at this problem with a fresh set of eyes, and discover something that all the other BMW top tuners have missed.

If they are able to figure this out, they will definitely have a lot of customers lined up to buy it.

[stylinexpat]

Originally Posted by TLud

The dip in power does register on the dyno for the stock system. The freer flowing exhaust seems to remove one bottleneck in the stock system. However, the power at the point in the rpm band where the dip occurs seems to be held back by something other than the exhaust. I seriously doubt that it's strictly a question of a/f ratio or timing or similar problem correctable with additonal tuning, although timing may play a role.

I remember the E46 ZHP had the same dip. LeMans Blue already pointed out how BMW handled the solution: lowering the rest of the rpm band so that the dip was less pronounced. The problem was likely caused by the different cams and timing in that car. The double VANOS system does make this a difficult problem to correct.

While the dip in the E46 ZHP was so annoying that I actually welcomed the BMW detuning, the dip in the modified E9X M3 seems even more troublesome because it occurs much lower in the rpm band. The dip will be much more pronounced there because the ratio of the drop to power output at that point will be much greater than it would if the same dip occured higher in the rpm band. Plus, down low is where this car is somewhat starved for power.

Hopefully, the dip can be mitigated somewhat with tuning, but I doubt it can be eliminated entirely.

F U C K Don't tell me that I bought another new car with another dip problem like my older E46 ZHP

[stylinexpat]

Originally Posted by Rom3n

Once AJ gets back we will look at trying to resolve the issue if we can. Other then the dip in power in the lower RPM's the exhaust is very nice and makes good power.

I know AJ is a brain when it comes to stuff like his. He was able to smoothen my car's dip out on my E46 ZHP in the past which had a supercharger on it but the dip did not vanish in the end. I look forward to seeing this one solved without a supercharger on it. My guess is that this dip is a lot worse with a supercharger on it like it was with the older E46 ZHP's...

[turbo8765]

The dip is not due to a change in AFR. It's due to the decreased back pressure. It will not be "fixed" by tuning. Increased timing and tweaked AFRs may ameliorate the decline somewhat, but in the end it's an unavoidable trade off.

[TLud]

Originally Posted by Lemans_Blue_M

Well Andy, actually quite a few BMW performance software engineers have tried to fix this rpm power dip phenomenon over about a 10 year period. (on a few different BMW cars)

To date, none of them have been able to fix the problem without making the compromise I explained earlier.

So despite the fact that their is still no good solution to this problem, I can assure you it wasn't from a lack of trying.

Earlier this week, I was talking the the software engineer over at Dinan about the power dip that they were getting in the upper rpm band with their new M3 X-pipe. (just released a few days ago) They also have not been able to fix this problem either. He explained to me how complicated it would be to correctly 'fix' one isolated portion of the rev band...without throwing everything else off in the process. There are limits within software tables to tune the AFR's without upsetting the apple cart. (a delicate balance must be maintained)

Now consider that Dinan (unlike an independent aftermarket tuning shop) has a direct relationship with the BMW software engineers in Germany. (who wrote the original code) So more than any other tuner, they actually have access to the all tools necessary to fix this problem. (in theory) Not only do they have access to the un-encrypted original base code structure, but they also have access to the engineers as well. So they can dissect and understand the methodology of how and why the code was written in a certain manner.

I can't think of one other tuner (besides Dinan), who would have that kind of access.

That's a HUGE advantage in regards to solving a software tuning issue.

And even with all that help in their corner...they still couldn't fix the power dip they experienced during their dyno testing of this new X-pipe.

So as you can see Andy, this "little problem" is not going to be so easily solved without some type of innovative out-of-the-box solution.

The standard software tweaking approach has not been successful thus far.

It would cost quite a bit of of money (and R&D time) to figure this out, so I'm not sure how many more tuners are going to pour xxxxxxx amount of resources into a project that may or maynot bare fruit.

I certainly hope that ESS can look at this problem with a fresh set of eyes, and discover something that all the other BMW top tuners have missed.

If they are able to figure this out, they will definitely have a lot of customers lined up to buy it.

+1,000 Unfortunately, I think you've hit the proverbial nail on the head here. Well said.

Originally Posted by stylinexpat

F U C K Don't tell me that I bought another new car with another dip problem like my older E46 ZHP

I'm right there with ya, man. I'm curious to see what effect forced induction has on the dip. If it's significant, that would be the final straw convincing me to go the stroker route instead.

Edit: I just saw that the stroker engine suffers the a similar "dip" issue down low. Hmmm....

[sales@ESSTuning]

Its not an AFR issue. It is an issue that might be able to be corrected.

[MrHarris]

Can anyone post some dyno graphs of this dip? I want to see exactly where it's at, how long it lasts and how much of a TQ hit there is.

[turbo8765]

Originally Posted by Rom3n

Its not an AFR issue. It is an issue that might be able to be corrected.

How?

Higher flow exhaust systems commonly cause a slight decrease in low rpm trq. Motors that produce peak power at higher rpm are more likely than motors that produce peak power at lower rpm to suffer a loss in trq at low rpm with a higher flower exhaust. This is a common trade off that is nearly unavoidable.

I would be quite impressed if you were able to gain top end with no loss in the bottom end.

I say just enjoy the increase in top end power, where the S65 is at it's best anyway. Downshift

[TLud]

Originally Posted by turbo8765

How?

Higher flow exhaust systems commonly cause a slight decrease in low rpm trq. Motors that produce peak power at higher rpm are more likely than motors that produce peak power at lower rpm to suffer a loss in trq at low rpm with a higher flower exhaust. This is a common trade off that is nearly unavoidable.

I would be quite impressed if you were able to gain top end with no loss in the bottom end.

I say just enjoy the increase in top end power, where the S65 is at it's best anyway. Downshift

True to some extent, but this is not a general loss of low rpm torque. It's a specific dip at one point in the rpm band.

[askiles]

Right. It only dips for a small RPM range (2k-2.5k) before it picks up again, and is way up on power.

-Andy