Full exhausts: Dip in HP at low rpms

[Lemans_Blue_M]

Originally Posted by 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

It will interesting to see if ESS can address this dip, without watering down the overall performance of your Akrapovic header back exhaust.

[Subw00er]

As part of the design of the Bates exhaust (see my signature), we consciously decided to leave in the bends and natural restriction of the OEM exhaust because I also noticed that many aftermarket exhausts cause a loss in power below 3K rpms due to loss of back pressure. For day to day driving, this is a pretty significant RPM range to consider IMO. I'm thinking about going next week for a dyno to see what the graph looks like open vs closed valves. Should be an interesting graph!

If there is a dip with the valves open, and there are HP/TQ gains with the valves open, I was wondering if this could be solved with an active Bates exhaust. We could leave the valves closed, or partly open, then as 3K RPM hits open them up automatically (then close again at a stop - there would be a lot of experimenting and logic to decide how to control the valves optimally). Perhaps this is why the c6z06 has active valves?! My Kawasaki z1000 bike does as well.

Interesting topic btw.

[MMMorish]

That's it! No full exhaust system for me. I'm just gonna stick to a cat back.

[askiles]

The small dip is very not noticeable while driving, and worth it to have the gains everywhere else on the power band.

-Andy

[stylinexpat]

Originally Posted by 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

That would depend on how much more the gains were than the losses in the dip. If you only gained what you lost then you are pretty much only breaking even in the short run but in the long run it is a different story. I do wonder though if the losses in the dip are any different if one were running a 3.62 final diff..

[DevJ]

So can someone please clarify for me? I'm a little confused...

Any aftermarket x-pipe, paired with an aftermarket muffler, will have a brief dip in HP somewhere across the powerband?

[michaeldorian]

Originally Posted by DevJ

So can someone please clarify for me? I'm a little confused...

Any aftermarket x-pipe, paired with an aftermarket muffler, will have a brief dip in HP somewhere across the powerband?

Well, the stock car also has a dip in the lower RPM range. The issue is, aftermarket setups, though making more power at the top, tends to also amplify this effect.

[michaeldorian]

Originally Posted by TLud

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



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....

It look's like the ESS SC unit smooths out the dip just a bit. It doesn't completely remove it, but looks like it helps.

[stylinexpat]

Originally Posted by michaeldorian

It look's like the ESS SC unit smooths out the dip just a bit. It doesn't completely remove it, but looks like it helps.

Much better than what it was on the older E46 ZHP's which were supercharged.
The dip in the graph doesn't look too bad. My guess is that they should be able to get something close to it without the supercharger on there..

[mixja]

Originally Posted by stylinexpat

That would depend on how much more the gains were than the losses in the dip. If you only gained what you lost then you are pretty much only breaking even in the short run but in the long run it is a different story. I do wonder though if the losses in the dip are any different if one were running a 3.62 final diff..

You gain far more than what you lose, from around 3000RPM upwards you are looking at a torque gain of 10% until around 6000RPM where the torque gain is around 5% through to redline...

This is not the type of car that should be WOT @ 2500RPM anyway

[askiles]

When I say it dips between 2K-2.5K, I mean it loses power, and dips below for about 500RPMS. After that, it pick up quickly, and I gained a ton of power from there. It is really weird, but makes sense.

-Andy

[lucid]

Originally Posted by mixja

This is not the type of car that should be WOT @ 2500RPM anyway

+1

Folks lose sight of that fact when staring at dyno charts. Even in a drag race from a stand still, this comes to play just once, maybe not even that since you'll be traction limited in 1st taking off.

During daily cruising around, there are many other factors that play into the responsiveness and power delivery of the engine when you step on it that the dyno charts do not reflect/represent.

[golemite]

Originally Posted by mixja

This is not the type of car that should be WOT @ 2500RPM anyway

+1

[AMPowerJ]

I have felt that dip at 2.5K since my car was brand new. Always thought it was just tight and would get better after break-in but I guess not. Almost feels like the engine hesitates and passengers have commented on it as well.

[CanM3]

The Dinan literature states that the 'dip' is between 6600-7200 rpm, not what I would consider a low rpm dip. Does the addition of a midpipe move this anamoly further up into the rpm band I wonder?
Sure would be nice to see a dyno from this pipe just to see how bad the tested 'dip' actually is.....Lemans_Blue, any info on this??

[Singletrack]

Originally Posted by Subw00er

As part of the design of the Bates exhaust (see my signature), we consciously decided to leave in the bends and natural restriction of the OEM exhaust because I also noticed that many aftermarket exhausts cause a loss in power below 3K rpms due to loss of back pressure. For day to day driving, this is a pretty significant RPM range to consider IMO. I'm thinking about going next week for a dyno to see what the graph looks like open vs closed valves. Should be an interesting graph!

If there is a dip with the valves open, and there are HP/TQ gains with the valves open, I was wondering if this could be solved with an active Bates exhaust. We could leave the valves closed, or partly open, then as 3K RPM hits open them up automatically (then close again at a stop - there would be a lot of experimenting and logic to decide how to control the valves optimally). Perhaps this is why the c6z06 has active valves?! My Kawasaki z1000 bike does as well.

Interesting topic btw.

That's an interesting idea. I believe the Aston Martin Vantage uses a bypass valve as well.

[stylinexpat]

Originally Posted by CanM3

The Dinan literature states that the 'dip' is between 6600-7200 rpm, not what I would consider a low rpm dip. Does the addition of a midpipe move this anamoly further up into the rpm band I wonder?
Sure would be nice to see a dyno from this pipe just to see how bad the tested 'dip' actually is.....Lemans_Blue, any info on this??

Makes you wonder why so many vendors/manufacturers only place claims of HP gains on their website for exhaust systems that they sell without Dyno graphs to back them up.

[CanM3]

Originally Posted by stylinexpat

Makes you wonder why so many vendors/manufacturers only place claims of HP gains on their website for exhaust systems that they sell without Dyno graphs to back them up.

Well, as was mentioned by another member before, if the manufacturers posted Dyno graphs, there is the potential for unhappy customers unless dyno's matched curve for curve. I understand why they do it, but it doesnt mean I'm happy about it.

[mixja]

I'm curious as to whether this so called "dip" occurs with X-Pipe systems mated to the factory exhaust...

For example, Encore X-Pipe dyno does not show this dip and in fact around 2500-3000RPM is where the most torque gains are made:

[mixja]

Originally Posted by Subw00er

As part of the design of the Bates exhaust (see my signature), we consciously decided to leave in the bends and natural restriction of the OEM exhaust because I also noticed that many aftermarket exhausts cause a loss in power below 3K rpms due to loss of back pressure. For day to day driving, this is a pretty significant RPM range to consider IMO. I'm thinking about going next week for a dyno to see what the graph looks like open vs closed valves. Should be an interesting graph!

If there is a dip with the valves open, and there are HP/TQ gains with the valves open, I was wondering if this could be solved with an active Bates exhaust. We could leave the valves closed, or partly open, then as 3K RPM hits open them up automatically (then close again at a stop - there would be a lot of experimenting and logic to decide how to control the valves optimally). Perhaps this is why the c6z06 has active valves?! My Kawasaki z1000 bike does as well.

Interesting topic btw.

Back pressure does not increase torque and a lack of back pressure does not decrease torque - this a common misconception. Generally what causes the drop in low-end torque as the result of a bigger exhaust system is the reduction in exhaust gas velocity. Getting optimal power at a certain RPM is a balancing act between maintaining high gas velocity and minimal back pressure.

I'm curious as to whether the M3 aftermarket full exhaust systems actually use larger piping. If an aftermarket exhaust system used the same piping diameter as OEM but reduced backpressure through high-flow cats or catless design, then I would expect there to be no torque losses...

[askiles]

Originally Posted by mixja

I'm curious as to whether this so called "dip" occurs with X-Pipe systems mated to the factory exhaust...

For example, Encore X-Pipe dyno does not show this dip and in fact around 2500-3000RPM is where the most torque gains are made:

There is no dip in this graph.

-Andy

[Cloud]

The trend seems to be that full exhausts which delete the primary cat have the dip.