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yoeddynz

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Can I ask this question?

In a road vehicle where harmful emission reduction is not legislated for.

Does EGR aid in reduction of fuel consumption?

In the situation of pumping losses. BMW Valvtronic system uses variable valve lift to reduce the valve lift and minimize pumping losses rather than EGR.

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Off topic to the above, but something I'm hoping to gain some insight into when my dual VVTI motor is running again, and I've got two different exhaust manifolds to test (A long 4-2-1, and a much smaller lighter 4-1)

Is, will a MAF sensor see a change in reading based on your exhaust manifold? I'm thinking yes. 

If extractors pull out a higher percentage of the old bad gas from the previous combustion event, then there's more room for fresh air in. 

Which means more air gets pulled through the intake, which means higher MAF reading. Something you wont necessarily see just with a MAP sensor as MAP reading could be identical.

I'm looking to gain some insights into exhaust side VVTI tuning this way and then see if the big heavy 4-2-1 is actually worth keeping. 
 

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Just now, japawagons said:

Can I ask this question?

In a road vehicle where harmful emission reduction is not legislated for.

Does EGR aid in reduction of fuel consumption?

In the situation of pumping losses. BMW Valvtronic system uses variable valve lift to reduce the valve lift and minimize pumping losses rather than EGR.

I think because of the advanced cam timing they can achieve the exact same results without the EGR valve, since the engine just stops pumping anyway.

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In theory a MAF system really only depends on the air flow behaviour in the tract surrounding and including the MAF sensor so I wouldn't expect the changed exhaust manifold to throw your MAF calibration off.

That being said, MAF systems are real and therefore won't match the ideal theory perfectly so you may well see some change. That change could possibly be ironed out just by changing the sampling rate/lag averaging factors though.

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Just now, Roman said:

Off topic to the above, but something I'm hoping to gain some insight into when my dual VVTI motor is running again, and I've got two different exhaust manifolds to test (A long 4-2-1, and a much smaller lighter 4-1)

Is, will a MAF sensor see a change in reading based on your exhaust manifold? I'm thinking yes. 

If extractors pull out a higher percentage of the old bad gas from the previous combustion event, then there's more room for fresh air in. 

Which means more air gets pulled through the intake, which means higher MAF reading. Something you wont necessarily see just with a MAP sensor as MAP reading could be identical.

I'm looking to gain some insights into exhaust side VVTI tuning this way and then see if the big heavy 4-2-1 is actually worth keeping. 
 

This would only occur if you are using Valve Overlap??

Or if the manifold is not allowing full cylinder emptying on the exhaust stroke?

But yes, I'm sure you would see a difference.

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Just now, Roman said:

Off topic to the above, but something I'm hoping to gain some insight into when my dual VVTI motor is running again, and I've got two different exhaust manifolds to test (A long 4-2-1, and a much smaller lighter 4-1)

Is, will a MAF sensor see a change in reading based on your exhaust manifold? I'm thinking yes. 

If extractors pull out a higher percentage of the old bad gas from the previous combustion event, then there's more room for fresh air in. 

Which means more air gets pulled through the intake, which means higher MAF reading. Something you wont necessarily see just with a MAP sensor as MAP reading could be identical.

I'm looking to gain some insights into exhaust side VVTI tuning this way and then see if the big heavy 4-2-1 is actually worth keeping. 
 

With the correct valve overlap I would expect to see a higher MAF reading with a better exhaust. At a certain RPM at least anyway, and as long as the intake isn't the restriction.

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Just now, japawagons said:

Can I ask this question?

In a road vehicle where harmful emission reduction is not legislated for.

Does EGR aid in reduction of fuel consumption?

In the situation of pumping losses. BMW Valvtronic system uses variable valve lift to reduce the valve lift and minimize pumping losses rather than EGR.

It's so damn hard to find any good information on stuff like this, because like mentioned earlier.
When you're paying someone $100 an hour to tune your car on a dyno, you're not going to ask them to spend 50 hours testing lean burn air fuel ratios for cruising. 
Most people dont even want to fork out the money for getting cold start working nicely. 

Another roadblock to getting reliable information is that as you go leaner, or start adding EGR the combustion speed slows down by heeeaapppsssss
You need WAY more ignition timing. So the problem is, people get as far as trying a different AFR but then their car becomes sluggy as hell because it doenst have the timing. 
So they are convinced they need to go richer again. 

Like imagine you want to test 10 combinations of AFR, 10 combinations of ignition timing and 10 combinations of cam timing. 

That's 1000 combinations. Now add exhaust side cam timing in 10 iterations and you've got 10,000 combinations to go through.
Its little wonder why there's actually no one around who can tell you how to tune cam timing properly without just "suck it and see" on a dyno.
With varying degrees of success for reasons above.

Which is why I'm trying to find some better methods to streaminline the process. but still get accurately to the best settings.
I've found that best economy equates to intake cam position that generates the strongest vacuum. Which is weird because that's the opposite of reducing pumping losses.

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Just now, ajg193 said:

In theory a MAF system really only depends on the air flow behaviour in the tract surrounding and including the MAF sensor so I wouldn't expect the changed exhaust manifold to throw your MAF calibration off.

That being said, MAF systems are real and therefore won't match the ideal theory perfectly so you may well see some change. That change could possibly be ironed out just by changing the sampling rate/lag averaging factors though.

What he means is he should be able to graph the improvements of the exhaust by plotting the MAF. If the tuned pulses from exhaust aid cylinder extraction and scavenging it should allow the engine to breathe more air which will show a higher MAF value, which shows more power without having to use a dyno.

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Just now, Yowzer said:

I think because of the advanced cam timing they can achieve the exact same results without the EGR valve, since the engine just stops pumping anyway.

I'm of the opinion that EGR is completely detrimental to Power and Effeciency and that is purely used to allow Nox reduction in a Startified Charge condition, because Nox would be prolific in that situation.

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Hold up a second, are we intended to be discussing MAF calibration here or actual air flow through the engine?

I figured Roman was talking about MAF calibration, where the measured air value deviates from the actual value based on exhaust but you are looking from the other side where if the air flow is increasing.

Of course we would see a difference in measured airflow if one manifold works better. (ignoring effects on calibration and assuming engine efficiency stays the same)

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Just now, Spencer said:

On a MAP only tune wouldn't you just see that as a need for more/less fuel in the table?

Yes but with nowhere near the clarity of reading MAF
(Have done it both ways)

I think maybe because there are so many variables that contribute to your oxy sensor reading, where as a MAF is just reading airflow directly and very accurately.

At lower engine speeds/load, wideband latency is a real ball buster too. Where as MAF gets an instantaneous accurate value.
 

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Just now, ajg193 said:

Hold up a second, are we intended to be discussing MAF calibration here or actual air flow through the engine?

I figured Roman was talking about MAF calibration, where the measured air value deviates from the actual value based on exhaust but you are looking from the other side where if the air flow is increasing.

Of course we would see a difference in measured airflow if one manifold works better. (ignoring effects on calibration and assuming engine efficiency stays the same)

No I'm not talking about the MAF calibration being wrong. 
I'm talking about, will MAF paint a really clear picture of changes to your exhaust, because changing your exhaust alters the airflow through the engine. 
Or, is there another mechanism by which an exhaust manifold helps make power or not. (thinking not)
It seems obvious that a MAF sensor would read an increase in airflow, but, since MAFs are a forbidden word in aftermarket ECUs there's zero data on this that I can find anywhere.

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Just now, Roman said:

Yes but with nowhere near the clarity of reading MAF
(Have done it both ways)

I think maybe because there are so many variables that contribute to your oxy sensor reading, where as a MAF is just reading airflow directly and very accurately.

At lower engine speeds/load, wideband latency is a real ball buster too. Where as MAF gets an instantaneous accurate value.
 

I feel like this very situation would be much more ideal for tuning VVT in general? Being able to measure the Air Flow increase or reduction in real time.

If you could fit a MAF as an overall tuning reference on a Dyno I feel like it would be a very helpful signal, even if it's outside the ECU loop.


Could you put a MAF or similar sensor in the exhaust also?

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A quick google search of scientific literature indicates that exhaust manifold design does have an effect on thermal efficiency of an engine. Therefore you won't necessarily be able to quantify the difference between two manifolds based purely on MAF readings, you'd need to compare measured power output against your sensor data.

I don't know how much of an effect on thermal efficiency you will observe, if it is small compared to the changes in MAF values then you will obviously be able to use MAF as a reasonable indicator (I'm saying shit you obviously already know, aren't I....)

How do you define your performance characteristic anyway? Are you using MAF@RPM&TPS as a property or something else?

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On my current engine I've only got intake side cam timing. 
This graph below is doing a full throttle run with zero degrees advance, then 5, then 10, etc etc.
The colour scale is intake cam advance amount in degrees.
The lines are showing how much airflow there is per individual cylinder event. 
Whatever line gives the highest number at a given RPM, produces the highest cylinder fill. 
So at this stage it's not about optimizing power, it's about optimizing how much air you can stuff into the engine.
Which then represents power potential once you've got your AFR and igntion timing correct. 
An exhaust manifold can affect thermal efficiency because a restrictive exhaust leaves more left over gas in the cylinder from the last combustion event.

What I am expecting to see is that the big dip at low rpm there, where high cam advance eats shit. 
Is caused by  a reversion effect from my current manifold, I'm expecting to see that move around a bit with a different exhaust.
Or, once I've got exhaust side cam timing too I'll be able to minimize that dip even further. 
graph.png.2a759b77cedb5e78143b5187096b1e01.png

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http://www.tjprc.org/publishpapers/--1378453552-2. Experimental analysis.full.pdf

This (somewhat dodgy) research paper indicates that for their particular exhaust system higher flow rates correspond with higher efficiency so you get a win win situation.

If your engine responds even remotely similarly to theirs you could probably safely assume that if your MAF increases at WOT for a given RPM then you are getting more power and better efficiency (but probably not better economy).

Other than that you really can't say too much without an accurate dyno.

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