Exhaust note/tone on the Barra

[solarite_guy]

Originally Posted by Mercury Bullet

https://www.fordforums.com.au/showthread.php?t=11469280

Alright, so that is a start in the direction of dynamic valve timing control, which is resulting is changed LSAs to increase overlap in a narrow range of criteria.

[Maka]

Originally Posted by burnz

the only good sounding 6 that I heard, 245 hemi..
under gentle throttle sounded great, nice bark..

I've had one, a VG Pacer & yep sounded great all through the rev range (for a na i6) though my current daily, a Au Xr6 vct with straight through exhaust & modded intake etc sounds better especially when the vct kicks in.

cheers, Maka

[Bossxr8]

Originally Posted by solarite_guy

Then what would the lobe separation angle be under operation?

Wouldn't have a clue. All I know is they are fixed at installation and the vct does not advance or retard in factory turbo engines, just NA ones.

With the new sct software giving access to the vct tables it can be activated now by the sound of it though.

[arronm]

100% genuine imitation cam......

[solarite_guy]

Originally Posted by Bossxr8

Wouldn't have a clue. All I know is they are fixed at installation and the vct does not advance or retard in factory turbo engines, just NA ones.

With the new sct software giving access to the vct tables it can be activated now by the sound of it though.

This is something I am surprised hasn't taken off sooner with the turbo ecu tuning crowd, and not just for the sake of a hot rod style idle.

When I first read the article I posted earlier on page 1, I actually laughed that some only now realize what the old time hot rodders have known and put into play since putting down their WWII air craft tools and starting up the post war aftermarket industry. Even still, it seems many are shunning it because it's strange and new in their world.

If limits remain in place for vct, etc, options for example, like Haltech still exist.

One of the next steps in this area is to re-engineer the phasers so the blind concept of lockouts and limiters can go the way of the Edsel.

Folks are still thinking "in 1 dimension" when it comes to valve timing.

[GASWAGON]

The whole concept of 'VCT' is to advance and retard inlet AND exhaust camshafts under different low or high speed loads to obtain optimum AFR's from idle RPM and then ALLL the way up to the Redline.

This is why the Barra I6 N/A and Turbo engine is so good!!!

Never driven one but just have a look at what some of you XR6T/F6310 drivers are getting out of the Barra after some mods and tuning.......

[solarite_guy]

Hey CB here's a graphic example, from the article on page 1 of this thread, of what you are describing when someone has access to the VCT tables and modifies the cam center lines relative to crankshaft position, which alters the LSAs, lobe separation angles.



Under the condition of acceleration underload the tuner established a baseline with the cam position tables left stock. Then he altered the tables controlling cam positioning as described here:

In 2009, Bryan Medway (formerly of GST Motorsports), a well known Mitsubishi ECU calibrator from the Bay Area of San Francisco, was one of the first to begin openly testing the new MIVEC system using various amounts of overlap and openly posting the results online. He tuned a completely stock Evo X and had a little extra time to test his recalibrated MIVEC maps (VVT settings) directly against the factory values. Medway took his recalibrated tune and pasted the factory MIVEC maps back into it and reflashed the ECU, he then compared the dyno results to his recalibrated VVT tables and then posted the results on several online forums.

From the factory, Mitsubishi seems to focus overlap during mid to high RPM cruise and light throttle cells, with its main function as an internal EGR component, and then fully advancing the exhaust cam at moderate loads and anywhere beyond that.

Compared to stock, Medway’s revised VVT maps retarded the intake cam slightly in low load cruise cells and was left about the same as stock in higher load cruise areas. In mid to high load spool up cells from 2,750 RPM to 4,500 RPM, the intake was heavily advanced, before retarding back to the floor by redline. The exhaust cam was retarded aggressively in cruise cells and quickly advanced as load and RPM increased.

These changes under the conditions described above resulted in the stronger mid range gains on both tq and hp visible in the graph.

For the purpose of this test using same boost, same cams, just different cam positions relative to engine load and rpm: Other than the extra power in the rpm mid range WHILE under load, where the cam positions were altered, the engine will idle as normal. Then past the mid range rejoin the intended factory power up top.

That was for this test.

A relatively new concept for many of today's tuners of turbo engines.

Note: results will vary depending type of turbo.

With the state of current cam phaser architectures, when building high powered turbo engines, the practice is to limit over all phaser travel or lock it out all together when swapping to many "bigger" and "more aggressive" cams.

This results in an old time raucous idle and a power band that comes in later in the rpm range when the "bigger" and "more aggressive" cams are installed. The phasers are not compatible with greater spring rates needed by the "bigger" and "more aggressive" cam lobes needed when hunting for very high outputs. The current hydraulics of the phasers just can't do their jobs with the added spring pressures.

If the VCT concept is to be utilized in the very high output combinations while at the same time giving us the day to day drive-ability they can offer, then the phaser architectures used today need some re-engineering.

[FG50T]

Originally Posted by arronm

100% genuine imitation cam......

Will be interesting to see how standard Barra valve springs cope with this then if it's able to be utilised like the MIVEC system or if aftermarket valve springs will be able to function the same on the stock cam with adjusted LSA's?

[solarite_guy]

With the standard cams and rpm ranges the standard valve springs should work alright. Increasing boost will have limits. Most limiters can work well with a limited amount of increased spring pressure and/or boost.

Where increased spring pressure becomes important is:

• Increased RPM
• More abrupt direction changes of the cam lobes
• Faster cam lobe ramp rise and fall rates
• Increased lobe lifts
• Added boost
• Especially all 5 above combined at once

Just looking at the cam lobe, the first 4 items above are closely interrelated. One alone can make a stock spring inadequate. Combined the greater demands on the valve spring and depending how much any of those areas are increased, the stock valve springs quickly become useless, even dangerous to the engine.

Re-engineering the phasers so limiters and lockouts are not needed, will result is a different approach to cam lobe design as well.

Lift, is still lift in this scenario.

Many years ago, Harvey Crane put the phrase critical valve lift area into hot rodding jargon. There is something called valve curtain area. The simplest description of this is the area formed by the circumferences of where the valves and valve seats meet multiplied by the max distance the cam moves the valves off the seats.

Depending on cylinder displacement, rpm and valve curtain area, the incoming cylinder air/fuel charge can reach the speed of sound if the valve curtain area is not great enough to keep the incoming charge traveling below this velocity for the combination of the other 2.

When/if the incoming charge reaches the speed of sound it goes into a state of sonic choke. The rate of the incoming charge will no longer increase past that point. (There is another story behind the implications of that.)

Under boosted conditions, the exact same thing does not happen, as the incoming charge is under a pressure density situation, yet it is a form of artificially raising boost. This is not a good thing. This is a waste of a portion of the systems overall boost potential. I want my boost to raise because the cylinder is being overfilled.

...need to address something and will finish up later...

[lucas2]

The Might Car Mods Barra powered Cresta sounds closer to an RB due to the straight through exhaust - https://youtu.be/QCa4ORTQ8pM?t=16m24s

Would the tone largely be related to the differences in the stroke of the engine, firing order and exhaust/manifold style?

[burnz]

Originally Posted by lucas2

The Might Car Mods Barra powered Cresta sounds closer to an RB due to the straight through exhaust - https://youtu.be/QCa4ORTQ8pM?t=16m24s

Would the tone largely be related to the differences in the stroke of the engine, firing order and exhaust/manifold style?

all I6 and I8 have the same firing order, two versions of the I4 and V6,
four versions of the V8, V10, V12, V16 and 6 version of the V24..

[Bossxr8]

Originally Posted by CoolBFWagon

The whole concept of 'VCT' is to advance and retard inlet AND exhaust camshafts under different low or high speed loads to obtain optimum AFR's from idle RPM and then ALLL the way up to the Redline.

This is why the Barra I6 N/A and Turbo engine is so good!!!

Never driven one but just have a look at what some of you XR6T/F6310 drivers are getting out of the Barra after some mods and tuning.......

The VCT isn't in operation in the factory turbo engines though. All the tables are set to zero so there is no advancing or retarding the cams at all. Ford didn't see it necessary to use it as they got their power targets without it and making the vct work would have required more R&D dollars.

[solarite_guy]

Originally Posted by lucas2

The Might Car Mods Barra powered Cresta sounds closer to an RB due to the straight through exhaust - https://youtu.be/QCa4ORTQ8pM?t=16m24s

Would the tone largely be related to the differences in the stroke of the engine, firing order and exhaust/manifold style?

You are on the right track.

The exhaust system and displacement play roles, as does RPM. It's amazing how rpm makes just about any engine configuration play beautiful music.

[solarite_guy]

Originally Posted by solarite_guy

Where increased spring pressure becomes important is:

• Increased RPM
• More abrupt direction changes of the cam lobes
• Faster cam lobe ramp rise and fall rates
• Increased lobe lifts
• Added boost
• Especially all 5 above combined at once

Earlier, we talked a little about lift.

Often increased lobe lift and/or rocker/follower ratio requires a different valve spring and even installation of the valve spring to accommodate the greater lift. Usually greater spring pressure is needed for controlling greater valve movement and often greater rpm allowed by the increased lift, as touched on earlier.

Valve timing: When does the valve open? How quickly does it accelerate on opening and decelerate as the cam reaches the nose, where max lift exists, then accelerate off the nose and start downward toward closing, decelerate again as the valve is about to close and then when does it close?

All these are components of valve timing. The cam lobes are at the heart of this.

Taken together, most cam suppliers provide duration and lift numbers to convey how "big" or "aggressive" a cam is.

Duration = Number of crankshaft degrees the lobe is at and above a specified lift point (.004", .006", .010", .015", .020", .050", .200", .300").

Valve Lift = ((Lobe Lift * rocker/follower ratio) - Lash). Direct acting cam over bucket systems don't have rockers and (Lobe Lift - lash) = Valve Lift. Desmo systems I am familiar with have a pair of rockers per valve and will follow the initial definition of Valve Lift. Where Lash = 0, then 0 is subtracted.

As a side note, an interesting discussion of a Ducati motoGP desmo system can be found at this PDF file here: https://www.google.com/url?sa=t&rct=...2nbA03DG3cMhT7

Duration does not by itself require anything special about the spring, however the increased rpm usually associated with increased duration does. Faster valve movement requires increased control of the valve train to maintain stability.

The faster movement can be at all points around the cam lobe due to increased rpm, or at localized locations due to the shape of the lobe. If you are paying close attention at this right now, you will realize trying to compare numbers from 1 cam to another, often even from the same manufacture can not always be done.

With that behind us, when considering fixed valve timing, any given cam design is going to be a compromise. Among other things, the components of lift (and rate of lift), duration, lobe separation angle (LSA) and Intake Center Line (ICL) are put in place by the designer to give the best overall compromise of tq, hp, rpm, driving quality, mileage, etc for a given engine and car combination. Too much or too little of any of these components will result in less than the engines potential performance.

Too much duration and/or LSA's too close together and idle quality, low speed driving, fuel mileage suffer. Not enough lift and/or duration and high rpm suffers, etc.

With fixed valve timing, the single design has to cover all the bases.

With this ground work in place, I need to address a few other thins again, then will talk about how VCT, VVT, TiCT, etc give the designer additional dimensions for cam design.

[GASWAGON]

1.5.3.6.2.4 is ALL i know!!!

[solarite_guy]

Duration.

As discussed earlier, duration tells us how many crankshaft degrees the lobe is above a specified lift. As a reminder, lobe lift is different than valve lift in most cases (See note below).

A conventional characteristic of camshafts intended to increase power levels is increased duration levels.

Makes sense, right? More duration = more time for the cylinder to breathe.

Coincidentally, increased duration also adds to the rough, rumbling idle favoured by hot rodders around the world. Unfortunately, an engines lower rpm tq, power and road manner degrade as more duration is increased.

Trade offs begin here. What is too rough of an idle? What is poor low rpm road manners? What is not enough hp? What suits one, doesn't suit all.

Interestingly enough, a couple or more decades ago 2 cam designers left me with some words of wisdom I hold on to.

1. Most people think the job of a cam is to keep the valves off the seat as long as possible. Actually, the job of the cam is to keep the valves ON the seat as long as possible.

2. It's not so much how much duration a cam has, instead it is where that duration exists.

Both 1 and 2 basically tell the same story, and also, re-enforce the earlier comment of trying to compare cams by looking at numbers in catalogs.

When it comes to cam lobes, a lobe is not a lobe is not a lobe.

One may want the maximum raucous idle possible yet the other may want a more civilised idle, yet both want the same measured duration.

Alright, that's possible by using 2 different shaped lobes yet both have the same measured duration.

Or, there is another and more common way. Change the LSA. The one with a closer LSA, say 108* will sound rougher than the one at a wider LSA, such as 112*, each using the same lobes.

But remember, with a fixed valve timing arrangement, you are stuck with what you order. Similarly, with a limited valve timing arrangement, there are limitations as to what VVT, et al, can supply in variability and outright lift.

All this is more background.

We didn't cover the whys and wherefores durations and LSAs have the effects they do. This is more background in need of covering or the rest of the discussion to make sense, instead of "because that's the way it is".

I want to put that information into a following post(s).

[Maka]

As always SG, you are a true beacon of engine knowledge & i enjoy reading the technical side of engine operating characteristics etc you provide us.

Keep up the great work & a big thank you to you for going to the trouble of enlightening & educating us here at AFF mate!!

cheers, Maka

[93EB_SXR6]

To be blunt, I prefer the way the sohc 4.0 sounds with a mild cam, pacemakers and a nice exhaust but I much prefer the way the barra drives... Much more power and torque... Makes up for sounding a bit lame.

[TICKFORD220]

I had a twin 2.5 venom system on my stock g6et and it sounded better than stock,not too much louder at idle but once opened up it sounded a lot crisper.

[Trevor 57]

:

[wildpete]

Originally Posted by lucas2

The Might Car Mods Barra powered Cresta sounds closer to an RB due to the straight through exhaust - https://youtu.be/QCa4ORTQ8pM?t=16m24s

Lol, If that is what a RB sounds like then I will pass. I remember that episode and didn't they even admit that it sounds pretty awfull down the strip.

Also agree with Maka, SG those are some amazingly detailed posts and I thank you for the time you are putting into this discussion.

Please no offence intended here Boss but is this 100% ligit. Since day 1 the turbo barra models are fitted with VCT but doesn't actually do anything and its taken 14 years for the tuners to get tools to unlock the timing? That is unreal.

[solarite_guy]

We didn't cover the whys and wherefores durations and LSAs have the effects they do. This is more background in need of covering or the rest of the discussion to make sense, instead of "because that's the way it is".

Rough hot rod idle.

Then, with everything else being equal, why does closing up the LSA make an idle rougher? More like a hot rod. ? Same with adding duration while everything else is left equal.?

What effect do those two changes, either by themselves or together, have on an engines valve timing?

They increase the amount of duration that both the intake and exhaust valves remain open at the same time while the piston dwells around TDC.

This is overlap.

Okay? So what does overlap do? Well, from the perspective of an engines power output it does good and bad things.

The good with fixed length induction and exhaust systems:

Using the simplest explanation, within the IC engine during the intake and exhaust cycles, each of the associated subsystems (induction and exhaust) experiences a sound pulse wave each time the valve opens. Both sides, induction and exhaust, experience this.

We are talking about the initiating sound pulse moving from the valve seats and outward away from the cylinder. Each time there is a sound pulse termination point within each subsystem, such as header primary pipes dumping into the collector or the intake runner dumping into the plenum there is an instant sound pulse wave reflected back towards the valve seat.

Guess what happens with all these pulses initially moving from the seat then a reflection back to the valve seat...a few times?

This sets up situations where pulses can help charge the cylinder with each returning pulse in the induction side. On the exhaust side these pulses can help scavenge the spent exhaust gases from the cylinder.

Typically a well designed 4 into 1 or 3 into 1 exhaust will have 3 scavenging pulses for each primary pipe and max hp rpm. Sometimes, due to physical space issues, some of the primary pipes may have to be a cut to a complementary length for the max rpm. Maybe longer or shorter, resulting in fewer or more scavenging pulses.

A similar situation exists on the induction side. Again, 3 pulses usually gives a combination of best tq and hp. This is easy to do with a tunnel ram or even the newer intake manifold designs for many EFI systems. This can be a little tricky with the more conventional single plane carbed style intakes. With these it is easier to get the outside 4 runners to hit the ideal length for 3 pulses, but the inside runners are doing good to be at 4 pulse, then 5th pulse. Maybe these inner runners wind up at a length to suit a different rpm. This can happen on the exhaust side too. Some times on purpose.

Okay, so we have these pulses bouncing around with the potential to help the engine breathe better. Both on the induction and exhaust sides.

Wouldn't it be nice to have both sides in sync with each other?

This way, during the overlap period at max performance rpm, the induction and exhaust can work together to fill the cylinder more than without this built in aid to increase volumetric efficiency. Don't confuse this with "ram charging" which is another aid to over filling the cylinder. We will talk about that later.

So, what is this "max performance rpm"? For racers it is an engines max hp rpm and rpm regions near.

Let's talk about the bad things overlap does. Remember, we are looking at this from the power perspective.

Have to ask another question. What is the inherent max power rpm, so you know what rpm to design your induction and exhaust to?

There are a lot of contributors to this. The primary players are cylinder displacement, cylinder head ports, flow and valve sizes, and good old valve timing. Many cam designers consider the point where the intake valve closes as the single most important valve timing point. This is the point where the door on ram charging is closed. It is also the point at which dynamic compression ratio calculation is based. Note, most dynamic CR calculators do not take VE% into dynamic CR calculations.

What this boils down to is when the design rpm of the induction and exhaust are not only in sync with each other AND with the inherent rpm of the engine, the world is wonderful.

Last question for this post. With a focus on overlap what happens when the engine rpm is outside the magic rpm the engine together with the induction and exhaust subsystems are designed to?

[Maka]

"With a focus on overlap what happens when the engine rpm is outside the magic rpm the engine together with the induction and exhaust subsystems are designed to?"

If i read your question right & i may be wrong haha (its all in the name of learning right SG lol) power / hp starts to diminish after peak hp is reached as the engine starts to suffocate or cant breath due to its particular existing cam design etc?

cheers, Maka

[lucas2]

Originally Posted by wildpete

Lol, If that is what a RB sounds like then I will pass. I remember that episode and didn't they even admit that it sounds pretty awfull down the strip.

I meant in terms of the higher pitch compared to the typical deeper tone you'd hear from a more common 4inch exhaust system on a Barra. The RB's definitely have more of a scream to them that I'm yet to hear on a Barra.

[ratter]

Originally Posted by Bossxr8

The VCT isn't in operation in the factory turbo engines though. All the tables are set to zero so there is no advancing or retarding the cams at all. Ford didn't see it necessary to use it as they got their power targets without it and making the vct work would have required more R&D dollars.

it is operational and does work

[Bossxr8]

Originally Posted by ratter

it is operational and does work

In both BF and FG? I'm sure I had heard another tuner say the VCT table values in factory turbo engines were all zero's.

[ratter]

I’d have to recheck BF but pretty sure it’s there as well

[solarite_guy]

Originally Posted by Maka

"With a focus on overlap what happens when the engine rpm is outside the magic rpm the engine together with the induction and exhaust subsystems are designed to?"

If i read your question right & i may be wrong haha (its all in the name of learning right SG lol) power / hp starts to diminish after peak hp is reached as the engine starts to suffocate or cant breath due to its particular existing cam design etc?

cheers, Maka

You are on the trail Maka, yet there is more involved than falling off the peak up top.

We know greater overlap leans in the direction of giving the rough and rumbling idle. When the rpm hits the sweet spot where induction, exhaust and engine are all in sync, we hear a symphony. Below that rpm we hear what sounds like the symphony warming up, or maybe the percussion section is warming up to Led Zeppelin. On the other side of the power peak, it sounds a little like a singer stretching their voice past their limit.

So the power with a close LSA with increased overlap tend to have peaky tq and power curves, where as the wider LSA and reduced overlap tend toward plateaus.

That peaky tq number of the big overlap can result in a higher max tq number, but over a shorter rpm range. The wider LSA can result in a higher max hp across a broader rpm range. Two different mouse traps for two different type of mice.

So to complete the answer to the question, the large overlap combinations tend to fall away from the tq and power peaks quicker, with the potential of making more max tq. They also will tend to spend more of their rpm range with rough idle and overall running, giving less drive-ability for a greater rpm range.

There are ways to "tune" an engine configuration to either moderate or enhance those atributes. Those are the tendencies.

That is some of the bad side with a definite good side thrown in the mix. Of course, many consider the radical rough idle to be on the good side too.

Now folks have figured out modern turbo engines with VVT can benefit from these principles.

Better yet, as ratter has mentioned, turning on the radical idle could be a push of a button away soon. Or at least, this is how I interpreted it.

I think that is enough groundwork. We can talk about where to go with these ideas in the world of vvt and even further with re-engineered phasers.

Cheers

[solarite_guy]

Originally Posted by ratter

I’d have to recheck BF but pretty sure it’s there as well

You and the team of folks you work with should be commended for the work you are doing in this area. Honestly, I am surprised this has flown under the radar for so long.

The ball is rolling now. Keep it rolling.

[solarite_guy]

Originally Posted by Bossxr8

In both BF and FG? I'm sure I had heard another tuner say the VCT table values in factory turbo engines were all zero's.

This is interesting how the information is surfacing.