Flow bench results

[swampbuggy]

Warpspeed, overlap is a necessary evil....agreed....but do we not construct refined exhaust systems to play a part during the overlap area of the 720 degree cycle. Mark H. BTW i have watched some of the Tues. morning NASCAR teardown and inspection from Concord, via NASCAR.com.I saw Chad Little looking pretty hard at an exhaust system after it was pulled out from under that car. Can one build an illegal exhaust in NASCAR Cup

[Rick360]

It would probably be a good idea to flow forward and reverse from .05" to full lift.

How can you have reverse flow in an engine when the valve is at full lift, or anywhere near full lift? What can you possibly learn from this?

Reverse flow below .100" would be where I'd be interested.

Rick

[groberts101]

Yes to a point ... I have broken a lot of rules with camshaft events just to see what happens the interesting thing is I have not seen the results we are taught in school and books .... because of this I wanted to try some very odd grinds just to see ... crane cams who I used years ago refused to grind them even though my only question for them was will it fit the core ...

So are you really implying that disconnecting the intake from the exhausts inertial tuning will NOT have an impact on peak VE being developed from a more highly developed street or race combination?

Don't think in terms of IF we can design motors like that.. but more WHY we don't design and use model T cams like that for higher strung 4 stroke gas engines. It's not just about the delay of gasses during higher rpm piston movement that dictates the valve timing.. it's also well known and time tested that inertial tuning of each system and specifically timing how they react to one another is key to increasing VE. Piston speed and overall cylinder demand is key to maximizing the interdependent effects of each system, otherwise you'd see extremely high VE in lower rpm applications.

Any statement taken to the extreme can be made not to work .............

First off ... I do street cars and engines not race only ....

VE is the total fill of the cylinder from the total induction cycle ...... the first few degrees before tdc and before you have any real cylinder volume is not going to be why you get a high VE .... what will is airflow as the piston descent happens and the closing point after bdc .....

On the exhaust side there is tuning and a lot of times you are doing well to get it to empty the cylinder .... but any tuning you do is good for only a small rpm band ... what about the rest of the time ? In what I build the exhaust system that fits gets used so I would assume it's not tuned and wrong yet I make lots of power so if it is a help it's like a few HP not the reason peak is made ... and if overlap hurts at very low rpm to only help a little at high rpm then for me on the street less overlap for better part throttle and off idle is worth the price

Scott, first off I wasn't trying to imply that you're going to get "high VE" during that phase of piston position.. only that it could be made to "go higher" if the rest of the systems are tuned in tandem to work cooperatively with each other. And of course that's only possible if there is some degree of overlap window left to allow that to happen. Time/area phasing of cam events is one concern.. while the pressure differentials created between those systems within that time/area allowance is entirely another. At this point in my engine building I'm all about trying to perfect those pressure differentials to allow better timed valve events and more properly sized overlap windows. Needing fewer bandaids can equate to wider fuller powerbands without killing the peak numbers in the process. Furthermore, there is the possibility that engines having wider powerbands can and do have multiple wave events to help cylinder filling. Make the powerband too narrow and peaky and you won't see that same cumulative effect.

Also wasn't trying to imply that it would only happen at very high racing only piston speeds either. I'm sure you're well aware that a larger displacement and/or very long and properly tuned intake system can affect VE, BMEP, increase cylinder fill, mass flow or whatever term you want to toss at it. And on the other side of the engine shrinking exhaust valve/port sizing and/or utilizing smaller or longer length primary's, sizing steps, 4-2-1's, various merge's and choke sizes can effectively allow a larger mass to be moved into the cylinder by reducing pressures on that side of the cylinder head. Of course quieter chambered muffler full length street exhausts can effectively piss much of those gains away but still allows potentially higher cylinder filling if it's tailored to avoid as much backpressure and velocity snuffing as possible during it's design phase.

All I was really trying to say is that shortening the cams timing or overlap events to bandaid a poorly designed cookie cutter induction and/or exhaust system is in fact still a bandaid all unto iteself. An engine is just a series of forced compromises from one end to the other but it helps to mitigate the bigger ones whenever possible to allow fewer and smaller bandaids being applied overall. And I surely understand that we only "get what we get" when working within a standardized rpm range using preselected market available shelf parts and just have to make do by adjusting other build parameters to end up at a happy medium by adjusting the powerbands sweet spot to match that particular application. But that still doesn't make it right or fully optimized to say the least. It all depends on the combination of parts, what's expected of them, and ultimately how much time and cash we spend.. to where we'll usually end up.

[DrillDawg]

The slug of exhaust gases going down the pipe is heavier than the air and the intake charge is heavier than air, get the effective pressure of these two higher than the cly. pressure when the intake valve opens and you won't have or will have less reversion.

[groberts101]

The slug of exhaust gases going down the pipe is heavier than the air and the intake charge is heavier than air, get the effective pressure of these two higher than the cly. pressure when the intake valve opens and you won't have or will have less reversion.

Exactly. And shrinking exhausts nearer towards the point that the engine will become choked at any specific power output/mass flow potential is one of the keys to getting and keeping things moving and helping to stay moving in the correct direction. Shits being made in a "one size fits all" mentality. Higher compression ratio also helps in somewhat similar manner. Livens up the induction quicker and hits the pipe harder.. allows the motor to come up on the cam quicker. Win win.. unless somethings severely anemic or severely choked to begin with.

[Carnut1]

It would probably be a good idea to flow forward and reverse from .05" to full lift.

How can you have reverse flow in an engine when the valve is at full lift, or anywhere near full lift? What can you possibly learn from this?

Reverse flow below .100" would be where I'd be interested.

Rick

Rick, do we really know that the flow at full lift is in one direction? How about cylinders that fire sequentially and rob from each other? The idea of flowing from .05" to full lift is it would give you an idea of the flow efficiency forward vs. reverse across the lift curve. Thanks, Charlie

[Warp Speed]

It would probably be a good idea to flow forward and reverse from .05" to full lift.

How can you have reverse flow in an engine when the valve is at full lift, or anywhere near full lift? What can you possibly learn from this?

Reverse flow below .100" would be where I'd be interested.

Rick

Rick, do we really know that the flow at full lift is in one direction? How about cylinders that fire sequentially and rob from each other? The idea of flowing from .05" to full lift is it would give you an idea of the flow efficiency forward vs. reverse across the lift curve. Thanks, Charlie

And what do you learn from flowing forward vs reverse in lift ranges that it never happens in?

[Carnut1]

Warp, read that again. I thought I answered that. Thanks, Charlie

[Warp Speed]

Warp, read that again. I thought I answered that. Thanks, Charlie

I've read it several times, and still don't get what your after!

[GARY C]

It would probably be a good idea to flow forward and reverse from .05" to full lift.

How can you have reverse flow in an engine when the valve is at full lift, or anywhere near full lift? What can you possibly learn from this?

Reverse flow below .100" would be where I'd be interested.

Rick

Rick, do we really know that the flow at full lift is in one direction? How about cylinders that fire sequentially and rob from each other? The idea of flowing from .05" to full lift is it would give you an idea of the flow efficiency forward vs. reverse across the lift curve. Thanks, Charlie

How high will a digital manometer read? it seems you could install an L shaped probe into the runner through a grommet and read forward and reverse action. I don't know what you would do with the data.

[Stan Weiss]

This is not really a very aggressive cam. But we can see how much flow area there is where the piston is going in the wrong direct. If we are only looking BTDC still more then some would think. Remember that many cam master lobe lists show tappet lift @ TDC.

Stan

ab-lift-comp161.gif

[CGT]

Reversion is always a problem and anything you can do to help minimize it is a good thing .... testing is one way to see how the port and runner will behave when the flow reverses

Then wouldn't it make more sense to test reverse flow at lifts where reverse flow is most likely to occur? Like, when the piston is going in the wrong direction?

Yes

It would probably be a good idea to flow forward and reverse from .05" to full lift.

How can you have reverse flow in an engine when the valve is at full lift, or anywhere near full lift? What can you possibly learn from this?

Reverse flow below .100" would be where I'd be interested.

Rick

How can you have reverse flow in an engine when the valve is at full lift, or anywhere near full lift? What can you possibly learn from this?

Reverse flow below .100" would be where I'd be interested.

Rick

Rick, do we really know that the flow at full lift is in one direction? How about cylinders that fire sequentially and rob from each other? The idea of flowing from .05" to full lift is it would give you an idea of the flow efficiency forward vs. reverse across the lift curve. Thanks, Charlie

And what do you learn from flowing forward vs reverse in lift ranges that it never happens in?

Charlie, you may consider spending some time with a shortblock and a degree wheel.

[Scotthatch]

[/quote]

Scott, first off I wasn't trying to imply that you're going to get "high VE" during that phase of piston position.. only that it could be made to "go higher" if the rest of the systems are tuned in tandem to work cooperatively with each other. And of course that's only possible if there is some degree of overlap window left to allow that to happen. Time/area phasing of cam events is one concern.. while the pressure differentials created between those systems within that time/area allowance is entirely another. At this point in my engine building I'm all about trying to perfect those pressure differentials to allow better timed valve events and more properly sized overlap windows. Needing fewer bandaids can equate to wider fuller powerbands without killing the peak numbers in the process. Furthermore, there is the possibility that engines having wider powerbands can and do have multiple wave events to help cylinder filling. Make the powerband too narrow and peaky and you won't see that same cumulative effect.

Also wasn't trying to imply that it would only happen at very high racing only piston speeds either. I'm sure you're well aware that a larger displacement and/or very long and properly tuned intake system can affect VE, BMEP, increase cylinder fill, mass flow or whatever term you want to toss at it. And on the other side of the engine shrinking exhaust valve/port sizing and/or utilizing smaller or longer length primary's, sizing steps, 4-2-1's, various merge's and choke sizes can effectively allow a larger mass to be moved into the cylinder by reducing pressures on that side of the cylinder head. Of course quieter chambered muffler full length street exhausts can effectively piss much of those gains away but still allows potentially higher cylinder filling if it's tailored to avoid as much backpressure and velocity snuffing as possible during it's design phase.

All I was really trying to say is that shortening the cams timing or overlap events to bandaid a poorly designed cookie cutter induction and/or exhaust system is in fact still a bandaid all unto iteself. An engine is just a series of forced compromises from one end to the other but it helps to mitigate the bigger ones whenever possible to allow fewer and smaller bandaids being applied overall. And I surely understand that we only "get what we get" when working within a standardized rpm range using preselected market available shelf parts and just have to make do by adjusting other build parameters to end up at a happy medium by adjusting the powerbands sweet spot to match that particular application. But that still doesn't make it right or fully optimized to say the least. It all depends on the combination of parts, what's expected of them, and ultimately how much time and cash we spend.. to where we'll usually end up.
[/quote]



From my standpoint I do not in any way believe in wave tuning on the induction side I am a straight ram tuning guy and in that model VE is based on raw fill and closing point of the intake valve .... I believe this because I can calculate HP based on this model and it comes out right ... if I need more HP I can up the cfm or move the closing point of the intake valve out more ... now this just deals with peak HP .... the next part is low end HP and torque ... this is controlled by the fill from tdc to around peak valve lift ... if you plot out the needed cfm flow and the exposed valve flow at the same points most of the time you will find you are behind the curve on filling ... I tend to pick on one point and that is peak piston velocity only because it gives me a good target to try make better and the rest of the cycle start will just follow along ... now to have more exposure at this point you have to open the valve sooner and you can do this in two ways .. you can move the intake centerline to a tighter lobe center like David does .... the problem with this is you then are closing the intake valve sooner and giving up peak power or you can add duration so it starts sooner but then ends latter too ... or you do both ... you fix the closing point and add duration but put it all at the start and let lobe center fall where it will .. so more duration and little tighter lobe center ... the problem that comes up when you do this is with a tighter lobe center and more duration if you just match it on the exhaust side you get more overlap ..... again from my standpoint overlap is bad ... on the exhaust side I do believe in wave tuning and have seen good things from doing so but I do street cars and like you said a full exhaust system tends to kill it plus to tune an exhaust system will mean building headers and a lot of fussing about ... so most of the time I am building an engine that will use off the shelf headers ... I do my best to get the system to flow well enough to support the engine but that's all the tuning it gets ... is that leaving HP on the table? Maybe ... but it can't be a lot and if I need more it's just cfm and intake closing point to get it .... so why is overlap bad? With my untuned exhaust I am bound to have some pressure left so I am better off not letting it contaminate the incoming charge yet I need to open the intake soon enough to fill the cylinder ... this is a hard line to walk .... what I do is to never let the ex valve close after tdc I give it to within a few degrees of tdc to do my best to finish the exhaust cycle ... most people will say this is ending the cycle too soon and leaving to much exhaust gas ... not true ...we have gotten so busy looking at overlap we forget that the exhaust cycle starts at the exhaust valve opening and to get a better cylinder dump on the exhaust cycle I open the exhaust valve sooner than most .... so I am not giving up duration on this side either just moving it to sooner in the cycle..... what this gains me is less contamination of the charge at overlap low rpm and better exhaust gas dump at high rpm which gives me better high rpm power and carryover ..... so what I am getting is a wider power band and more flexible engine .. this is not a Band-Aid ...though I know it's a different way to approach it I feel it is more practical then trying to make it like a race car on the street and don't feel like I have given up anything

[Warp Speed]

From my standpoint I do not in any way believe in wave tuning on the induction side

Many will say that is exactly what will keep you from going further in the development of performance engines!

[HeinzE]

Scott,

Very interesting description of the way you approach the exhaust cycle timing. I have wondered about the relative merit of intake wave tuning also, but I have also been able to do a lot of dyno tuning with intake tract length changes and for sure can really affect the power and power band. My pet engine is a 350cc single, push rod, two valve, 11.78/1 CR, Peaking at 7,800 and making 40.4 Hp at the rear wheel with pk torque of 28.8 lbs coming at 5,700. The intake tract length is 12.2" from valve seat to atmosphere. Shortening or lengthening this by as little as 1" has a noticeable effect and will drop the power in each case without benefit to the overall powerband. From this I took it to mean that the wave tuning of the inlet was a reality and, in conjuction with my exhaust "tuning" of valve and port size and pipe length and sizing worked to clear and fill the combustion chamber during overlap and gave a head start on VE. The intake tract ID and CSA I sized to get the most inertia into the intake charge without chocking before pk rpm for best possible fill at IVC. From the results, the engine performs pretty much as penciled out and the "wave tuning" effects seemed to jibe with expectations.
However, as you describe, maybe things are not happening as I imagine and, or, if I altered the exhaust event the engine may run better. Since I have not been able to do this I can't know one way or the other. If I understood you correctly you don't feel the wave tuning of the intake has much merit?
And that tuning for wave interaction at overlap is not the best way to go. Please understand that I am not arguing or sugesting you're wrong...quite the opposite. I found your description well thought out and most interesting. In your engines do you always strive to eliminate the overlap window as much as possible? Does advancing the exhaust timing as you describe require you to treat the intake side differently? On engines that can run an open intake and exhaust do you think this approach is as sound as with engines requiring "streetable" exhaust systems. I found your post quite thought provoking.

Karl