Flow bench results

[Scotthatch]

I am wondering if figuring out a way to factor in flow numbers that we see by sucking on the Exh port ( with the whole Intake tract bolted on . with both valves open as the would be during overlap can shed some light on things?
Of course closing / sealing off the the test cylinder to simulate piston position would be nessary .

In my experience overlap is not the key to power ... I even had a cam that ended early to lower overlap and move the ex cycle out of overlap and it made great low end power and peak was as calculated .... I think a lot of times the mistake is thinking overlap is helping when it is really just early opening of the intake valve and valve exposure at peak piston velocity that is helping ...

Overlap is just a necessary evil! Lol

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 ...

[randy331]

that is except during the overlap period when a good tuned Exh system aided with some inertia tuning can really make for high VE numbers!

So just how high of ve is possible with both valves open and the piston close to TDC ?


Randy

[groberts101]

that is except during the overlap period when a good tuned Exh system aided with some inertia tuning can really make for high VE numbers!

So just how high of ve is possible with both valves open and the piston close to TDC ?


Randy

Wouldn't that be entirely dependant on the induction and exhausts inertial tuning?

Surely one affects the other.. and getting both optimized to work together for any particular application and rpm range is key to maximizing VE?

[Stan Weiss]

that is except during the overlap period when a good tuned Exh system aided with some inertia tuning can really make for high VE numbers!

So just how high of ve is possible with both valves open and the piston close to TDC ?


Randy

Randy,
How does someone measure VE for only a small section of the intake cycle?

Stan

[groberts101]

In my experience overlap is not the key to power ... I even had a cam that ended early to lower overlap and move the ex cycle out of overlap and it made great low end power and peak was as calculated .... I think a lot of times the mistake is thinking overlap is helping when it is really just early opening of the intake valve and valve exposure at peak piston velocity that is helping ...

I guess "key" may not be the best word to describe it.. but higher overlap sure seems to show it's potentially beneficial merits in larger quantities of unburnt and reignited fuel dumping out the exhaust systems of highly developed peak power combo's.

Maybe Warp can reply with his viewpoint on the subject.. but I'd have to guess that if nascar didn't have to worry about power restrictions/engine efficiency/fuel consumption(added pitstops) or safety concerns in the pits?.. they'd be belching fire out their tailpipes like many others do as well.

[mag2555]

I was wondering if there's a way to meaningfully integrate such flow numbers into the whole power picture?

[Scotthatch]

In my experience overlap is not the key to power ... I even had a cam that ended early to lower overlap and move the ex cycle out of overlap and it made great low end power and peak was as calculated .... I think a lot of times the mistake is thinking overlap is helping when it is really just early opening of the intake valve and valve exposure at peak piston velocity that is helping ...

I guess "key" may not be the best word to describe it.. but higher overlap sure seems to show it's potentially beneficial merits in larger quantities of unburnt and reignited fuel dumping out the exhaust systems of highly developed peak power combo's.

Maybe Warp can reply with his viewpoint on the subject.. but I'd have to guess that if nascar didn't have to worry about power restrictions/engine efficiency/fuel consumption(added pitstops) or safety concerns in the pits?.. they'd be belching fire out their tailpipes like many others do as well.

So your thought is that burning fuel in the exhaust system is a goal???

[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.

[groberts101]

In my experience overlap is not the key to power ... I even had a cam that ended early to lower overlap and move the ex cycle out of overlap and it made great low end power and peak was as calculated .... I think a lot of times the mistake is thinking overlap is helping when it is really just early opening of the intake valve and valve exposure at peak piston velocity that is helping ...

I guess "key" may not be the best word to describe it.. but higher overlap sure seems to show it's potentially beneficial merits in larger quantities of unburnt and reignited fuel dumping out the exhaust systems of highly developed peak power combo's.

Maybe Warp can reply with his viewpoint on the subject.. but I'd have to guess that if nascar didn't have to worry about power restrictions/engine efficiency/fuel consumption(added pitstops) or safety concerns in the pits?.. they'd be belching fire out their tailpipes like many others do as well.

So your thought is that burning fuel in the exhaust system is a goal???

More of a sign that scavenging affects mass flow through the engine by pushing excess fuel out the pipes. And when peak output is the goal, yeah AFR's well richer than what an OEM concerns itself with will always make more power.

[CGT]

An intake port may flow better backwards due to the pressure recovery that is improved due to the port shape instead of flowing to a more open chamber. On my Dart 215 thread I was flowing 315cfm forward and 285cfm backward and I was told the reverse flow was way high. I though that was a good number.

Why would you be flowing in reverse at max lift or max cfm on the bench?

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?

[Scotthatch]

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

[Scotthatch]

Why would you be flowing in reverse at max lift or max cfm on the bench?

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

[Erland Cox]

Gotcha, yea the exhaust SYSTEM pulling on the intake side during overlap at high RPM's like in NASCAR stuff really interest's me. Something else to add, i was just reading yesterday where one of the well known outfits in this business had said in an engine labs interview, flow the intake backwards (air on the exhaust setting) less flow is BETTER because that will help reduce reversion. Mark H.

I have done a lot of reverse flow tests and it is almost never lower in reverse... normal street parts are almost always 5 % higher in reverse

An intake port may flow better backwards due to the pressure recovery that is improved due to the port shape instead of flowing to a more open chamber. On my Dart 215 thread I was flowing 315cfm forward and 285cfm backward and I was told the reverse flow was way high. I though that was a good number.

That must be very good. What seat angles did you use and how does the edge of the intake valve look?

Erland

[Carnut1]

Why would you be flowing in reverse at max lift or max cfm on the bench?

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?

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

[Carnut1]

I have done a lot of reverse flow tests and it is almost never lower in reverse... normal street parts are almost always 5 % higher in reverse

An intake port may flow better backwards due to the pressure recovery that is improved due to the port shape instead of flowing to a more open chamber. On my Dart 215 thread I was flowing 315cfm forward and 285cfm backward and I was told the reverse flow was way high. I though that was a good number.

That must be very good. What seat angles did you use and how does the edge of the intake valve look?

Erland

45 seat, square edge on valve. It is an old testing valve with low margin. Thanks, Charlie