mid-lift flow
Moderator: Team
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bsfc9
mid-lift flow
hello, i would like to enquire about a quote from "secrets of a 740hp winston cup engine". could the statement "Actually the valve spends the least amount of time at the mid-lifts." be explained or clarified. i think most people would agree that the mid lifts make up most of the area "under the curve". thanks.
Damn it, I forgot to add that one to my "10 Engine Wives‘ Tales - Debunked" article
http://racingarticles.com/article_racing-56.html
"Actually the valve spends the least amount of time at the mid-lifts."
Exactly!
Actually I think my graph is still too generous to the mid-lifts, but you get the point.
Others argue the valve sees mid-lifts twice, well what they fail to realize is the valve does not spend as much time as they think because it's moving so fast. At the bottom of the lobe the valve has to be slowed down and stopped. At the top it must stop and change directions. If they had a Cam-Doctor(R) they'd understand.
Thanks, I'm glad you posted.
http://racingarticles.com/article_racing-56.html
"Actually the valve spends the least amount of time at the mid-lifts."
Exactly!
Actually I think my graph is still too generous to the mid-lifts, but you get the point.
Others argue the valve sees mid-lifts twice, well what they fail to realize is the valve does not spend as much time as they think because it's moving so fast. At the bottom of the lobe the valve has to be slowed down and stopped. At the top it must stop and change directions. If they had a Cam-Doctor(R) they'd understand.
Thanks, I'm glad you posted.
In Memory of Don Terrill
SpeedTalk Owner/Admin
SpeedTalk Owner/Admin
Flow #s are important all the way up but the least important are those high advertized flow #s .
For example if your max lift is .700" then the flow of a head starts when?
When the valve starts to open and stops when the valve closes right.
So the flow #s have to be as strong as possible from the moment the valve opens to about .650" and as long as the flow doesn't drop at max lift thats a good strong port.
Another thing to check is how much loss you have when the intake is bolted on and then the Carb or TB depending on setup.
Too many times I've tested heads with great hi #s but lost 10-25% flow once we bolted on the intake and carb.
For example if your max lift is .700" then the flow of a head starts when?
When the valve starts to open and stops when the valve closes right.
So the flow #s have to be as strong as possible from the moment the valve opens to about .650" and as long as the flow doesn't drop at max lift thats a good strong port.
Another thing to check is how much loss you have when the intake is bolted on and then the Carb or TB depending on setup.
Too many times I've tested heads with great hi #s but lost 10-25% flow once we bolted on the intake and carb.
Tom K.
www.tkrace.com
tkracehead@hotmail.com
I love motorsports because all other sports require only 1 ball!
Cheap...Powerful....Reliable...Choose only 2 of the 3
www.tkrace.com
tkracehead@hotmail.com
I love motorsports because all other sports require only 1 ball!
Cheap...Powerful....Reliable...Choose only 2 of the 3
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bsfc9
don, thanks you clarified that for me.
tom, also thanks for your response, but you mentioned that flow starts from the moment the valve opens and i do agree with that. why then do some start flow testing .300" lift? it seems that some(drag race?) head porters are not so concerned with low or mid lift numbers or even with a big peak high lift number, but are more concerned the the port does not back up or go turbulent. any comments from don would also be interesting. thanks[/quote]
tom, also thanks for your response, but you mentioned that flow starts from the moment the valve opens and i do agree with that. why then do some start flow testing .300" lift? it seems that some(drag race?) head porters are not so concerned with low or mid lift numbers or even with a big peak high lift number, but are more concerned the the port does not back up or go turbulent. any comments from don would also be interesting. thanks[/quote]
I used to work with Ray Barton (Hemi Guru over 25 NHRA records)
and we always started at .100" and went up to .850" but the flow #s that mattered were from .100-.800" and the smallest possible port size for velocity.
Without velocity the car falls flat .(On the dyno you make more HP but in the car it goes slower)
and we always started at .100" and went up to .850" but the flow #s that mattered were from .100-.800" and the smallest possible port size for velocity.
Without velocity the car falls flat .(On the dyno you make more HP but in the car it goes slower)
Tom K.
www.tkrace.com
tkracehead@hotmail.com
I love motorsports because all other sports require only 1 ball!
Cheap...Powerful....Reliable...Choose only 2 of the 3
www.tkrace.com
tkracehead@hotmail.com
I love motorsports because all other sports require only 1 ball!
Cheap...Powerful....Reliable...Choose only 2 of the 3
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Lasher
With respect to the not careing about flow under say .300 lift.....If you look at many large cams ..especially ones with 1.7 or larger rocker ratios and long durations ...you often times find the valve open from say .180 to .280 lift at TDC... The amount of real intake airflow during the overlap peroid is small compared to the amount of air that the intake will flow after the ex valve has closed...at that point the intake lift will be higher still....from then on to 70 or 80 deg ATDC the piston is really decending quickly and is allowing the intake port to fill the cylinder with high speed air...... as the piston moves past 90 deg and gets to the point of the intake lobe centerline you getting to max lift and dwelling at the high lift lobe area for sometime as the piston continues twords BDC allowing the highlift and midlift on the closeing side to continue to allow the coloum of air to enter the cylinder......at some point after BDC the piston will be moveing back up and chasing the valve closed....
Defining low/mid/ high lift might need some discussing......
I have heard some say that due to a zillion different ports and cams available that..... one could think of low lift area as being the lift from where the intake valve actually opens to TDC......That figure could be as small as
.say .020 lift at TDC on small economy cams to .300 + on giant cams....
Others may have a different idea of what each lift area might be defined as.....
Do you guys have any thoughts of defining these different lift areas ?
Defining low/mid/ high lift might need some discussing......
I have heard some say that due to a zillion different ports and cams available that..... one could think of low lift area as being the lift from where the intake valve actually opens to TDC......That figure could be as small as
.say .020 lift at TDC on small economy cams to .300 + on giant cams....
Others may have a different idea of what each lift area might be defined as.....
Do you guys have any thoughts of defining these different lift areas ?
Great post Lasher!Lasher wrote:one could think of low lift area as being the lift from where the intake valve actually opens to TDC......That figure could be as small as say .020 lift at TDC on small economy cams to .300 + on giant cams....
About 10 years ago I wrote a program that would put my Cam-Doctor data with piston motion data - looking at the valves relation to the piston was a real eye opener.
Right or wrong though, when people talk about high/mid/low lift, they're talking about dividing the lift in thirds.
Ok Lasher, you've got the low/mid lift point set, what about the mid/high lift point? We'll call it the Lasher Method
In Memory of Don Terrill
SpeedTalk Owner/Admin
SpeedTalk Owner/Admin
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Lasher
LOL.... Thanks Don....but I'm afraid I cant take credit for that idea....I read that from Harold Brookshire . I really dont know if that low lift area difinition was Harolds or someone elses .... But I read it from one of his posts.
Many people look at a lobe spec book and see what the lift at TDC is so they can get an idea of what P/V clearence they need.... but often dont use that info for their port data. Some cam mfg do better jobs than others at giving out that data.... Isky does adv dur , .050.100/.200/.300 and others just adv , .050 and .200....still other none at all.
hmmm.... Have to think more about those difinitions....
Many people look at a lobe spec book and see what the lift at TDC is so they can get an idea of what P/V clearence they need.... but often dont use that info for their port data. Some cam mfg do better jobs than others at giving out that data.... Isky does adv dur , .050.100/.200/.300 and others just adv , .050 and .200....still other none at all.
hmmm.... Have to think more about those difinitions....
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Lasher.
Hmmm..... I may end up rambleing here....
Ya know this low lift area is one that has all kinds of problems to it..... With respect to the intake opening you have the problems of an intake manifold that in most case has little or none to alot of intake manifold vacuum.... and with the piston approaching TDC there can still be some residual ex still in the chamber that looks at the ex port and sees some backpressure or at least stmospheric pressure and then looks at the intake and sees manifold vacuum ( negitive Pressure ) .... so where does it want to go.... liekly into the intake... ( reversion )... untill after TDC and the piston creates a depression tha the intake atmospheric pressure wants to fill.........
The low lift area on the intake closeing seems to have a simular problem with the valve still open late after the piston has dwelled at BDC and starts to accend....that if open long enough the piston could push the A/F back into the intake port.. ( reversion )....before the valve closes.....
On the exh opening you have a very hot turbulent high pressure ..granted a declining pressure but still high..... so when the ex valve starts to open it would seem that you would have a large amount of pressure release ( blowdown ) so that by time the piston dwells at BDC a fair amount of pressure has been released.....by the time of the ex lobe C/L the piston is riseing and the valve is all the way open allowing any remaining pressure and residuals to escape....but by the time the intake valve starts to open and during the overlap when both intake and exh are in the " low lift area "
your back to square one again....with the potential low lift problems.... and reading that statement by Jere Stahl about on a late closeing ex valve the possibility in a high manifold vac situation ( maybe haveing to lift in a turn ) of the piston decending and the exh being sucked right out of the exh port and back into the cylinder
..... That sure seems scary....
So it seems that the Ex opening is the only one that could do actual positive work at the low lift area...... It would seem improbable in 99.9 % of most situation for ex back pressure to be so great as to impede the initial blowdown escape of pressure....
Darn low lift flow 3/4 of the time is a PITA... LOL.
This sort of has to do with my skeptism of the " scavaging " thing going on.....
Mid/ high lift flow.... definition.....hmmmm........ perhaps it's the point where on the intake opening side .... where after the ex valve has closed and the piston is decending creating that strong initial pull prior to 90 deg ATDC through to the point where the where air flow stream must maintain it's momentum without the aid of piston movement...... so depending on stroke / rod length / cam timing ect maybe 40-50 deg ATDC to 60-50 deg BBDC.?? Heck I dont know..... So many variables.....Does this make any sence ?..... BTW I did just make this one up. LOL
Ya know this low lift area is one that has all kinds of problems to it..... With respect to the intake opening you have the problems of an intake manifold that in most case has little or none to alot of intake manifold vacuum.... and with the piston approaching TDC there can still be some residual ex still in the chamber that looks at the ex port and sees some backpressure or at least stmospheric pressure and then looks at the intake and sees manifold vacuum ( negitive Pressure ) .... so where does it want to go.... liekly into the intake... ( reversion )... untill after TDC and the piston creates a depression tha the intake atmospheric pressure wants to fill.........
The low lift area on the intake closeing seems to have a simular problem with the valve still open late after the piston has dwelled at BDC and starts to accend....that if open long enough the piston could push the A/F back into the intake port.. ( reversion )....before the valve closes.....
On the exh opening you have a very hot turbulent high pressure ..granted a declining pressure but still high..... so when the ex valve starts to open it would seem that you would have a large amount of pressure release ( blowdown ) so that by time the piston dwells at BDC a fair amount of pressure has been released.....by the time of the ex lobe C/L the piston is riseing and the valve is all the way open allowing any remaining pressure and residuals to escape....but by the time the intake valve starts to open and during the overlap when both intake and exh are in the " low lift area "
your back to square one again....with the potential low lift problems.... and reading that statement by Jere Stahl about on a late closeing ex valve the possibility in a high manifold vac situation ( maybe haveing to lift in a turn ) of the piston decending and the exh being sucked right out of the exh port and back into the cylinder
..... That sure seems scary....So it seems that the Ex opening is the only one that could do actual positive work at the low lift area...... It would seem improbable in 99.9 % of most situation for ex back pressure to be so great as to impede the initial blowdown escape of pressure....
Darn low lift flow 3/4 of the time is a PITA... LOL.
This sort of has to do with my skeptism of the " scavaging " thing going on.....
Mid/ high lift flow.... definition.....hmmmm........ perhaps it's the point where on the intake opening side .... where after the ex valve has closed and the piston is decending creating that strong initial pull prior to 90 deg ATDC through to the point where the where air flow stream must maintain it's momentum without the aid of piston movement...... so depending on stroke / rod length / cam timing ect maybe 40-50 deg ATDC to 60-50 deg BBDC.?? Heck I dont know..... So many variables.....Does this make any sence ?..... BTW I did just make this one up. LOL
Cam Events
This whole thread has reminded me how little attention the Exhaust closing and the Intake opening get - probably justified.
Lasher, how about the fact that airflow numbers vary depending on whether the valve is opening or closing (Hysteresis)?
Lasher, how about the fact that airflow numbers vary depending on whether the valve is opening or closing (Hysteresis)?
In Memory of Don Terrill
SpeedTalk Owner/Admin
SpeedTalk Owner/Admin
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Lasher.
You nailed it.... Thats the problem with trying to define something that is as dynamic as this subject....... The low lift one is easy if you use TDC as a fixed refernce since no matter how small or large the cam they all still have a TDC.
But the high lift ...well thats a far more dynamic equation..... a % or certin lift within a given lobe could be used also...... But every engine is going to react differently how the cam dictates the valve movement and therefore the air movement..... The coluom of air must react in someway to the
change of air movement VS change of cam motion and what the engine geometry will allow.I tried to have some example of that in there but it's not really someting easy to pin down as it's mighty hard to look into a running engine and see where the air is slowing down it's rate of filling the cylinder . But it does address various lobes from small to large as they all at seat timing open BTDC and close ABDC and most stroke/rod combos will be creating a nice depression by 70 deg ATDC..... but that second part of is alittle more suspect with respect to air col momentum ....
No doubt it's far to cumbersome or esoteric as a definition as it's mostly theoretical anyway....
Many people consider the duration @ .200 to be the " High Lift " area....but even that leaves alot to be desired with respect to the various lobe heights.
Do you think that cutting the lobe up into thirds is valid ? or something else ?
But the high lift ...well thats a far more dynamic equation..... a % or certin lift within a given lobe could be used also...... But every engine is going to react differently how the cam dictates the valve movement and therefore the air movement..... The coluom of air must react in someway to the
change of air movement VS change of cam motion and what the engine geometry will allow.I tried to have some example of that in there but it's not really someting easy to pin down as it's mighty hard to look into a running engine and see where the air is slowing down it's rate of filling the cylinder . But it does address various lobes from small to large as they all at seat timing open BTDC and close ABDC and most stroke/rod combos will be creating a nice depression by 70 deg ATDC..... but that second part of is alittle more suspect with respect to air col momentum ....
No doubt it's far to cumbersome or esoteric as a definition as it's mostly theoretical anyway....
Many people consider the duration @ .200 to be the " High Lift " area....but even that leaves alot to be desired with respect to the various lobe heights.
Do you think that cutting the lobe up into thirds is valid ? or something else ?
Valve Lift
100% of the people I know think this way. Maybe you travel in more creative circles. Can I join?Lasher. wrote:Do you think that cutting the lobe up into thirds is valid ?
In Memory of Don Terrill
SpeedTalk Owner/Admin
SpeedTalk Owner/Admin
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Lasher
" Can I join "...you ask ? LOL.... Looks to me like you are already a lifelong charter member of the " Think Outside The Box " mindset. Your racing history and this site are proof of that...... But as you know sometimes looking outside the box can get one in trouble.....and every once in a while you'll see something that everyone else missed..... I wouldnt want to live there but aint afraid to visit there now and then...... It's hard to succede if you are afraid of failing.... And lessons learned no matter if the task was simple or very difficult are still lessons learned.... and all learned things are good.