Intake ports

[Anonymous-0]

why dont anyone talk about the mach index of a intake port?

 

[DAVE Thompson jr]

A speed shop uses those formulas for high rpms. Explain how it applies to antique tractors.

 

[PopinJohn]

Just curious
Did you mean mach as in the speed of sound?
Or did you mean match as in manifold to cyl. head port matching?
I did research several years ago with the speed of pulses in exhaust manifolds on turbocharged engines.
MikeS.

 

[Anonymous-0]

mach speed of sound . dave jr updraft carb needs velocity dont you think?

 

[Anonymous-0]

(quoted from post at 18:36:34 01/16/11) mach speed of sound . dave jr updraft carb needs velocity don't you think?

OK since I cant get to many to nibble . I was looking at crank stroke affects on piston speed . piston speed on airflow velocities then the csa and intake valve size for a specific head as to what rpm the head would be considered choked . .

 

[wi50]

Depends on the breathing dynamics of the engine. Say for example the allis, progressive fireing order on a siamesed port is going to be different than in another application, or how a typical 6 cyl would breathe. Couple those factors allong with intake signal and runner length and it gets complicated.

 

[wi50]

I've been working on a new intake manifold to change carbs on an engine, but I can only hope it works, no way to tell for sure untill it's tested. Then how a particular carb will act weather it's a Holley, BG or an Edelbrock each is going to have some slightly different charistics

 

[wi50]

It's been a lot of years agoe since I worked with intake design, runners, plenum and the exhaust system, but I alwayse felt that the exhaust was more important than the intake, as a good exhaust can help to cover up a limeted intake system.

As long as some people are thinking about the subject, I'd like to point out another factor and give something else to work on at the same time that is related to the intake cycle, likely overlooked by most. Or something to at least factor in that may be of greater importance when trying to figure when "running out of breath" will happen.

Maybe even more important than the intake cycle is the ehaust. A well designed exhaust (to a particular engine combination) will add or subtract torque, RPM range and power band. Take the same engine in the same situation (on a dyno) and make some changes to the exhaust and it will respond to them.

On a low speed tractor engine the results may not be as drastic as on one that is set up to run at higher speeds, and some engines are more prone to being sensative. Depending on the club, rules etc. manifolding restrictions play a large part in what you can and can't do, a typical 2 cyl JD won't notice the change that a tuned 6 cyl case would.

 

[Anonymous-0]

Cant get anyone to talk about the mach index of a intake port . I hear all kinds of people are wanting tech. articles in the magazines . This subject is about as technical as it comes.
Always willing to learn what others have found out about exceeding .6 mach.

 

[Crutch]

LOL, nobody buys a head based off of velocity. CFM sells, and thats also why most guys want the biggest valves they can squeeze in, not realizing what goes wrong.

FYI, when you start researching this, 690 fps is the max, but you will not reach that in this life time on a tractor head. Also there is mean flow, measured on a flow bench. Shoot for 250, about 330 is max, only reachable on ultimate heads like Pro Stock.

Not enough research has been done on velicity, with a "no short turn" heads. Even the pro's are not giving up any info on velocity with these type heads because they have no data, from what I have found.

 

[Anonymous-0]

Crutch I was looking at a 7 inch crank with a head of a csa a little over three inches could get into power reducing frequencies toward 2200 rpm and go subsonic at a rpm just below 3 grand.

 

[Crutch]

A body in motion wants to stay in motion. When it is forced to stop, it builds pressure. In this case air pressure. In other applications is it possible to build pressure above Atmospheric pressure at IVC. In low rpm applications it is a little more difficult since early tractor heads are low port heads.

Very small, high velocity ports will have an issue with pumping loses and turbulence.

Very large, high CFM ports will have issues with cyl filling and fuel falling out of suspension.

Formulas are usefull with setting choke points for rpm limits to keep tension loads in check and set the torque/hp curve in right place for gear ratios.

For instance, Joe puller heard that 300 cfm can be gotten out of X head, so he has to have that to feel competitive. What he doesn't know is that he has to turn 2000 more rpms to make any logical use of it. So he puts the monster head on and its a dog on the track. But, his head still flows more than somebody else's head. When he gets beat, the other guy is cheating. Go figure.

These are just my opinions. Do with them as you will.

 

[Anonymous-0]

(quoted from post at 11:15:21 01/17/11) Crutch I was looking at a 7 inch crank with a head of a csa a little over three inches could get into power reducing frequencies toward 2200 rpm and go subsonic at a rpm just below 3 grand.

If I was going to do advertizing to market a head it would be tested with the largest bore fixture my flow bench would support and numbers at high lift stated.

 

[Crutch]

You mean go Sonic at 2200? The data is for a well designed port. A sharp edge, guide protrusion or a pinch point can bring on a local sonic area and screw things up.

Fill in the blanks. Hope this helps.

LPV = Limiting Port Volume
RPM = Max. RPM for a Perfromance Engine
S = Stroke of the crank
B = Bore of the engine's cylinder
CA = Minimum Port Cross LPV = .00353 x RPM x S x B^2/CA Sectional Area in Sq.In.

 

[Anonymous-0]

been using
Piston Diameter : (Inches)
Valve Diameter : (Inches)
Engine RPM : (typically peak)
Engine Stroke : (Inches)
Maximum Valve Lift : (Inches)
CFM (@28" of water : (Inches)
Cross Sectional Area : (to figure CA click here

 

[Anonymous-0]

I meant transonic .

 

[DAVE Thompson jr]

Thanks I learned something today.

 

[Anonymous-0]

(quoted from post at 14:05:10 01/17/11) Thanks I learned something today.

I truely hate that. knowing the mach index can let you know what to do with intake opening and closings .The higher the value of the mach index the later the intake valve should be closed to increase and maintain volumetric efficiency.

 

[gtx1967jewison]

i love this stuff! remember the old chrysler cross-rams?!

 

[Anonymous-0]

Here is a ballpark formula for Minimal CSA.


mcsa=rpm*S*B^2/190000

so what i get is 2200 x 7 x 4.5^2/190000=1.64

No where limited from what I can tell, except I guessed at 4.5 bore. Also the constant might need to be adjusted for VE.

 

[Anonymous-0]

(quoted from post at 21:37:20 01/17/11) Here is a ballpark formula for Minimal CSA.


mcsa=rpm*S*B^2/190000

so what i get is 2200 x 7 x 4.5^2/190000=1.64

No where limited from what I can tell, except I guessed at 4.5 bore. Also the constant might need to be adjusted for VE.

Well guest crutch me and regular crutch were talking mach iindex not minimal cross section area.

 

[Anonymous-0]

Mitch, the MCSA is what sets velocity. There will always be a mcsa and at that point velocity will be the highest. Some say it should be the throat, others say futher back up the runner. In either case, at peak torque rpms, with velocity the highest, VE should be the highest. With it futher up the track, the thought seems to be port volume to feed the cyl after piston reaches bdc. Others think the velocity has to remain high until it passes the valve seat. Again, with the low port heads, who knows what you get into trying to make the fuel/air turn.

 

[Anonymous-0]

(quoted from post at 06:34:30 01/18/11) Mitch, the MCSA is what sets velocity. There will always be a mcsa and at that point velocity will be the highest. Some say it should be the throat, others say futher back up the runner. In either case, at peak torque rpms, with velocity the highest, VE should be the highest. With it futher up the track, the thought seems to be port volume to feed the cyl after piston reaches bdc. Others think the velocity has to remain high until it passes the valve seat. Again, with the low port heads, who knows what you get into trying to make the fuel/air turn.

http://www.v-eight.com/tech_forum/viewtopic.php?t=148
http://www.v-eight.com/tech_forum/viewtopic.php?t=148

 

[Crutch]

The cross rams used the lenth of the runner to time the reflected "finite amplitude wave" which bounces back and fourth and moves particulates with it. I think they set it to catch the 3rd harmonic, which helped fill the cyl at IVC at a specific rpm.

Join high rpms (high piston velocity) with high velocity intake charge, short (2nd harmonic) tuned intake ports and you end up with very high output. like indy or race bikes.