N/A AFM tune + Abuse + BHP predictions etc...
02-03-2016, 03:15 PM
#16
good luck.Don't slide off the beaten track! Read the post...
R
Last edited by 924srr27l; 02-09-2016 at 04:59 AM.
02-03-2016, 03:19 PM
#17
The math you did with the 951 AFM isn't apple to apples... on an NA car, you have engine vacuum on one side of the AFM and atmospheric pressure on the other. On a 951 you have a much larger pressure differential acting across the AFM opening due to the turbo cold side drawing through it. I also believe the spring is much stiffer to compensate for the larger flow volume when in boost.
Between the two...Does the N/A have 30? 40? % less area flow as it's not forced induction?
R
02-03-2016, 03:32 PM
#18
Rennlist Member
It isn't that simple of a relationship, you'd have to dust off the Bernoulli equation and have some data concerning the vacuum induced between the turbo and AFM. The takeaway isn't the numbers, it's that with an NA car, you are relying on the pressure difference between the atmosphere and the cylinder pressure (vacuum) to induce airflow between the outside world and your intake ports.
Whatever you can do to avoid impeding that flow allows you to fully utilize the engine's displacement. So things like an extrude honed manifold (is that a touchy subject still?) aren't hurting anything but... have you ever been stuck right behind a really tall person at the theater?
Whatever you can do to avoid impeding that flow allows you to fully utilize the engine's displacement. So things like an extrude honed manifold (is that a touchy subject still?) aren't hurting anything but... have you ever been stuck right behind a really tall person at the theater?
02-03-2016, 05:02 PM
#19
It isn't that simple of a relationship, you'd have to dust off the Bernoulli equation and have some data concerning the vacuum induced between the turbo and AFM. The takeaway isn't the numbers, it's that with an NA car, you are relying on the pressure difference between the atmosphere and the cylinder pressure (vacuum) to induce airflow between the outside world and your intake ports.
Whatever you can do to avoid impeding that flow allows you to fully utilize the engine's displacement. So things like an extrude honed manifold (is that a touchy subject still?) aren't hurting anything but... have you ever been stuck right behind a really tall person at the theater?
Whatever you can do to avoid impeding that flow allows you to fully utilize the engine's displacement. So things like an extrude honed manifold (is that a touchy subject still?) aren't hurting anything but... have you ever been stuck right behind a really tall person at the theater?
Let me guess your favourite subject.........The door ?
R
02-03-2016, 05:38 PM
#20
It isn't that simple of a relationship, you'd have to dust off the Bernoulli equation and have some data concerning the vacuum induced between the turbo and AFM. The takeaway isn't the numbers, it's that with an NA car, you are relying on the pressure difference between the atmosphere and the cylinder pressure (vacuum) to induce airflow between the outside world and your intake ports.
Whatever you can do to avoid impeding that flow allows you to fully utilize the engine's displacement. So things like an extrude honed manifold (is that a touchy subject still?) aren't hurting anything but... have you ever been stuck right behind a really tall person at the theater?
Whatever you can do to avoid impeding that flow allows you to fully utilize the engine's displacement. So things like an extrude honed manifold (is that a touchy subject still?) aren't hurting anything but... have you ever been stuck right behind a really tall person at the theater?
hich is exactly the same as the throttle body Inlet. That's got to of been a calculated.......
R
Last edited by 924srr27l; 02-09-2016 at 05:00 AM.
02-03-2016, 06:07 PM
#21
Rennlist Member
See comments...not trying to act like I have all the answers for tuning engines, but in this case we know the physics.
You mention here "Whatever you can do to avoid impeding that flow"
Are you referring to the afm flap ?
I mean literally anything that stands in the way of air freely flowing into the engine. Even a blank pipe poses a restriction technically.
So if I've got this right ? .....when the butterfly opens say a 1/4 the amount of vacuum and (25% of what it could be) the flap will also be (sucked ) partly open, and the ecu will be reading the butterfly Throttle position (TPS), also the flap position...and temp?
Engines actually draw the most vacuum at low-load conditions because the throttle is shut and there isn't much air allowed into the intake. And at WOT, the pressure inside the manifold is (ideally) equal to the atmosphere because the there is nothing between the atmosphere and the intake ports. The AFM is pushed open by the flow of air, not sucked open by the vacuum. The flow is a consequence of the vacuum of the cylinders aspiring to neutralize pressure, if that makes any sense. The flow loses energy when it has to resist the spring reaction (kinetic energy being stored potential energy in the spring) and it loses kinetic energy due to the physically smaller opening (google: pipe major loss. other recommended reading is the pressure head form of the Bernoulli equation. I'm a pipeline engineer for a living so I think it's an interesting read.)
Also, the TPS is not sending any data to the DME unless the throttle is 0% open or 100% open.
This continues all the way till 4500RPM when the flap goes fully open but the throttle butterfly might not be, but the flap nestles inside the afm and leaves a perfect square tunnel so where the restriction ?
See above
There is some resistance to open the flap, but surely a big four cylinder is going to make a fair amount of vaccum to open the flap with ease? and
Porsche would not of installed something and a size where it was borderline on being a restriction...
See above
Quite the reverse is Porsches trademark, every component is more than competent by a large percentage, not just a little...
And lastly many engines have a secondary flap in the inlet system which aids torque, it's a version of a variable inlet..where the smaller diameters increase the air speed, as opposed to a large bore where the velocity is slow but the volume big..
That's for tuning intake resonance, it doesn't impede flow...it increases apparent volumetric efficiency
You only have to look at the size of the trumpet on the Inlet airfilter pipe
Out from the box from memory it's 80mm OD, and at the end where the air comes in 60mm which is exactly the same as the throttle body Inlet. That's got to of been a calculated.......
It is port matched to the AFM. I modified mine to make it larger.
R
Are you referring to the afm flap ?
I mean literally anything that stands in the way of air freely flowing into the engine. Even a blank pipe poses a restriction technically.
So if I've got this right ? .....when the butterfly opens say a 1/4 the amount of vacuum and (25% of what it could be) the flap will also be (sucked ) partly open, and the ecu will be reading the butterfly Throttle position (TPS), also the flap position...and temp?
Engines actually draw the most vacuum at low-load conditions because the throttle is shut and there isn't much air allowed into the intake. And at WOT, the pressure inside the manifold is (ideally) equal to the atmosphere because the there is nothing between the atmosphere and the intake ports. The AFM is pushed open by the flow of air, not sucked open by the vacuum. The flow is a consequence of the vacuum of the cylinders aspiring to neutralize pressure, if that makes any sense. The flow loses energy when it has to resist the spring reaction (kinetic energy being stored potential energy in the spring) and it loses kinetic energy due to the physically smaller opening (google: pipe major loss. other recommended reading is the pressure head form of the Bernoulli equation. I'm a pipeline engineer for a living so I think it's an interesting read.)
Also, the TPS is not sending any data to the DME unless the throttle is 0% open or 100% open.
This continues all the way till 4500RPM when the flap goes fully open but the throttle butterfly might not be, but the flap nestles inside the afm and leaves a perfect square tunnel so where the restriction ?
See above
There is some resistance to open the flap, but surely a big four cylinder is going to make a fair amount of vaccum to open the flap with ease? and
Porsche would not of installed something and a size where it was borderline on being a restriction...
See above
Quite the reverse is Porsches trademark, every component is more than competent by a large percentage, not just a little...
And lastly many engines have a secondary flap in the inlet system which aids torque, it's a version of a variable inlet..where the smaller diameters increase the air speed, as opposed to a large bore where the velocity is slow but the volume big..
That's for tuning intake resonance, it doesn't impede flow...it increases apparent volumetric efficiency
You only have to look at the size of the trumpet on the Inlet airfilter pipe
Out from the box from memory it's 80mm OD, and at the end where the air comes in 60mm which is exactly the same as the throttle body Inlet. That's got to of been a calculated.......
It is port matched to the AFM. I modified mine to make it larger.
R
02-03-2016, 06:08 PM
#22
Race Car
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you should stop trying to be an engineer. Most of the guys "spewing nonsense" at you went through the schooling you clearly did not and earned the title. You make these postulations based on what appears to be a highdchool level knoweldge of physics and they dont make sense to an educated person. You lack basic understanding of how an ICE works.
This is a technical forum, meant for sharing facts. In that interest, les try and keep the uneducated and false speculation to a minimum ok?
The above comment is to Roger, not Michael; who is one of the educated people I am referring to.
This is a technical forum, meant for sharing facts. In that interest, les try and keep the uneducated and false speculation to a minimum ok?
The above comment is to Roger, not Michael; who is one of the educated people I am referring to.
Last edited by Dougs951S; 02-03-2016 at 06:27 PM.
02-03-2016, 06:31 PM
#23
02-03-2016, 07:03 PM
#26
you should stop trying to be an engineer. Most of the guys "spewing nonsense" at you went through the schooling you clearly did not and earned the title. You make these postulations based on what appears to be a highdchool level knoweldge of physics and they dont make sense to an educated person. You lack basic understanding of how an ICE TEA works.
This is a technical forum, meant for sharing facts. In that interest, les try and keep the uneducated and false speculation to a minimum ok?
The above comment is to Roger, not Michael; who is one of the educated people I am referring to.
This is a technical forum, meant for sharing facts. In that interest, les try and keep the uneducated and false speculation to a minimum ok?
The above comment is to Roger, not Michael; who is one of the educated people I am referring to.
TYPOS !
On what ballpark figure this Engine of mine will likely achieve on the Dyno? .... with most importantly all the stock Bosch Air Flow Meter, Coil, Dizzy and ECU etc...
Stick to the question..........
02-03-2016, 09:57 PM
#27
Three Wheelin'
Your posts aren't exactly exemplary... and a bit silly don't you think? (The irony of his post wasn't lost on me)
I'm actually pretty keen to see how well your engine goes. I've seen engines modified to 2.7 or 2.8 before but they were usually turbos so pretty unique as an n/a in a 924S. I wish there were more 2L 924 n/a's with 924 turbo heads, high compression pistons and ITB's in the world.
I hope you get an AFM to suit, rebuilt (if not new) and calibrated to your application. I don't know if you've mentioned doing that yet.
I'm actually pretty keen to see how well your engine goes. I've seen engines modified to 2.7 or 2.8 before but they were usually turbos so pretty unique as an n/a in a 924S. I wish there were more 2L 924 n/a's with 924 turbo heads, high compression pistons and ITB's in the world.
I hope you get an AFM to suit, rebuilt (if not new) and calibrated to your application. I don't know if you've mentioned doing that yet.
Last edited by J1NX3D; 02-03-2016 at 10:25 PM.
02-03-2016, 10:06 PM
#28
Addict
Rennlist Member
Rennlist Member
165 crank hp.
02-03-2016, 10:20 PM
#29
Rennlist Member
Gah, promised myself that would be my last post here...this will be it though...we can explain it for you, but we can't understand it for you. The AFM presents a physical restriction in the airflow, period. It doesn't matter that Porsche chose it. What else were they going to do, it was 1982, this was the best solution at the time. Remember CIS? we don't use that anymore either.
Your post after mine asked a lot of questions about flow...I think enough has been posted already to communicate that having a physical obstruction in the flow is not a positive, or even neutral, addition to the intake tract. If you want to ignore that in exchange for stubbornness that is your right. Nobody here is profiting from what we are telling you, you asked and this is what we have found by spending our own money and using our own reasoning.
Your post after mine asked a lot of questions about flow...I think enough has been posted already to communicate that having a physical obstruction in the flow is not a positive, or even neutral, addition to the intake tract. If you want to ignore that in exchange for stubbornness that is your right. Nobody here is profiting from what we are telling you, you asked and this is what we have found by spending our own money and using our own reasoning.
02-03-2016, 10:41 PM
#30
odonnell, you have the patience of a saint. 924 if you keep making all of these friends the only one left to speculate and ogle over your car will be the gent in the mirror with all the charm. Best of luck on finishing your build, hope it is everything you imagined.