Increase flow, 16v head, just looking for data
12-12-2003, 09:37 AM
#31
Rennlist Member
On the debate between increasing boost vs increasing flow:
If octane is not a factor (however it is for most of us), increasing boost (obviously this will probably require a bigger turbo) is a viable way of making power. When it comes to packing air into the cylinder, pressure will always win over temp. Remember, if octane is not a factor, the heat issue is not an argument.
However, there is a point of diminishing returns with increasing boost and too much flow restriction. The more pressure you try to force through too small of an opening (intercooler, head/valves), the higher the percentage of that pressure you will lose by the time it gets into the cylinder. If you then argue that this pressure drop causes a cooler charge, it will be a net loss (pressure wins over temp.) In the end, the turbo will have to work too hard for a possible reduction in power.
If octane is not a factor (however it is for most of us), increasing boost (obviously this will probably require a bigger turbo) is a viable way of making power. When it comes to packing air into the cylinder, pressure will always win over temp. Remember, if octane is not a factor, the heat issue is not an argument.
However, there is a point of diminishing returns with increasing boost and too much flow restriction. The more pressure you try to force through too small of an opening (intercooler, head/valves), the higher the percentage of that pressure you will lose by the time it gets into the cylinder. If you then argue that this pressure drop causes a cooler charge, it will be a net loss (pressure wins over temp.) In the end, the turbo will have to work too hard for a possible reduction in power.
12-12-2003, 02:10 PM
#32
Race Director
"Here's more along the lines of what it should look like...."
Tony's right on again. We're always faced with packaging and manufacturing concerns vs. pure performance specs. Ideally, you want equal-length intake paths from the throttle-body butterfly to each intake-valve. Sure, you might have equal-length runners, but the plenum length and flow path makes a difference too; as is the angle the air path has to bend in order to reach each valve.
Tony's right on again. We're always faced with packaging and manufacturing concerns vs. pure performance specs. Ideally, you want equal-length intake paths from the throttle-body butterfly to each intake-valve. Sure, you might have equal-length runners, but the plenum length and flow path makes a difference too; as is the angle the air path has to bend in order to reach each valve.
12-12-2003, 02:35 PM
#34
Rennlist Junkie Forever
Danno
Send me a PM and let me know when you're going to be around... I tried to call you a few times a few weeks ago... but never managed to get you.
Send me a PM and let me know when you're going to be around... I tried to call you a few times a few weeks ago... but never managed to get you.
12-12-2003, 04:25 PM
#35
Three Wheelin'
Join Date: Sep 2001
Location: Calgary, Alberta, Canada
Posts: 1,596
Likes: 0
Received 0 Likes
on
0 Posts
Originally posted by TurboTommy
If octane is not a factor (however it is for most of us), increasing boost (obviously this will probably require a bigger turbo) is a viable way of making power. When it comes to packing air into the cylinder, pressure will always win over temp. Remember, if octane is not a factor, the heat issue is not an argument.
If octane is not a factor (however it is for most of us), increasing boost (obviously this will probably require a bigger turbo) is a viable way of making power. When it comes to packing air into the cylinder, pressure will always win over temp. Remember, if octane is not a factor, the heat issue is not an argument.
When Octane is a limit, that's when it gets interesting. I actually experimented by increasing boost from 5500rpm-7000rpm to overcome the drop in torque a year ago. It didn't work, the increased heat caused detonation. What worked was advancing the timing up there, which decreased the TQ drop resulting in a flat HP curve. Bonus is EGT's went down.
BTW - Welcome back Danno.
12-12-2003, 08:40 PM
#36
Pro
Join Date: Sep 2003
Location: Boden, Sweden
Posts: 603
Likes: 0
Received 0 Likes
on
0 Posts
There are a some that says Intake Temps will affect reliability, but in the testing that I've done, I don't see Intake Air Temp affecting Exhaust Gas Temps significantly, if at all.
What worked was advancing the timing up there, which decreased the TQ drop resulting in a flat HP curve. Bonus is EGT's went down.
Tomas
12-13-2003, 03:30 AM
#37
Addict
Rennlist Member
Rennlist Member
Adding to my previously post, I would like to reduce the two scenarios to a question that can be thermodynamically calculated.
Imagine a cylinder head with a pressure drop across the intake valve of 0.1 bar @ 2.0 bar abs manifold pressure (case 1) and another where the pressure drop across the intake valve is 0.2 bar also @ 2.0 bar abs manifold pressure (case 2) both at 5000 rpm WOT. What is the needed manifold pressure in case 2 to deliver the same air mass into the cylinder? And most importantly what is the resulting air temperature difference in the cylinder in case 2 (with the increased manifold pressure) vs. case 1?
If it is lower, then it should be fairly obvious, that power can be gained by a slightly restrictive cylinder head relative to a free flowing head.
If nobody jumps on this exercise, then I will take it up at a later date, when I get time to rehash my thermodynamics and fluid mechanics.
I think it is important in the decision on whether or not to go for a 4-valve head.
Laust
Imagine a cylinder head with a pressure drop across the intake valve of 0.1 bar @ 2.0 bar abs manifold pressure (case 1) and another where the pressure drop across the intake valve is 0.2 bar also @ 2.0 bar abs manifold pressure (case 2) both at 5000 rpm WOT. What is the needed manifold pressure in case 2 to deliver the same air mass into the cylinder? And most importantly what is the resulting air temperature difference in the cylinder in case 2 (with the increased manifold pressure) vs. case 1?
If it is lower, then it should be fairly obvious, that power can be gained by a slightly restrictive cylinder head relative to a free flowing head.
If nobody jumps on this exercise, then I will take it up at a later date, when I get time to rehash my thermodynamics and fluid mechanics.
I think it is important in the decision on whether or not to go for a 4-valve head.
Laust
12-13-2003, 09:13 AM
#38
My intake manifold is indeed constructed by SFR. Tony G is right about the possible unnequal flow didtribution between runners. An flow test performed by a independent shop shows flow difference as much as 10% between the outher runnes (1,4) and the inner ones (2,3). SFR insist the runners flow within 1 and 2% difference. I hope that if this uneven flow condition exist does not cause any significant problem. My goal is not to extract the last ounce of performance. I just want a reliable engine with a descent power amount to cruise during weekends. If any one think that this flow condition can cause reliability problems, let me know. I can perform a porting job to the intake to minimize this condition. Your feedback is appreciated.
12-13-2003, 11:17 AM
#39
Pro
Join Date: Jun 2003
Location: Bjärred Sweden
Posts: 600
Likes: 0
Received 0 Likes
on
0 Posts
TurboCab,
unfortunately it will be very difficult to compensate assymmetry in the manifold with assymmetry in the porting. Porting will have varying advantage over manifold assymmetry depending on rpm, flow and pressure. Equalizing in a flow bench won't help since the conditions are so different.
Bengt
unfortunately it will be very difficult to compensate assymmetry in the manifold with assymmetry in the porting. Porting will have varying advantage over manifold assymmetry depending on rpm, flow and pressure. Equalizing in a flow bench won't help since the conditions are so different.
Bengt
12-13-2003, 11:38 AM
#40
Pro
Join Date: Jun 2003
Location: Bjärred Sweden
Posts: 600
Likes: 0
Received 0 Likes
on
0 Posts
Laust I think you are correct in theory. If you can pump up pressure and temp for the intercooler to increase it's efficiency and then lower pressure afterwards you will have taken out more energy from the air and thus increased density (just like the condensor in the AC except for condensation) but.. normally this would be to the expense of turbo efficiency.
According to MotoTune ( very nice articles) there is a gain in having a restriction near the valve to stop backflow, especially if it is increasing air velocity.
I am convinced that there is a gain to be had using a four-valve pent-roof design even if Porsche did not succeed at the time.
Bengt
According to MotoTune ( very nice articles) there is a gain in having a restriction near the valve to stop backflow, especially if it is increasing air velocity.
I am convinced that there is a gain to be had using a four-valve pent-roof design even if Porsche did not succeed at the time.
Bengt
12-13-2003, 03:00 PM
#41
Rennlist Member
I think some of you are making this more complicated than it actually is. In the naturally aspirated world, engineers are trying to achieve 100% volumetric efficiency (no pressure drop into the cylinders). They don't say: "well, if we get 95% VE, we'll get a gain in density from the slightly cooler charge." That would be a net loss. With turbocharging, the effect is the same, only magnified a bit. Whenever there is a pressure loss, you will have less moles of air that cannot ever be made up by the corresponding decrease in temperature (gas laws in your science book). You will always make more peak HP with more valve area/high flow head; although not nessesarily good cylinder filling at low RPMs.
You obviously gain alot more density through an intercooler, but if there are huge pressure drops through it you have to remember that you'll have very high temps starting out before the IC
You obviously gain alot more density through an intercooler, but if there are huge pressure drops through it you have to remember that you'll have very high temps starting out before the IC
12-13-2003, 03:32 PM
#42
Pro
Join Date: Jun 2003
Location: Bjärred Sweden
Posts: 600
Likes: 0
Received 0 Likes
on
0 Posts
Tommy,
in the naturally aspirated world engineers are trying to achieve above 100% VE.
The way to do this is to increase the density of the charge by means of increasing pressure coming from transformation of the kinetic energy.
In a supercharged engine you have the opportunity to cool the charge since the pressure and related temperature increase makes it possible to cool with ambient air.
Yes there are flow losses in the IC due to friction which cannot be recovered, but if you use the same IC at a pressure induced higher temperature, to get a better heat exchange, you can then, after an efficient nozzle, achieve a denser charge.
Read the articles on the Mototune site (link in previous post) about the myths of bigger hole being better, where the kinetics of filling a cylinder is explained.
Yes if the higher pressure reduces the adiabatic efficiency of the compressor there may be a net loss.
Bengt
in the naturally aspirated world engineers are trying to achieve above 100% VE.
The way to do this is to increase the density of the charge by means of increasing pressure coming from transformation of the kinetic energy.
In a supercharged engine you have the opportunity to cool the charge since the pressure and related temperature increase makes it possible to cool with ambient air.
Yes there are flow losses in the IC due to friction which cannot be recovered, but if you use the same IC at a pressure induced higher temperature, to get a better heat exchange, you can then, after an efficient nozzle, achieve a denser charge.
Read the articles on the Mototune site (link in previous post) about the myths of bigger hole being better, where the kinetics of filling a cylinder is explained.
Yes if the higher pressure reduces the adiabatic efficiency of the compressor there may be a net loss.
Bengt
12-13-2003, 05:54 PM
#43
Rennlist Member
Bengt,
If you read my posts closely, you'll see that you're not really contradicting anything I'm saying.
I'm aware of "increasing pressure coming from the transformation of kinetic energy" to achieve high VE. However, high power is achieved when this condition is met at high RPM, and in order for that to happen you cannot have a restrictive head/valves. If you do opt for the higher restriction method, the high VE will happen at a lower RPM, that's all.
If anyone of us should take that Mototune site as "the new rave" we should inform the F1 teams that they should stay away from high flow, big bore, large valve area, heads.
Intercoolers are a great thing but if you try to force too much boost and/or volume through them, there will be a loss in moles of air. It gets to a certain point where the pressure and heat on the inlet side rises much more rapidly than just in a linear fashion. The IC cannot make up for this. On top of that is the power robbing effects of the increase in back pressure, which also goes up greater than linear
If you read my posts closely, you'll see that you're not really contradicting anything I'm saying.
I'm aware of "increasing pressure coming from the transformation of kinetic energy" to achieve high VE. However, high power is achieved when this condition is met at high RPM, and in order for that to happen you cannot have a restrictive head/valves. If you do opt for the higher restriction method, the high VE will happen at a lower RPM, that's all.
If anyone of us should take that Mototune site as "the new rave" we should inform the F1 teams that they should stay away from high flow, big bore, large valve area, heads.
Intercoolers are a great thing but if you try to force too much boost and/or volume through them, there will be a loss in moles of air. It gets to a certain point where the pressure and heat on the inlet side rises much more rapidly than just in a linear fashion. The IC cannot make up for this. On top of that is the power robbing effects of the increase in back pressure, which also goes up greater than linear
12-14-2003, 01:15 AM
#44
Addict
Rennlist Member
Rennlist Member
Bengt,
Those were my thoughts too, including the A/C analogy with the exception of the liquid to gas phase transition. If the increased pressure decreases the compressor efficiency too much, then the effect may be negated or at least diminished. A factor that speaks for a 4-valve head is (as far as I know) its better detonation characteristics (center sparkplug and cooler valves). It could be interesting to “run the numbers” anyhow.
Yes, the MotoTune article was interesting, but since it was a carbureted case, I wonder how much of the effect was due to better fuel atomization and mixing from the increased velocity.
TurboTommy
There simply is no normally aspirated engine analogy to the suggestion of increasing the intake pressure, take more (heat) energy out via the intercooler and subsequent cooling with a restrictive intake.
Also remember that many of the design decision on race car engines are based on a myriad of regulations created for many reasons (competitiveness, political, cost, safety, etc.). This idea would certainly not work for race cars with limits on the boost pressure.
Laust
Those were my thoughts too, including the A/C analogy with the exception of the liquid to gas phase transition. If the increased pressure decreases the compressor efficiency too much, then the effect may be negated or at least diminished. A factor that speaks for a 4-valve head is (as far as I know) its better detonation characteristics (center sparkplug and cooler valves). It could be interesting to “run the numbers” anyhow.
Yes, the MotoTune article was interesting, but since it was a carbureted case, I wonder how much of the effect was due to better fuel atomization and mixing from the increased velocity.
TurboTommy
There simply is no normally aspirated engine analogy to the suggestion of increasing the intake pressure, take more (heat) energy out via the intercooler and subsequent cooling with a restrictive intake.
Also remember that many of the design decision on race car engines are based on a myriad of regulations created for many reasons (competitiveness, political, cost, safety, etc.). This idea would certainly not work for race cars with limits on the boost pressure.
Laust
