S5 N/A power...
08-09-10, 08:12 PM
#26
rotarygod
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I adsolutely agree that for most applications it's a nonissue. Most people don't hit power levels high enough for it to be noticable. I actually run a stock air filter and box as I don't believe that a cone filter in the hot engine bay is beneficial and I used to have one installed.
The OP is mentioning 2 different afms. They are both flapper door style but the S3's is 4 sq in in and the S4 is 6 sq in. There's a difference there and the S3 is holding back power to a greater extent than the S4's is. The S5 cone style afm has less area than an S4 afm yet flows more due to it's smooth internal shape. The fact the cone is in the middle and air flows around it is irrelevant. Air flow is better. That's really the key. It's not so much how large is the opening but how well does air flow through it. Is there alot of turbulence? When there is laminar flow, which isn't going to happen through an afm, you can get tons of flow. Case in point being the restrictors on ALMS cars. They don't have plates but rather smooth venturis. The smallest point on the last rotary race car, the Courage C60 with the R20B 3 rotor installed, had a restrictor plate that was more or less equivalent to a 2-1/4" opening and it made about 450 hp. That's alot. To put that into perspective that's roughly the same total area as the S3 afm yet flows WAY more due to it's smooth profile.
Say NO to aux. bridging!
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Join Date: Jul 2002
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Posts: 3,862
I adsolutely agree that for most applications it's a nonissue. Most people don't hit power levels high enough for it to be noticable. I actually run a stock air filter and box as I don't believe that a cone filter in the hot engine bay is beneficial and I used to have one installed.
The OP is mentioning 2 different afms. They are both flapper door style but the S3's is 4 sq in in and the S4 is 6 sq in. There's a difference there and the S3 is holding back power to a greater extent than the S4's is. The S5 cone style afm has less area than an S4 afm yet flows more due to it's smooth internal shape. The fact the cone is in the middle and air flows around it is irrelevant. Air flow is better. That's really the key. It's not so much how large is the opening but how well does air flow through it. Is there alot of turbulence? When there is laminar flow, which isn't going to happen through an afm, you can get tons of flow. Case in point being the restrictors on ALMS cars. They don't have plates but rather smooth venturis. The smallest point on the last rotary race car, the Courage C60 with the R20B 3 rotor installed, had a restrictor plate that was more or less equivalent to a 2-1/4" opening and it made about 450 hp. That's alot. To put that into perspective that's roughly the same total area as the S3 afm yet flows WAY more due to it's smooth profile.
08-10-10, 02:33 PM
#27
Roto Racing Development
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i dont udersand all the fuss over afm and maf. the kid wants to run 14 add a turbo with a couple psi and afm and maf wont make **** worth of a diffrence
08-11-10, 12:09 PM
#29
I'm going to straighten a few things out there.
Air flow meters. Due to it's shape, the S5 afm flows more than the S4. Does either hurt power? Potentially. Above a certain power level. Keep in mind that when I ran flow tests with a couple of magnehelic gauges on my S5, I found that the AFM wasn't a restriction at all until full throttle above about 6000 rpm and even then only a very small one that was detected with a sensitive gauge. As rpms rise, that restriction gets higher and higher. At lower loads the rpms would have had to have been higher before any measurable restriction occurred. There is always a very small amount of restriction from the force that is required to pull the flapper door open but it is so little that it is of no consequence. If peak power occurs at 6500 rpm, from a functional standpoint the afm isn't hurting much. Power can still rise above 6K as we have seen many times. It may not be rising as fast though and at some point will really start to fall off fast. How high is that though? 9K rpm? 10K? Will it fall off before the intake runner tuning hurts the powerband?
Compression. Yes the S5 has a slightly higher compression ratio. Between about 9.0:1 and 11.0:1, any power difference at full throttle is negligable. The compression bump is a benefit at lower rpms and loads and decreases as load and rpms increase. Outside of this range and top end power goes down. Below this range, the entire powerband suffers.
ECU. The tuning between the S4 and S5 are so drastically different due to the intake manifold changes and effect of compression ratio on the low end/part throttle that it's hard to say how well things are going to work mismatched. I'm sure it will run fine but no matter what you are leaving power on the table if you aren't retuning it.
Intake manifolds. The S5 is superior. Forget what your eyes tell you and what you would logically think by visually comparing them. Logic would tell you that the simpler straighter runner S4 manifold would be better. However the S5 manifold is superior. Air is funny stuff. The whole point of the intake manifold change to the S5 style was a broader powerband. They got it and this is primarily where the top end power gain came from. What a dyno never shows is that are part throttle the combination of the intake manifold and higher compression has increased power on the S5 motor. Everyone always focuses solely on full throttle dyno charts which are a fraction of the total powerband and doesn't really tell you what is happening in the real world.
Air filters. Yes they are restrictive. However area is key as even a stock type of filter that is sized correctly is not a restriction. On paper the stock air filter is too small. On paper being the key. This is why going to another style may seem to give more power. The reality is though that going to a better flowing cone style filter is typically offset or more than offset by installing it in a hot air engine bay. If you want to install a cone filter, get it out of the engine bay. If you can't do this, then just insulate the back of the factory intake box. When I was doing those pressure tests with the magnehelic gauges, I found the air filter to be a smaller restriction than the afm! Remember the afm didn't really start to adversely affect power until above 6000 rpm or so. I don't really see the benefit from changing the air filter and I myself still even run the factory style paper element in my own car. On paper that cone filter may flow more and a static test may verify that it does. However if both filters can flow what the engine needs, any excess capacity isn't really all that useful which is why all that matters is what happens in the real world and not on paper.
Air flow meters. Due to it's shape, the S5 afm flows more than the S4. Does either hurt power? Potentially. Above a certain power level. Keep in mind that when I ran flow tests with a couple of magnehelic gauges on my S5, I found that the AFM wasn't a restriction at all until full throttle above about 6000 rpm and even then only a very small one that was detected with a sensitive gauge. As rpms rise, that restriction gets higher and higher. At lower loads the rpms would have had to have been higher before any measurable restriction occurred. There is always a very small amount of restriction from the force that is required to pull the flapper door open but it is so little that it is of no consequence. If peak power occurs at 6500 rpm, from a functional standpoint the afm isn't hurting much. Power can still rise above 6K as we have seen many times. It may not be rising as fast though and at some point will really start to fall off fast. How high is that though? 9K rpm? 10K? Will it fall off before the intake runner tuning hurts the powerband?
Compression. Yes the S5 has a slightly higher compression ratio. Between about 9.0:1 and 11.0:1, any power difference at full throttle is negligable. The compression bump is a benefit at lower rpms and loads and decreases as load and rpms increase. Outside of this range and top end power goes down. Below this range, the entire powerband suffers.
ECU. The tuning between the S4 and S5 are so drastically different due to the intake manifold changes and effect of compression ratio on the low end/part throttle that it's hard to say how well things are going to work mismatched. I'm sure it will run fine but no matter what you are leaving power on the table if you aren't retuning it.
Intake manifolds. The S5 is superior. Forget what your eyes tell you and what you would logically think by visually comparing them. Logic would tell you that the simpler straighter runner S4 manifold would be better. However the S5 manifold is superior. Air is funny stuff. The whole point of the intake manifold change to the S5 style was a broader powerband. They got it and this is primarily where the top end power gain came from. What a dyno never shows is that are part throttle the combination of the intake manifold and higher compression has increased power on the S5 motor. Everyone always focuses solely on full throttle dyno charts which are a fraction of the total powerband and doesn't really tell you what is happening in the real world.
Air filters. Yes they are restrictive. However area is key as even a stock type of filter that is sized correctly is not a restriction. On paper the stock air filter is too small. On paper being the key. This is why going to another style may seem to give more power. The reality is though that going to a better flowing cone style filter is typically offset or more than offset by installing it in a hot air engine bay. If you want to install a cone filter, get it out of the engine bay. If you can't do this, then just insulate the back of the factory intake box. When I was doing those pressure tests with the magnehelic gauges, I found the air filter to be a smaller restriction than the afm! Remember the afm didn't really start to adversely affect power until above 6000 rpm or so. I don't really see the benefit from changing the air filter and I myself still even run the factory style paper element in my own car. On paper that cone filter may flow more and a static test may verify that it does. However if both filters can flow what the engine needs, any excess capacity isn't really all that useful which is why all that matters is what happens in the real world and not on paper.
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