RSS Plenum
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What a shocker! And to think of all the butt dynos out there reporting they were able to actually feel increases in power. 
The way I read the results there is a noticeable drop in power in the mid range, less peak torque and an increase of only one peak hp with the plenum!
I’m no mathematician but performance numbers like these make the X51 kit look like a bargain.
The way I read the results there is a noticeable drop in power in the mid range, less peak torque and an increase of only one peak hp with the plenum!
I’m no mathematician but performance numbers like these make the X51 kit look like a bargain.
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Great thread. I'd like to pitch in some comments from my past experience in tuning naturally aspirated cars. I used to be a rabid E36 M3 enthusiast. I had a 97 M3 with the 3.2l obd II motor which put out about 210-215 rwhp (240 flywheel hp) on a Dynojet. I went thru a long and arduous process of clawing for extra horsepower - my goal was to match the output of the European S52 M3 motor which whose output was 321 flywheel hp or approximately 265 rwhp.
I did everything humanly possibly to the engine in terms of bolt ons - shorty/mid headers, cat delete, cat back low restriction exhaust, fan delete, ltw underdrive pulleys, larger intake manifold, larger intake, larger throttle body, traction control throttle body delete, fuel pressure regulator, larger fuel injectors, Shrick cams, software. I spent $$$$ to gain about 40 rwhp over 3 years.
While I did finally reach my goal, I found that along the way many mods produced no gains on their own or even lost power! The only sure bets were the mods which reduced drag on the motor - fan delete, ltw crank pulleys (ltw flywheel would do the same). Some mods made modest but appreciable gains - exhaust, cat delete, headers. Some mods made no real power difference or even lost power on their own - larger intake manifold, larger throttle body, cold air intake. However, the mods that made no difference on the intake side became beneficial when the volumetric efficiency of the engine was changed thru the cams and fuel system/software tuning.
The key is that these engines are basically just like any flowing system - take a freeway for instance. Opening up an extra lane on a highway for 2 miles is not going to increase overall traffic flow over a 20 mile span. The extra lane needs to cover the whole 20 miles to make a difference in flow. Sometimes opening up an extra lane for a short span actually worsens the traffic flow by introducing more turbulence! In other words intake mods usually make little to no gains on a n/a car unless the rest of the system has been changed/tuned to require additional intake flow.
I did everything humanly possibly to the engine in terms of bolt ons - shorty/mid headers, cat delete, cat back low restriction exhaust, fan delete, ltw underdrive pulleys, larger intake manifold, larger intake, larger throttle body, traction control throttle body delete, fuel pressure regulator, larger fuel injectors, Shrick cams, software. I spent $$$$ to gain about 40 rwhp over 3 years.
While I did finally reach my goal, I found that along the way many mods produced no gains on their own or even lost power! The only sure bets were the mods which reduced drag on the motor - fan delete, ltw crank pulleys (ltw flywheel would do the same). Some mods made modest but appreciable gains - exhaust, cat delete, headers. Some mods made no real power difference or even lost power on their own - larger intake manifold, larger throttle body, cold air intake. However, the mods that made no difference on the intake side became beneficial when the volumetric efficiency of the engine was changed thru the cams and fuel system/software tuning.
The key is that these engines are basically just like any flowing system - take a freeway for instance. Opening up an extra lane on a highway for 2 miles is not going to increase overall traffic flow over a 20 mile span. The extra lane needs to cover the whole 20 miles to make a difference in flow. Sometimes opening up an extra lane for a short span actually worsens the traffic flow by introducing more turbulence! In other words intake mods usually make little to no gains on a n/a car unless the rest of the system has been changed/tuned to require additional intake flow.
As I understand it, the tests you performed on dduncan's car were with a bone stock car with the stock exhaust? I also understand you are going fit a full AWE system (headers, cats, mufflers) to his car.
Assuming your exhaust gives the expected increases, this will mean that at full throttle, the intake will be flowing more air across much of the rpm band than with the stock exhaust. I'm simply wondering if the plenum might be more likely to show any increases when the intake system is being asked to flow more air than standard? Is this a test you intend to do?
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Having had some more time to digest the tests AWE have done, I have found one (very) minor inconsistency. It may be nothing and perhaps it's something Todd could explain in an instant. Anyway for what it's worth...
Day 1 - temp = 65F. Day 2 - temp = 78F. You would therefore expect that any results obtained on day 2 would be slightly lower than day 1.
This is borne out on dyno plot #2 where the car with plenum gives a 4BHP lower result on day 2 than day 1. No surprises here. However on dyno plot #5, the bone-stock car gives a 2BHP higher result on the hotter day 2. This is unusual.
Dyno plot #1 compares the bone-stock car to the plenum-equipped car on day 2 showing a zero HP increase at peak. If the day 1 numbers had been compared however, the bone-stock car would have given a lower result by 2BHP and the plenum-equipped car a higher result by 4BHP. This would have shown the plenum giving a 6BHP increase at peak. Almost as much as AWE's headers give on the plot on their site and a very different result indeed.
Food for thought? I don't know, but I'm interested in any comments anyone may have.
Day 1 - temp = 65F. Day 2 - temp = 78F. You would therefore expect that any results obtained on day 2 would be slightly lower than day 1.
This is borne out on dyno plot #2 where the car with plenum gives a 4BHP lower result on day 2 than day 1. No surprises here. However on dyno plot #5, the bone-stock car gives a 2BHP higher result on the hotter day 2. This is unusual.
Dyno plot #1 compares the bone-stock car to the plenum-equipped car on day 2 showing a zero HP increase at peak. If the day 1 numbers had been compared however, the bone-stock car would have given a lower result by 2BHP and the plenum-equipped car a higher result by 4BHP. This would have shown the plenum giving a 6BHP increase at peak. Almost as much as AWE's headers give on the plot on their site and a very different result indeed.
Food for thought? I don't know, but I'm interested in any comments anyone may have.
Last edited by Ian_UK1; Apr 19, 2008 at 06:58 AM.
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Gentlemen,
I posted my baseline dyno yesterday and I hope to have some more data tonight. My car is supposed to be dynoed again today, now with the plenum only as mods. Same as Duncan. I hope to have positive results.
I posted my baseline dyno yesterday and I hope to have some more data tonight. My car is supposed to be dynoed again today, now with the plenum only as mods. Same as Duncan. I hope to have positive results.
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This should be of help. I am glad to see you following through. I assume this is at an independent shop. Good luck, Gerry
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A few years ago I met some guys over at AWE while they were dynoing their 996 tts. Some of the results were disappointing to the owners. One of the guys (he is a great guy and on this board too), went back to his own shop and worked further on his car. He hoped to improve the results. He went back to AWE with his car post work and redynoed the car. To his dismay the results were worse. Now this guy REALLY knows his $hit. I don't believe his car was slower. What I believe is that, for better or worse, dyno testing is far from perfect. I think runs on a familiar street without shifting, say 3000 to 7000 rpm MIGHT be a better assessment.
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There is no more accurate testing method then a dynamometer. But agree with u in that ultimately its on the track that results are proven. Better to stay off the street.. hahaha... no need to risk the license.
Last edited by dduncan; Apr 19, 2008 at 03:33 PM.
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You know, I still believe that adding the Plenum to my car made a difference. Knowing that I'd get a full refund if it didn't make a positive difference, I went into skeptical- go back and read my waaay early posts on this elsewhere. Thinking it might be baloney, I was prepared for no impact.
But I really did feel a difference.
I just don't buy into this being nothing more than wishful thinking. Perhaps it made a difference to my car because I already had a chip and an exhaust? Whatever the case, I don't think I was nuts to say it made an improvement, and I'll be keeping my plenum right where it is.
For those who don't notice a difference, perhaps an exhaust needs to be mated to your system, to balance the increased air flow?
But I really did feel a difference.
I just don't buy into this being nothing more than wishful thinking. Perhaps it made a difference to my car because I already had a chip and an exhaust? Whatever the case, I don't think I was nuts to say it made an improvement, and I'll be keeping my plenum right where it is.
For those who don't notice a difference, perhaps an exhaust needs to be mated to your system, to balance the increased air flow?
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I have the plenum in my 997tt . My car has not been dynoed so I can't claim anything other than I do feel it has improved with TIME as the GIAC adapted .Is it wishful thinking? I don't know. I also have intake, intercoolers. headers, exahust .
The plenum was installed AFTER all the other mods had already been on the car.
I am considering future mods and amongst them are Turbo upgrades and AWE is one of several choices (OEM Gt2 Turbos are one choice too) but for now I am simply enjoying my car as it is . I would not rule out an RSS part or any other company as I am not married to any manufacturer but am choosing what works best in my car. If i like it I keep it. if not I take it off my car . I am not a mechanic or a technician either so trial and error and expense is part of this for me.
I do have a few questions though.
1) If the dyno is somewhat flawed . Is there a more accurate tool to measure and make claims ?
2) I do feel that most here view the stock plastic part as needing improvement. What are ALL the choices including the plenum as well as its competitors?
3) The dyno tests shown reveal a gap in the mid range . Can someone explain this ?
The plenum was installed AFTER all the other mods had already been on the car.
I am considering future mods and amongst them are Turbo upgrades and AWE is one of several choices (OEM Gt2 Turbos are one choice too) but for now I am simply enjoying my car as it is . I would not rule out an RSS part or any other company as I am not married to any manufacturer but am choosing what works best in my car. If i like it I keep it. if not I take it off my car . I am not a mechanic or a technician either so trial and error and expense is part of this for me.
I do have a few questions though.
1) If the dyno is somewhat flawed . Is there a more accurate tool to measure and make claims ?
2) I do feel that most here view the stock plastic part as needing improvement. What are ALL the choices including the plenum as well as its competitors?
3) The dyno tests shown reveal a gap in the mid range . Can someone explain this ?
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AWE may not have any more to say about any of this in public. The reprecussions of the testing already done will be far reaching as is.
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In fairness to RSS, I would like to see the results of their plenum mated to a high flow air box and headers but you still are left with restrictions in the OEM intake manifold and air flow meter. On the X51 kit, the air flow is improved stating with a twin snorkel high capacity air box, larger diameter sand cast intake manifolds, larger diameter air flow meters, flowed cylinder heads and larger diameter headers coupled to the PSE that is said not to improve performance but does offer less restriction when in sport mode. The X51 kit doesn't have the bottlenecks that the RSS plenum is left with.