The basic question is as stated:
Would you give up hp and tq at lower rpm to gain it up top?

The reason I ask is based on the intake system I just installed on my car. There is a definite loss of low end torque with the larger and free breathing intake.

Looking at the dyno charts from the company, the difference is the torque curve.
Factory rises fairly quickly and levels off, and the new intake graph is a more steady and gradual increase.
The lines equal out at about 3400rpm, and the new intake then goes up while stock stays fairly level.
The charts show an increase of 9hp and 10ft/lbs increase, at the cost of power below 3500rpm.

Seems like it might be a good trade off for a car that spends a lot of time in the higher revs, but not as good for a commuter car.

Can anyone explain why the opened intake looses power? I have already crossed out heat soak as a factor. The new system eliminated 3 resonance chambers and tripled filter area. It is still fed by the factory snorkel for cool air.

8/17/2015 10:18:24 PM

I would not give up hp and tq at lower rpm to gain it up top, at least not for a DD... But this is my take on it.


Most street drivers don't tend to spend alot of time in the upper RPM band. When I want power, I want it right then and now. Now I know to some degree this is apples to oranges, but this is my own experience.

My old 944 with the SBC LT1 v8 swap made 326tq from 1,500rpm all the way to 4,500. It was the flattest torque curve with only +/-2 ft-lbs deviation until the somewhat inverse parabolic drop after 4,500 rpm. The car did feel like it fell flat on it's face in the upper rpm band (5,500-6k), but it always took off like a rocket. With mostly city driving, this was very ideal. I never really felt like I was in the "wrong gear." From a dig, the car felt like a beast.

My c6 vette was built with top end power in mind. See dyno below;



I'm not saying the c6 is slow, but having had a chance to DD it for a few months now, I feel like it should be faster. The butt dyno in the 944 was much more appealing than in my vette, even though it had less power. Maybe it's perspective; the difference in how the Vette accelerates from 2,200-4,500rpm is night and day compared to 4,500-6,000rpm. The 944 didn't really have top end power, so the low rpm acceleration felt (relatively speaking) faster. By the time i'm up in the "fun" zone with the vette, my car is approaching the speed limit. I never felt like I had that problem having fun in the 944... Every stop light was fun. It was fun feeling the pull. If I was in 3rd gear going 25mph, the car would still pull hard. You could just feel it. The c6 doesn't have that same sensation. If I want the c6 to pull, I better have my rpms near 4k and that means downshifting a few gears and enjoying a pull for half a gear. I know the gear ratios and power levels are different between the two cars, but the 944 had more of a "Fuck it, floor it!" mentality that the c6 is just missing.

I like torque, and I don't think I'd give it up just for top end power, especially for something street driven.



[Edited on August 17, 2015 at 11:22 PM. Reason : /]

8/17/2015 11:15:04 PM

for a sports car? hell yes.

for a commuter car? I'm not fucking with it one way or another, so whatever.

8/17/2015 11:41:55 PM

leave it alone bruh, just leave it alone. shit, mod your kid('s stuff) or something

8/18/2015 12:42:43 AM

yeah what do you use the car for.

A commuter i'd prefer the torque.

I mean how do you drive? basically you need to figure out where you want the power ? Do you redline it all the time? Do you launch it with some sort of mid range rpm launch (slip clutch or stall torque converter) if not then... no...

On my dailys 95% of the time i'm below 3500 rpm and thus would prefer the response be there for passing so i don't have to drop a gear for a simple highway pass.

8/18/2015 7:34:21 AM

^His Maxima is saddled with the shit-tastic CVT transmission.

All Maximas are

8/18/2015 8:14:33 AM

this thread is

also, probably some type of ecm tuning/intake resonance thing going on.

also, welcome to the gains of any NA engine bolt-on

8/18/2015 12:09:17 PM

I get over 3500 rpm getting on the highway, passing, and occasionally from stop lights.
With the cvt, either you accelerate slowly and keep the rpm at about 2500, or quickly and they are 3500-4000 the entire time to 60mph.
Merging or -80, the rpm sit about 4500 till at speed.
Just seeing how quickly it can accelerate (stoplight racing) it will sit at 5800rpm the entire time.

So far I'm not missing the power. If I mashed the gas previously from a stop traction control would kick in and shut everything down (not as bad as VW) but now I only get a slight chirp. By that point the car is already on its way up past 2800 rpm.

It is different feeling though, and that is what I'm wrapping my head around. That and the loss in power from the increased intake flow.

8/18/2015 12:13:23 PM

big picture (@arghx to chime in) methinks is that its not always about reducing pumping losses.

8/18/2015 12:51:22 PM

^ I agree! but I'm trying to figure out what voodoo is going on in the intake as well.
Pretty sure there is going to be some interaction with the VAIS (variable air intake system) which has two different actuators in the intake manifold.

8/18/2015 6:22:28 PM

more restrictive/longer/smaller intake = better airflow/velocity at low rpm

and then it impedes flow up top

8/18/2015 6:48:44 PM

So if you go to page 6 of my big technical ramblings thread I go into air induction system design pretty deeply. http://www.thewolfweb.com/message_topic.aspx?topic=617123&page=6 I am referring to the air piping leading up to the throttlebody for an n/a engine or the compressor inlet on a turbocharged engine.

There are three aspects here:

1) intake air temperature, which we will assume is similar although I haven't seen any data

2) Restriction across the air induction system--which we will assume is lower if it is performing as advertised

3) dynamic tuning effects--the likely factor here


So your Maxima has the high output version of the transverse 3.5 liter port injected V6. Unlike the cheaper Altima version it has the exhaust variable cam phasing (VTC) and two different actuators for resonance tuning. One actuator changes the length of the runners. Another actuator changes the volume of the intake plenum, the collector. This architecture is very different from the 3.5 liter longitudinal mounted engine used in say the later 350Z: that engine has exhaust cam phasing but has independent intake systems for the different banks.

Now recall that there are pressure waves that occur in the intake system. For our purposes there are two effects:

1) Intake air reflected backwards as the intake valve closes--air hits a wall and reverses direction

2) Intake air pushed back into the intake port as the intake valve opens during overlap. This one's a little harder to visualize so here's a diagram:



See that little "Pint" line? That's backflow into the intake port during overlap. If the intake valve opens before top dead center the piston is still rising. If sufficient exhaust gases remain in the combustion chamber and exhaust pressure is higher than intake pressure there will be backflow into the intake port as the piston rises. The backflow will create a pressure pulse in the intake port that can be timed to push air into another cylinder as its own intake valve is closing.


Keep in mind that the general rule of thumb is that shorter piping length (including induction system before the throttlebody) tends to result in more sharper peaks that fall off early. Longer piping length results in fewer peaks and better higher rpm breathing. The Maxima has an actuator that switches between runner lengths to get a broader torque curve.



The Maxima does NOT have an actuator to adjust the length of the intake pipe leading up to the throttlebody (air induction system). Its geometry is fixed. When you change that, you change the pipe tuning effects. Some engines do have a variable air induction pipe length. The Rx-8 is one of those - I covered it in my thread.

Now keep in mind that much of this runner length effect is related to the intake valve closing timing (the pulses reflected when the intake valve shuts). The overlap effect gets into valve timing and scavenging effects. That has its own set of optimization that needs to be done regarding cam sweeps. I've covered a cam phasing sweep in page 7 of my thread, in the context of fuel economy, but it works for performance as well. So the valve timing can be optimized in simulation and it can be tested on a dyno, preferably an engine dyno where port pressures and cylinder pressures can be sampled on a crank angle basis.

The plenum can dampen the pulses and/or provide a reserve of air that can be drawn in. The general rule of thumb on an n/a engine with 1 collector is that larger plenum volume = better for high rpm, smaller plenum is better for low rpm. So you've got an actuator that switches between the conditions.

There's a chance you could restore some of the lost low end torque if you adjusted the VTC tables to change pulsation effects and scavenging, and/or moved around the switchpoints for the variable runner length and variable plenum actuators.

8/19/2015 4:00:51 PM

Also, this is an open element style filter right? And the factory air snorkel is just sort of showering air on it, rather than a sealed airbox design like stock? That right there shortens the effective length of the pipe, in addition to the loss of any plenum like effects from removing the resonance chambers. A larger pipe will also have more static effect (less pressure drop) at higher rpm, because pressure drop increases exponentially with airflow. See page 6 of my thread for a chart.

Can you post/link to a picture of the system?

8/19/2015 4:18:30 PM

Great info. Do you mind if I copy it to another forum?

They dyno charts are linked as well from the manufacturer testing
http://www.r2cperformance.com/nissan-maxima-3.5-cold-air-intake-09-15.aspx

Before, and very dirty:


After and wiped down:


[Edited on August 19, 2015 at 8:05 PM. Reason : .]

8/19/2015 8:03:48 PM

Unfortunately Those are not well put together dyno sheets on the manufacturer site. They are busy and hard to read. And I really don't like that it started at such a high rpm for the pull. It is missing the scavenging area under 3000rpm which is heavily influenced by Exhaust VTC tuning for additional overlap. Chassis dyno operators are scared or unconcerned about low speed full load but I've seen OEM guys agonize over it and make big changes to optimize torque at 1500 rpm. If you've got a loading dyno, start at 1200-1500 and run to redline with the dyno brake ramp control. It gets a more consistent pull. You'll see pulsation and tuning effects a lot more.

You can link to the post or quote portions of it but I'm concerned it would be out of context if you put the whole thing there as it refers to a long post on my other thread. The part about static pressure drop is covered in the other thread for example.

[Edited on August 19, 2015 at 10:35 PM. Reason : Don't be scared to lug it]

8/19/2015 10:30:02 PM

In would edit the text for context.

The problem with this car on the dyno is the cvt. it has a 'manual shift ,mode, but will automatically kick down on full throttle and up near red line. I agree that their sheets aren't very good and it took some time to compare them side by side to get the numbers and range mentioned in my previous posts.

If my local shop does a dyno day I'll probably get strapped on just for kicks.

8/19/2015 11:02:45 PM

I'm pretty sure it will go full load at lower rpm without kick down in manual mode if you don't physically put the pedal all the way to the floor. It will take some practice to get there. If you look at the throttle signal through a scan tool and at manifold pressure you'll be able to figure out how to do it.

8/20/2015 7:38:53 AM

Eh wish I could edit my post... I said longer intake pipe means better high rpm, that was a typo. It's shorter runners. You can see that in the graph. You know what I meant.

8/20/2015 1:11:53 PM

Quote :

"he problem with this car on the dyno is the cvt"

8/20/2015 3:17:43 PM

8/20/2015 6:29:50 PM

8/20/2015 10:30:16 PM

can't make a ho a housewife

can't make a maxima a sports car

8/21/2015 1:35:40 AM

But the sticker on the glass says 4DSC, that means sports car....

8/21/2015 6:14:11 AM