At what RPM does the Variable "intake" open at on a 2005 6spd (is the same on the auto)? Out of curiosity is it the same as the 2003-2004 6spds and autos as well?

 

4 pages on a cut springs thread yet no one has input on a tech thread?

I am guessing the the variable intake opens around 5200rpm but not sure. Is there a way to reprogram the ecu to open it a a different rpm or manually take it a part and keep it open all the time? (yes I realize there would be a loss in the low end)

 

The G/Z/FX/M VQ35 is not a variable plane design like the Maxima/Altima VQ35 and Sentra/Altima QR25. The G/Z/FX/M intake manifold is quite the marvel in that it delivers better low/midrange power than the Maxima/Altima VQ35 and above 5500rpms, it breathes harder and longer with no need for variable resonnance chamber. The G/Z/FX/M intake manifold offers as much as 105% volumetric efficency. That's quite impressive.

On the G/Z dynos, you can see a bump up power occuring at 5100-5300rpms. On a Maxima/Altima VQ35, that bump is easily attributed to the butterfly valves opening up to the resonnace chamber. On the G/Z, there aren't any butterfly valves opening up to the resonnace chamber. What we are probably seeing is the manifold's natural resonance tuning design and variable exhaust cam timing at work.

Sometimes I wish we had a variable intake manifold just so you could hear that cool switchover sound. I installed a JDM variable intake manifold on my 96 Maxima and I got addicted to that switchover sound. It sounded very much like a VTEC system hitting the larger cam lobe.

As for manipulating the switchover RPM on variable intake manifolds, the factory tuning is always best. That's typically 4900-5200rpms depending on the car. Open it too soon and you kill low rpm power and open too late and you're not utilizing the ideal power curve. On my Maxima, I experimented with various switchover points on the dyno. I opened it at 4500rpms and saw an immediated 15whp/15wtq loss in power from 4500-5000rpms. I then set it at 5200 and the power held perfectly steady and was ideal.

 

Thanks Dave for that detailed reply. Much appreciated! I thought there was a VI just by the fact there is a bump around 5200 on dynos which is very similar to 00-01 Max.

PS Are you excited about that cut springs thread. It is into 4 pages. WooHoo!

 

Cut springs on any car is a no-no. I don't care if it's Grandma's Crown Vic, a Civic, or a G. It's a safety issue.

 

Good post daveb I was wondering the same thing myself about the engine (since I noticed the same feeling as gting).

well of the 4 pages aren't half flaming?

 

The spike is probably due to variable VALVE timing vs a variable intake. ...And at what point the valve timing changes, I've no idea...

 

There's also the extra chamber in the muffler that opens up somewhere in the higher RPM range.

 

DaveB, nice expanation. The only thing I'm confused about is the Maxima/Altima configuration. You said you opened up the butterfly's at different rpms (how you do that anyway?). and that 5200 was the right number. My 03 Alti opens up right at 4000 rpm, no question, and there's a noticeable bump in power as a result (as well as a great sound). Am I misunderstanding?

 

On my 96 Maxima, I had an OEM variable intake manifold that was only used on some Japanese and Middle Eastern Maximas or "Cefiros". As you know, the ECU controls the vacuum system that opens the butterfly valves. Since my ECU didn't have this system, I had to make my own vacuum and control system. The system included a vacuum tank, hoses, RPM switch, and solenoid. I also had a toggle switch wired in so I could open the valves at any rpm which made for easy experiments on the dyno. After dyno testing my car and other cars with the same intake manifold, a 5200-5300rpm switchover showed the best power and most linear power delivery. The US 00-01 Maxima had a similiar intake manifold on the VQ30DEK hence the reason for much of the power increase (190hp to 222hp). This system had a switchover at ~5000rpms. The 02+ Maxima/Altima VQ35s seem to vary the switchover rpm depending on engine temp and load. I've seen switchover rpms on the 02 Maxima range from 4300-4800rpms.

BTW, most people think the variable intake manifolds on the Maxima/Altima employee two different intake runner systems, a long runner system for low/mid range power and a short runner system for high rpm power. It's not true. Nissan keeps the intake runners long, but they add a resonnance chamber. At a predetermined rpm, the butterfly valves open the intake runners to the resonnance chamber. What ends up happening is the resonance in the chamber actually speeds up the air flow in the long runners hence making them behave has if they were short runners. It's simple, yet very effective.

 

More good info, Dave. Seems that as the years progressed, the lower they went on the butterflies. Mine open right at 4000, and the difference is undeniable.