I am thinking they revised the lower plenum to allow more airflow to the front cylinders like you said, and that they could not mess around too much with the upper plenum because they want to be able to clear the engine cover and hood, so this lower plenum may add 5hp but we might see a drop in torque, just my insight on the matter

 

Jason from Performance Nissan has it on his car now and posted about it . Gained 8whp at the very top end . Move peak whp from around 6,250rpm to 6,650rpm .Trq was lost in low to mid range , about 7 to 9lb's of trq lose . Cant remember exact # but it close to what I stated . I think the main reason for the change was to get more air to front cyl.

 

The thread is here:
http://www.350zmotoring.com/forums/s...3&page=1&pp=15

So it looks like the new plenum gives 7 HP and about 5-7 ft lbs more above 6250 RPM. BUT ...below that, it loses about 5-10 HP, and 10-15 ft lbs (from 3000 RPM to 6250 RPM the original plenum gives better numbers).

It'll help for a track car that spends most of the time above 6000 RPM. For anything below that, it's weaker. Overall, a very interesting dyno and I'm appreciative that Jason put in his time to do this.

 

I would be interested see this lower plenum installed with crawford plenum and the TS ECU

 

What the heck..... so basicly the lower plenum would be pretty useless to us 03-04 owners since our redline is at 6600rpm. I wouldn't trade low-mid range power for gains above 6250rpm - it makes no sense. A plenum spacer is a much more useful in that it increases both power and torque throughout the entire rpm range!!!

I am guessing the new lower plenum is only useful in conjunction to other interior alterations and updated ECU on 05 6MT vehicles. From the data thus far this is not a very efficient bolt on mod for our cars.

 

Well that's disappointing. It's kind of what I figured though with the shorter runners. Clearly the lower manifold was designed for use with the revised cams and higher revving assembly. If you were to do this mod to a 03/04/05 auto or 03/04 6 speed, you'd have a slower car. The 05 6 speeds already come with the manifold and are tuned to make it work effectively.

 

From Jason's dynos looks like it's not worth the trade off for a shift of power into the higher rpm band for the pre '05s. I'd rather have usable torque. But still an interesting experiment nonetheless.