Hey guys,

This thread
https://my350z.com/forum/na-builds/4...enum-test.html

and Phunks new plenum
https://my350z.com/forum/forced-indu...or-my-car.html

had me thinking about plenum volume on FI cars.

So we have all seen Tony from MD's plenum spacer data showing that the 5/16 made the best hp over the 1/2" and the 3/4" actually lost power. But that was on some weaksauce NA motor. I mean who cares about NA!

Then you look at Sgsash and Phunk's tests. Sgsash made 15 hp more (336whp is pretty sick for a NA DE) just by allowing the runners essentially limitless air and Phunk's new plenum is almost 2x the magic "plenum volume should be at least the same volume as the motor' theory. SP seems to make very solid power with it...

So whats the deal with adding plenum volume through doubling up spacers. You can get 2 blox spacers for a total of 1.25" for under 200$.

Rough estimate
5/16" MD spacer alone only adds 0.75L
5/8" spacer adds 1.5L
2x 5/8 spacers adds 3.0L

Assuming they fit (solid motor mounts to lower the engine), how would this effect a CAMMED boosted car? No regard to off boost performance.

The general rule is that the bigger the plenum volume, the more right shifted the power curve gets.

I've search the webs but couldnt find what I was looking for. I know Supra guys musta played with this but my search terms must be too vague.

Ideas?

 

I wish dynapacks would die already.

I remember awhile ago when SFR was doing NA testing on their twin plenum design, they had one model that actually lost power on NA. Im not an engineer or I would have more to contribute to this thread.

 

The biggest consideration when making an intake manifold is the length of the runners. The length of the runners depends on the power curve you are trying to achieve

 

I *think* that there would be diminishing returns beyond the magic point you specified with a trade off in decreased throttle response. If the turbos can maintain plenum pressure, regardless of absolute volume, then I think other factors will be more important in terms of power production.

Wouldn't be too hard to put to the test I suppose.

 

one thing i read is that larger plenum volumes allow for better 'smoothing' of the air.

had SP done a before and after, that woulda solved everything. I;ve only seen those SFR dynos for their dual TB manifold. I've never even seen a pic of Tim's single TB manifold.

again, I am not making a manifold, I am wanting to increase the overall volume of the stock one.

 

In my brief foray into crude plenum r&d (testing baffles), I found that under low velocity, low pressure conditions, mechanical factors affected mass air flow (using MAF sensor measurements in runners) much more so than at high pressure/velocity where it seemed that the only thing that became singularly important was the pressure (and temperature of course, but that was constant).