My flow bench construction project is complete and I have finally had a chance to use it to identify some of the restrictions in the intake of my 370 (VQ37VHR). The first project was to measure the pressure loss through a stock 370 intake system with the stock throttle body shaft vs a thinned throttle shaft. Picture of the throttle shafts is attached. Another test easily performed on the flow bench was measuring the pressure loss through various drop in air filters.
Assuming 100% volumetric efficiency for a 3.7 liter engine, the calculated air flow through the tb at full throttle and 7300 rpm is 238 cfm. However, adding more rpm, improved intakes and exhaust plumbing to the engine will add some additional cfm. I swagged the additional flow at 10%. and did the pressure loss tests at 262cfm for one throttle body. It is interesting to note the the R2C flow air filter reduced the pressure loss about the same amount as the thinned throttle body shaft. Both are effective.

Here are the pressure drops for each complete stock 370z intake configuration in inches of water:
Stock NAPA Gold air filter, stock throttle shaft: 11.09
Stock NAPA Gold air filter, thin throttle shaft: 10.23
R2C Black Hex air filter, stock throttle shaft: 9.81
R2C Black Hex air filter, thin throttle shaft: 9.04

It would be interesting to test the system with the post MAF tubes and /or a bored throttle body. If anyone in the DFW area has an aftermarket cold air intake or the tubes or throttle body to loan for a day, I would be glad to test any of them and post the results.

 

For the unaware, one atmosphere = 407.189 inches of water. So, the pressure drop of 11.09 inches equals a 2.7% loss, assuming swag is close. 9.04 = 2.2% loss.

I would hope there is lower hanging fruit than thinning the throttle shaft. It's nice to know the filter made a real, if small, difference

That said, great job! This kind of info is sorely lacking on this site.

 

It will be interesting to see if boring the throttle body reduces the pressure loss more than the thinned shaft. Of course both could be done to get the combined effect.

Probably the lowest hanging fruit on the stock intake system is the MAF tube diameter., but enlarging that complicates tuning.

 

If you have a "flow bench" why did you calculate the CFM?
I thought flow benches measure CFM at a specific pressure level? (in inches of water)

From what you posted, it sounds like you made a manometer.
What was the air density during your testing?

I like what you are doing and I'm trying to understand your results.

 

My flow bench (like others) measures air flow at a particular pressure across the test piece. This project was to identify the pressure loss of different air filters and different throttle shafts. I know from data logs on my engine that it is running at around 100% volumetric efficiency. So I calculated the cfm at 100% efficiency and 7300rpm, adjusted the air flow on the test piece to that amount then noted the pressure drop to achieve that flow.

My flow bench was built from the PTS Flowbench web site plans and uses a digital manometer. Some construction pictures are attached.

 

Oh yeah. Auotmotive ****