s2000Junky

This is the vac gauge I use. It plumbs right into the nipple of intake. It has a vac reading on side and a re set button. You can see if any/how much vac is pulled. I go WOT on the street so its real world, then check gauge. I do this at all rpm points until I see it pulling vac or not at that rpm to see where restriction point is. As mentioned previous filters I tried started pulling vac at 7k rpm. Bellow is the filter I tested/now use to insure no restriction- vac. Notice the measurements. It just barely fits in the stock gutted factory box. It probably has 1/3 or better the surface area over the stock cone filter, and that's no small filter. The stock size KN drop in filter pulled no vac either, but that was without use of a velocity stack.


This rather common shape/size filter I tested pulled vac at 7k along with the Comptech foam filter of similar shape/size

flanders

How much vacuum did you see?

s2000Junky

-8 to-10

s2000Junky

Considering the trial and error I went through with these filters, im really curious if the 4" short ram you tested which made the most mid range but fell flat at peak rpm was actually pulling a vac/filter restriction because the pipe config actually flowed better putting more duty on the filter in that rpm range. Its interesting that it actually made more mid range power. That very well could have been a factor of pipe tuning, but part of me wonders now. The way to have tested that theory of course would have been to eliminate the filter and do another run, in hindsight.

flanders

I'm guessing that's in millimeter water, so not much restriction but worth noting.
I think I'm using a similar CT filter (Icebox) that you mentioned with 4" hose to the airbox and I can notice 1-2kPa (10-20 mmH2O) vacuum close to redline.
Think it was similar with just bare velocity stacks and 4x51mm throttle bodies though so not really sure were the restriction is.

s2000Junky

Just for reference the s2000 typical idle range is -20 -22 for whatever that's worth. My feeling is pulling any amount of vacuum is significant if the goal is to improve flow performance from stock. -10 is something for sure, however I cant say what that equals in whp lost when occurs. Stock pulls no vac, and some have reported to have seen positive pressure waves at around 1/2psi, which I have witnessed on my own psi gauge. I no longer run a pressure gauge since removing my Superchrager, but I might hook it back up for shits and giggles.

flanders

You could always monitor the stock MAP sensor via the OBD-port, refresh rate is not the best but might be enough if you only log RPM and MAP.

liquid_helix136

-8 to -10 vacuum is significant for sure.

To think of it from another perspective, it would be like running 5psi of boost if stock was 10psi (not exactly, but same concept). Obviously the more load you can place on the engine, the more performance you will obtain. However I'd be surprised if 0psi or any positive pressure was possible, unless manifold pressure measurements are different than intake tube pressure measurements.

When I was running my SOS kit without the blower, just the aftercooler, the boost gauge was still installed, and vacuum would drop to around -8mmHg near redline and the car DIED up top.

Right now with just the stock intake arm, no airbox, my datalogs show a solid -3mmHg across the rev range. Increasing to 0psi or even positive pressure would be phenomenal however, and surely would increase power.

s2000Junky

Not surprising you saw vac with your aftercooler still installed N/A, that's quite an obstruction. Ive had to run this way in past too so I know how much of a dog the engine feels in this config. Interesting you noted -8 vac in that state. If vac is vac/apples to apples, that would verify a significant measure in power loss. In stock form though I measure 0 easily after about 35% throttle opening which happens to be when the stock ecu goes into open loop, not sure if that was intentional (probably was) or an arbitrary coincidence). Based on my tuning tinkering and what I see the vac/oem fuel tuning do through data logging, there is fuel enrichment/open loop when vac subsides starting at -5 into 0 pressure. that is the stock fuel enrichment point. Positive pressure sweeps have been seen N/A as well, 1/2psi possibly near 1psi in some cases. I actually had a gauge with a boost recall button that I could go back and see what was going on.

At WOT or 35%? throttle opening and above, the pressure between the manifold and intake tube should be equalized/same. Its all based on how far that TB is open. If the filter doesn't breath well enough for what the motor wants at that rpm (cfm goes up with rpm) then its effectively acting like putting another valve/closed TB in front of the intake tube and you start pulling vac again. There is a relationship/fight in essence between what the motor wants at a given rpm and throttle opening and what the end of the straw ( intake tube/filter) can allow it to eat.

Id say to anyone, if they want to see if they are getting the full meal deal out of their custom or off the shelf intake, plumb one of those vac gauges in the intake tube and see if you pull a vac or not. Their primary use was to tell you when it was time to clean or replace your filter. This is a critical part of getting the most out of the motor, and obviously overlooked. Nothing like spending thousands on bolt ons, even good sounds ones, only to find the filter is undersized and squandering a portion of it.

flanders

10 mm H2O = 0.014 PSI
But I'm guessing you are referring to inch Hg then, stupid murrican units..