nmartin

From what I've read, the long smooth CAI inlet to the MAF yields HP. Also the cooler air yields HP, but I hate the filters. (I've done filter dp tests on K&N, stock, and Green filters and the stock filter does a MUCH better job of filtration at or BELOW the pressure loss of a K&N) Foam filters are just plain lousy at filtration. So I took a thermocouple and measured the air temp going into the stock airbox while driving on a warm GA afternoon. The air temp when moving is ambient outside air temp - no hotter. Only while sitting still did the temp start to climb, and fell quickly again when rolling. So the dyno results comparing CAI's to stock are junk unless they put a big 30 mph fan in front of the car. The MAF inlet issue, MAF/TB proximity issue, and the resonance issue could still yield some HP. The stock inlet position wouldn't be too good for the first couple seconds a drag race or autocross, but after a few seconds the air is cool in the stock config.

I was thinking about making a better filtering CAI by using the really short PR CAI pipe piece next to the TB, then running tube to the airbox and tube out of the airbox to a bellmouth behind the headlight. The length of tube between the MAF and the airbox would be about the same as the CAI pipe if I use the short PR pipe between the TB and the MAF, so I should get about the same resonance characteristics as the PR pipe. I could move the battery for more length if needed. A small scoop could deflect extra air up from the spoiler (next to the fog light) and help keep hot air from migrating over to the inlet. I think this would be a decent CAI with excellent filtration and none of the water issues or filter changing issues.

Comments from the wise ones?

 

Nismo87SE

I suggest measuring the peak MAF voltage. That will tell you which intake is flowing more air. Also you might want to check out these threads below.

http://www.sr20forum.com/showthread....take+power+CAI
http://www.sr20forum.com/showthread....take+power+CAI

__________________
91 Nissan Sentra SE-R: KYB AGX's, eibachs, prothane mounts, ES suspension bushings, addco RSB, FSTB/RSTB, CAI, JWT C2/ECU, 3in B-pipe, UR UDP, nitrous
Best ET: 13.57 @ 99mph

nmartin

Thanks - I did read those extensively. I found another thread that stated Mike's PR CAI was the old design that had the MAF up near the stock position. IIRC, he found that the closer the MAF is to the TB the more HP - and the new PR design is about 4" away (their new filter sucks ***).

So exactly how should I measure the MAF voltage, as in what pins on the connector? Measure pin to ground? Pin to pin?

nmartin

More notes -

The flow path in the stock MAF fixture is pretty bad. The passages are belled some, but not enough for upper rpm, higher flow conditions. I think a flanged bell mouth (one for the main,and one for the sensor) upstream of the MAF would gain some flow. Downstream of the MAF, the ugly flow needs at least 5 diameters to get somewhat smooth before entering the TB. Well, there isn't enough room in the engine bay for that, but the more length between the MAF and the TB, the smoother the flow EXITing the MAF and therefore more flow thru it. An eccentric exit bell ?

I am still figuring on how to get the MAF inlet about 10 diameters of smooth pipe. That's over two feet, and even without the battery in the way there isn't that much room. Then add a filter on top of that.

Also, the PR billet MAF adapter doesn't match the MAF inlet ID. That step might cause a small separation of the boundry layer, and maybe send vortices downstream into the MAF sensor under higher velocity conditions. That step should be smoothed or eliminated (not enough material to grind it away ***).