GPA951s

So I built a cold air box. Basically on the opposite side of the car where the factory location is. Being a track car my washer bottle is gone. Built a alu box. Out of that box I have a 2-1/2” alu pipe going to the factory air meter ( car has to be. “ stock” per PCA racing rules.)
anyhow, no question I am getting cooler air and there is no power loss or any issues down low. However at the track last week the car was “ hesitating” above 5000. At sustained WOT. Didn’t have the chance to go back to the way it was but would a 2.5 tube with two 15 degree bends in it that is about 16 inches long hinder top end? If so would a 4” x 2.5” oval pipe do the trick? I only was basing the 2,5 off the fact the factory plastic has spots where it’s smaller than that and about the same length..
come on engineers… appreciate your input!

V2Rocket

If you're still running the factory AFM it's not going to be a restriction.
However it'd be interesting to look at a wideband O2 sensor if you have one during those stints - at WOT the DME ignores the AFM signal and just dumps fuel, estimating how much air is coming in (since the flapper door isn't working at that moment).
Might even be possible that your new intake, freer flowing than the stock snorkel, could cause the AFR to go lean (since the DME hasn't changed how much fuel its dumping but you might be allowing more air through).

GPA951s

Lol. I was STARRING at the wideband on the straights… 11. Almost solid. Once in a while I’d see a 10.8 blip… but could of swore it was a touch leaner than that before… and my tailpipe used to be golden brown and now it’s a little darker…. I have a fuel pressure gauge but it’s useless under the hood.. getting a remote one soon.

jerome951

Glen, I think you answered your own question. If you weren't seeing higher-than-normal AFRs, the hesitations likely weren't due to your new intake.

GPA951s

ya know, sometimes after doing hours of fabrication, and things didn’t work out QUITE the way we planned… we hope there is something we missed… hence the post.. but it just takes someone to confirm what I was already suspecting..crap… you’re right..
well new plan, cut the tube lengthwise. Add 2” of flat top and bottom to make a 2-1/2 x 4-1/2 tube and try that… good thing I just purchased more aluminum filler rod..
thanks man!!

jerome951

Do you have cool air being ingested by your new intake or pulling from the hot engine bay? If you're going to modify some more, may as well address that potential issue.

Oh, and what filter are you using? Stock filter housing or aftermarket. Could the filter be a restriction?

GPA951s

They say a picture is worth 1000 words. And this is the same air filter that I was using.. the only thing I didn’t do was take my blinker out and open up the back to jam air into the box

chartersb

F = πPr4 / 8nl

GPA951s

Yea…F=. The biggest F’n pipe you can fit..

Mike Goebel

This kid can explain it easily.


Mike G.

fast951

Under WOT the DME does use the signal from AFM. The O2 sensor signal is not used.

I would use the largest pipe I can fit. The length of the pipe plays a role as well as the ID. You want the least restriction on the suction side in front of the turbo.
Since you verified your AFRs are fine under WOT, then you CAI is probably not the cause of the hesitation.

GPA951s

Just a FYI. My car certainly ignores the O2 sensor.. because I don’t have one, nor does the car have an ISV. And the chips are custom dyno- tuned. And truth be told. I’ve never driven a nicer starting/ idling / wot car in my life.. which makes this tiny problem all that much more of a mystery.. but I have a plan, and should be able to confirm when I get back to the track at the end of this month.. I keep the car on the street just to test but it seems the hesitation is over 5 k and typically around 120 mph …all the way to 135- 140 mph cops might take issue with that test on the street.