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DIY Stock Intake Mod

39845 Views 90 Replies 34 Participants Last post by  foreverkidd
Hi Guys,

Well, I got to thinking about the stock dual stage intake and figuring out a way to keep fender side intake opening open all the time. In case you didn't know, the fender side intake opening is closed until around 3600rpm, which is when it opens up, thus resulting in the now infamous and much beloved "IS-F Roar". As you can see from the picture below, all I did was just pull off the vacuum hose from the actuator and plug off the other end with a vacuum cap. Now the "IS-F Roar" comes on around the 2300rpm, and to me atleast, there seems to be a bit more power down low...which makes since because now the engine can breathe a bit better down low with both intake opening being open all the time. The only downside would be if this throws off the air/fuel ratio's from stock. I don't think it will drastically, but I'm not sure. Anyway, try it out and let me know what you guys think. Oh yeah, no check engine light either! Have fun...Darshana S...

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I can't believe you guys missed this thread over CL, this is what I found about this mod last year...

Originally Posted by Juanca:
OK guys, I have hard data about this mod. I did it last Sunday and you can feel the difference right away. First of all you can hear the intake way earlier, from around 2K RPM. Just the sound makes you believe that your car is faster, maybe more HP I thought? So I went to the track today and tried my ISF. I did about 7 runs and I knew there was something wrong, my times were a little bit slower than 2 months ago, I was runing 8.7 at best in the 1/8th mile. Even though I could swear that the car was faster, the slips were saying otherwise. For my 8th run I decided to take this mod back to the way it was stock and I immediately picked up 2 tenths! I couldn't believe it so I did 6 more runs and I ran consistently 8.5 (all runs). My trap speed also jumped from 84MPH to 86MPH. So I'm taking the intake back to the way it was, and I'll enjoy that lovely sound from 3600RPM, not before.
Originally Posted by Supraman16:
This is some great real world data. However, I do have a couple of questions:
1. Was the flap mod done RIGHT BEFORE doing the runs, then put back to stock after finding out the slower times, or was the flap mod done for awhile before doing the runs? The reason I as is to see if the ECU had properly compensated, for what I would assume increased air from the opened flap.
2. Are you still running the stock air filter, or an aftermarket one (K&N or Amsoil)?
3. Have you done the vaccuum cap mod as I showed in the intial post, or just disconnected the plug for the flap accuator? The reason I went with a vacuum cap mod rather than disconnecting the plug was because of my concern that disconnecting the plug may alter what the ECU was reading and change something around in terms of the A/F ratios or something else. By just doing a vacuum cap to plug it off, it doesnt change anything electrical, I would assume just fools the ECU to thinking that it's still stock. Once again, this is all hypothetical.

I returned my airbox to stock after reading your post last night and driving the car this morning, to me at least, seems sluggish compared to with when the flap was open. Fig also showed a 5hp gain and to me, I agree with this that there is a increase in HP and torque with the flap open. However, I know that Fig also has a Amsoil filter in place.

Inregards to why the factory that this intake flap was put into place, I believe it to be mainly for the purposes of perserving the luxury and quietness of the car in the lower RPMS. I don't believe it to be due to performace reasons...once again, hypothetical. I don't see how having the flap closed in lower RPMS can increase the HP or torque, or for that matter increase it in the higher RPMS when it opens.
Originally Posted by Juanca:
Here are my answers:

1. I did the mod last Sunday and drove that way for about 250 miles before I went to the track.
2. My car is completely stock except for tints.
3. I did the mod just as you showed it on the first post, so it's confirmed, I used a vacuum cap.

As I said I thought my car was faster. When I went to the track 2 months ago the air temp was about 86F, so this last Wednesday I was expecting better times because of this mod, and also because air temp was 66F. Two months ago I was runing [email protected] in the 1/8 mile, and you can imagine my surprise when this week my best run out of the first 6 passes was [email protected] I wondered if the mod had something to do with being slower when I should be faster (at least because of the cooler night), so I removed the cap and connected the hose back. I had another pass right away and bam! [email protected] The following 5 passes were similar. This experience showed me that the mod doesn't help performance-wise.
Originally Posted by anajri:
what were youre 60 foot times.. maybe you had more wheel spin during the launch ? or maybe que amsoil filter was ofsetting any negative drop need more testing......
Originally Posted by Juanca:
My 60 foot times were always around 2.1, with and without the mod. Wheelspin is there, I can't avoid it, these stock Bridgestone don't help launching the car and the track isn't the best either.

I don't have any aftermarket part on my car, not even the air filter, I'm stock.
Originally Posted by stick:
20 degree difference in air temp.......good for intake air, bad for tire grip. The warmer day will have a hotter track and give better grip. Too many variables. I don't know if the mod works, but a more controlled environment is needed for testing.
Originally Posted by Juanca:
This is why I posted times before and after the mod. I basically picked up 0.2s in the 1/8 mile after pluging the vacuum hose back. These runs where done one after the other, during the same night, so conditions were identical.
Originally Posted by lobuxracer:
Sorry, but MPH trumps all. Better MPH means the engine is making more power. End of story.
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