Who would have thought a stock airbox could be so restrictive

[inmyshadow]

I was surprised to find my boost fall off was related to my airbox. I was running the stock airbox because of the convertible. I wanted to keep the noises down and the surprise factor high.

Besided I've seen several people run 20lbs off boost, run 12s and make mid 200whp on TII airboxes. Even my car non intercooled nearly made 200whp with one very weak cylinder. So I figured, a 90+ airbox should be able to the do the same.

So last year when I setup my car for 20lbs of boost. I added a k&n panel filter for extra flow. Well since doing this last year, I couldn't hold 20lbs of boost. My boost was more like a 20lb boost spike at 3000RPM. As the rpms climbed to redline, boost fell off to 14lbs.

As luck would have it. One of my exhaust hangers broke, causing my downpipe to fall out of the car. My rush job in repair my car last thanksgiving, after waiting two months on TU finally caught up to me. So I drove around running 20lbs of boost to see if the exhaust was the restriction. Nope.

So last night, I decided to run my old red shadow's cold air intake I made. This way I could rule either the airbox or intercooler as my restriction.

Well, as I turned onto my test road, I nailed 1st gear. To my amazement, I just lit the tires up with 20lbs off boost. Second gear was just as fun. Problem found.

So after turning my boost controller down several times and by alot, I was able to hold 20lbs of boost in all my high gears. The difference is night and day.

My car always felt lazy for my 14.0 100 mph. Most times, I had to reframe from races from a roll becaues my car just lacked any good power on the topend. The car just plain sucked on the highway. Not anymore.

So, I'm thinking TII airboxes good. 90+ airboxes bad.

[GLHSKEN]

So, I'm thinking TII airboxes good. 90+ airboxes bad.

yep, I've seen 330whp with a TII airbox and K&N. My son't 90 Daytona will lose it's stock airbox first thing.

[inmyshadow]

Perhaps the next time I head to the dyno, I'll test airboxes.

I have a TII airbox, 89 TI airbox and 90+ TI airbox with K&N filters.

yep, I've seen 330whp with a TII airbox and K&N. My son't 90 Daytona will lose it's stock airbox first thing.

[turbovanman²]

Nice find. I am curious on the dyno results, should be fun,

[Whorse]

I noticed a huge difference when I went from my VNT airbox to just the open face airbox with a siliconed K&N filter in it. Even bigger difference when I went to a K&N cold air intake.

[Marcus86GLHS]

JAMES glad you found the choke point. good work.

for the readers, i dynoed my glhs in 2004 with the original airbox fully installed including filter, then 15 minutes later dynoed the car with the airbox totally removed, no box, no filter, a direct shot right into the compressor (no other changes).

results: dyno HP and tork were the same.

thats why i stuck with the stock airbox setup, it works fine.

[GLHSKEN]

Marcus... Stock Tii intake... Not a 90+ set-up.. They even look restrictive!!

[Marcus86GLHS]

KEN so the 1990 and up setups are not that good? i am still learning.

i have seen JAMES's airbox it looked good who wouldve figured the airbox as such a choke point. looks like it pays to test this stuff out.

i rode in his car and saw the boost keep dropping off from 20 to 14, i knew something needed to be fixed. i had no clue what, i just knew it wasnt right.

next thing you need JAMES is to get rid of all that very large, very soft vacuum tubing you got on your MBC, put in some small dia. hard plastic lines you'll see its easier to manage boost. i got the stuff over here cost is free.

12's???

[inmyshadow]

Man if I didn't know better Mark, you want to see me run 12s like you.

That or you are trying to distract me, in my search for a 240sx.

I am tempted to head to LVD tomorrow to get kicked out.

KEN so the 1990 and up setups are not that good? i am still learning.

i have seen JAMES's airbox it looked good who wouldve figured the airbox as such a choke point. looks like it pays to test this stuff out.

i rode in his car and saw the boost keep dropping off from 20 to 14, i knew something needed to be fixed. i had no clue what, i just knew it wasnt right.

next thing you need JAMES is to get rid of all that very large, very soft vacuum tubing you got on your MBC, put in some small dia. hard plastic lines you'll see its easier to manage boost. i got the stuff over here cost is free.

12's???

[turbovanman²]

Why would you get kicked out?

[inmyshadow]

Convertible.

Considering I went 14.0 last year with 3cylinders, stock TI airbox and a turbo that failed 5miles for the track.

I figure, my car should be good for 13s now.

Why would you get kicked out?

[turbovanman²]

Convertible.

Considering I went 14.0 last year with 3cylinders, stock TI airbox and a turbo that failed 5miles for the track.

I figure, my car should be good for 13s now.

Wow, you guys need a roll cage or bar for 13's in a convert? weird. Were allowed to run 12's, lower and you need a cage.

[GLHNSLHT2]

Marcus I thought you left on the back of the airbox and the hose going to the turbo?

At the track I went from an open T1 mitsu airbox to Turbo hose to a 3" mandrel bent with big K&N cone pipe that was still in the engine bay open sucking hot air and picked up 1 MPH consitently. Haven't been back since I've sealed it in it's own cold air box.

[John B]

I have a T2 airbox and a '91 T1 airbox and the filters are pretty close in total area although the T2 is slightly larger. I can't imagine it making much difference. I'm not disputing your results, it's just surprising that such a small increase in filter area could make a huge difference.

[turbovanman²]

I think the design has alot to do with it. The T2 does look like it flows alot better than the T1.

[ShelGame]

Hmm, I'm running a stock '89 T1 airbox (different from the '90+ T1 airbox). It's nearly the same shape as the T2, but with a BOV installed right in front of the pipe to the turbo inlet. Seemed restrictive to me, and I don't need a BOV (auto trans, drag race only). So, I pulled out the stock BOV, and plugged the hole. I've also got an Accel foam filter. Supposed to flow more than the K&N (according to Accel, of course). I wonder how it compares, flow-wise?

[John B]

I found an easy fix on my '91. I removed the drop-in filter, made a gasket for the airbox, and plumbed a cone onto the airbox inlet.

[iTurbo]

I was running a '90 airbox with KN drop-in filter on my Shelby Lancer for a long time. I dynoed it at 14 psi and it managed 196 WHP and 242 WTQ. Just a couple weeks ago, I ditched the setup because the hose attaching to the turbo inlet had ripped.

I made a mandrel bent aluminum intake for it with a 3" open element filter from ATP Turbo. There was a big difference in seat of the pants power but I haven't dynoed it again yet. The turbo is much more audible and it spools up much faster than before. I agree the ealier TI/TII airboxes were decent, but the '90 + is crap.

[Dave]

It wont get much better than this:





3" ram air intake... this would be my suggestion to everyone. Screw the airbox crap.

[John B]

Looks good!