today i raced my friends 2002 sentra spec. V, and i had him in first, and second gear but once i put it in third he pulled away from me. It felt like i lost power or something. I looked at the boost gague and it showed 12 or 13 psi. Its a 97 A4 1.8t fwd 5 speed, with Giac chip upgrade, ngk spark plugs, straight exhaust, and a home made CAI.

 

Its called a small turbo.

 

but why does 1st and 2nd gear pull so well? when i get 2 third he passes me like im standing still. and is 12psi normal for a giac 1.8t?

 

Sounds a tad low, check for leaks. Giac is supposed to be around 17-19psi

 

we wanted to go to awe and buy a diverter valve from there on monday so right now were running with the stock one. Could this be the problem? At idle i have -20psi of vacume is that normal?

 

A 97 with the standard K03 won't get 19 psi, mine can only put out about 18 psi with my MBC set at max. A GIAC file on a 97 will only get around 15 psi and drop off to around 10 after 4k.
You definately need to upgrade the diverter valve, mine blew up in a week when i raised the boost.

 

on the drive home after getting the chip installed i hit the gas and it hit 18 to 19 psi and it kept doing it all day. after a couple days it would produce less and less

 

it will spike to 18 or 19, but wont be able to sustain that much boost until redline.

as for the lower gears pulling better, its all in the gear ratios, and is generally how all cars work. but what auditech says is certainly true - a bigger turbo will pull harder in ALL gears, but even then, the lower gears will still be pulling harder because of the gearing

 

I agree with the problem being a small turbo.. And Sentras weigh 3 lbs.

But w/ GIAC and stock n75 I peak at 20, hold 17/18 for a bit and then it falls off around 4500 rpm's.
With a different n75 (H/race valve) I was hitting 22/23 psi at times.
When I used a mbc the most I could get was 18 psi.

What mbc are you using? I had terrible luck using one w/my car. It was a gated turbo smart knock off from ebay like $20. It was pretty smooth, but I would constatnly get throttle cut w/EPC light (high boost @ low rpm's) and then a CEL and "tq limit exceeded" fault code. Sorry to jack this thread, but it's on topic, right?

 

i used to peak 18 to 19psi but now all i can get is maby 14 peak and then drop off to 12 psi. I gona go to awe on monday and buy the diverter valve they sell there, it goes for about $130. would it be worth it if i do a test pipe and a front mount would i get allot more power or would it be a waste of time and money?