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Old 11-20-2009, 07:45 PM   #21
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Bringing back my almost 2 month old thread to try and get some help about power. It was my birthday a few days ago, so I got a day pass for my car and took it for a good burn. I now have a PLX wideband, so I was able to do some basic road tuning, but it was wet most of the day, and under full throttle car would just go sideways. Here's my current timing chart now:

There's no longer a dyno on the island I live on, so finding out what my hp/tq is at the moment is difficult... I also haven't driven the car since August, so I can't say whether it's any faster or not. I was hoping a new timing chart might help my power issues, but I'm not sure it did (still have way more to add, but ran out of time). The problem I was having was that I was making insane torque down low (210 ft/lbs at just over 3000rpm), but a max HP of 186. After 5000 RPM, everything nose dives bad - HP drops just under 100HP, and torque drops to 130. So the car is a weird driving experience, it hits so hard off the line, but then just runs out of breathing room. It's hitting 16psi down low, and then at 5000psi it stabilizes to 12.5psi. This makes drag racing pretty useless. My best time was 14.4, and of course I had a huge start, but once I get up into changing gears in higher revs, I'm way out of my powerband.

I think I should be making for then 99HP and 135 torque at 6800rpm at 12.5psi... Now don't laugh, but is my entire problem here that I'm running a 2.25" exhaust after the downpipe? My downpipe is a divorce gas setup that merges into a 2.5" tube. Would upgrading to a 2.5" exhaust suddenly open up the top end? Should I get a new wastegate that can hold boost? Is my turbo just too damned small? I've read somewhere that the T25 300ZX is smaller then the conventional T25's found on SR20's...

Thanks for any advice folks
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Old 11-22-2009, 06:00 PM   #22
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I am a newb to FI but if you are forcing x amount of air through your 2.25 exhaust down low then try to force dubble that amount up high, yes you will have a drop off. Since you can only push so much through a small opening. Hustler may be able to confirm this. I am shure that if you get a full 2.5 exhaust that you may just find the lost power that you are looking for. A larger exhaust will allow the trubo to spin freely insted of the exhaust backing up and preventing the turbo from continuing to push as much air through the exhaust. The restriction is very simmiler to having a cloged cat.

If I am wrong please correct me. I would assume it the same reason that you would not have a 2in turbine outlet and run 1.5in tubing to the intake manifold.

Have a great day,

Last edited by Jfornachon; 11-22-2009 at 06:03 PM. Reason: Poor spelling
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Old 11-22-2009, 07:52 PM   #23
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Why don't you have a 3" exhaust?
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Old 11-22-2009, 07:56 PM   #24
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Hustler, Seems like you have it down pretty well. About how much time did you spend on the dyno to get your tune dialed in with that much detail?
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