So is there anything I can do about the torque loss beside get another exhaust? Also has anyone with a real HKS had this problem?

 

get an x pipe welded into the system

 

I calculated out the density altitude for July 20 and August 24 and unfortunately, there isn't much difference in conditions between the two days.

July 20 between 6pm and 10pm DA 1300'-1900'
August 24 between 6pm and 10pm DA 1600'-2100'

The conditions were obviously worse on August 24, but they weren't remotely bad enough to suck out much ET or MPH.

I hate to say it, but I think people put way too much faith in these aftermarket exhaust systems for the Z and G. I had a Borla TD on my G and noticed the same exact thing as yourself, an utter lack of low/midrange power. I've never believed in the notion of needing to reset the ECU to allow it to learn because these ECUs are designed to learn all the time therefore there is absolutely no need to reset the ECU. Regardless, the ECU on my G was reset because I detached the battery while installing my Borla exhaust. After a week of driving with the Borla exhaust, I removed it because it was basically just a noise maker. The G owner that bought my Borla system gained a whopping 5whp with it and only from 5500-6500rpms. Hardly worth it, IMO and that kind of gain wouldn't do jack for the 1/4 mile performance.

 

your runs are consistent, as an automatic should perform.
my advice as with other have said. reset the ECU. and also i might add, instead of shifting yourself, try making a few passes with the tranny in D(as a comparison to your shifting runs).
also yes practice your launch rpm, figure out where the tires break loose, and slowly lower the RPM at where they first broke loose. also tire pressure is key here as well.
also finding a higher stall torque converter helps greatly with launch.

also try borrowing a friends 17" or 18's.... it'll screw with the speedo but you should see some sort of a difference with your times, whether they get better or worse is up in the air.

of course all of this should be done after you reset the ECU.

this is the part of 1/4 mile runs that people tend to not pay any mind to.
try playing with all of these options. youre bound to get it lower than your 13.9 runs soon

 

Even so, but MPH is an indicator of HP and he didn't change his driving style. If the exhaust really gained him power, it should have shown up in MPH. I'm convinced that these true dual exhausts cause a serious lack of exhaust velocity in the lower rpms and that the stock exhaust systems on these cars are pretty damn close to ideal for a naturally aspirated VQ.

 

Thanks for the advice guys. I did meet up with other guys that were with me on the 20th and their times were off by about 3-4 tenths also so I didnt feel to bad. I'm not giving up on the exhaust just yet. I believe I just need to pull more air in to make it work properly. So I'm going to invest in a spacer and mrev2. Still deciding on going with a cone filter.A few people suggested that in my other thread. https://my350z.com/forum/intake-exhaust/295863-x02-exhaust-sound-clip.html If the weather is any better this friday I'll go back to see if I can get better results.

 

I think spacer is more then enoiugh on an 04. mrev2 is more geared towards the revvup motor

 

Maybe a bone stock VQ ---- try cams, headers, plenum, and see what happens....low end exhaust velocity may show in city driving and pulling away from a light slowly but launching hard and shifting hard will have you in the last 2K of the rpm band EXACTLY where this exhaust makes the most power....if you wanna race minivans in traffic...keep the stock exhaust....if you wanna redline and make the most power and the quickest ET's ....get a lightweight true dual along with other mods so they work together

The mere fact he picked up 2mph (over his previous back end acceleration) on the back end shows he is making more power...the dynos from this exhaust proves it makes power and for $550 its well worth the cost

 

There's really so many things wrong with this post, that its hard not to point out.

What difference does putting it in D make, rather then shifting it yourself. In D its proabably not going to shift as high as you can go in manual mode. Do thats dumb. The idea is just kinda dumb in general.

What is there really to practice in a launch in an auto car. You hold the brake, you hit the gas. Its pretty simple really. If you have any sort of good tire, traction shouldnt be that much of a problem, UNLESS the track is prepped poorly.

Tire pressure is important I suppose, so you get a point back for that.

You want him to get a higher stall converter for a car that is N/A with mild bolt-ons, street driven, and only tracked every now and then. OK, thats worth it.

How will changing the diameter of you rims, effect your speedo? Oh wait, it doesnt. It has nothing to do with the rim size, it has to do with the tire size. If you shop for your tires correctly, your tire size shouldnt change by more then 3%, because if it does our cars will get pretty fussy with you. But you already knew that Im sure.

The significance of resetting your ECU, still has not been shown to me. I would like to see it and welcome anyone to show me. I will gladly reset my ECU next time out.

We are trying to help people in this forum. Not just suggest them to buy things they dont need, ie higher stall converter, or tell them false things, rim size effects your speedo. So please, STOP THAT, thanks!