I dyno'd my 2003 5AT G35C, 2 weeks ago, after adding a Z-tube and K&N. The only mod I had was my Invidia G200 exhaust.
I lost more HP and TQ under 6,000 RPM While the car was on the dyno, the tech told me he could feel the car bog.

Before
231.55 HP 216.77 FT-LB

After
234.31 HP 212.49 FT-LB

This past Saturday I reset my ECU, disconnected the negative battery cable and pumped the brake pedal. The car seems to drive a little better. I'll try to do a dyno run this next Friday to see if resetting the ECU made any difference. The down side the temperature is 15 to 20 degrees cooler than when I did my first dyno runs.

 

First off, I'm glad to see that you understand that you are missing power in the powerband and that gaining a few HP/tq at the top of the curve is pretty meaningless

Yes, something is going on. It actually concerns me somewhat because we saw the same thing with the 95-99 Maximas. The Maxima guys would replace the inline resonator (much like the one G35) with a straight pipe. This added some sweet induction noise and what we thought was more power since the resonator looked restrictive and really quieted down the induction noise. No one ever did a comparison dyno to know for sure. Then last year someone did do a comparison run. Sure enough, the resonator does in fact help power. Just like your dyno, we saw gains of ~5-12whp from 3500-5200rpms with little change at peak. I put the resonator back on and my Maxima ran it's best ever of a 14.3@99mph.

It turns out the stock resonator was actually a helmhotlz resonator that improved the air movement into the engine. Is the G's intake pipe doing the same? Why doesn't the Z have the resonator then?

Maybe I'll put the stock pipe on and let you know what I feel.

Here's the Maxima dyno, with and without the resonator. It looks pretty similiar if you ask me:

 

Well, I swapped on the stock resonated intake pipe and drove around for an hour tonight. The car didn't feel as frisky. When I swapped on the resonated intake pipe on my Maxima, the power increase was pretty noticable. I don't know what to tell you.

My best guess is your car might have been a bit heat soaked this go around

What did your other pulls look like? What were the conditions between the two days?

 

DaveB,
Thanks for your interest and input. My goal was to increase the overall power of my G, without any side effects.
I post my dynos so people don’t have the same problems and/or frustration, I do.

Both days were @ 95 degrees, live in the DFW area. I've done a total of 9 runs on the same dyno, stock, Invidia, and Z-tube+K&N. Each run made more power, the shop though it was odd, since normally the 3rd pull, during the 3 , is normally lower than the 2nd .

Monday I had the ISO Thermal Kit and ½” MD spacer installed. I didn’t have time to dyno my car, I’m going back this Friday. The downside, it’s about 15 degrees cooler, this week. Hopefully the curve will be
more consistent with the spacer installed and ISO Kit.

I’ve talked to 2 shops about adding an X-pipe to my Invidia exhaust. That’s my last ditch effort to get my TQ back to/or above stock.

 

Hey Strongman,

I think it was probably your ECU going into lazy mode. Before you go into the shop, do several passes in front of the shop in 3rd or 4th gear from 2K rpm to redline.

This will tell your ECU you mean business and spank it into performance mode.

Another thing to do is to actually turn your AC on while pulling into the shop and while preparing for the dyno. Leave the AC on low. The point is to get the radiator fans going.

When the fans are on it will pump out a lot of heat from the engine. The objective is to get your coolant temps down. While the fans are on let the engine rev at about 2K while in neutral. This will get the water pump going and your car will cool down rapidly in about 3 minutes.

Everybody should do this before going to the dyno or even between runs at the strip.

From 170'F to 220'F in 10 degree intervals. I measured engine performance Vs engine coolant temp.... and it makes a big difference.

 

Thanks for your suggestions Hydrazine. I just had the ISO Thermal Kit and 1/2" spacer installed Monday, headed to the dyno Friday (10-14).
I planned on disconnecting the negative battery cable and pumping the brake pedal. It's a 50 mile drive from my house to the dyno. I'll break 100mph two to three times on my way The computer should know I mean business by the time I make it to the dyno shop

Also I purchased my Z-tube from www.worldpartsexpress.com The inside of the Z-tube has a rubber coating , it's not smooth like the outside .
Has anyone else examined there's before installing it?

 

I myself have noted a difference between the z-tube and the g-tube. Although the z-tube sounds better and provides better top end results, I think the g-tube gives better low end results. Anyone else have any experiences? I would like to investigate this further.

 

Thats a very long drive and your entire car will be really heat soaked by the time you get there. So you might try turning on the AC shortly before arriving. Just put it on low.

I also suggest doing the WOT passes just before getting on the dyno. Keep the ECU from going into the lazy mode.

 

Could have sworn I noticed more power everywhere not just low end. Curious to see what more people have to say about this.

 

Props for the post. A lot of us have the z tube/kn filter combo.

 

how do you guys feel about the NISMO colda air intake system instead of the ztube? isnt the ztube a cheap alternative? any of you guys get the unichip ecu mod? i have the chip and the nismo intake and i notive more power around higher RPM's and a more aggresive sound.

 

I have the Z-tube and the JWT Pop Charger. I love the aggressive sound, but my car benefits on the low end as far as performance goes.

The cold air intakes have mixed results. If the Nismo is working for you, keep it. Where are you located? That will tell us if you're gonna benefit much from the Nismo intake.

 

So should I put my stock tube back in and leave the K&N?

 

Realgone,
If you didn't feel a dip in power after you added your Z-tube. Leave it on the car.
My big concern was I bought a knock off or unfinished Z-tube.

 

Donovan, I dynoed a best 234.95 hp and 222.30 tq with the UT G Tube Carbon Fiber with KN Filter and a 10 wire grounding kit (gordgee).