I've been lurking on this board for a while, so forgive me if I end up rehashing some previous data. For those interested (I know this information has probably been posted elsewhere so maybe not everyone would like to know) I have the following information to report:

2005 G35 Sedan 5AT Modified with the following:
MREV2 plenum + 1/2" Spacer $688
DC Sports headers $426
Stillen Z-Tube $75
All prices include shipping to my residence

Before Modifications: 210.2 whp 203.8 tq in third gear
After Modifications: 239.3 whp 216.9 tq in third gear
Just for kicks 4th gear non-mod: 192.1 whp 223 tq, but oddly enough it also made 239.3 whp and 221 tq after modifications, close to the third gear pulls.
Before modifications I drove an hour running errands, and after modification is obviously with a cold engine.
Before: 90 degrees, 61% humidity, 30.14 in-Hg
After: 95 degrees, 59% humidity, 30.17 in-Hg
No tune, no ECU reset, A/F unchanged at 13.5 between modded/unmodded

After modifications my power curve looks just like it did before modding, and my driving impressions confirm this. The main difference is the big jump in power. In my attached picture (I know it's not the best thing in the world but I have no scanner) I have attempted to graph my dyno with comparisons to other cars of interest. Mine are the thick blue and red lines. I am unsure if other people's dynos are overstating power or if mine is understating power, but I have reason to believe that mine should be accurate since I drive an automatic and have approximately 25% drive losses. This would give me approximately 300 to 318 hp at the crank after mods I assume. I was able to run against my friend's G37 coupe automatic and everytime I was nearing my shift point he would start pulling (as evidenced by the dyno the G37's power is up top), then I would pull away slightly upon my car's next upshift. This repeated until about 70 mph when he finally caught up with me and we were unable to continue due to legality, or at least I wasn't willing to continue (we started running at the same time after both paying tolls, therefore no street race). I have not been to a track yet, but based on this performance I am willing to bet my car has a 0-60 time of 5.7 to 6 seconds now, and runs the quarter in 14.01 to 14.2 since those are the published times of the G37. For those wondering how it sounds, the car sounds absolutely stock most of the time (aside from the modifications, everything else is stock), which I am more than pleased with. I do not plan on getting a cat-back. When I really open up the throttle, however, the induction noise really comes alive and the normally muted baritone resonance (I don't really know how to describe our engine sound, but it's the warm trombone/baritone/french horn sounding tone) becomes fairly loud and I love it, but like I said it's simply the stock sound amplified. Kind of like talking to a co-worker next to you then raising your voice to talk to the guy in the cubicle next to you. Nothing has changed, not even the exhaust sound. What is interesting though is now the car makes a blow-off valve type sound when it upshifts under load, but at no other time so it is not audible during normal driving. We checked for leaks and as the smooth dyno graph I have will attest to there is no loss of power. I don't know if anyone else with my mods has this trait. Inside the car the mods have gotten rid of the annoying VQ drone my car had and is strangely quiet now. I hope this review helps, and if there are questions please ask me.

End result: Parts + $600 install labor = $1883 for nearly 30 whp. I think it was worth it as I have no further modifications plans for this car.

 

So you did headers, but kept the stock exhaust? That's pretty interesting.

I've been thinking about doing some moderate NA mods similar to what you have done. I've been tempted to get an exhaust, but I've had so many loud cars that I think I'm ready for a quiet one now. Are there any true exhaust systems out there that produce power, but keep the noise down?

Actually, lemme reiterate that last part. I don't mind loud cars under WOT, but when I'm just cruising/commuting, I like things mild. Has anyone messed around with butterfly valves for more flow at higher RPM?

 

So no CAI/pop charger? Using the stock one?

 

That's correct I kept the factory exhaust for the same reason you have - to keep things as quiet as possible, and I am overjoyed that it worked. If someone had a donor exhaust for me to test with I'd be happy to do so, but I am not going to buy an aftermarket exhaust just to see how it sounds. For the most part though I see only 4 to 5 hp gains on most people's G35s so I'm guessing the factory exhaust flows good enough for my NA application and will not take the extra step just for the sound. As for the intake, you are also correct. I kept the factory airbox and filter and used only the Stillen Z-Tube. My whole goal was to be street legal (or at least appear to be street legal, as the intake plenum mods are not CARB exempt but are as stealthy as Motordyne claims). The purpose of these mods was to fulfill a promise to my brother who passed away last Christmas. This car will not be sold or traded, ever, and I am soon going to purchase another car after retiring this one to occaissional weekend duty.

 

Damn good job on factual data! This place needs more of this.

 

Stillen CAI looks pretty close to stock, if you would like to install it. I to have stock exhaust and will probably just go with HFC later on.

 

How many pulls each time? Do you have the numbers for all the pulls?

I wanna say first thanks for posting this. The only problem I see is that you did the post-mod pull with a cold engine. I'm not sure how much of the difference that accounted for. In any case, even if you only got 20 hp, I think that's a good improvement.

 

I do not have the numbers on the graph they gave me, but in both cases we chose to use the lowest numbers to be conservative. The max hp my car made for before mod was 216 but don't quite remember the torque value obtained on the third run. The low value of 210 comes from the 4th run. Max hp for after mod was 253 and the torque was 221, obtained on the second run. For the before mod dynos, we did 5 pulls non-stop so the engine got pretty hot. Stupid of us for sure. After mod we did 5 pulls back to back to let the engine warm up, let the car rest for 10 minutes, then pulled 5 more runs for a total of 10. You see now why I am babying the car; it's been through a lot. The lowest value of 239 hp came from the 8th run. What is very interesting is that it made 240.2 hp exactly from runs 3 to 7 each time, with slight fluctuations in the power curve only. A very consistent performance that surprised everyone for sure. I'll see if I can make it to the dyno to ask for my numbers if I have time after work. They have my values stored. I am dying to hit the track to see how the car really performs. I also plan to dyno again at the end of the week to see if the ECU has made any adjustments. They say the computer is smart enough to detune all bolt-ons and it's impossible to make power NA. I want to see for myself.

 

Why do you guys want to push a CAI/Pop-charger on him?

It's not like it makes any power, and in hot weather it's certainly prone to losing power over the stock setup.


As for a possible exhaust mod, Motordyne will be coming out with the sedan systems soon. Tony has a system called the "VQ" which is very quiet and similar to a Fujisubo without any of the downsides. He is claiming great gains with his line of systems, so after someone tests them to confirm, you might want to look into it for some more power.

Also a reflash to take advantage of the extra flow from the headers, the exhaust, and the spacer + MREV2 will certainly bump you up some more. I see no reason why you can knock on 265-270whp after those mods (more if you install HFC's/test pipes).

Great data!

EDIT:Here is the link to Tony's exhaust thread. This is the page with the pics/info.

https://g35driver.com/forums/showthr...216529&page=21

 

I don't think anyone was really "pushing" it, but I agree, I can't see any advantage. The stock setup is really quite impressive, IMHO. I had a couple of folks at the last autoX looking at it and questioning whether it was really stock. They believed it to be aftermarket.

 

Well I finally took it to the track. I had wanted another dyno and to pull out my old data but the shop was closed by the time I got off work. Unfortunately I have no baseline to compare against. This was my first time at the dragstrip and it was a blast, so forgive me if some things look "sucky." I find it amusing though my car number was my area code.

Temperature: 84 F
30.17 in-Hg
78% humidity

R/T: .547
60': 2.359
330: 6.456
1/8: 9.791
MPH: 73.97
1000: 12.655
1/4: 15.049
MPH: 92.52

I didn't do any fancy burnouts or anything of that nature to warm up my tires, etc. being a newbie at this. I left VDC on, brake torqued and took off at 2000 RPM. At least I think that's how the magazines did it. The car next to me was a 135i and it was a good school bus length ahead of me by the end. If anyone can interpret this data for me it'd be great. All I know is plugging it into a horsepower estimator it's giving me about 218 to 225 at the flywheel depending on the website. I know this is wrong because I've already dynoed near those numbers at the wheels stock. I'm guessing it's because I drove 2 hours to the track, idled in line, and did the run. Also I've noticed that my engine cover rubs on the hood, but it's minor. I can live with it.

 

Where's this track? Reason I ask is because those times are rather slow, even in 84 degree weather. A stock G35 5AT in 85 degree weather with elevation in the 1000' range should be able to get into the 14.7-14.8@94mph range. With my G, I've never noticed in real difference between running with a screaming hot motor or a stone cold motor. The car, at least mine, seems to get quicker when I hot lap it (back to back runs).

My G has done high 14.4s@97mph in 75 degree weather (1000') when it was stock, but who's to say if you wouldn't run quicker at my track. That's why I'm asking about the location of track. I'd like to calculate out the density altitude.

 

I'm shocked you even got 2.3x 60' with the technique you used... 2.3 is not good necessarily, but considering you left the VDC "on" and brake trqd to 2K launch - that would spin most street tires and cause the VDC to go into a tizzy fit! Not to mention the brief power cut from brake and throttle...

Anyway - at least turn VDC off next time. And try launching off idle for 1 run then 2K launch - see how much difference you have in you 60' and ET

 

I took it to Houston Raceway Park in Baytown, between Houston and Beaumont. I'll remember the techniques next time. A girl who took a look at my timeslip said my R/T was decent, so I suppose I did one thing right.

 

I think you should invest into a UTec or get a reflash. With the mods you have you can gain alot more than 30hp.

Who is doing your work and tuning?