I hope I am not the only one who did this mod ..

 

Yeah, I realize that...but the point is that we still don't know if the car can overcome the aerodynamic drag of speeds greater than 155 MPH, especially considering the higher gearing. In other words, will the engine have enough power to offset the new gearing & aerodynamic drag to the point that it will pull past 155 MPH in top gear (assuming that the governor is disabled)? It just might, but there's no way to tell unless someone actually tries it. You really can't figure it out with math.

 

OK I see now. I was never trying to argue with you in the first place. I think we were saying the same thing all along. I am speaking from my experience with Mustangs, where the higher gears will improve acceleration and top speed. I only wish this mod was as cheap on the G's as it is for Mustangs.

 

Is this mod doable on a 7at ?

 

doable on 5AT, 6MT, and 7AT. On the auto's though, you risk losing cruise control.

 

Never Bone stock could you pm me or possibly post the link or part number and where you bought it?

 

I'm not too impressed with this community to tell you the truth. This should be the number one mod for any car that has low torque down low and decent or high horsepower up high. All the car needs is more leverage off the line and lower gears provide just that. In my mind, you are one of the few guys that have done it right.

I can't believe people will spend over a grand for a cat back exhaust (that's only half the exhaust system by the way) or $500+ for an intake, but not spend money on something that will really make the car move like gears or a shift kit. Heck, you use the word "gears" on this forum and some people still think you are talking about the transmission.

I have not done this mod to her car because it's an auto and would lose cruise control. That's not an option. If I were to do it, a new limited slip differential would be put in place of the factory pos.

You don't "risk" losing the cruise control with the automatics. You WILL lose cruise control. It has to do with the cruise control logic which was explained earlier in this thread.

 

Yes, you can.

Figure out how much output is produced by the car, and then figure out how much aerodynamic drag is produced by the car (Cd x frontal area, both of which are published). If there is more hp than drag, then you can go faster.

This is done with CFD analysis every day by race teams and high end aftermarket part manufacturers.

The G has more than enough power to go beyond 155. Hell, my 4 banger Honda does more than that with less power, and my G35 did more than 155 with less horsepower.

Too true. Anyone who does any real performance modding pretty much gets ignored or flamed. Look at LastChance. He tracks his car regularly, and gets almost nothing but flames for "making his car faster". Then there's the FI leg humpers. I would take Lastchance's car at a track over ANY of the FI coupes on this board.

 

LOL, you never fail to crack me up. Go ahead and do the math then...don't just tell me it can be done, do it. And let us know (using only math) what the actual top speed would be. I won't be holding my breath, so take your time.

Let me know when you figure out the aerodynamic drag and frontal area as well.

And somehow you seem to fail to understand that top speed is determined by far more than just HP. We're discussing gearing in this thread, which is obviously a HUGE determining factor.

 

Another thing I just thought about....years ago Car and Driver (or maybe Motor Trend, I don't remember for sure) decided that they were going to modify a Corvette to make it reach 200 MPH. I believe it was a C5 Corvette back then, so it still had a decent top speed (in the 180 range) but nowhere near 200 MPH. After all was said and done, the C5 Vette needed about 600 HP to even approach the magical 200 MPH mark. Think about that for a moment.....a standard C5 Covette had approximately 350 HP from the factory and could attain a top speed of approxmately 180 MPH. So to get another 20 MPH of top speed out of the same car required another 250 HP.

My point? Simple--just saying that the G37 has enough power to pull well beyond 155 MPH (especially after changing the final drive ratio) is nothing but a guess unless you've actually tried it. Is it possible to figure out mathematically? Sure, someone with all the correct data can come up with a rough estimate. Can you figure it out with math? Well, I'm still waiting.

 

Anybody that worries about the ability of going over 155mph has a death wish. There's no reason that a street car needs to go over 150+ (even that's realistically a lot). Unless you're taking the car to a mile stretch of road such as a runway, no need. Top speed is partially determined by horsepower, but transmission and gearing plays a huge role. Look at the old school muscle cars that have 400+ horsepower, since they have such low gears they normally max out around 130mph. I wouldn't mind sufficing 5mph for a lower final drive that increases acceleration. This WILL be my next mod.

Check this out; Top Speed Calculator

 

I grew up on American muscle cars and pony cars. I've run everything from 2.73, 3.08, 3.55, 3.73, to 4.10 in my Mustangs alone. I've swapped ring and pinion gears by myself and properly set the back lash. It seems to me that most of the people who post in this forum don't have that kind of background or experience with basic performance mods that involve gearing.

That said, I'd personally NEVER change the final drive in the G37. A lot of guys here who don't understand gearing probably won't realize that there are penalties to pay for the greater leverage you get from more aggressive gearing. To me, it's just not worth it in a car like the G37. If you're talking about a track car, then fine...that might be worth it. But a street car? No thanks.

So what's wrong with changing the gearing? Well, not only will your fuel economy suffer (all else equal), but even more importantly, your car will forever be revving at a higher RPM. I like the fact that 6th gear is very much overdriven to the point that the car just hums along easily and quietly at highway speeds. My old 5.0L Mustang came with 2.73 gears and the car felt much more alive after I swapped in a set of 3.55 gears. But long highway trips sucked because the car was noisy due to the fact that the engine was now at a substantially higher RPM in every gear, including overdrive. It was fun zipping around town, but highway trips became something that I'd avoid. Another thing I like about the G37 is the long pulls between gear changes. Our engines aren't exactly high revving engines, but with the stock gearing the car pulls for a fairly long time between shifts. That's something that will change to some extent by swapping in more aggressive gears. I don't know, I just think of my G37 as more of a grand touring car than a stoplight racer. I'd personally never want to make the sacrifices necessary to change the stock gearing. The stock gearing is the perfect compromise IMO.

 

I'm not advocating driving 155 MPH. I'm just making the point that changing gears has benefits and drawbacks. For the most part, when you swap gears that allow you to accelerate faster, you lose absolute top speed.

 

Drag: (FD)= CdqA = (Cd(1/2) r V2)A

Where:

Cd = Coefficient of Drag is a reflection of the aerodynamic efficiency of the shape
q = Dynamic Pressure in the Test Section
r = Mass Density of Air
A = Frontal Area of Vehicle
V = Velocity


Aero Horse Power: Horsepower required to move the shape through the air at a specified velocity.

1HP = 745.7w

P = F · V
P = (1/2)(rho)(V³)(A)(Cd)


Where,
Cd = Coefficient of Drag is a reflection of the aerodynamic efficiency of the shape = 0.29 (published figure, includes rolling resistance)
V = Velocity in m/s
A = Frontal Area of Vehicle = (roughly) Length x width * .85 = 2.53847234 m^2 * .85 = 2.15770149 m^2
rho = Mass Density of Air = 1.2kg/m3

Width (in.) 71.8; Height (in.) 54.8

Using the formula above:

1HP = 745.7w

P = (1/2)(rho)(V³)(A)(Cd)
(330hp)(745.7w/hp) = (0.5)(1.2)(V³)(2.15770149m²)(0.29)

[(330)(745.7)]/[(0.5)(1.2)(2.15770149)(0.29)] = V³
[246081]/[0.37544] = V³
655446.942 = V³
V = (655446.942)^1/3
V = 86.8652047 m/s = 194.311929 mph
V = 190 mph (using significant figures)


This, of course, assumes that you're making 330hp at 190mph, which would require that a gear hit 190mph at peak power. Oh wait, using a 4.08 FD just HAPPENS to be able to hit 189 mph in 7th gear at redline. Funny.

I just did.

 

4.08

Maximum speed in first gear: 29.7 mph
Maximum speed in second gear: 45.8 mph
Maximum speed in third gear: 71.6 mph
Maximum speed in fourth gear: 103.6 mph
Maximum speed in fifth gear: 146.1 mph
Maximum speed in sixth gear: 169.9 mph
Maximum speed in seventh gear: 189.7 mph


3.36 (stock)
Maximum speed in first gear: 36.1 mph
Maximum speed in second gear: 55.6 mph
Maximum speed in third gear:87 mph
Maximum speed in fourth gear: 125.8 mph
Maximum speed in fifth gear: 177.4 mph
Maximum speed in sixth gear: 206.3 mph
Maximum speed in seventh gear: 230.4 mph