Ya they told me they would run it in 4th gear because there was not enough power to run it in 5th. They told me they knew 5th gear was 1:1 but they would get as close as possible to it. They were working on two older GTRs and a massively hooked up 350Z so I took their word for it. They told me just to do any future runs in 4th gear. Regardless, I would think the numbers are correct due to both runs being in 4th. If one was in 5th and the other in 4th then I could understand. I remember a previous post from a G37 vendor who also did their runs in 4th gear so I took this into account as well (this was months ago when the G was first released). I am not a dyno expert nor claim to be so if anyone could shed some light on this then please post something.

 

ive done all mine in 3rd normally

 

Ya, it would be great to know what the big deal with doing it in 5th (1:1) really is. I really don't see how the numbers would be off for gains IF you did all your runs in that gear. So Solo, if you do all your runs in 3rd gear then I wouldn't see a problem same as me doing mine in 4th. Where are all the experts on dyno testing. Not the ones who have done a couple and think they are but the ones that do it for a living for a shop. We have to have at least one on this forum.

 

i didn't do the pulls. i was never the driver. others did them and they all said 3rd gear for some reason. no clue why

 

Hey guys, this is what I have heard.

Dyno jet dyno: do 2nd to 3rd to the rev limiter
Manual: 3rd gear if you have 5 speed, 4th gear if you have 6 speed

It also depends on the dyno dynamics.

 

as long as your baseline run is consistent with all the other runs then that is the only thing that matters...(ie same dyno, same gear, etc.)

 

Hello guys, MaxToTheG37 requested that I come on here and give you some information regarding dynoing on a Dynojet Dyno.

Having read through this thread, one thing that seems to keep getting asked is what gear to dyno the cars in. The rule of thumb for a naturally aspirated car is always the 1:1 gear. The theory behind this is that in a lower gear, HP/TQ is being used to accelerate the inertia of the drivetrain faster than the tires, so more power will be lost through the drivetrain than in the 1:1 gear. The same holds true for overdrive gears...more power is used to overcome the intertia of the drivetrain than in 1:1, as the gearing takes away torque multiplication. Here is a graph that illustrates the point. Shown is a 2nd, 3rd, 4th and 5th gear run, known as the all-gear pull.

In the case of bboysteele's car, as mentioned above, as long as the before and after runs are run in the same gear, the dyno will show repeatable and consistent dyno runs, although the peak numbers will typically be lower than what would be found in the 1:1 gear.

Looking at the dyno runs that bboysteele attached to one of his posts, the biggest thing I see affecting the power increase is the air/fuel ratio. If you view the dyno run using our WinPEP 7 software, you will see that the air/fuel ratio after his new cats is almost a full point leaner than the previous runs. This is likely due to the efficiency of the aftermarket cats versus the restriction of the stock ones.

For peak power, most tuners target 12.9:1-13:1 air/fuel ratio when tuning. Seeing that his car made around 12:1 with the stock cats, then around 13:1 after the new cats, I would attribute most of the power gains to this.

As I am not familiar with the G37 tuning and ECU capabilities, I can only give basic information on what normally happens. In the case of most cars, they have a "target" air/fuel ratio that they attemp to achieve. When things change, like changing to aftermarket cats as above, the air/fuel ratio may change for a short period of time, as the car samples O2 sensor readings and tweaks the short term and long term fuel trim values. Typically, with some driving, you will find that the car will identify the lean or rich condition, and adjust to match it's target A/F ratio again. The only way to keep the power gains associated with the power made by A/F ratio changes, is to program the ECU to target those values instead.

Hope this helps.

 

Thanks Keith

 

Thank you for the explanation DJ_Keith. If I understand the last part of the post, basically the gains will be nullified by the ECU's programming once it gets used to and adjusts for the leaner A/F mixture. If that's true, I may wait to get exhaust mods until a reliable ECU reflash is available.

 

Thanks Keith, that explains the air/fuel ratio I saw when I did all my runs. On the runs I did in the Springs and the runs I did in Denver before I got my CATS had the air/fuel ration bouncing up and down close to 6k and above. It ranged from 11 to 15 if I remember correctly. Before 6k it was relatively flat. After the HFC install, the air/fuel ratio was rather flat throughout the RPM curve.

 

I see ... yes after looking closely at the 350z thread it is an exhaust "component" so I imagine that it will be able to be used in conjuction with any exhaust system... that's good to know!

 

Ya is Black Betty's assuption correct? There will be little to no gains from an exhaust, HFC, or intakes unless we can get an ecu reflash?

If so that is rather disapointing.

 

I am not sure Keith will be back guys... I emailed a ton a dyno companies yesterday and He was the only one that was nice enough to come over to the thread and clear some things up... He may be back....He may not... I dunno... but just a heads up tho...

 

I can't say how much of the power gained is from A/F getting closer to what it should be, or how much was from the cats. The only way to know would be to let the car "learn" the fuel trims and re-dyno. Air/Fuel should be back to what it was before (around 12:1). Then, the gains left would be from the restriction loss only.

Thing is, there will also be some inconsistency in the vehicle that you can't account for. Normally, we'd like to see testing all done on the same day, as close in time as possible.

 

What about Resetting the ECU... Is it going to learn the new flows and adjust to the new flow...or will it learn and adjust it back down to 12:1 or what?

thanks again for helping us understand bro...