Final Drive Ratio, wheel, and WHP changes
 

So with the imminent install of my 4.08 gears, I thought I'd document my findings here, but I wanted to open up the conversation early and and reserve the second post for the results. I'm also testing a couple other theories having to do with wheels and tires on the dyno. Some othe things I'll be looking at are:

Final drive WHP changes. We've seen final drive ratios reduce WHP numbers by 10-15whp. I wanted to do a back to back dyno to get an accurate number.

Wheel weight and diameter changes. Theory says that it should improve dyno results. The shop has a set of 18" Forgeline wheels that weigh 18lbs to try.

Variables to take into play: Increased efficiency with the wavetrack differential compared to the VLSD. Polyurethane bushings and subframe collars reducing slop and movement. This should improve efficiency in putting power down; not sure if it's measurable difference.

Somehow magically, the weather is still mild here in Tampa with only 30% humidity and the high only reaching 68 degrees today. Shop temps should be around 75-78 degrees for reference and we are sea level with pressure around 29inHG. Just the other day she laid down a high 342/274 number, so this should be the benchmark.

Feel free to comment on thoughts and ideas. It would be nice to show higher numbers than 342, but I don't know. I have my reservations.

I admit I have trouble understanding this, as I sometimes get it backwards. But since you're planning on going FI, won't a 4.08 be counterproductive? You'll have such a huge power:weight ratio, you'll have difficulty hooking up the rear wheels for consistent launches...unless you plan on dropping the clutch in 2nd gear or something. Also, if you'd like to get 0-60 times (if I understand the relationship correctly), you may have to shift from 2nd to 3rd before reaching 60 -- or at least be way outside your powerband before 60 in 2nd. Feel free to correct me if I've misspoken!

Good luck with your experiment!

Well, FI is a year+ down the road. But as I see it, it's a way to limit the amount of torque I "need". I wouldn't need 600lbft for it to feel like it has that much. With future cam/ ATI damper, oil pump gears; 8krpm should maintain a similar powerband. It won't feel like I'm running out of rpm before I get to speed. I've always been a proponent of reigning in torque to whats actually manageable to drive. Managing torque output will make it much easier to power out of a turn without all the drama. To put some perspective; a new 2018 5.0 makes nearly 400WTQ stock. It has to manage that with less tire. 500WTQ is stock Viper torque output. I think anywhere in there would be a good goal. If it's too much and traction is just bad, it would be easy to find another 3.69 set.

yeah i had a thread about this years ago
setup for the car was same for both dyno's

http://www.the370z.com/engine-drivet...ifference.html

If you are going turbo... 4.08s are the last thing you want. May be worth while with a supercharger?

Subd for results regardless.

I see. Good read. I'm hoping to add some additional input as it will be same day with identical conditions and how adding more efficient parts might show up.

Agreed there my tuner said if I was going turbo I would switch back to stock gears since I’m going supercharged he said to stick with the 4.08

I scored a complete pumpkin, with stub shafts, seals, wavetrac lsd, 4.08 gears, and z1 diff cover for $1500. It was already assembled by Z1. Was used for maybe two weeks. I drained the fluid to open it and the fluid was still clear. I can still see the machine marks on the gear lol. So I'm going to run that 4.08 and figure out future issues when I have them :)

I've got 4.08 with six speed and first gear is almost useless. Rev limiter comes on super quick. Second gear feels like a tall first gear. But, second, third and fourth feel great. Overall, I like the lower gearing because of what it does for the gears I'm in the most.
My supercharger build will be finished up this week (a2a and e85). We'll see how it feels with the extra hp. I'll be having an os giken lsd installed soon, I can always go back to the 3.69 at that time if I don't like the 4.08.

One thing is for sure; You should be able to get an accurate whp/tq with 4.08’s...as it won’t over speed the Dyno in 5th gear (1:1)
Your 4th is 1.27:1 & an auto is 1.41:1,
Some tuners avoid 1:1 in these cars because of the higher speed @7500+ R’s
Good Luck & post some #’s ... as 5th will yield higher ones than 4th gear,
And don’t be surprised if your #’s Dropoff a tad; because it’s easier for the engine to turn 4.08’s vs. 3.69 or 3.36’s

There is not much of a power difference doing a dyno in 4th or 5th gear with the 4.08 you yield just about the same numbers..
I was at 320whp with the 3.36 and with the 4.08 301whp

In the link below post 4 it has my dyno comparison. It has a fourth gear pull a fifth gear pull in the 4.08 gears compared to the fourth gear in 3.36 gears

https://www.myg37.com/forums/ecu-tun...-new-dyno.html

chuckie311;
Do have the 6sp.man or 7sp.a/t?
As i haven't made a gear swap/just dyno comparison between 4th & 5th gears...
The torque made a larger increase than the hp did (in 5th 1:1),as my jump is from 1.41 to 1:1 (50mph difference w/3.36's)
I can see a stick shift Z,not as big of difference (1.27 to 1:1),,,but i see your point w/4.08's not making much of a difference between the 2.
Firehawk is experimenting w/wheel tire weight & differences in VLSD vs. Helical locker.
Unsure on these differences; as from old school (Chevy/Ford) the 9" ford diff supposively took less hp to turn than the GM 10/12 bolt.

I have the 7at auto..
When I did those dyno runs I had 20 inch rims I have now switched to 18’s but haven’t been back to the dyno my next dyno will be when I supercharge the car sometime next year..

Yeah, at 25k miles, my rear subframe diff bushing was shot. Had fluid all over the diff cover. $hits the truth, they're trash. You might as well just replace it.

Those Z1 bushings are really damn nice btw. They aren't drilled, and definitely beefier than the whiteline or energy bushings that came with the pumpkin. So kudos to them on that.

Things got delayed when we couldn't find ta stub shaft seal in town and my stock axles are threaded. So hopefully today.

Man... I'm seeing some interesting numbers. Definitely contrary to what has been said and what I thought. Still waiting on Dyno passes with stock wheels, but the Dyno brake temp sensor is being a bitch and killing the fun