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

347WHP/276WTQ

Regardless, the numbers kind of speak for themselves. I don't think there is any difference in dyno readings with the gear change. Which totally goes against what people were saying. I was expecting something in the 330whp neighborhood. The fact that it made 347 in the same conditions as the last dyno?!? Sorry for the abrupt end to the video, I shut the video early on accident. I wish I could've gotten my wheels on the dyno for a good reference. The dyno brake temp sensor took a dump before I could run with my normal wheels. I'll go back and get those done when the dyno is back up.

https://farm5.staticflickr.com/4478/...63c72d09_b.jpg

Making old school dodge viper number with 4 less cylinders

Good Job,
Didn’t realize your 342whp was made in 1:1 as well.....When are you putting in the Cam’s?
I’m ready to see it jump over the 375whp mark. :)

Heh, I need to recover after spending some money on these + the install. I'm just so confused that power didn't go down.

Yeah, the 285/30/18 tires and wheels had to have definitely helped, just not 20WHP helped if you know what I mean. Theres a 2" diameter difference, the tires are 3lbs lighter than mine, and the wheels are lighter; I didnt have a scale, but the weight diff wasn't more than 7-10lbs max.

It was warmer outside last night than before, but the shop temps were the same. It's just interesting to me. Now I'm so closed to 350WHP, my balls hurt. And for reference, there was no retuning, just dyno. Afterwards I dropped by Martin's house and he kindly updated my gearing tables to fix SRM.

Your speedometer stayed dead on because of speed sensor location,didn’t it?

Not sure. I just know at 80mph I'm well over 3400rpm
And Ecutek fixed my SRM. It started screaming at over 100mph.

DUDE. That is some serious NA power.

Finishing testing Monday evening when I get back home. Wife says my car doesn't know how to shut the f#$k up and makes all kinds of noises lol

I'm still waiting on the diff work to be complete, but I was doing some more research and this is what I came upon.

If you change your final drive, it should not reflect on a dyno when using a 1:1 gear. If you're running a lower final drive any dyno in 4th; your numbers will be lower because the rpm delta is greater when you calculate 4th gear with the lower final drive gear.

formula: rpm = (mph x final gear ratio x 336*) / tire diameter
(you get the gear calculation by multiplying the transmission gear ratio with the final drive gear ratio)

Using 4.08 as my final drive
with a 1:1 gear; 75 x 4.08 x 336 / 26.9 = 3822rpm
with a 1.27:1 gear; 75 x 5.1816 x 336 / 26.9 = 4854rpm
delta = 1032rpm

Using 3.69 as my final drive
with a 1:1 gear; 75 x 3.69 x 336 / 26.9 = 3456rpm
with a 1.27:1 gear; 75 x 4.6863 x 336 / 26.9 = 4390rpm
delta = 934rpm

Hopefully this helps make a bit more sense. There was a post on a forum talking about how the dyno calculates power, but I can't find it in my search history. It was a lot of math. But the calculations above at least make sense to my why anything but 1:1 reads lower.

it did change my dyno numbers.. went 3.36 to 4.08 big change size
no matter what gear we dyno'd in the numbers were different..
both Dyno's between the 2 gears were exact same setup for my car..
i have done lots of research to find the answer and almost every forum i went to everyone had a change in dyno number with a gear change .
why your did not change is weird..

https://www.corvetteforum.com/forums...post1590896300

I'm gonna find out soon on mine next month.
7A/T made 309/253 whp/tq in 4th gear (1.41:1) & 314/264 in 5th (1:1)
5th was on same type Dynojet Dyno at different place,,,as when tuned-Tuner's Dyno didn't support speeds above 170mph....so should be under the 170 mark w/3.69 gearing in 5th.
Only performance changes since tuned are the up-graded hi-flow air filter kit from Z1.

So I finally got my car back in the shop to finish Dyno testing. The only changes made was my oil and I added Z1 motor and transmission mounts.ill post up data when I have the DRF's. I'll also combine the videos of the runs. Temps were mildly warm and humid, but not terrible. So the runs...

4th gear... 331whp
5th gear: 340whp 3x in a row.

When I had 3.69's and the same wheel/tire combo, I made 342. So between environmental variables, I'll say its negligible. The 347whp result must be a combination of a 12lbs loss of wheel weight and a smaller diameter wheel and tire combo.

So you’re the guy off YouTube. Ha great numbers! Car looks great.

Un-sure what kinda #'s mine will make on 12/9,,,but gonna roll with what's on the Z.
Wheel's & tires are a bit heavier than last tuning; but it's what i'm running & gonna hit the dragstrip with same set-up.
I'll post up when i get result's...Most importantly want the AFR/Timing correct on Z for optimal power for the few mod's i have.
Then we're going down in the 12's w/345's on 12's & 285's up front on 10's.....Wheel/tire setup will change for the dragstrip for sure-as i know these will stunt me back somewhat.

Heh, yeah, I make a few. Mostly Mexico stuff. Idk. I just started playing with Adobe premiere and I have a Go Pro and Waylens set up. Thinking of getting an OBD2 splitter and run Harry's lap timer as well. Debating doing a car overview, but idk if I want to do all that video blog ****. Most of the time I like straight and too the point.

Hi Guys,

Been reading this thread and trying to understand all the numbers because I have been thinking about making a gear change as well. I have a 2010 with a 6MT with Stillen Gen 3 CAI, Berk Resonated test pipes, and Ark DT-S exhaust. My diff let got the other night and fortunately for me I already have an appointment to have and OS Geiken 1.5 diff installed. I was thinking of going up to a 3.9 or 4.08 but want to understand if will have the desired effect I am going for, which better acceleration for drag/roll racing performance. It seems like from the info post that the WHP will go down some but the torque will go up. Will this give me that improved acceleration I am looking for or am I misunderstanding?

OS Giken is a good choice. When my car just had bolt on's, I had 4.08's installed. It definitely helped with low end performance. I feel it's a good upgrade for a car with bolt ons. Once I went forced induction, I went back to the stock 3.69 ratio. First gear became absolutely useless and the lower gearing isn't needed with added power. That's just my opinion.

:iagree:

N/A, the 4.08 works good for the strip. Going boost. Most guys want to go to the 3.54, or the 3.30 gears. As 1st gear, and the bottom of 2nd gear is overpowered by engine torque.

Using the OS Giken diff. You have to use the OS Giken lube to keep it quite. Otherwise, it gets noisy. After install, change the lube after 1000 miles. The lube used to be $70.00 a liter. Now I see it's $50.00 a liter. I have one, and it works great. Get the Z1 finned diff cover too. I recorded temps of 265F in my diff. The cover will hold an extra 1/2 liter of lube.

Thanks for the info and advice. Yes I already have the z1 diff cover on the build list. It is getting done July 9th. Unfortunately I am down until then as the planetary gears in the stock diff let go Thursday night. It is totally dead for now.

If you go boosted, you will want 3.33 gears. If you don't know which way to go stay stock gearing for now.

:iagree: