tpereira

I was just curious if anyone has actually changed their transmission's 5th gear for better acceleration in a standing mile event ?

When I did MileMarker-1, the car pulled to 150 very quickly, but when shifting to 5th, the rpm's dropped out of the power band, which slowed the rate of acceleration dramatically.

I cant help but think a gear ratio between 4th and 5th would be perfect, and have the current 5th gear become 6th.

Is this even possible ?

NASTY ZO6

Wanting to go faster this October? lol! Sorry can't help you with this, but it will give ya a bump!

Hope to see you @ the next event!

tpereira

hahah yes !

Im thinking change gears, add fuel system, and see what she does... I want to do it again, but need to make some changes to make the drive worth while...

tpereira

Fiss

Might be easier and cheaper to try and use a zo6 tranny

Fiss

or just change out rear end gear ratio

tpereira

the Z06 has the same 5th gear, and I would rather not affect all the other ratios by changing the rear end ratio (especially 1st & 2nd).

waltershu

use a ZR1 trans it has different 5th and 6th gear ratio.

tpereira

Oops I was wrong about the Z06 ratio... Its 0.74 vs the 0.71 I have in with the Z51 package.

ZR1 has 0.81 5th and 0.67 6th... Sounds perfect... Now will the price make me do this

Joe_G

Put in 4:10 gears instead. They provide value from 5 mph to 185 I can attest. They make the car feel 500 lbs lighter. You will love them I promise.

But the C5z trans has a lower 5th than ours, my buddy maxed his out at about 140 or so and had to go to 6th.

Have a listen. Hope to see you in Oct!

drivinfast

Seems like you would get better results than you are getting. I have the Z51 gears and went 201 mph in the standing mile in 5th. see sig video. our 5 speed is not that much difference.

you have 700+ hp according to your profile
In the 201 mph run i had 757hp. (cold day, great tailwind.

better and easier alternative. I have a set of 4.10s used if you are interested. Save you a couple hundred on parts.

tpereira

My official best mph was 180.6. Most people were posting that the timing system was off 4 mph . My GPS said 185. On the run I had a passenger as well (actually for a bunch of runs), and always had at least a half a tank of gas (recommended to cool the fuel pump).

Im thinking if I got rid of the body, reduced some weight, let the car cool down more between runs, went back to lighter oem wheels with NT05Rs, I would have done much better. But definitely not 200mph.

Im thinking a fuel system (to allow more power), and a gearing adjustment would bring me a lot closer.

I dont think I would enjoy the 4.10's on the street. It would just make it harder to hook up, and I would be shifting all the time...

as for c5z ratios, I think 5th is perfect, but 6th would be an issue:

Transmission
Gear Type 6 Speed Manual
Final Drive 3.42:1
1st Gear Ratio 2.97:1
2nd Gear Ratio 2.07:1
3rd Gear Ratio 1.43:1
4th Gear Ratio 1:1
5th Gear Ratio 0.84:1
6th Gear Ratio 0.56:1

that 0.84 would get me to 180ish a lot faster...

I keep thinking about the runs where 1-4 gets me to 150 quick, then 5th takes a while... at 150+ mph your covering a lot of ground. If I can get to 180 quickly, then hit my current 5th (as a 6th gear) at a point where I have an additional 100 rwhp, I could probably do much better.

The question becomes how do I get there, and how much will it cost

drivinfast

^^^

yep. i had 4.10s and when i went SC i went back to 3.42. the shift betweeen 1-2 is so fast...so its work on the street like you say

lighter wheels. and drag radials will improve maybe 5 mph. it did for me.

what about oversize tires, last time i used toyo 335 R888 which are undersize about 3/4". next time i will use MH 345 which are 28" dia. about an inch over size.

no passenger and getting the car lighter will help a lot.
the fuel system will only be needed if you are loosing psi on top. do you have a secondary fuel sysem with your setup?

about the transmission. i had mine redone. and seems like the tech said the 1-4 gearset comes as one and then you can swap out 5th...so i kept the stock Z51 gear ratios. i would be surprised if it is cheap

All_Motor_C5LS6

At 70mph, which gear set will pull harder from that mph with all engine mods being the same and a 6800 redline. 3.42s in 2nd or 4.10s in 3rd?

Joe_G

A car with gears will always pull harder at a given MPH than a non-geared car because the car with gears will be at a higher rpm for a given MPH.

let me demonstrate this with some dyno work we did a long time ago.

Here I am, pre-FAST compared to Chad, a guy with a FAST, same cam as me, same stock heads, but stock gears vs my 3.90's, with our dyno sheets overlaid...dyno sheet below laid out by RPM.

No, it's not the same car. Trust me.



Now...here are our same dyno runs, with the x-axis being MPH vs RPM. Note that my car, the top line, has 30 RWHP almost any RPM due to my RPM's being higher for a given MPH. This graphically shows why gears make a huge difference in how your car feels. It also helps with drag racing immensely to get out of the hole. I noticed that 4.10's are easier to launch than 3.90's.



You don't shift any more with gears, you still get into your cruising gear like you would with stock gears. You might shift a little faster. You do not spin more, you spin less with gears as the car quickly "catches up" to the spinning tires with gears. I lost 1 mpg (I track all my gas usage) with gears, I can send the spreadsheet if anyone is interested. These facts on gears are well discussed and dealt with in many threads in this forum if you are interested.

That's enough talk on gears, Pre-Z06 I don't want to hack your thread any further.

The C6Z51 trans has a good 5th gear for top speed, that's how they got the 186 stock rating out of it. The C5Z has a much shorter gear that maxes out a lot sooner and the car can't pull it's 6th gear.

You can play with the gearing effects on top speed the following website, choosing different cars, transmissions, rear gears, tire sizes, etc. if you are interested.

http://xse.com/leres/ss/calculator.html

tpereira

My goals are a nice street able car that can do 200mph in a standing mile Part of that is being able to daily drive without hating life if I get caught in traffic. I have an RPS twin carbon clutch, its great, but its a little firm when in traffic so the fewer shifts the better (maybe I should work out more because my leg gets tired lol). Ive heard this theory that gears make the car hook up faster. I never understood why though. Your not catching up to anything sitting there spinning tires. Guess I should go research it on my own.

Ive been using this site http://www.car-videos.net/tools/speedrpm.asp to view the gearing changes. It lets you change the rpm increments for better speed resolution.

I sent an email to RPM Transmissions today. They can build a Level 5 with custom gear ratios. 5th at 0.83 and 6th at 0.70. The price isn't bad, and I could probably use the beefier transmission anyway. Time to go use the site and see what it looks like for speeds and shift point vs dyno sheet.

tpereira

I was using MT 345/35-18's (27.5" diameter) which are taller than the NT05R 345/30-19's (27.36" diameter). Both are taller than the 345/30-19 PS2's (27.2" diameter) I had on the car before.

I looked up the R888 and could only find them in an 18" for 335, and these were 26" diameter. These would provide a nice gearing advantage.

The taller tires will give you more ultimate top end if you want to find out maximum speed of the car, but the shorter tires will get you there faster (which is what is needed for standing mile).

I have a Boost A Pump on the car.

Joe_G

Tires are much cheaper than gears or a transmission. I have 275/40/17 mickeys that are 25" tall. Plug those in and see what that does to gearing. You are welcome to borrow them if you come back for a mile event to see. I personally don't run drag radials at 185+ but some do, my buddy borrowed them last time with no I'll effects. He borrowed mine as a matter of fact.

Please do some research on gears. You have the common misconceptions I used to hear....they aren't true but don't take my word for it. I love gears as do those that end up getting them. Only time I wouldn't recommend gears is if you do a lot of road course work, this comes from road course guys.

drivinfast

If you run across a program/spreadsheet that can simulate all of this at once, please inform me. I would be interested...at the Texas Mile seems like the supras that do 240+ had very large dia slicks...while the Ford GTs in the same mph were limited to stock size dia because of the wheel well limitations.
Coeff of F
tire diameter
gears
HP/tq
track length
end speed (calculated)
elapsed time (calculated
etc.

you are correct on the r888s when i used the R888 at 26 dia they seemed slower that my previous drag radials. course there was a big headwind and it was hot too.

tpereira

I plugged in the 17's. Big difference... 5th gear went from a maximum of 211 mph to 197mph. Meaning it would definitely pull harder. The bad thing is that I still hit 5th gear around 4700rpm.

If I change 5th from 0.71 to 0.83 Im around 5400rpm which is a big difference in power (+100 rwhp). With the gear change, 5th is only good till 180, then I would jump to 6th for max speed (now gear limited to 211).

If I head down in October and haven't done the transmission, I may very well try those tires. Im sure I would be a lot faster with them.