im finally ditching the ten bolt, cant really complain maneged to pull 1.5x 60' times on stock 2.73s. Now the question comes 3.50s or 3.70s in the 9".

Car has been a best of 6.49 @110 in the eighth. The car is on the limiter(6400) in 2nd(th400) when crossing the traps. Its going to get more boost and heads for next year. I would like to see high to mid 5's out of it.(trying to be reasonable here). I wont turn it any higher than 6800-6900rpms.

It will see mostly 1/8th mile stuff, going to a 1/4 track maybe 2-3 times a year. I dont really care about driving it on the highway, if it needs to go somewhere it will be on a trailer, although it does see decent street miles, gotta get to work on a nice day ya know?

I put this in here because gearing for turbo cars always seems to be different than everything else, thought this place would have the best knowledge.

i didnt make it a poll because no one reads what you typed when they can just vote and be done with it.

 

With an 88 and possible 1/4 passes, I damn sure wouldn't go lower than the 3.50. You need to load the turbo, and you don't want to run out of gear in the 1/4. When you make the kind of power you are talking about, toss N/A ratios out the window. With a turbo400, pick the right stall and let the turbo work. Steep rear gears are for cars that don't have ludicrous torque.

 

dont worry about "loading the turbo" Just gear it for the traps liek you would any other car...odds are you will 60ft better and have a lower ET.....Not that my turbo owning experience would mean much...

 

3.5 if you re planning on mid 5s

 

I think you answered your own question in your post,150 60 ft.with 2.73s,car on the limiter when you go through the lights,going to make more power later,etc.I wouldn't even think of going any higher than 3.50's.

 

I wouldn't go to any gear higher than 3.25. My 60's and 1/4 mile improved when I went from 3.50 gears to 2.75's. I don't run a lot of tire though. The gearing you choose depends a lot on your setup. In my case the 3.50's wouldn't let me leave on any boost, with a tight converter. That caused me to spool slower since I was leaving at 0psi. With the 2.75's I can leave at 5psi and be at full boost as soon as I release the trans brake. I could have fixed the spool issue with the 3.50's by going to a looser converter but chose gearing instead because of streetability.

If you are able to launch hard enough to spin with the 2.73's then I don't think you need to go to a much higher gear since all it will really do is cause you more traction issues.

 

still gonna be chassin a lil import

stick with 3.25's of 3.08's there is a reason i told you to trade for those gears in the ten bolt in the first place. But what do i know, i drive an import

 

please explain to me how changing the rear gear will change your transbrake rpm? (car not moving)

secondly, if the engine is allready working as hard as it can to get down the track, how does going to a lower gear somehow summon more power?


you gear a car based on shiftpoints, tire size, and max mph needed in high gear. for an auto you need to figure in your slip%

heres one of many calculators for example
http://www.wallaceracing.com/calcmph.php

 

I don't think you understand what I'm saying. It doesn't change the RPM you leave at (at least not directly, it can indirectly by going to a higher boost level on launch which of course pushes the converter to higher rpms). I'll try to clarify a bit.

With 3.50 gears I could not get traction if I left with more than 1psi of boost off the trans brake. With the 2.75's I could leave with 5psi and traction. My setup has a tight converter and not leaving on boost causes slower spooling, slower spooling = less power put the the ground = slower times.

Say from 0psi it takes me 2 seconds to reach 18psi from dead stop. If I build 5psi of boost before launching it now only takes me .25 seconds to reach 18psi. But if I have the extra torque multiplication of 3.50 gears vs my 2.75 gears I can't hook the extra torque and end up spooling slower. It's a giant balancing act of traction, spooltime and torque and every setup is different.

Going from a 2.73 gear to a 3.50 gear will not improve times if you can't hook the extra torque and end up spooling slower as a result. This varies with different setups. There are a lot of variables in play, torque converter, how fast the turbo spools, how well the car can hook, etc.

I think my car can leave in the 1.4x range with some susp work and a well prepped track (something i rarely get to run on). Having less gear like I do requires me to leave on more boost to make up the difference in applied torque. I could leave the same way I do now even if I changed to 2.40 gears, I would probably have to leave on 10psi vs 5psi though. The amount of boost you leave on is affected by gearing, if you are racing competatively you probably don't have 3-4 seconds to sit on a transbrake to get 10psi so this can affect your gearing selection as well. You might choose to sacrifice better ET's for time need to to stage the car properly.

For the record, most people think i'm nuts to run 2.75 gears in my car and don't understand how i'm able to leave as hard as I do with such a "crappy gear".

 

ok so yes the calculations assume you are not spining the tires.

 

If we all had perfect traction drag racing would be simple to the point of boring. Although from some of your old wheelstand pics I guess you don't have a lot of issues in that area.

 

im not worried about traction, it will get a set of 325's with the rear end. If i cant hook that then i need to get out of the drag racing thing.

It has a good bradco converter in it. It leaves way too soft right now, and i know putting a lower gear in it will help, so 2.xx is out.

 

zombie i get what you are saying now, your first post just didnt mention that more gear made you spin is all.
i understand that avoiding spool up during a run is very important to ET, so if having too much gear makes you spin (and you can't adjust anything else) and leaving easier gets you into spool problems, that dropping gear is a good solution.

i just wanted to remind all that gear set up is math not opinion or feel or advice etc.
to get the car to the other end as quickly as possible, you want to have as much tq going to the ground as possible, which means run as tall of a gear as you can given your tire size, max rpm, and ideal trap speed mph considering converter slip if you have one.

i run a 3.42 gear with my 4l80 and due to how fast the car ended up running this year (i figured the car would drop mph with the auto swap) i am just on the wrong side of things and would do better with a 3.23. moser doesn't do that ratio so i'm looking at a 3.08 OR putting a large tire back on the car for next year.

 

Big boost doesn't need big gears unless you're camming for high rpm with a solid roller, etc.

I dropped from a 3.73 to a 3.08 to a 3.00. Even dropped 1st gear down to a 2.10....so my overall 1st gear is 6.3 : 1 ......runs 5.8 in the 1/8th ....9.2 in the 1/4 at 3700ftDA 1.37 sixty when it hooks up....rev limiter at 6500 rpm...3800lbs....with 325's I'm still fighting traction problems......boost > gear.

 

Zombie you racing on 26's? 26's vs 28's, there is a big difference in terms of possible traction.

Coop run some numbers thru that online calc link that was posted, you can see that a 3.70 would be pushing it for mid 5's and a peak rpm of 7000. I am running 3.50's and have not even come close to maxing out my rpm potential. According to the gear calcs and assuming I go up to 7400 next time I can do 167mph.

 

My tires are a hair shorter than 26, they are 275/50/15 Hoosier DR's. My car is traction limited due to me not having anything done to help traction. I'm working on fixing that next year though. I don't even have a pair of skinnies for the car yet, i just run the stock SS wheels.

I'd like to try a 27-28" tire to see how it work on my car with my crazy gears. I didn't want to give up my ABS yet though.

 

I think 28's and 2.73's will be hard on the converter.

 

I am running the 2.75 gears after discussing it with you via pm's (I'm the guy from montana)

I am on my 2nd set of 325 mt dr's. I have a full suspension set up & it will waste the mt's on the street. My car is strictly a street driver & I have no regrets with this gear selection.

This is on a little 347 & tc76 turbo.

 

When I crank up my car to 14 psi I think the tranny takes a terrible beating.

Earlier this year it crushed the planetaries when I hit second. I should post a pic of it.

 

I think it's too much tire as well, that's why i've stuck with 26" max so far. I've got 200+ passes and 5000+ miles on my setup now and haven't had any issues. Still the same rossler trans and vig converter, fluid looks/smells brand new.

Glad to see that you are happy with the choice. I was skeptical about going to 2.75's myself but have ZERO regrets for doing it. It makes a really great street car when you only have 3 gears and short tires.

Not many manual trans people want to race from a roll either once they find out I shift the 2-3 at 110 mph.

My theory was that I could gear my car to run the 1/8 mile like a power glide and just let the performance in 3rd fall where it does. I trap 6.5-6.7 @ 105-107 in the 1/8 mile on a good pass and pickup 26-28 mph by the 1/4. Once I get the chasis good I'll probably be going 6.2-6.5. 2.75 gearing is outside of the box thinking, but it's worked pretty good so far. I'm a full weight street car and don't want a race only car. I drive it about 100 miles / week.