high power; gear ratio? ideas please!

hello sirs! It's me again XD

Lets say you had a stroked turbo ka24de worth around 300-400rwhp, lets also assume the rev limiter would stay pretty similar to factory rpm, possibly pushed up 250 or so.. (I don't have this, but I'm thinking about throwing globs of moneys at my car ^_^ )

What kind of recommendations would you guys have on desirable gear ratio solutions, I would probably be adding an inch of diameter to the rear tires by the way.

I'm figuring said car would have pretty much 0% chance of traction with the factory final gear ratio, but I'm wondering what would be the most beneficial ratio to work with, (Unless any one says otherwise it's my understanding the best place to make this change would be in the diff.)
Right now on my ka24e you hit about 30-35mph in first gear at the redline.. my THEORY is that stretching first gear out to about 50-55mph at the redline might not be such a bad idea considering the ambitious power goals (and of course all other gears would be pushed up similarly).

any one think that would be excessive or not enough? I don't actually have a lot of experience with how changing the gear ratio is going to affect my performance, I DO understand what all the trade offs are though.

Any advice would be most appreciated, if I'm completely retarded please let me know before I waste money! =D

first off why stroke the ka? You dont need to at all.....

search on ka-t.org or something. The rear differential swaps have been covered. They give all the ratio's etc too. Even though its only changing the final drive. It really depends if you want top end or quick acceleration. Keep in mind your going to be shifting like a mofo.....which is fun but not fun at the same time.

Wouldn't I be shifting less? Also I figured why not stroke the engine a bit since it would be going in for a complete rebuild any way to be able to handle that kind of power, at that point wouldn't be not very expensive to just stroke it in the process, also stretching out the power band would offset some of the disadvantage of the longer gears. (at least that was my theory!)

a numerically higher, what is considered LOWER GEARING..... odd isn't it... makes you have BETTER traction..........

believe it or not, the only thing your going to do with lower numerical gears, say like 3.80 compared to the stock 4.03 is have a higher MPH in each gear... if your already spinning tires, you will just spin even MORE cause you will get more wheelspeed when the tires are roasting.... thus creating more smoke etc.. I guess this would be good if your a drifter, or this would be good if your going for topspeed... I have no idea what the stock 240sx tops out at in 5th gear with the stock 4.03 rear end at say 7,000 rpm....... would be interesting to find out...

but if you want more traction you need a higher numerically gear ratio.. there is a R32 or some JDM 180sx's had them I believe its 4.36 ratio... this would be good... sure you will shift more and your cruising rpm's will be higher..

my opinion, unless you need more topend speed, or if your N/A and looking for every little bit to accelerate faster... just keep the stock rear gears...

theres other things you can do to take care of traction, better tires, wider tires, good LSD....... subframe spacers, traction arms, toe arms, and springs and dampers designed for drag racing in the rear, HKS makes some coilovers for drag racing that are supposedly badass.......

hope this helps, if u have any other questions please shoot away!

a numerically higher, what is considered LOWER GEARING..... odd isn't it... makes you have BETTER traction..........!

no.

a numerically higher ring gear would have more torque multiplication so you'd break traction easier.

not that a ring gear has anything to do with traction.

for the sake of saving time, everything you posted was wrong.

Drifting you want a closer gear unless you have an asston of torque and a really wide power band, or else you'll be coming in and out of power and your driving will suffer.

Big power cars will benifit from a wider gear because they'll have more time in boost and/or on power and moving.

High Revving/peaky N/A cars will benifit from a closer gear because they'll be in powerband more and the torque multiplication with the same final speed in each gear will net a faster car.


I recently went from a 4.08 to a 4.36. its really a fun difference, the difference in torque is really noticeable and on most courses it moves the third gear portion a little up in the RPM band to make it easier to carry.

I've got stock 7000 redline, if I were spinning to 8+ I would have gone with a 4.6

You should really appreciate the 4.3 in whatever car you put it in, unless you're planning on making big power for a wide RPM range.

But that shouldn't be an issue since your powerband on a 400+hp 2.x liter will always be less than 4000rpm.

oh yeah, The OPs assumptions were correct.


however with under 400hp you won't have the power to really push through the taller gear and take advantage.

500+ is really where you'll start thinking about taller gears

My concern is that riding in my friends 375hp corvette, which weighs more than a 240, has way better suspension, and a larger contact patch on the rear tires, that car is still squirrelly with the traction control ON let alone off...

I'm pretty certain almost tripling the power on my 240 would require a significant uh. "tall-en-ing" of the gears.

I think the 240 governs at 115-120 from the factory, on stock gear ratio you would rev limit in 5th gear right around there any way, 122-125 probably.

The powerband is actually one of the reasons I was thinking about stroking the engine, should widen up a bit =o

dude you dont need to stroke a KA!!!!!!!! its has plenty stock.

Why wouldn't I though? I mean the engine would be going under for a complete rebuild any way, the additional cost of stroking it since I'm replacing every part of the engine any way isn't very much extra, and since I want to stretch the gears out, stroking would be a pretty significant benefit to the powerband. stroke + turbo has some nice synergy!

I dunno that was my idea any way.

Vettes can do that because of their powerband.


even a stroked turbo KA won't touch a LSx's powerband.

Vettes can do that because of their powerband.


even a stroked turbo KA won't touch a LSx's powerband.

Yeah I understand that, my intention is not to stretch the gears out as far as the corvettes are, but factory gear ratio certainly will be too short.

My concern is that riding in my friends 375hp corvette, which weighs more than a 240, has way better suspension, and a larger contact patch on the rear tires, that car is still squirrelly with the traction control ON let alone off...

I'm pretty certain almost tripling the power on my 240 would require a significant uh. "tall-en-ing" of the gears.

I think the 240 governs at 115-120 from the factory, on stock gear ratio you would rev limit in 5th gear right around there any way, 122-125 probably.

The powerband is actually one of the reasons I was thinking about stroking the engine, should widen up a bit =o

yes, its governed at 118mph IIRC. But you should be hitting the speed limiter in 4th, not 5th...

yes, its governed at 118mph IIRC. But you should be hitting the speed limiter in 4th, not 5th...

I hit the rev limiter in 4th gear at just over 100mph

corvettes have a rear end ratio in the 2's.... like a 2.xx

my personal experiences from changing gear ratios in personal Chevy cars and trucks....

a higher number provides better traction... the slower you go in any gear the better traction you will have, and the more power you can put down...

I do this for a living and drive many many many cars that I just drove before and after gear changes, and its amazing at what you would immediately feel after going from say a 3:42 to 4.10..... to each their own though

this holds true for trucks and since they have a split ratio transfer case, it is even more dramatic, if any of you have 4x4's to test my thoughts...

put it in a mud hole in 4 wheel high, then put it that same hole in 4 wheel low....

now since the 4 wheel high option allows the tires to reach a higher speed, they will turn much faster with the same amount of power... however this leaves you sitting there flinging mud and getting stuck.......

now try this in 4 wheel low, this option cuts your gear ratios in about half on most modern 4x4's..... Ford/Chevy/Dodge..... 2.72:1 transfer cases... now you have the same amount of power going down to the wheels, but instead of the tires being able to spin to 30mph, they only spin to 15mph.... provides INSTANT hit and torque applied to the wheels, and since they cannot spin very fast, all that power goes to propelling the vehicle MUCh easier to only half the speed....

basically you have more power to obtain something easier... and the something you are trying to obtain is movement of your car from a dead stop

if you still don't belive a higher number rear end gives you better off the line traction.........

EVER HEARD OF GEAR REDUCTION?

enough said

You hear stroke and automatically think good. Know what it actually does to the engine and what its doing to your engine before you just jump into doing it.

READ
http://www.ka-t.org/forums/viewtopic.php?t=7184&highlight=stroked

the KA has a long ass stroke! just imagine how fast the piston is traveling, or piston speed... just even making it move a few more millimeters increases its speed and friction also forces on the piston/rod/crank dramatically.. it has to move more space in the same amount of time........

the KA is already stroked, just think of it like that lol.... the increase you get from stroking the KA could easily be countered by a better tune and a few more PSI.... say stroking it would give 20 more horsepower... well you have a turbo, its ability to make 20 more horsepower is all in the computer and fuel used.....

don't forget, theres always nitrous

Hmm, it seems I might have to reconsider stroking the engine... gonna have to find another place to dump that money.. I wonder how far I can push that redline up without destroking =)

KA head chokes too bad to have a high redline.


God knows why you kids want 400+ out of KA/SRs. all those cars feel stupid to drive despite the zomg jerkoff 120mph trap.

so what car would you say doesnt feel stupid to drive then?