S13 LSDs & Higher Gearing

[Edub1]

I am building my S13 KA-T for goofing around on road and spirited freeway driving.

I have found a 3.69 rear end that will fit. This will make my gears 10% longer. I will lose some torque, but I will be able to stay in a lower gear a little longer. I like the sound of this but I'd like to hear from someone who has tried it. No speculation unless you really know for sure.

Plus, this thread has been severely hijacked so just hit reply now or skip to the last few posts.


Modified by Edub1 at 9:50 PM 2/21/2006

[Nismo_Freak]

You aren't going to "improve top end" by going to a higher gear. The stock gearing goes plenty fast and odds are you lack a sufficient aero package and/or suspension harmonics to safely go that fast.

[Iamjohnhayes]

as far as i know the reason the turbo z diff will not fit is just the physical size of it. Also i think it has different ouput shafts which would require more parts than just the diff.

And Personally i would like to have a slightly higher gear in the rear b/c i have heard first gear can be rather useless when you put a lot of power out and more importantly for me im tired of being at about 3000rpms doing 60 mph down the highway. even if i could just drop it down below 2800 would make me happy since i do a lot of highway driving and saving gas is always good

[Edub1]

The 1st gear is made for a 140CHP motor and it's pathetically short. My car stock will spin the tires straight threw it under a hard launch.

Question is, can the pinion gear be taken from the Z32 turbo rear and put into a non-turbo rear?

By the way, 85 is typical cruising speed on a Detroit freeway.

[Nismo_Freak]

The 1st gear is made for a 140CHP motor and it's pathetically short. My car stock will spin the tires straight threw it under a hard launch.

Question is, can the pinion gear be taken from the Z32 turbo rear and put into a non-turbo rear?

By the way, 85 is typical cruising speed on a Detroit freeway.

1st gear is made solely to give easy take-offs, and you will never have traction in first gear, so why bother.

The Z32 turbo rear pinion is a R230, meaning it is 230mm, 240's have 200mm rings.

Dropping the ratio will just make your car slower, especially a turbo Z32 gear.

85mph is no where near the peak rev the engine can sustain. I fail to see the problem.

[Iamjohnhayes]

gear be taken from the Z32 turbo rear and put into a non-turbo rear?

By the way, 85 is typical cruising speed on a Detroit freeway.

It was where i lived in NJ too, but now i live in the worlds bigest speed trap. I got a ticket for going 55 in a 45 when i got pulled over the 55 mph sign was dead even with my side mirror.

[Edub1]

For the same reason the engineers at Nissan put a higher rear end in the turbo Z32 - because it will lengthen the 1st gear power band enabling you to have a usefull 1st gear with boost.

Think about it. What offers more torque, the higher rear end in 1st for an additional 2-3 seconds, or the lower one in 2nd, 2-3 seconds later?

As for top end - I like a car with top end. My car, my choice.

By the way, I meant the ring gear, or both.

[Nismo_Freak]

For the same reason the engineers at Nissan put a higher rear end in the turbo Z32 - because it will lengthen the 1st gear power band enabling you to have a usefull 1st gear with boost.

Think about it. What offers more torque, the higher rear end in 1st for an additional 2-3 seconds, or the lower one in 2nd, 2-3 seconds later?

As for top end - I like a car with top end. My car, my choice.

By the way, I meant the ring gear, or both.

It's not even a debate. If you want traction in 1st gear, get some drag radials if you don't have alot of power, or get some slicks.

Reducing the gearing will not resolve a tire spinning problem in 1st gear. The multiplication is too high through the gearbox.

As far as top end? Where the hell are you going to do over 150 MPH? You will go faster with the 4.083 rear end anyways because the 240SX is drag limited in 90% of the case, and those 10% that have enough power to push the envelope well I hope you have some aero modification or good life insurance because a 240 gets mighty floaty around 140 MPH.

BTW they put the higher rear end gear in the Z because it makes alot more torque. The first gear in a Z32 sucks anyways.

[nismofly]

if youre so dead set on it i think the s15 has a 3.69

[crzycav86]

you're saying the ka doesn't have torque?

[Edub1]

I'm glad we agree that this is not a debate.

I simply asked if it was possible to put a higher gear in an LSD and fit it to our cars - not whether or not I ought to.

I am thinking of aerodynamic improvements. I even made a post about it. And, I don't want my rpms screaming at a constant 6k should I decide to open it up a bit.

Engineers that make six figures put higher gears in turbo cars for a reason - and it isn't because they are dumb.

The 1st gear in our cars sucks donkey **** because the car is geared for a whimpy motor. Since a turbo motor has sufficiant power, we can use gearing that is actually usefull to get the car to move forward instead of just being there for lost shifting time. In fact, the guy I bought my car from told me he frequently started off in 2nd because 1st is so low. I don't do that but it's tempting.

How much you want to bet that if we could add 10MPH to 1st gear, 1/4 mile time would drop significantly. Plus we could stretch out 2nd and 3rd that much more.

Anyway, perhaps we should agree to disagree and return the thread to a discussion about ways to increase the gear ratio for those of us who decide to do so.

[nismofly]

i started my car in 3rd one time by accident, i was tired as **** and not paying attention, i thought something was wrong cause it lagged a little bit, but i was amazed how it picked right up

it got going better in 3rd than my dads car does in 2nd

also fyi SR has same ratios with 65 more hp stock

[nb07bcar]

I don't know, but the subaru diffs work for 510. I don't know if the 240sx have the same diff. Its a R160 and I think the 240 is a R180. Not sure about all of this.

[180sx]

if u do a search on google...well 1 day i did and found out that there is bmw diff with better gear ratios that just drops in , some dude on cardomain swaped it in.

[Edub1]

I don't know, but the subaru diffs work for 510. I don't know if the 240sx have the same diff. Its a R160 and I think the 240 is a R180. Not sure about all of this.

What are you saying here?

[Nismo_Freak]

I don't know, but the subaru diffs work for 510. I don't know if the 240sx have the same diff. Its a R160 and I think the 240 is a R180. Not sure about all of this.

Those diffs are weak.

[Nismo_Freak]

I simply asked if it was possible to put a higher gear in an LSD and fit it to our cars - not whether or not I ought to.

For reasons that were incorrect in both reality and judgement.

I am thinking of aerodynamic improvements.

Such as?

Engineers that make six figures put higher gears in turbo cars for a reason - and it isn't because they are dumb.

Higher gears in turbo cars? Kinda like the Silvia and 180SX that both have 4.08 rear ends? Kinda like the GTR that has a 4.10, kinda like the GTS25T and GTST that both have 4.10 rear ends? The 300ZX is one of a kind when it comes to the gear ratio, and it's because the car wasn't built to fit a performance niche. It was built for the 30+ yr. old professional that wanted a Z car. The fact that it was the only turbocharged Nissan available to the US market does not change how it was engineered for the rest of the market.

I'm an engineer as well, big deal.

The 1st gear in our cars sucks donkey **** because the car is geared for a whimpy motor. Since a turbo motor has sufficiant power, we can use gearing that is actually usefull to get the car to move forward instead of just being there for lost shifting time. In fact, the guy I bought my car from told me he frequently started off in 2nd because 1st is so low. I don't do that but it's tempting.

3.321 - 7200 RPM - 25" Tire - 4.083 = 39.54 MPH3.321 - 7200 RPM - 25" Tire - 3.693 = 43.68 MPH

You won't gain 10 MPH, you will gain all of a whopping 4.14 MPH.

Hub Torque

3.321 - 4.083 - 250 Tq. = 3390 Lb. Ft. 3.321 - 3.693 - 250 Tq. = 3066 Lb. Ft.1.902 - 4.083 - 250 Tq. = 1941 Lb. Ft.

Notice the large difference between torque figures between 1st and 2nd and the relatively small difference between the two ratios.

You will still have wheel spin, the car will accelerate slower, and you will not be fixing any issue. Maybe one day you like listen to people that have more knowledge and experience on these matters.

So by all means, go and spend your time chasing a pipe dream.

[Edub1]

Look, I'm not trying to convince you of anything.

My concern isn't wheel spin. My concern is with having to lose time shifting 1/2 second after launching the car with a useless gear that brings you to ~ 20 - 25MPH tops.

I don't know what to make of those numbers you posted but even 5MPH is 20 - 25% longer in 1st gear while boosting.

If you have put a higher gear in one of these and have seen what happens that is one thing. But, aside from that it's mostly speculation and personal prefferance.

I preffer to look for a way to stretch out my gears a little. To be honest, one reason I want it is just because that short 1st gear is a real pain in the ***. If I'm wrong it's my problem ok. I do however, appreciate your concern.

[Nismo_Freak]

My concern isn't wheel spin. My concern is with having to lose time shifting 1/2 second after launching the car with a useless gear that brings you to ~ 20 - 25MPH tops.

I don't know what to make of those numbers you posted but even 5MPH is 20 - 25% longer in 1st gear while boosting.

20 - 25 MPH tops?

A completely stock S14 SE with a rev limit of 6700 RPM on stock tires will do 37 MPH in first gear. Going to a 3.69 rear end gear will get you to 40. Thats such a superficial change it's funny.

If you have put a higher gear in one of these and have seen what happens that is one thing. But, aside from that it's mostly speculation and personal prefferance.

Yeah a friend of mine had the brilliant idea of putting a Q45 diff in his S13. I'm trying to put some sense in your head to avoid this mistake.

Physics is not speculation BTW.

[Nismo_Freak]

Is your car even turbo yet?

[nismofly]

the s15 was 3.69 or whatever too, but that was only to correct for the 6 speed transmission, right Alan?

[Nismo_Freak]

the s15 was 3.69 or whatever too, but that was only to correct for the 6 speed transmission, right Alan?

Yeah it was built for the closer ratio 6-speed.

I prefer 5-speeds.

[nismofly]

as do i

doing anything special for your SRX car?

i have to leave it stock for SR

although i am allowed to swap the rear ratio keeping on topic with this thread, i might experiment by running a 4.36 one weekend to see what it does for my lap times

[crzycav86]

Physics is not speculation BTW.

It's more like "Nismo_Freak is not speculation"

[Edub1]

I understand people with the J30 rear end do like the slightly higher gear. J30 diffs have a 3.916 ratio, which is 4% taller than the stock open differential.

Anyway, I'm not planning on running my car past 6000RMP - but let me see if I'm understanding you correctly.

You are telling me that a higher rear end will only stretch my 1st gear power band by an insignificant amount. But at the same time, it will make my car much slower.

Anyway, the thing is, I'm not really trying to build a dragster. I'm just after a car that is fun to drive. I personally find the short gear annoying. 1st is too damn short and the car revs too high on the freeway. IMO, it gives the car a cheep, econo-box feel.

I have no doubt that you know a lot about cars. I'm just not convinced that you are giving the idea a chance. Like I said, guys with the J30 rear say it's an improvement. So, say I get a 3.916 rear and up size the tires by 2" - that should yield about a 12% longer final gear ratio if my math was correct. 12% in 1st is subtle; only 4MPH, but I'm thinking it might be just right for accomplishing what I'm trying to accomplish. I can always drop the tire size back down if it turns out a flop.

What was the result of your friends Q45 swap? What is the ratio of the Q45?

Modified by Edub1 at 4:46 PM 2/16/2006
Modified by Edub1 at 6:04 PM 2/16/2006

[Nismo_Freak]

as do i

doing anything special for your SRX car?

i have to leave it stock for SR

although i am allowed to swap the rear ratio keeping on topic with this thread, i might experiment by running a 4.36 one weekend to see what it does for my lap times

4.36 + Z32 Gearbox

[nismofly]

z32 transmission? i cant wait to run srx, you guys get all the fun stuff...haha

my primary track ill be running is watkins glen, thats why ill be testing it to make sure im not holding the redline for half of each lap, in case you didnt know its a very fast track

[Nismo_Freak]

If you wanna go tearing apart differentials then go for it. I think it's lame to drop a gear ratio for the sake of comfort in a sports car.

[Nismo_Freak]

z32 transmission? i cant wait to run srx, you guys get all the fun stuff...haha

my primary track ill be running is watkins glen, thats why ill be testing it to make sure im not holding the redline for half of each lap, in case you didnt know its a very fast track

Your gearing is optimized if you can hold traction on gear exit and still hit a suitable top speed down the straights. Corner exit acceleration is more important.

Top speed on my engine build is in the 200MPH range, thats using up to a 4.63 rear end gear. Getting traction with that kind of gear and the powerband this car will have is going to be funny.

[nismofly]

good point

ill definately plan on running the 4.36 then, not like i need anything lower for ITA / SR with the ~150 - 160 rwhp the car will have

probably only going to hit 130 ish on the straights there