Results with a higher differential ratio?

[pdxvento]

Hey all,

Ive been searching and searching about diff ratios, and all i can find is what each car has. my question that i couldn;t find the answer to is what happens if you put say a 3.70 differential into a transmission and engine that originally had a 3.54 diff, assuming they were both r200s? ive been told that any r200 differential will work on a tranny with an r200 originally, but what does the diff size have to do with anything? thanks for the help!

jason

[allknowingbald1]

the increase in gear ratios increases your accelleration properties. that's why you see most muscle cars with at least 3.73 or higher gear ratios. 4.11 is very common in those respects. and you are correct in the sense of "if it came from an R200 it will fit in an R200." hope that helps ya some,

[pdxvento]

so it only helps? so a 300zx LSD which is an r200 3.70 will work well on an r200 that used to be a 3.54? thats what i wanted to know! thanks

[Mr Camouflage]

If you had a 3.54 ratio and swapped it with a 3.7 ratio diff it would mean that the accelaration would be better.

The engine would have to rev more though to achieve the same speed as the .54 ratio, which means worse fuel economy.

Hypothetically For example to do 100mph with a 3.54 in top gaer the engine would have to be turning over at 3592 rpm

to do 100 with the 3.9 you'd have to rev the engine to 3754 rpm.

check out this link

http://www.geocities.com/z_design_studio/

[pdxvento]

great!. thanks a lot guys. i really apprciate it

[Royce]

Here I go again with the fancy Z ratio tool again. I added this to the links on this site under "Z car transmission calculator"

See http://www.geocities.com/z_design_studio/ and you can graphically compare different preset Z trans, diff ratio, and tire combinations. So you can see what the difference really is in terms of top speed or revs and any MPH or vis-a-versa. It is very cool and I used it a lot when comparing different parts I found for my car.

The key to gear ratios is that in performance situations you want to "have the engine where you want it!" That means so that you are not waiting for the torque or power to kick in when you need it. When you go to a lower ratio diff ratio, higher numerically, you not only get the engine into the higher revs sooner but you also shorten the distance between each gear change. An example of changing to a lower ratio is going from 3.54:1 to 3.9:1. But it really depends on how your engine makes torque/power and how you are going to be driving the car. Whether it is an R180 or R200 doesn't make any difference in the ratio itself, except for the fact that some ratios are more available in a particular style of diff. The big difference between an R180, R200 or R230 is the size of the gears and the amount of abuse a particular design of diff can handle.

Limited Slip(LSD) or open diff is again another style of design. An open diff is what came in most Z cars, and most any stock car for that mater. This is were if you get stuck in the mud and only one wheel turns when you gas it. With a Limited Slip both wheels would turn. This also applies to accelerating out of a corner. If you give it a lot of gas with an open diff the inside tire may start to spin and slow you down. While with the LSD diff will supply power to the outside wheel as well and you get out of the corner faster. POSI, locker, and welded diffs are a variation of the them. They are each quite different but are to achive the same goal which is to supply power to both wheels.

Sorry for the long winded response. Hope it makes sense. I got on a roll and couldn't stop myself.

Have fun!

[pdxvento]

no no, thank you for the help!

i was trying to find a car that had an LSD standard, and i found that some 300zxtt's did. i have to have an LSD, and i wanted to know if it fit and work. i have an LSD in my vento (pictured in my avtar), and i love it. so i guess my question is answered. thanks for your help!

[Royce]

One thing I didn't really touch on is the external differences between the diffs. Remember the diff assembly has many pieces. There is the diff carrier which is generally what you see on the outside. Then on the inside you have the ring and pinion gears and all the bearings and other bits. The interior and exterior of the R180 and R200 are different. The R180 diff assembly is physically smaller and lighter than a R200 assembly. The big difference, as far as compatability is concerned is that they require a different rear suspension member on '70 and '71 model 240Z's. The early 240Z's had a straight rear suspension member, not sure of the technical work for it. Starting with the '72 model 240Z the diff was moved back and from that point on all the first gen Z's had the bent rear suspension member. The R200 also requires a modified or different mustache bar. The R200 has larger rear mounting bolts and so the holes in the mustache bar are larger to fit. The R200 mustache bar is also wider and a better choice than modifing the hole size of a R180 bar. I thought I used the same front diff mount and insulator but that was a long time ago. I have read some people say they need a different special R200 insulator and that may be the case. I used my existing drive shaft and half shafts when I swaped in a R200 unit for my original R180. You can buy a LSD unit for either a R180 or R200 unit but they can cost a few $$$. I believe a unit made by Quaife can cost $800+ and that doesn't cover the installation in the diff carier.

I am not very familiar with the R230 but I get the impression it is the same case as the R200.

There is a lot more to the Z diff story but I think that should get you on your way. There are many other posts that talk about different options. You might want do a search for "diff ", "LSD", "welded", and probably some other associated words. Another good one is "Subaru" because some Subaru's came with LSD assemblies that are very similar to Datsun 510 and Z units and can be used in Z cars with some modification.

Damn this post just keeps growing and growing. I'm going to have to stop there!

Again, I hope it makes sense!