Lower diff ratio?

Hey guys,
I have an 87 ca20e w/ 5 spd. So I think I have a 4.111 in the rear. The problem is that I drive to Vegas fairly often, which is a five hour drive. Well the real problem is that I have a lead foot. So I'm usually driving betw 85 and 95 mph. At that speed I'm turning around 4,500 to 4,700 rpm. She runs just fine but it aint too great on gas, and it cant be too good on the valvetrain.
So I was wondering if I could swap in a center section from a car with a 3.545. Has anyone ever done this? There is a link to a site that has all the different diff ratios in
http://home.att.net/~jason510/tranny_ratios.htm
I am completly confident in taking apart the pumpkin and reassembling it. I just wanted to know if I had to switch the rings or if I could stick in the pumpkin.

I don' know if a FWD R&P can be swapped in or not. Your best bet would be one of the 720's. It probably uses a very similar casing for the front but its only a 3.9. I should be getting a CA soon and will be looking into the difficulty of swapping in an R200 if that helps.
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[jeff]

87/88 SE V6 icon_mrgreen.gif
[like me, its starting to fall apart]

"You only hurt the one you love."
That may be true, but better said:
"You only hurt the one who loves you."

I have done the a/t to m/t swap. I have theIRS from the automatic on my car right now. the manual donor car had solid axle, so I left it on that car. I heard that the gear ratios are different between the auto and manual diffs. any truth to this? any help to explain this for me? I don't know driveline stuff, just motors and electrical. does it mean that I am scrificing torque for speed or sacrificing speed for more torque? please help!

p.s. - you're gonna have to use some layman's terms, kinda new to this end of the vehicle. icon_redface.gif icon_confused.gif
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club s12's northernmost member!!!

Nate Wolfe

no. The ca20e's and ca18et's came with 4.10 and the vg30e's came with 3.90 ratios respectivly.
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Randy

My understanding is that the Z-car came with a R-180 and the Z 2+2 and turbo zx models came with and R-200. All 300zx's had the R-200.

I guess, depending on the the pumpkin setup (long/short shaft) and the half shaft setup would determine if you could do a direct swap. If not just make sure that the gear set has the same ring bolt size etc...

Nice web page. Do you still have the 510 ?
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87 V6

Jeff

is there any significance between a 4.11 and a 4.10 final drive?
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Nissan RPS12

"you don't realize how much of a luxury cup holders are until you don't have em" ~Indecisive

the number is how many revolutions the drive shaft make for ever one the axle makes. so a 4.11 gear will turn the drive shaft 4.11 times every time the axle makes one rotation.
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Dan

so .01 rotation wouldn't really matter unless the diameter of the driveshaft was HUGE then....
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Nissan RPS12

"you don't realize how much of a luxury cup holders are until you don't have em" ~Indecisive

what rear end is in the VG30's S12's ?? Just a question.
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Alex Ruc
1985 Notchback CA20ET /w t25 and all the accessories (blown head gasket at 10psi)
Current rebuild in process. Massive Rebuild.

^ I think it's 3.9 to 1.
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Dan

the vg30e 200sx have the r200 3.90. the CA18ET has the 4.10/4.11 (not sure of the exact ratio as I don't have my book here) r200.the CA20E has the 4.10/4.11 R180(except for the 1984 models whick have the live axle instead).
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Randy

any difference between the R200 and the R180?
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Nissan RPS12

"you don't realize how much of a luxury cup holders are until you don't have em" ~Indecisive

I ask, because if i were to go to a junkyard and pull the guts from a VG30 200SX, would it fit into my CA20E 200SX? This would give me a slightly lower gear end ratio. Would this not be an advantage for lower RPM's at higher speeds?
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Alex Ruc
1985 Notchback CA20ET /w t25 and all the accessories (blown head gasket at 10psi)
Current rebuild in process. Massive Rebuild.

I wouldn't sugest (spelling) doing that. With the mods that you are doing I would look for a 4.3 - 4.8 rear axle ratio. In fact if I could find a 4.6 at a reasonable price, I would install that in my car.

The guts would not fit your ca20 diff (R180) but would fit your old turbo car (R200).
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87 V6

Jeff

basically if you have a ca18et you can use the ring and pinion off the vg30 equiped s12's or z31's, if you have a ca20e you either have to swap the whole rear end.. carrier and halfshafts or you really cant do much
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bart
'86 INTERCOOLED Turbo
1/4 mile: 14.964 @93.02mph
CEO of:
"Barts Parts Incorporated"
http://geocities.com/bartc_j
http://members.cardomain.com/bartc_2

A 4.11 to 3.9 swap wouldn't really make a diff( icon_rolleyes.gif )erence ...

You have to make a bigger step to feel anything.

Diff ratios are confusing ... when you say a "bigger or taller" ring gear, it actually means numerically smaller.

But yeah ... quick explanation here ... it's all about torque multiplication.

The S12s 1st gear is 3.592, the rear pinion is 4.11

so let's say my car makes 250 hp at the crank, in 1st gear that's 898 hp into the transmission, and 3691 hp at the rear wheels. (heh, I know it seems ridiculous, but it's true)

So you have 3691 hp off the line ...

Swap in the 3.9s ... 3502 ... yes, that's 191 hp, but in these terms, pretty meaningless ...

You might drop 100-200 rpms off cruising speed.

In my Charger, I started out with 2.74 rear gears. Total higway gears, even with a 3 spd 1:1 gear, it could idle at highway speeds. But it was a pig off the line.

So in went the 3.91s. Huge difference, and 1/4 times dropped almost a full second.

The 3.91s were whining when I put them in, and eventually they were swapped out for 4.11s. (4.56s are my next option, but not likely)

The 3.91s had a higher trap speed by about 4 or 5 mph, but 1/4 times stayed the same.

With such a short ratio tranny, I wouldn't recommend anything higher numerically (smaller physically). 1st gear once you're making power is almost negligible. With 456s or higher, you might find yourself starting up in 2nd gear, and topping out at 100 mph.

I'd like to find a set of 323s or 355s. Wouldn't hurt off the line performance that badly, but would open up the top end.

If you want a cheap alternative to swapping in highway gears, get a set of 16 or 17" rims and tires.

Taller tires will reduce your final drive ratio, shorter tires will make you faster off the line ... so running 14s for you slow guys with sticky rubber can make you a bit quicker.
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1987 200sx CA18ETi
1972 Dodge Charger 413ci/6.6L
1968 Mercury Cougar 289ci/4.6L ForSale
Matt Lamperd
http://www.angelfire.com/freak/brutesquad/index.html

as far as getting tires and rims it will only make a diference when you pair them up in a way that the diameter of the new tire is larger or smaller... otherwise if its the same size it wont do anything, also you speedo will be off as well, but it would work
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bart
'86 INTERCOOLED Turbo
1/4 mile: 14.964 @93.02mph
CEO of:
"Barts Parts Incorporated"
http://geocities.com/bartc_j
http://members.cardomain.com/bartc_2