AMK521 Posted February 11, 2015 Report Share Posted February 11, 2015 I have a 72 521 and I'll be swapping a ka24de soon so having a 5 speed will help but I plan on going on quite a few road trips in the near future and would love it if I could find some substantially taller gears. If I'm not mistaken I should have 4.88's at this point. what are my options? 1 Quote Link to comment
datzenmike Posted February 11, 2015 Report Share Posted February 11, 2015 Only the L521 ('69) had the 4.875s in them. All PL (L16) 521s '70-'72 had 4.375s in them. The '79 620 with standard transmission had 4.11s but this isn't enough of a change. Check out the 720 2wds. They range from 3.889 to 3.70 to 3.545 and as low as 3.364. There is an engine tag under the passenger side hood hinge on the inner fender that shows the differential installed by the factory. Lower right corner.... HF38 means H-190 3.889 HF37 would be 3.70 HF35 would be 3.545 and so on. 2 Quote Link to comment
Dime Dave Posted February 11, 2015 Report Share Posted February 11, 2015 The 3.89 from a Roadster or 510 Wagon can be installed if you swap side gears to the larger truck spline diameter. Also the '82-83 200SX (S110) live axle cars have an H190. These are 3.545 and have large spline axles, but hard to find. 1 Quote Link to comment
DanielC Posted February 11, 2015 Report Share Posted February 11, 2015 Substantially taller gears = substantially slower acceleration. Go too far with the gear ratio change from 4.375, and you will literally need a fan to get away from your own exhaust. From what I have read about the KA 24 DE, it still have a torque peak in about the same RPM range as the stock L-16. Datsun engines are a lot more happy at higher RPM's than most people driving them think they are. 2 Quote Link to comment
jrock4224 Posted February 12, 2015 Report Share Posted February 12, 2015 i put my wagon gears in my truck and loe it .... with a l 20.... with my l 16 right now its little not fun onthe highway ...... also running a z morph tranny ... 1 Quote Link to comment
AMK521 Posted February 12, 2015 Author Report Share Posted February 12, 2015 Very helpful information, thank you! The ka I'm going to install has a few mods, I pulled it out of my buddies 69 510 and when it was in his car (which had a Subaru lsd with I think 3.70s ) he could burn the tires through 3rd and chirp 4th gear so I was figuring the 3.54's datzenmike mentioned would be sweet in that little pickup. Traffic in Washington moves along at 80-85 all the time so.. Any thoughts? 1 Quote Link to comment
DanielC Posted February 12, 2015 Report Share Posted February 12, 2015 Modifications done to engine to increase the horsepower usually shift the RPM the engine makes peak torque higher in the RPM band. this robs torque at lower RPMS. Go too far with the gear ratio change from 4.375, and you will literally need a fan to get away from your own exhaust. And a headwind. 1 Quote Link to comment
EastBay521 Posted February 12, 2015 Report Share Posted February 12, 2015 id go 3.7 or the 3.54 if you can find one. especially if you are going to commute in it like I do. I love the 3.889 in my 521 I I had a ka id want lower 1 Quote Link to comment
TENDRIL Posted February 12, 2015 Report Share Posted February 12, 2015 Does any one know the spline count on the side gears? And if it's a 8" And the length of the spline shaft? 1 Quote Link to comment
TENDRIL Posted February 12, 2015 Report Share Posted February 12, 2015 If everything matched p to some numbers I have, there might be a LSD option .... 1 Quote Link to comment
Z-train Posted February 13, 2015 Report Share Posted February 13, 2015 To keep the way it "came" from the factory, if you have increase HP 10 %,then you can drop gear ratio 10%.This is just one of those pesky little auto math formulas. 1 Quote Link to comment
datzenmike Posted February 13, 2015 Report Share Posted February 13, 2015 id go 3.7 or the 3.54 if you can find one. especially if you are going to commute in it like I do. I love the 3.889 in my 521 I I had a ka id want lower Don't change the differential. The KA truck 5 speeds have over drives in around 14%. The car KA transmissions are usually equipped with an over drive similar to the one in the 280zx. It's about 25% over drive. Get one of those and keep your gears. Acceleration will be impressive but once in 5th the revs come down. Say you drive at 3,000 RPMs and 50 MPH on the highway with your current 4 speed. Here's what these two over drive 5th gears will do at the same 50 MPH ... 14%...... 2,580 rpms this is the same as a 3.76 differential with the old 4 speed 25%...... 2,250 rpms this is the same as a 3.28 differential with the old 4 speed. 1 Quote Link to comment
Z-train Posted February 13, 2015 Report Share Posted February 13, 2015 Don't change the differential. The KA truck 5 speeds have over drives in around 14%. The car KA transmissions are usually equipped with an over drive similar to the one in the 280zx. It's about 25% over drive. Get one of those and keep your gears. Acceleration will be impressive but once in 5th the revs come down. Say you drive at 3,000 RPMs and 50 MPH on the highway with your current 4 speed. Here's what these two over drive 5th gears will do at the same 50 MPH ... 14%...... 2,580 rpms this is the same as a 3.76 differential with the old 4 speed 25%...... 2,250 rpms this is the same as a 3.28 differential with the old 4 speed. Not disagreeing with the math,but I would argue that the .25 drop would be too much for the motor and actually hurt economy. Quote Link to comment
EastBay521 Posted February 13, 2015 Report Share Posted February 13, 2015 The KA truck 5 speeds have over drives in around 14%. The car KA transmissions are usually equipped with an over drive similar to the one in the 280zx. It's about 25% over drive. Get one of those and keep your gears. Acceleration will be impressive but once in 5th the revs come down. I thought a stock s14 swap in a 510 with 3.36 rear and zx 5speed with 3adults in the car was impressive. he also has a 521 with an s13 swap with 4.88 rear end but that thing is just not practical, the wheels just spin when ever you touch the pedal. Though the guy he bought it from was going to make it a "drift truck" and welded the rear end but never completed it so maybe that might have something to do with it. i just have a preference for lower gearing since im always on the freeway. 2 Quote Link to comment
datzenmike Posted February 13, 2015 Report Share Posted February 13, 2015 Not disagreeing with the math,but I would argue that the .25 drop would be too much for the motor and actually hurt economy. Overdrive isn't meant for acceleration like the bottom four. It's only for steady speed cruise to drop the RPMs. Besides the 240sx has a 4.083 diff ratio and has to be heavier than a 521. 1 Quote Link to comment
AMK521 Posted February 14, 2015 Author Report Share Posted February 14, 2015 Don't change the differential. The KA truck 5 speeds have over drives in around 14%. The car KA transmissions are usually equipped with an over drive similar to the one in the 280zx. It's about 25% over drive. Get one of those and keep your gears. Acceleration will be impressive but once in 5th the revs come down. Say you drive at 3,000 RPMs and 50 MPH on the highway with your current 4 speed. Here's what these two over drive 5th gears will do at the same 50 MPH ... 14%...... 2,580 rpms this is the same as a 3.76 differential with the old 4 speed 25%...... 2,250 rpms this is the same as a 3.28 differential with the old 4 speed. I think the math there is right but here's the thing. I know a big cam can be bad for low end but I'm comparing an 2200 lb truck with an l16 to a ka 24 which has way more torque to begin with and I don't have that big cam so I think I'll be good on torque and I'm not planning on driving around at 50 mph. I'm aiming more for being able to cruise nicely at 70-75. An engine doesn't necessarily get better mileage tho just because the rpm are lower. Cruising at an engines peak power ( or just below) is often times the best so where is the ka's peak power is the good question right? With my tire size and the overdrive behind the ka a set of 3.54's lands me at about 2750 rpm at 70 mph. That's about right isn't it? 1 Quote Link to comment
datzenmike Posted February 14, 2015 Report Share Posted February 14, 2015 I think you mean peak torque. Peak power would be above 5,500 RPMs and you would be going over 100MPG. Peak torque is measured at full throttle which isn't happening if you are just cruising. Best cruise MPG/MPH would depend on vehicle wind resistance mostly. Going 60MPH requires 4 times the power needed to push through the air at only 30 MPH. If your MPG suddenly drops above 65 then 60 isn't necessarily your best cruise speed, this is likely where your secondary opens and begins dumping fuel in. You will always get better mileage going slower. Your best cruising speed is a compromise between economy of fuel and economy of time. If you have the time cruise at 50. Peak torque is 150 @ 4,400 for the E and 160 @ 4,400 for the DE. In comparison the Z24 is 134 @ 2,800 rpms. 2 Quote Link to comment
Z-train Posted February 15, 2015 Report Share Posted February 15, 2015 Overdrive isn't meant for acceleration like the bottom four. It's only for steady speed cruise to drop the RPMs. Besides the 240sx has a 4.083 diff ratio and has to be heavier than a 521.I get that.But the highway speeds would be so low that the timing won't be all the way in and will completely offset any MPG gains by lowering the RPMs. Quote Link to comment
DanielC Posted February 15, 2015 Report Share Posted February 15, 2015 When the 521 was brought into the USA, they had the J-13 engine, and a 4.875 rear axle ratio. There was gas price changes going on in the late 1960's and early 1970's. Datsun decided that with the freeway speed limit reduced to 55, a really good engine and rear axle was the L-16, and 4.375. In fourth gear, at 55, the engine is turning around 3600 RPM, it's peak torque number. This is not a coincidence. It was planned that way. 510 sedans, and goons had a different, taller gear ratio. they were not a truck, with a 1440 payload. You are swapping a KA 24 DE. I would choose a rear axle ration similar to what other KA 24 DE vehicles use. If you are using your 521 as a truck, hauling heavy stuff, go slightly lower. Going too high (taller, faster), you will turn the truck into a slug. If you take the engine too far below it's torque peak, at freeway speeds, you also will actually lose fuel economy 1 Quote Link to comment
TENDRIL Posted February 15, 2015 Report Share Posted February 15, 2015 So does i put my wagon gears in my truck and loe it .... with a l 20.... with my l 16 right now its little not fun onthe highway ...... also running a z morph tranny ... So did you have to swap the side gears? Quote Link to comment
TENDRIL Posted February 15, 2015 Report Share Posted February 15, 2015 And if so can it be the opposite. Putting a truck pumpkin in the goon with goon side gears? 1 Quote Link to comment
datzenmike Posted February 15, 2015 Report Share Posted February 15, 2015 So does So did you have to swap the side gears? Car side gears are usually 23 spline to match the axles. Trucks are 29 spline so swapping the truck side gears into the H-190 will allow a car diff to work in a truck. Or the other way. The Roadster, 510 goon, 810 goon, Maxima goon, and the S110 ('82-'83 200sx) all use a 23 spline side gear. The first year (half year actually) S12 (200sx) also uses an H-190 differential but with truck 29 spline side gears. 1 Quote Link to comment
TENDRIL Posted February 15, 2015 Report Share Posted February 15, 2015 found this on the relm. do you know if this is a direct bolt in, or if anyone has used it for truck or goon? they are not very clear if the make it with different side gear spline counts or not. http://www.tractionconcepts.com/Datsun-510-Wagon-H190-Diff-Lsd-Kit-p/tcxda9031.htm 1 Quote Link to comment
datzenmike Posted February 15, 2015 Report Share Posted February 15, 2015 Groan. That's basically a Phantom Grip with a different name. How it works is it thrusts the side gears outward and jams the thrust washer against the differential case to 'lock' them. Presumably the force isn't enough that turning a corner forces the steel thrust washer to slip. Real clutch LSDs use many layers of friction material and steel discs. Forcing this much pressure on a tiny thrust washer never intended for this is foolhardy. 2 Quote Link to comment
Z-train Posted February 15, 2015 Report Share Posted February 15, 2015 When the 521 was brought into the USA, they had the J-13 engine, and a 4.875 rear axle ratio. There was gas price changes going on in the late 1960's and early 1970's. Datsun decided that with the freeway speed limit reduced to 55, a really good engine and rear axle was the L-16, and 4.375. In fourth gear, at 55, the engine is turning around 3600 RPM, it's peak torque number. This is not a coincidence. It was planned that way. 510 sedans, and goons had a different, taller gear ratio. they were not a truck, with a 1440 payload. You are swapping a KA 24 DE. I would choose a rear axle ration similar to what other KA 24 DE vehicles use. If you are using your 521 as a truck, hauling heavy stuff, go slightly lower. Going too high (taller, faster), you will turn the truck into a slug. If you take the engine too far below it's torque peak, at freeway speeds, you also will actually lose fuel economy This^^^^^^ 1 Quote Link to comment
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