Dawgz83948 Posted November 21, 2011 Report Share Posted November 21, 2011 Looking for a 3.89 diff that will fit in a 620. Link to comment
datzenmike Posted November 21, 2011 Report Share Posted November 21, 2011 Easiest route is a 2wd 720. Look for '80 (L20B) '81-'82.5 (Z22 and SD22 motors) Nov.'82 and on (SD25motor) with 2wd, manual transmission, reg/long/long cab trucks. Do not bother with 4x4s. Totally wrong gear ratios to '82.5 and wrong differential type after. The above is very rough so it's easy to check the engine tag under the hood. It's located on the pass side inner fender just below the hood hinge and looks like this: Look in bottom right corner for the ratio. 38 means 3.889. A 41 would be 4.11, 43 would be 4.375 and so on. This may be a 3.889 but is for a 4x4 and the differential carrier isn't an H-190 but a c-200 . Link to comment
Dawgz83948 Posted November 22, 2011 Author Report Share Posted November 22, 2011 Thanks for the info. Link to comment
Dawgz83948 Posted January 14, 2012 Author Report Share Posted January 14, 2012 Ok, so where is the ratio on the early trucks? I found an 80 720 and the fender tag has no transmission or rear end tag. The late trucks do, but the hf87 won't work right? Can I get the whole axle and swap it in? Link to comment
Dawgz83948 Posted January 14, 2012 Author Report Share Posted January 14, 2012 Err HF37 Link to comment
wayno Posted January 14, 2012 Report Share Posted January 14, 2012 81 datsun/nissan 720 and on have the tags with the info, 80 doesn't have the tag. 37 is a 370 gearset. Link to comment
Z-train Posted January 14, 2012 Report Share Posted January 14, 2012 What motor is gonna be in front of the 3.70's/3.89's? Link to comment
Dawgz83948 Posted January 14, 2012 Author Report Share Posted January 14, 2012 What motor is gonna be in front of the 3.70's/3.89's? L20B/5sp 280z tranny. The HF37 diff wont fit in my 620, right? They look the same. Will the whole hf37 rear end fit in the 620? Is there anywhere that I can see the 80 720 rear end ratio? Link to comment
datsunaholic Posted January 15, 2012 Report Share Posted January 15, 2012 The '80 720 should have a 4.11 anyway. The only ratios in '80 was 4.11 and 4.38. What you want is one from a 2WD 81-86 720 with the Z22 or Z24 and a manual transmission. I know my '83 has a 3.89. Link to comment
Z-train Posted January 15, 2012 Report Share Posted January 15, 2012 L20B/5sp 280z tranny. The HF37 diff wont fit in my 620, right? They look the same. Will the whole hf37 rear end fit in the 620? Is there anywhere that I can see the 80 720 rear end ratio? A stock L20B with a 3.70 or 3.89 will be a pooch of a truck.You will NOT be able to use it as a "real" truck.Meaning it will not haul any weight.Acceleration will be unbelievably slow. :( Link to comment
Dawgz83948 Posted January 16, 2012 Author Report Share Posted January 16, 2012 A stock L20B with a 3.70 or 3.89 will be a pooch of a truck.You will NOT be able to use it as a "real" truck.Meaning it will not haul any weight.Acceleration will be unbelievably slow. :( Well I bought a 3.70 from an 85 720. Also bought the speedo gear. I'll let you know how it feels once it's in. This truck is useless as a truck on the freeway when you're trying to spin the hamsters out of their wheels spinning 3800 @ 65. My L20B is a fresh rebuild with a weber carb and no smog equipment (except the PCV system). Out of curiousity I can buy 3 more if anyone is interested I can get them and sell for $125 (which is what I'm paying for them) + shipping. Link to comment
wayno Posted January 16, 2012 Report Share Posted January 16, 2012 I put 389s in my 71 datsun 521 with an L20b/dogleg 5 speed, it had a W53 head with 280Z valves and dual SUs, it worked fine on the hiway, and as long as I wasn't on a hill at a signal, I had no issues, but when I loaded it and/or connected the trailer to the truck I had issues, big issues, I could smell the clutch daily, it just was never meant for 389s, as long as I treated/used it as a car, no problems. I hope you have a really strong engine, your going to need it with 370s. I use my truck for work, and I abuse it daily, I have 437 gears in the rear, and a LZ23 engine, and I would'nt have a prayer of getting it moving with 389 gears. I know that you won't use it like this. But it doesn't take much to get to a ton either. 370 gears were meant for the torque created by the Z24, which it does have torque, way more than the L20b, or my LZ23 for that matter, if you use your truck as a car, you will probably be fine, hell, I put 350 gears in my 521KC with a SD25 diesel engine(71hp), but I have lots of torque to get it moving, and it is basicly a car anyway. Link to comment
datsunaholic Posted January 16, 2012 Report Share Posted January 16, 2012 3800 is NOTHING. Some folks simply can't wrap their head around the fact that these engines can turn 5K with no problem. Peak HP is at 5600 RPM. These aren't old pushrod V-8s. They're meant to rev. Though 3800 @ 65, you'd have to be in 4th gear. A stock 4.38 and a 280Z 5-speed in 5th would be turning less than 3300. That or running miniature tires. I'm running 205/70R14s in back, and I'm not QUITE turning 3800 @ 65 (just a tad under). And I have stock rears and a 4-speed. I run a 4-speed '76 with stock gears at 65 every day (90 mile round trip) and every year a 300-mile cross-State trip at 75 to 80MPH in the open range areas. 70MPH clears 4K. 80MPH clears 4650RPM, and I did THAT for over 2 hours straight trying to catch my convoy once. I plan to put a 5-speed in it, I even have the transmission but I'm not going to do so until the clutch needs changing OR I have the need to pull the engine. It's a "Nice to have" not a necessity. I'm not saying that the 3.70s won't work. If you don't care about the sluggish acceleration and do a lot of driving at constant speed on very flat roads with no load then they'll be OK. I'd be concerned with lugging the engine and burning up a lot of clutches though just to get moving. The 3.70s were meant for an engine with a LOT more (25%?) torque and HP than the L20B. Link to comment
Dawgz83948 Posted January 16, 2012 Author Report Share Posted January 16, 2012 3800 is NOTHING. Some folks simply can't wrap their head around the fact that these engines can turn 5K with no problem. Peak HP is at 5600 RPM. These aren't old pushrod V-8s. They're meant to rev. Though 3800 @ 65, you'd have to be in 4th gear. A stock 4.38 and a 280Z 5-speed in 5th would be turning less than 3300. That or running miniature tires. I'm running 205/70R14s in back, and I'm not QUITE turning 3800 @ 65 (just a tad under). And I have stock rears and a 4-speed. I run a 4-speed '76 with stock gears at 65 every day (90 mile round trip) and every year a 300-mile cross-State trip at 75 to 80MPH in the open range areas. 70MPH clears 4K. 80MPH clears 4650RPM, and I did THAT for over 2 hours straight trying to catch my convoy once. I plan to put a 5-speed in it, I even have the transmission but I'm not going to do so until the clutch needs changing OR I have the need to pull the engine. It's a "Nice to have" not a necessity. I'm not saying that the 3.70s won't work. If you don't care about the sluggish acceleration and do a lot of driving at constant speed on very flat roads with no load then they'll be OK. I'd be concerned with lugging the engine and burning up a lot of clutches though just to get moving. The 3.70s were meant for an engine with a LOT more (25%?) torque and HP than the L20B. Thus my problem, I have a 280z 5sp and it's running at 3800@65 in 5th. I think this truck has 4.65 rear in it. That being said, I'm not planning on towing with it or carrying more than 500lbs in the bed. What I do plan on doing is driving it on the freeway, here's to hoping the 3.70's will net better than 22mpg which is only 2 mpg better than my 400hp v8 944. Link to comment
Dawgz83948 Posted January 16, 2012 Author Report Share Posted January 16, 2012 So assuming my calculator is correct (and it has been) 3.70 rear w/ 280zx trans @ 65 the engine should be turning 3000rpm's in 5th gear. Link to comment
datsunaholic Posted January 16, 2012 Report Share Posted January 16, 2012 Depends on what you used for tire size. With my tires (205/70R14) it would be 2761. That's a pretty big difference. 4.65 gears are the rarest of the stock H190 gears. Only used on 73-74 Automatics, although maybe they were used on the cab & chassis versions too. Tell you the truth, though, it's still higher RPMs than if running the 280ZX (82-83) trans that I ran with an L18 and stock rear gears. Combined with the close-ratio 1-4 gears it made for very painful slow acceleration, but awesome gas mileage as long as I stayed off hills. I got 35 with that truck. And I did haul loads, but had to run in 4th most of the time. Link to comment
Dawgz83948 Posted January 16, 2012 Author Report Share Posted January 16, 2012 Depends on what you used for tire size. With my tires (205/70R14) it would be 2761. That's a pretty big difference. 4.65 gears are the rarest of the stock H190 gears. Only used on 73-74 Automatics, although maybe they were used on the cab & chassis versions too. Tell you the truth, though, it's still higher RPMs than if running the 280ZX (82-83) trans that I ran with an L18 and stock rear gears. Combined with the close-ratio 1-4 gears it made for very painful slow acceleration, but awesome gas mileage as long as I stayed off hills. I got 35 with that truck. And I did haul loads, but had to run in 4th most of the time. I have 195 65 14's.Once my old diff is out I'll look at the numbers. Link to comment
Z-train Posted January 16, 2012 Report Share Posted January 16, 2012 370 gears were meant for the torque created by the Z24, which it does have torque, way more than the L20b, or my LZ23 for that matter, What are you making for torque with your LZ-23 Link to comment
wayno Posted January 17, 2012 Report Share Posted January 17, 2012 What are you making for torque with your LZ-23 I don't have any numbers, but everytime I do an upgrade, it gets better, my L20b wouldn't pull itself out of a hole(customers steep driveway) without getting a run at it, keep in mind that I am pulling a trailer most the time, and have a load of debris in the truck itself, most the time I suspect I am moving an average of a ton and a half, or more if the bed is full, and if it is raining, it is even heavier. The LZ23 is a great upgrade for me, my power went up, and so did my gas mileage, I am not floored all the time anymore. I am having issues though, I keep blowing headgaskets because I stripped the headbolt hole out closest to the thermostat housing, I used the wrong headbolt in that hole, I have had it fixed, I also installed a stud kit ARP #202-4201, and have put it back together, but have not had the time to put the engine back in the truck, at the moment it has an L20b in it again, and I am not that happy about it, but I will find the time to make the swap again, it takes about 5 hrs. to change them out. Datsunaholic, I have a 1980 datsun 4X4 with somewhere around 460 gears in it, both the front(R180) and back(H190), are they really that rare? Link to comment
Dawgz83948 Posted January 17, 2012 Author Report Share Posted January 17, 2012 Does the -10hp and +25 lb" really make that big of a difference? Link to comment
Z-train Posted January 17, 2012 Report Share Posted January 17, 2012 These are the dyno results from my LZ-23 Link to comment
Dawgz83948 Posted January 17, 2012 Author Report Share Posted January 17, 2012 Those are wheel numbers? Link to comment
wayno Posted January 18, 2012 Report Share Posted January 18, 2012 Most of my power is between 3000 and 4000rpms, it starts falling off after 4000rpms dramaticly, but it can pull a lot of weight out of the hole, and really starts kicking in at about 2000rpms(1st gear), but that is the only gear I am in at that low of a rpm, except when driving around in the city/back streets. I guess I really don't think that much about city driving, it's when I get on the hiway that I notice the lack of power, I just want to keep up with the flow, and I figured out that if the head has big 280Z valves installed, and the heads intakes are ported to match intake manifold, if I run a stock L20b cam, I have the best all around power I am going to have, tons of torque, and I can keep up on the hiway. Link to comment
Z-train Posted January 18, 2012 Report Share Posted January 18, 2012 Those are wheel numbers? Yes.Stock head-no port work,L-16 manifold & DGV.Cam is from Rebello. Link to comment
Dawgz83948 Posted January 18, 2012 Author Report Share Posted January 18, 2012 Yes.Stock head-no port work,L-16 manifold & DGV.Cam is from Rebello. Very nice. I swapped the diff on my truck. It's nice to not have to shift every 1/3 of a second. Very useable power and tq with my L20B. I'm going to strap my 3000lb car to it and see how it does towing...... Link to comment
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