gear ratios???

[510kevin]

searched and couldnt find any info on how to check the gear ratio for my car.

i found a r180 for $50 with 3.36 gears

 

the problem im having is that i cant figure out the ratio on my rearend. i have no tach or speedo right now, but my car is wound up pretty tight going down the freeway.

 

was looking for a better ratio, but dont want to spend the money til i find out what mine is.

 

thanks!!!!!!

 

 

car is a 70 510 with a dogleg 5speed

and 195 50 15 tires on 15x7 wheels....

[I'm BLUE]

Ok ,

 

(1) What vehicle/year ?

 

(2) What Trans type , and speed ( if manual )

 

(3) Tire Size

 

:D

[510kevin]

Ok ,

 

(1) What vehicle/year ?

 

(2) What Trans type , and speed ( if manual )

 

(3) Tire Size

 

:D

 

 

sorry, 70 510 with a dogleg and 195 50 15s on 15x7 rewinds

 

thanks dtp!!

[69FJWagon]

sorry, 70 510 with a dogleg and 195 50 15s on 15x7 rewinds

 

thanks dtp!!

stock rear gear in most if not all 510s is 3.90s

[510kevin]

i know the stockers were mostly 3.90. im wondering how i identify mine.

like any marks on the case? or do i have to open it up to check gear ratio???

ive only had the car a few months and dont know if its a stock rearend.

[jesusno2]

3.36 you car will be horrible to drive, with any engine combo really. I'm pretty sure the DL 5spd's had a terrible 5th gear ratioo (not to familliar with them) 280zx 5spd's had good tall ratio 5th gears. The 3.90 is about the perfect gear ratio for a 510 I honestley like em with a 4.38. I personally would hunt for a zx trans if your runnin a L series motor. Some others may dissagree but I think the trans is what you should change. Your would need to have a driveline made, but I think it would be a wiser investment than a diff swap.

[wayno]

Hi there 620kevin, Going from 390 gears to 336 gears is a big jump, it's almost like starting in second gear. Depending on what your exhaust is, the sound might be deceiving you on your RPMs. OK, if you do not have a positrack rearend, you lift one rear wheel off the ground on you car, make sure you block the front tires so the vehicle will not move forwards or backwards, put the car in neutral, release the e-brake so the rear wheel will turn, make a clear, preferably white mark on the pinion flange on the rearend that the driveline bolts too facing you, make another mark on the tire(I use strait up), then turn the wheel off the ground two complete revolutions, while counting how many times the white mark turns on the flange. 3 1/2 turns is 350 gears, almost 4 turns is 390 gears, just over 4 turns would be 411 gears, 4 &1/3rd turns would be 437 gears, and so on. You have to turn the wheel 2 complete revolutions, and the otherside(wheel) must not move. If you have a posi rearend, you lift both rear wheels of the ground, and turn the wheels one complete revolution, and count how many times the mark on the flange goes by. wayno

[kmc63]

searched and couldnt find any info on how to check the gear ratio for my car.

i found a r180 for $50 with 3.36 gears

 

the problem im having is that i cant figure out the ratio on my rearend. i have no tach or speedo right now, but my car is wound up pretty tight going down the freeway.

 

was looking for a better ratio, but dont want to spend the money til i find out what mine is.

 

thanks!!!!!!

 

 

car is a 70 510 with a dogleg 5speed

and 195 50 15 tires on 15x7 wheels....

I am kinda in the same boat 71 510,15x7 wheels zx 5-speed im running a vg motor and its reving pretty high around 70 mph on the freeway,just as I imagine your is.If you have the stock rear-end which I do the next higher you can go is 3.70,which I was told in another thread would only drop my r.p.m by a few hundred. I am looking to upgrade my third member to a lsd unit but dont want the viscous which of course comes in more desireable ratios from what I have read. So I sit and ponder what to do,sorry im not much help,but atleast your not the only one wondering about this.

[69FJWagon]

I have a ZX tranny and had a 4.38 R180 with a nissan comp LSD and could roll down the freeway at like 75mph and was only turning about 3800rpm or less I now have a subby 3.70 LSD installed and can roll down the freeway at 85ish mph at like 3400rpm my speedo is way off so I had my girlfriend pace me so I know what approx. RPM I am turning at 65,70,75

 

I would NOT rely on the factory speedo to be accurate so when you say it sounds like your RPMs are high maybe your going faster than you think

 

the only way you can really know is to check the numbers on your ring gear and do the math but you can also do the old turn the drive shaft one complete turn and count how many times the wheel turns or vice versa...LOL cant remember

[510kevin]

thanks for the help guys. ive decided against the 3.36. im gonna hook up my tach (should've done in the first place) and have my wife pace me on the freeway.

 

then ill go from there.

[datzenmike]

car is a 70 510 with a dogleg 5speed

and 195 50 15 tires on 15x7 wheels....

 

Unless the diff was changed you're good. The 5th gear in the dogleg drops the highway RPMs about 14.6%. So if your highway RPMs are say 3,000 when you shift they will drop to 2,562

[jon521]

Not sure if this is the right place to ask, but i was told by a datsun guy (he isnt on here) that i can swap out my 3rd member (i have a 71 521) to a 83 or 84 720 2wd 3rd member and that i would have a way better gear ratio and that it would bolt right up, is this correct?

[ggzilla]

Both use H190 differentials.

 

But the 720 gear ratios are not better, they are actually worse performing. Because the 720 has a larger engine, they fit low ratio "highway" gears in them for better fuel economy. The big 2.2 and 2.4 liter engines can lug along this way.

 

The better solution is to fit a 5-speed to your 521, then you can keep the original ratio for good acceleration, and still get fuel economy when you put it into 5th gear on the highery.

[jon521]

i see...because i have stock everything drivetrain, and i feel (dont have a tach, yet) like im at the high end of fourth going 60 :mellow:. and i would like to be able to go highway speeds comfortably, and this guy, who is a datsun guy, say it is way easier to swap a 3rd member from a 83 or 84 720 2wd than fit a 5 speed in.....but i dont know:confused:....obviously :)

[datsunaholic]

Trust me Jon, a bone-stock '71 521 has no problem doing 80. It's noisy, true. That's just how they are, at 60 you're barely over 3000RPM. These aren't V-8 American cars, or modern cars with lots of sound deadening. These engines aren't even making max power until past 5000RPM, and you'd be close to 100MPH by then. The engine can take the truck way past what's safe considering the brakes and suspension.

 

My '76 620 has the exact same gear ratio, and the same 4th gear of 1:1. I ran 3/4 the way across the State doing 80. It's fine. Going too overboard with the rear gear (like using the 3.8-ish 720 ratios) will make it a total slug leaving stoplights. If you were to do a KA24 swap, then yeah you'd want the lower ratios. But with the L16 the 4.38 is the best overall ratio. A 5-speed really is the better way to go, though it's a more involved swap. But you don't lose the takeoff power that swapping rear ends causes.

[jon521]

Trust me Jon, a bone-stock '71 521 has no problem doing 80. It's noisy, true. That's just how they are, at 60 you're barely over 3000RPM. These aren't V-8 American cars, or modern cars with lots of sound deadening. These engines aren't even making max power until past 5000RPM, and you'd be close to 100MPH by then. The engine can take the truck way past what's safe considering the brakes and suspension.

 

My '76 620 has the exact same gear ratio, and the same 4th gear of 1:1. I ran 3/4 the way across the State doing 80. It's fine. Going too overboard with the rear gear (like using the 3.8-ish 720 ratios) will make it a total slug leaving stoplights. If you were to do a KA24 swap, then yeah you'd want the lower ratios. But with the L16 the 4.38 is the best overall ratio. A 5-speed really is the better way to go, though it's a more involved swap. But you don't lose the takeoff power that swapping rear ends causes.

 

 

sweet. thats really good to know. Thanks man! i guess i will have to run down to autozone a buy a tach and actually see what im running. thats why i wanted to make sure before i went and put one in.

 

whats the best 5 speed swap for a 521? i know you can swap any 5 speed from a L motor, and i dont have the bench seat, so it doesnt matter where the shifter comes up, i would like it if i didnt have to shorten my driveline, but i dont know if thats possible? i know i have to build a custom trans mount whatever i put in.

 

would this be the best?

 

Would love the tailstock from a 2wd shorty. Only takes a few min to remove it. Actually the whole tranny as it has better ratios for a car that the 4x4 one.

 

Here's one with an L front case on it. Perfect for the 510, even has the speedo on the correct side.

 

Edited July 14, 2011 by jon521

[jrock4224]

I have that transmission above with a l housing attached to it ... so going to a 3.89 or 3.50 with a l20 and morph tranny is bad? ....my plan is to hover in the 24-2700 at 75 mph...was thinking with 17's and a 389 and that tranny and a l20 should get me there...

[Laecaon]

3.89 is not bad. I have 3.89 with a dogleg and a L18 and have no problem maintaining 85.

 

Going down to a 3.5, you may find out your car doesnt have enough torque/hp to maintain that speed, especially considering 17's...

[yello620]

Going down to a 3.5, you may find out your car doesnt have enough torque/hp to maintain that speed, especially considering 17's...

 

This is exactly what happens when you get greedy on the gears. At 3.70 gears, i was into the secondaries constantly while trying to maintain any speed above about 65. At that point gas mileage suffered horribly. I did not have that issue with the 3.89 gears.

 

At certainly dont have that issue now with a VG30 in front of them. :D

[jrock4224]

sweet thanks yello i will just start with 3.89 .....and see where i am at...a vg huh... yeah not much issue running 75 too...

 

laecon, my dumb ass forgot to say i got a 521 sorry....noit a 510 on 17's that way to big a wheel for a 510

[Laecaon]

laecon, my dumb ass forgot to say i got a 521 sorry....noit a 510 on 17's that way to big a wheel for a 510

 

I dont care weather you have a 521 a 510 or magic carpet, the larger the wheel the more torque required to turn it. I didnt say it for reasons of looks.

[DanielC]

I cannot speak for any Datsun, or Nissan engines larger that an L-18. I have no experience with them. I can tell you about L-16, and L-18 engines.

 

Both of these engines like to rev. That is why they have an overhead cam, and not pushrods to run the valves. If you look at a stock 1971 510 tachometer, I believe it shows a yellow zone starting at 6500 RPM, and a red zone at 7000. The torque peak on a stock L-16 is about 3600 RPM. The L-16 is not really happy running below about 2500 RPM. If you insist running the engine that slow, you are lugging it.

 

Running an engine at it's torque peak RPM, is where it is most efficient. Ideally, this is the speed you like to cruise at. That would give you the best economy.

 

Making the engine run below it's torque peak RPM gives you less power. When you open the throttle to accelerate, that causes the manifold vacuum to drop, and in many cases, if the manifold vacuum drops too much, that causes carb to enrich the fuel mixture to produce the power needed. This causes the fuel mileage to drop.

 

When Datsun designed the cars, and trucks in the 1960's and 1970's they were concerned about economy, and performance. If you are running a stock sized engine, there is really not a lot to be gained by putting in a radically higher geared (low numbers) rear axle. If you never haul a load in your 521, you might gain a bit by going to a rear axle ratio close to a 510, (3.90 to 1) but much more than that, and you will lose economy, and you may end up with a vehicle that will need a fan to get away from it's own exhaust at a stop light.

 

For the 521 five speed, any L-series five speed will fit. I have long shaft Z car five speed in a 521 with a bench seat. The biggest issue with the 521 transmission swap is the stock 521 4 speed has a first gear ratio of 3.6 to one. Most five speeds have a first gear ratio of around 3.3 to one. If you have to haul a load, this might be an issue. If you usually do not haul anything in a 521 you probably can get away with a five speed transmission running with a 3.3 first gear.

[jrock4224]

I dont care weather you have a 521 a 510 or magic carpet, the larger the wheel the more torque required to turn it. I didnt say it for reasons of looks.

 

 

lae, i know but like i said my dumbass never clarified what i was talking about so sorry....and yes i do have a magic carpet...i understand the torque aspect wsa just stating i wouldnt put 17's on a 510...thats it ... but thank you for th eifo...

[Laecaon]

ooo a magic carpet! What sort of MPGs do you get with one of those?

[jrock4224]

u caught me daniel i am a lugger .....i do it on my bikes, atvs and cars, and anything with a working tranny... i call it short shifting but i am a lugger...and thanks for the info on trannys... wayno and d-mike already went about teaching me about what tranny i want to come through the stock shifter hole and be about the same legth as the stock on...which didnt really matter since i will go to a one piece driveshaft anyway... so my tranny thread is three pages of trying to get my shift lever back where it started...hahahha

 

 

i am working on building a ducted fan for under my truck for acceleratng from lights... i call it a psuedo hybrid

 

thanks for all the info, i am searching for a 3.90