question: 81zx 5 speed in 510 with L16 or L20?

[Dirty Evo]

going today to pull front struts off local '81 280zx parts car to use for my 510 track cars.

 

Currently, with my L-16 (117hp dynoed at crank, car weighs about 1800lbs) i am using a 4 speed 240Z tranny with a R180 diff (welded). no issues with 1-3 gears, but 4th gear a little "tall" (is that correct term?). the drop in RPM from 3rd into 4th is HUGE and creates a problem in a few spots on the track. L20 will be put int he car in about a year (should be about 200hp).. but for now, just sticking with the REbello built L16.

 

I am not racing, i am not going to win anything, this is just for fun, about 20 track days a year at Infineion, T-hill, Laguna Seca... so i don't want to go hogwild pouring money into anything, BUT if the '81 ZX 5 speed would give me less of a drop from 3rd to 4th and was a simple bolt in replacing my 240Z tranny, i would pick it up.

 

Any thoughts from you guys that know?

 

SHould i pick it up. . he wants $300 for the tranny, so its not a steal or anything..

 

ANy other parts i should be pulling off this '81 ZX for my 510's ? anything useful / swappable besides front strut / brake assemblies?

 

 

thanks

[datzenmike]

You have an R-180, so likely from a z car and in the 3.70 to 3.889 range, and possibly lower. IF your fastest top speed at your track is say 80 MPH but the car's top speed is 110 then you are not reaching your potential. Running a higher ratio rear gear set will increase low speed acceleration and lower your top speed. No sense shifting into 4th at 75MPH only to run out of track at 80 MPH and down shifting. 4th gets very little use. Get an R-180 with 4.11 or 4.375. They even go as high as 4.625. If you race at the same track, find the one that works best there. If you race at faster or slower tracks you can change the rear diff easier to give higher or lower top speeds.

 

Changing tire diameter is also an option as this affects overall 'gearing'.

 

BTW changing the transmission may not help. All 4 and 5 speeds have the same 4th gear ratio... one to one. So your top speed won't be changed in this gear. The z x 5 speed does have a 'close ratio' gear set with less rpm drop on all 1 to 4 shifts... but you don't get something for nothing, you will loose slightly on the take off in first as it is higher geared. The good news is you seldom have to stop when racing.

[Dirty Evo]

QUOTE: The z x 5 speed does have a 'close ratio' gear set with less rpm drop on all 1 to 4 shifts UNQUOTE ---- i think that is a trade off that works for me for this particular car and what i use it for. its 100% track car, never street, never autocross, never nothing but beating the hell out of it on a race track for 2 hours a day maybe 20 days a year!

 

 

thanks datzenmike.. you always give VERY helpful good info. I appreciate it.

 

What i noticed at Thunderhill last weekend (first time ever having a 510 on the track, its the lowest HP car i have ever tracked) was that coming out of a turn onto a "straight" i would have good strong acceleration out of 3rd gear... but then when shifting into 4th, it was such a huge drop... which resulted in slowing me down, lost a lot of momentum that i then have to try to make up down the straight in 4th... top speed in my E30 on front straight (or another spot on the track) was a little over 100mph.. through turn 8 i was at 90mph at apex. In the 510, i can't even come close to reaching that speed in either of those spots on the track because i lose so much on the upshift 3-4.

 

I know i can't make a gold brick our of a turd... but the power to weight ratio of this car is very comparable to my Spec E30 car (i had 138hp at the wheels and car weight 2890 lbs with me in it) and in fact the 510 was nicer through the twisties than my E30 (lighter weight, more nimble, and actually felt like it accellerated better coming out of 3rd gear turns).... so i was shocked with just how much of a dog it was once i had to upshift out of 3rd. 3rd is GREAT. 4th SUCKS

 

I do understand what you are saying with the diffs... long term it might be fun to mess with different diffs, but for my meager mechanical skills and limited time to work on the car between track days , i don't see it happening (until my kids leave for collaege in 13 years!). I just won't be swapping them out all the time.

 

1st / 2nd gear are completely un-unimportant for what i am doing with the car.. so losing a bit at takeoff, NO PROBLEM.. it won't matter for my fun track days. But 3rd-4th are where i spend 99.9% of my time on any of these tracks locally.. and its less about actually track time than the "fun" factor, and current doggishness in 4th gear saps a little bit of fun..

 

So, the diff suggestion aside, you are thinking that the 5 speed 280zx tranny MIGHT actually give me just a little less RPM drop from 3rd up to 4th, right? Won't work a miracle, but could improve things? I lose a bit in 1-2 but will have a better 3-4 for my purposes?

 

ANd if i really want to get it right, then i need to try different diffs, right?

[Stupid_fast]

The ZX n/a 81-83 is the 'close ratio' 5 speed. I don't know why, because the 1980 5spd has a shorter 5th gear. The 1979 box has a shorter 1st>2nd which makes 2nd>3rd shift drop quite large. I currently have the 79 box on my L20b, and I'm going to put in a CR 83 box.

 

According to sources online, the 240z 4 speed has these ratios 1st 3.549, 2nd 2.197, 3rd 1.42/, 4th1.00 These are extremely wide gears, but would work with a low geared rear end(3.54-3.70) for decent street driving.

 

The 'CR' box has the following ratios 1st 3.062, 2nd 1.858, 3rd 1.308, 4th 1.00, 5th 0.745 which is good for use with a high geared (3.90- 4.6 ) differential.

Dropping in the ZX box will make the first 3 gears much taller and closer to 4th, if you currently have a 3.90 rear end this will be an optimal setup for the track.

 

This will completely fix your problem, 4th gear WILL be the same, but you will use 3rd gear for longer, and have a more usable 2nd gear for low speed(45-50mph) corners.

 

Unfortunately, you will get a ton less acceleration off the line in 1st gear with a low torque L16, and it might feel a bit sluggish until you get to the powerband in 1st, after that you are going to be going a lot faster. This effect will decrease depending on your rear end gearing, a 4.3+ would be very nice for an l16 or even l20b and may make 5th gear usable.

 

 

Short story: GET THE CR BOX!!! You will never regret it!

[Dirty Evo]

thanks.. youre description of the 81ZX box SOUNDS like what i want. The only time i EVER am in first gear is heading out of the paddock. Since only track day (not actualy RACING) i have no need / concern to get a jump on anybody off the start.. slow in 1st is fine.

 

It sounds like maybe i should get the ZX box and then later can worry about trying to find another diff?

 

 

So, should i get anything else of the ZX? DIFF ? other? anytyhing useful there besides the tranny and front struts?

[Stupid_fast]

@Dirty Evo,

 

Definitely the CR box will give you a huge boost in track performance, you will love it!

 

Does your 510 have stock 3.90 gearing ?? If so that will be okay for the ZX box, but 4.1, or 4.3's would be better for track-only use. Calculate top speed in 5th gear and choose your gear ratio off that IMO.

 

The ZX uses an R200 diff, not bolt on for a 510. I don't think there is much else you can use off one.

[Dirty Evo]

actually have NO IDEA the gearing, because just found local R180 diff out of a Z car on craigslist and bought it for $80, was close and cheap i don't know. Is there a way to check by looking at it? It was a diff a TRIUMPH guy had for his TR4, but never used, said it came out of a Z , he had no idea what year or anythying.

[Stupid_fast]

@Dirty Evo, Mark the output ( side flange... use either side) with a sharpie or white-out at 12:00 position, spin the input until the output has completed 1 full turn, count how many times you rotated the input...you now have the gear ratio.

Other option: Do you have a GPS speedo? What rpm is 60mph in 4th ? What tire size?

 

Also, your speedo is probably wrong because the speedo cog gear in the tranny is for a 3.9 ratio differential .

 

if a Z car diff its probably a 3.54 .. which is horrible for a low torque l16.

[Dirty Evo]

another stupid question: driveshaft... will the the driveshaft i am using now witht the 240Z tranny (obvviously i had to have it shortened) work with the ZX tranny, or will i need o find a new driveshaft or alter existing?

[Stupid_fast]

You will need to take to a driveshaft shop to shorten it, also the shifter sits about 2" further back.

 

There are lots of threads and info around on the ZX trans swap.

 

 

Why don't you put back the stock 510 r180 ???

Or even better a 4.11 from a 84-88 N/A 200sx ?

[Dirty Evo]

You will need to take to a driveshaft shop to shorten it, also the shifter sits about 2" further back.

 

There are lots of threads and info around on the ZX trans swap.

 

 

Why don't you put back the stock 510 r180 ???

Or even better a 4.11 from a 84-88 N/A 200sx ?

 

I thought stock 510 diff was R160? I picked up R180 only because i was told they were stronger, would withstand track use (abuse) better and i plan on having rebello L20 built next year at about 210HP and was told the R180 would be more durable. That was the only reason.

 

I will try to find a 200SX diff since you are saying that would be better.. will keep my eyes peeled..

 

so the driveshaft already shortened for my 240Z tranny, needs to be further shortened for the ZX ? ok... and shifter even FURTHER back (already moved back when swapped the 510 4 speed for the 240Z 4 speed.)

 

Hmmm. so much to learn.. its all new to me!

[I'm BLUE]

stock 510 diff is r160.

 

4th gear is always 1:1 ratio

 

r180's are typically 3.36 and 3.54. ( from datsun zcar's )

240z manual trans = 3.36

240z auto trans = 3.54

 

r180's come from other cars as well such as some 280zx's , 720 front diff's and !?

 

Late zx 5spd trans + 3.90 diff (anything r180 or r200) is optimum for zcar daily driver duders cat's meow.

Unless major power than 3.54 is cool for zcar guys as well lol.

[Stupid_fast]

I thought stock 510 diff was R160? I picked up R180 only because i was told they were stronger, would withstand track use (abuse) better and i plan on having rebello L20 built next year at about 210HP and was told the R180 would be more durable. That was the only reason.

 

I will try to find a 200SX diff since you are saying that would be better.. will keep my eyes peeled..

 

so the driveshaft already shortened for my 240Z tranny, needs to be further shortened for the ZX ? ok... and shifter even FURTHER back (already moved back when swapped the 510 4 speed for the 240Z 4 speed.)

 

Hmmm. so much to learn.. its all new to me!

No, I am wrong, I'm forgetting the 240z 4 speed is a longer gearbox. It is the same length as the late 5 speeds AFAIK!!

 

Shifter is only 2" back from STOCK 510 4 spd. you will not need to worry about this, then.

 

I'm unfamiliar with this, I started out with a ZX 79 5spd and already shortened driveshaft.

 

 

 

stock 510 diff is r160.

 

4th gear is always 1:1 ratio

 

r180's are typically 3.36 and 3.54. ( from datsun zcar's )

240z manual trans = 3.36

240z auto trans = 3.54

 

r180's come from other cars as well such as some 280zx's , 720 front diff's and !?

 

Late zx 5spd trans + 3.90 diff (anything r180 or r200) is optimum for zcar daily driver duders cat's meow.

Unless major power than 3.54 is cool for zcar guys as well lol.

*facepalm* I forgot the stock diff was a r160, the r180 is definitely a good upgrade for power.

 

280zx NA 80-83 come with 3.90 R200's, 79 came with 3.54 R180's in some situations according to the gear ratio sourced I'm seeing.

81+ turbo cars came with 3.54 R200's.

 

According to some info, 3.90 and 4.11 R180's came in 720's, R180 4.11's came in NA 84-88 200sx. There are a lot of info around about what diff came in what car.

[Dirty Evo]

@Dirty Evo, Mark the output ( side flange... use either side) with a sharpie or white-out at 12:00 position, spin the input until the output has completed 1 full turn, count how many times you rotated the input...you now have the gear ratio.

Other option: Do you have a GPS speedo? What rpm is 60mph in 4th ? What tire size?

 

Also, your speedo is probably wrong because the speedo cog gear in the tranny is for a 3.9 ratio differential .

 

if a Z car diff its probably a 3.54 .. which is horrible for a low torque l16.

 

no speedo. not sure tire size... 13 inch wheels and slicks, but can't recall tire size, need to check. was told by guy behind me we were at about 105mph at end of front straight prior to braking for Turn 1 at Thill..

[datzenmike]

The 1980 Long bed 4x4 720 had 4.625 R-180s in them...

All other '80-'82.5 720 4x4s had 4.375 R-180s in them.

The '84 and on 720 4x4s used a 4.11 R-180 in them.

 

The R-180 you got off line could easily be a 3.364 or even 3.545 from a 280z or zx car. The stock R-160 would be far far better gearing than those.

[Dirty Evo]

went ahead and got the tranny even though not sure exactly what i got.

 

Its a 5 speed out of 81 zx NA. HOWEVER suppesedly this tranny is brand new build, geared with the same ratios as the TURBO trannys.... going to try this week to get the owner to confirm exact ratios... but IF what he was saying is true, then

 

 

 

3.500

 

2.144

 

1.375

 

1.000

 

0.780

 

 

hopefully can confrim things next week... then can source a diff with the right ratio and make this thing RIGHT...

 

if tranny really is geared as per above, then? good? or bad? or????

[datzenmike]

None of the non turbo trannys had the turbo gearing. Even so you now have 1st 3.549, 2nd 2.197, 3rd 1.42/, 4th1.00 with the older Z car tranny so no real improvement here.

 

The FS5W71B 280zx non turbo 5 speeds look like this....

 

The FS5R90A (Borg Warner T-5) turbo zx 5 speed looks like this...

 

 

 

 

 

 

.

[wayno]

The rear diff. gearing is everything to the track guys, if you have 370 gears in the rear, and the engine isn't strong enough to get it up to speed buy the end of the straight, and you have not gotten to redline(when your power starts dropping off and it would be time to shift), then try 411s, it will make your engine seem to have more power, what you need is to almost hit redline when you have to let off the pedal for the corner, if you hit redline before you get to the corner with 411s and still need more speed, then you need 390s, if you have not gotten to redline, then you need to use 437s, it's all about keeping it in the power band.

Once the engine is the best it's ever going to be, it's all about the rear diff. gearing, the transmission is just a tool to use the rearend gearing.

[datzenmike]

Well put Wayno

[Dirty Evo]

then i need to find 411 diff that is fo sure will start looking

[Stupid_fast]

Is the gearbox you are getting an FS5W71B or NWC borg warner T5 ???

 

The output spline of the T5 is different than the nissan box.

 

Either way its still a lot better than the 4 speed !! you can even make use of the 5th gear with better rear end ratio.. with 4.1, 4.3, or 4.6 you can choose your top speed .

[Dirty Evo]

its FS5W71B but "supposedly" custom geared, just built (rebuilt) within last 6 months with the same gear ratios of the T5.. that is the "story"...you know how it is, i am sure there is 20% truth and 80% BS in the story... no way to know for sure until i try iot. supposedly its not stock FS5W71B gearing. WHY? the guy it came from is into hot-rod Zs.. they drag race and drift and all sorts of crap. The car was '81 NA with 5 speed, the guy had the engine heavily modified for more HP and he had the tranny rebuilt also to accomadate and then proceeded to total the car (bent frame) within a couple months.. car was unloaded to his buddy to repay a debt... the "buddy' was keeping the engine for his car and had no use for rest of the parts and thus was parting out the car everything except engine. I got the front strut / rotor / caliper assemblies and the tranny for $300, he helped me pull everything off ... so i figure if nothing else, it will be a spare for me in case i jack up my 4 speed. and if it doesnt work.. well, it will be posted for sale someday then!

 

But yeah, you guys gave me a TON of help on the diff.. i am going to try to source maybe a 4.1 rear diff.. sounds like a better fit for me!

[Stupid_fast]

That is strange, the 81-83 ZX n/a box is the most close ratio optimal 5 speed for almost any situation!

The ZX turbo T5 ratios are MUCH wider ! Still better than a 240z trans.

 

Do you have the gearbox ? Get a marker, sharpie, white-out whatever, put trans in gear ... turn input shaft 1 full turn while counting how many times the output shaft goes around ... find the ratios.

[Dirty Evo]

i do have it in my garage... and the guy could be totally full of crap for all i know.

 

i will see see what i can figure out.

[Dirty Evo]

i am wondering if what he really did was rebuild it to closer ratios ... i.e. like the factory comp trannies? that would make more sense if you were going to put all that effort / money into regearing, i would think you would want to copy the nissan comp tranny???

 

who knows..