Drivetrain Which First Gear To Go With?
- Thread starter FastDriver
- Start date
-
Sponsors (?)
re: Speedo Drive Gear - oh ...eeks that will be a lot of teeth on the speedo cable's gear to compensate
Yes trying to keep it original.
And yes I will be going with an Eaton TrueTrac helical-gear style, limited-slip differential. I'll be storing the original open diff along with the original 3spd Top Loader, and original bell housing.
Yeah I know the 351w has a potential for a good amount of HP, but requires visible enhancements like ; Headers, heads, etc.
Any power enhancements would have to be stealthy. Thought about going to EFI for driveability sakes (the original autolite 4300 is currently giving me problems (bogging on accel) ) . The system is under the air cleaner so out of sight.
I bought the car in 1992 from the original owner, a vietnam vet who bought it as a present to himself for surviving his tour.
not really, I forget the torque numbers, but on the street that's what matters, look for HP to weight ratio, write down where the torque band is on each, you have to look at tire heights, gear ratio, first/second trans gear if you wanna get really techy, it's easy going 80-100 MPH, it's getting there that matters.
Old school rules: heavy car, more gear (higher numerical) still sluggish, more torque (more cubic inches)
I'm getting chatty, sorry.
here is the torque/hp curve for a stock 351w4v
That's stock 5spd 5.0 fox territory. Our cars are so slow, stock.
You should prolly know, assuming your speedo is calibrated like ours are, that the 23-tooth driven gear you'll need for 3.73s will tear up over and over and lead to speedo bouncing and eventually no speedo.re: Speedo Drive Gear - oh ...eeks that will be a lot of teeth on the speedo cable's gear to compensate
Yes trying to keep it original.
And yes I will be going with an Eaton TrueTrac helical-gear style, limited-slip differential. I'll be storing the original open diff along with the original 3spd Top Loader, and original bell housing.
Yeah I know the 351w has a potential for a good amount of HP, but requires visible enhancements like ; Headers, heads, etc.
Any power enhancements would have to be stealthy. Thought about going to EFI for driveability sakes (the original autolite 4300 is currently giving me problems (bogging on accel) ) . The system is under the air cleaner so out of sight.
I bought the car in 1992 from the original owner, a vietnam vet who bought it as a present to himself for surviving his tour.
That's a real beauty. Though I've never owned one, my pop had a 70 Boss 302, and a 68.5 428 Super Cobra Jet. So, I have a special appreciation/love for those body styles. But... I wouldn't hesitate to modify one to suit my tastes. I don't care if I can beat the 2030 electrified Honda Minivan that'll run an 8 second 1/4, but I do want to smoke the tires at will.
Awesome choice on the diff. Didn't know what kinda budget you were thinkin of. I have a Truetrac in 2 out of 3 of my cars, and it might be 3 of 3 if I turn out to not like the S-trac in the monster I started this thread about. Love that True-Trac. WAY better than the trac-loc.
Well damn he had some nice cars!!!! can't get much better than those two.
that's kind of the goal.....beating a the mini-van was just for added bonus. I KNOW my 350z whips my Mach 1's ass and gets DOUBLE MPG.
Yeah the fact that I don't have to run friction modifiers with the true-trac and the reviews were so good it was the choice....I thought about going with a nodular gear case, but think it is overkill for such a low HP car (about a $500 difference). BTW I'm getting the whole center section so I can keep the original senter section as a unit.
yeah....hence the eeeks .....the alternative is replace the speedo drive gear to either a 6 or 7.....but ugh I don't want to remove the transmission.....I might hire someone to do that if it is an 8tooth....what colors were the 6,7,8 tooth ones....do you know?
I took a little liberty with the dyno, as they ended the run at around 5,300 and it looks like your optimum shift points are higher in all but 3rd gear. So, I extended the curve out to approximate what it looks like the rest of the dyno would look like (yellow). Then, I plotted the shift points such that the rising HP curve in the next gear intersects the falling HP curve in the current gear (Green). If your car runs like the one in the dyno, these will be your approximate optimal shift points with your T5. Word of caution: Don't overshoot, as the HP curve is dropping off precipitously. You're better off short-shifting than over-revving.
Here's what that looks like on my gear gonkulator:
Note the "Max RPM by gear" was used in this case instead of the "Max RPM (all gears)," which allows for adjustment by individual gear. So, if you look at the orange/red column under "RPM Input," you'll see the speed you should be shifting out of each gear. As you can see a 3.75 ratio would be optimal for a car that traps 111mph in the 1/4, or perhaps slightly higher. So, if you wanted an optimal ratio for the 1/4, it would be WAY high... like 4.50s area, assuming a trap speed in the 93mph range. I'm assuming you'll outperform the stock 1/4 you quoted before (86mph), because you have an extra gear which not only gets you into the powerband faster, but it keeps you in the powerband better between gears. The optimal shift RPM in each gear is independent of your rear gear ratio.
Side note: I have been in soooo many debates about HP vs. torque and can plot optimal shift points using either curve, though the torque curve requires replotting the curve multiplied by the gear ratio in each gear, which is harder. So, I did it on the HP curve in this case. If anyone comes in here and starts to argue with me, please just take my word for it as I'm not going to debate this topic any longer. It is my least-favorite discussion amongst enthusiasts.
Here's what that looks like on my gear gonkulator:
Note the "Max RPM by gear" was used in this case instead of the "Max RPM (all gears)," which allows for adjustment by individual gear. So, if you look at the orange/red column under "RPM Input," you'll see the speed you should be shifting out of each gear. As you can see a 3.75 ratio would be optimal for a car that traps 111mph in the 1/4, or perhaps slightly higher. So, if you wanted an optimal ratio for the 1/4, it would be WAY high... like 4.50s area, assuming a trap speed in the 93mph range. I'm assuming you'll outperform the stock 1/4 you quoted before (86mph), because you have an extra gear which not only gets you into the powerband faster, but it keeps you in the powerband better between gears. The optimal shift RPM in each gear is independent of your rear gear ratio.
Side note: I have been in soooo many debates about HP vs. torque and can plot optimal shift points using either curve, though the torque curve requires replotting the curve multiplied by the gear ratio in each gear, which is harder. So, I did it on the HP curve in this case. If anyone comes in here and starts to argue with me, please just take my word for it as I'm not going to debate this topic any longer. It is my least-favorite discussion amongst enthusiasts.
Last edited:
Just a word of caution here, I'm not sure and in fact I don't think that after market companies all use the same color scheme.
I typically use my gonkulator, but here's a couple helpful tables from something I saved some time from before I can remember... If you stick with an 8-tooth:
If you go with a 7-tooth:
If you go with a 6-tooth:
Here's what the gonkulator says:
6 tooth:
7-tooth:
You've already seen the 8-tooth gonkulation in an earlier post. I don't know why the gonkulator disagrees with the tables, but I trust my math. So, I'd go with the gonkulator. The 7-tooth with a 20 is very, very close.
Edit: Matter of fact, yes I do know why they disagree. The tire size isn't accounted for in those tables and your cited tire specs should make your tire taller than a stock fox's, and the gear ratio is off by a fraction. If you have an exact tire size, we can put that in there. The manufacturers exact tire sizes don't match the sidewall specs exactly, but they usually publish their tires' circumferences.
Last edited:
Thank you for your time. Even at age 59 I can learn things and do frequently....most helpful
I believe I changed my speedo gear to an 18tooth when I put the T5 in ....I have to get gas for the old girl...I 'll compare the iphone's GPS and see what the MPH is reading on the dash at 45mph on the phone. I'll report back.
I believe I changed my speedo gear to an 18tooth when I put the T5 in ....I have to get gas for the old girl...I 'll compare the iphone's GPS and see what the MPH is reading on the dash at 45mph on the phone. I'll report back.
Attachments
EXACTLY where I am getting my complete center section...with the Eaton.....I have to do some measurements of the yoke to make sure I get the right one.
No problem, bud. I like this stuff! Anyways, if you know it's an 18 tooth, then we can figure out the drive gear by the difference between the GPS & the speedometer... probably. Do me a favor and get 2 different speed reading differentials. The peg in the speedo can also be offset, which would throw off the calculations, too. If we have 2 speed readings against their GPS speeds, then we can still figure things out.
Try to get them as widely apart as possible, within reason. Like going as fast as safe and comfortable on the highway as possible, and then another at say 40-45 mph, like you said.
FastDriver has you lined out but I thought I would share my combo with the T5.
I have a T5 with 3.73's in my Coupe and I wish I would have gone with 3.55's due to how fast 1st gear runs out and the rpm's at 70 mph are a little high. I put a 6 tooth drive gear on the output shaft of the T5 and with the 275/40R17's I run a 17 tooth driven gear on the speedo cable and its just about dead on. I have a couple of speedo gear calculators saved but this one is pretty easy:
I have a T5 with 3.73's in my Coupe and I wish I would have gone with 3.55's due to how fast 1st gear runs out and the rpm's at 70 mph are a little high. I put a 6 tooth drive gear on the output shaft of the T5 and with the 275/40R17's I run a 17 tooth driven gear on the speedo cable and its just about dead on. I have a couple of speedo gear calculators saved but this one is pretty easy:
@FastDriver
Some MPH numbers with my current setup of a T5 and 3.00:1 rear....Assuming I have an 18 tooth speedo cable gear. (I found my receipt from Modern Driveline for the 18 tooth gear)
I am so sorry I made a mistake in the tire size ...they are actually currently 215/60R14 not 225
The numbers were all taken with the car was in 4th thus a 1.00:1 ratio at the transmission
The Stewart Warner tach is suspect, I think it is about 200 rpm off (reading slower) at above 1000rpm. I have an induction tach that seems to report spot on with the SW tac at idle , then the SW goes a little awry the faster you go. trying to read the RPM while driving was a little hard so the numbers are all over the place and I'm not sure the tach is super accurate as it is from the 60s too.
Did a lot of spirited driving today and am now "fearing the gear" :-( Right now I'm out of first gear around 20MPH at 3000rpm, but then again I'm out of 1st gear in the 350z at about the same speed. Also I am running smaller diameter tires than I should be so...maybe my fear would go away after I get the taller tires.
Can you do your math and figure out if I have a 7 tooth or 8 tooth T5 speedo drive gear?
Some MPH numbers with my current setup of a T5 and 3.00:1 rear....Assuming I have an 18 tooth speedo cable gear. (I found my receipt from Modern Driveline for the 18 tooth gear)
I am so sorry I made a mistake in the tire size ...they are actually currently 215/60R14 not 225
The numbers were all taken with the car was in 4th thus a 1.00:1 ratio at the transmission
The Stewart Warner tach is suspect, I think it is about 200 rpm off (reading slower) at above 1000rpm. I have an induction tach that seems to report spot on with the SW tac at idle , then the SW goes a little awry the faster you go. trying to read the RPM while driving was a little hard so the numbers are all over the place and I'm not sure the tach is super accurate as it is from the 60s too.
| SW RPM | GPS MPH | DASH MPH |
| 1200-ish | 29 | 30 |
| 1300-ish | 38 | 40 |
| 1500 | 40 | 42 |
| 1500 | 43 | 45 |
| ?? | 45 | 45 |
| 1700 | 48 | 50 |
| 2200 | 58 | 60 |
| 2000 | 58 | 60 |
Did a lot of spirited driving today and am now "fearing the gear" :-( Right now I'm out of first gear around 20MPH at 3000rpm, but then again I'm out of 1st gear in the 350z at about the same speed. Also I am running smaller diameter tires than I should be so...maybe my fear would go away after I get the taller tires.
Can you do your math and figure out if I have a 7 tooth or 8 tooth T5 speedo drive gear?
Yep, sure thing.
One thing that looks nice is that the speedo gear set up you have now is calibrated right. You consistently stayed 2mph off from true (GPS). If it weren't calibrated right, then you'd notice the gap between true and speedo indicated change as you sped up. That just means the peg/needle is off by 2 mph, but the speedo gears are calibrated right.
Ok. So, according to your earlier assertion that you have an 18 tooth driven gear, the math says.... drum roll please....
For the math to be perfect, based on all the inputs, you have a 7.187 speedo drive gear. There's slop in all measurements. When you get to splitting hair, the tire circumference isn't going to be perfect according to the calculations due to manufacturing, wear, tire pressure, etc... The GPS and Speedo readings are going to be at best within ~1mph (2% at 50mph), etc... So, if you really do indeed have an 18-tooth driven gear, then it looks like you have the 7-tooth speedo gear you suspected.
Given that you thought you had an 18-tooth driven gear, and also stated you thought you had a 7-tooth drive gear, and given the fact that the math works out to support that idea, I'd say that's what you have. That's great news! That means that if I do successfully convince you to go 3.75, a 20-tooth driven gear will work perfect, and it won't chew up like an 8-23 speedo drive-driven gear setup would.
If, on the other hand, you find a 20-tooth driven gear when you get in there, then you'll know you have an 8-tooth speedo drive gear:
... but it sounds like you've validated your 18-tooth driven gear assertion.
Now, with regard to your tach, here's what the math says (based on GPS Speed, which is assumed to be true):
So, to me, your tach doesn't seem consistent. At some speeds it's close, and at others it's far off. What's really weird is that at the same speed it's different and at the same RPM it's different. Almost seems like electrical interference to me.
I guess I'm the weird one. I've never had "too short a gear" in 1st. The whole point of 1st is to get off the line and quickly into your powerband. It's pretty amazing to be able to get out into gear, just off idle, and then just let the gear do the work instead of doing all the pedaling balancing the gas and clutch to avoid bog. I honestly LOVED my T5's 3.35 1st and the 4.10s. I'd roll out at 1500-2k RPM and then go flat on the gas. I cut a 1.83 60' time that way on stock sized (225/50/16) Goodyear All-season tires (link). I've been in the game a long time and I've never heard of anyone do that on that kind of tire. Plus, when you have a cam that bucks below 1,500 RPM, like my e-cam, it's nice to have a very short gear that I can do just 9mph at 1,600 RPM in a parking lot or in traffic.
I have the opposite problem, right now. I have a T56 I decided to use because it was already on the garage floor. Unfortunately, it has a 2.66 1st, and I wanted 3.73s for a couple of reasons (2nd in Auto-X is very important, and 4th on the quarter should put me approaching 6k RPM if I can get my trap speed up to ~128mph. However, 2.66 with 275/40/17s & 3.73s is a DOG! I'm currently launching off of the stock limiter and still struggling to avoid bog. I hope the nitrous and my future build gives me the boost in torque it needs to get the car off of the line without blowing off the tires. If I ever rebuild the T56, I'm going to go with a 2.97 1st gear, for sure.
One thing that looks nice is that the speedo gear set up you have now is calibrated right. You consistently stayed 2mph off from true (GPS). If it weren't calibrated right, then you'd notice the gap between true and speedo indicated change as you sped up. That just means the peg/needle is off by 2 mph, but the speedo gears are calibrated right.
Ok. So, according to your earlier assertion that you have an 18 tooth driven gear, the math says.... drum roll please....
For the math to be perfect, based on all the inputs, you have a 7.187 speedo drive gear. There's slop in all measurements. When you get to splitting hair, the tire circumference isn't going to be perfect according to the calculations due to manufacturing, wear, tire pressure, etc... The GPS and Speedo readings are going to be at best within ~1mph (2% at 50mph), etc... So, if you really do indeed have an 18-tooth driven gear, then it looks like you have the 7-tooth speedo gear you suspected.
Given that you thought you had an 18-tooth driven gear, and also stated you thought you had a 7-tooth drive gear, and given the fact that the math works out to support that idea, I'd say that's what you have. That's great news! That means that if I do successfully convince you to go 3.75, a 20-tooth driven gear will work perfect, and it won't chew up like an 8-23 speedo drive-driven gear setup would.
If, on the other hand, you find a 20-tooth driven gear when you get in there, then you'll know you have an 8-tooth speedo drive gear:
... but it sounds like you've validated your 18-tooth driven gear assertion.
Now, with regard to your tach, here's what the math says (based on GPS Speed, which is assumed to be true):
| GPS Speed | RPM in 4th gear |
| 29 | 1,211 |
| 38 | 1,586 |
| 40 | 1,670 |
| 43 | 1,795 |
| 45 | 1,878 |
| 48 | 2,004 |
| 58 | 2,421 |
So, to me, your tach doesn't seem consistent. At some speeds it's close, and at others it's far off. What's really weird is that at the same speed it's different and at the same RPM it's different. Almost seems like electrical interference to me.
When you run those 225/70/14 (right?), that's a pretty big difference. To have the same effective gear ratio, you'd already need 3.27s. That would keep it driving the same way it is now. So, keep that in mind.
I guess I'm the weird one. I've never had "too short a gear" in 1st. The whole point of 1st is to get off the line and quickly into your powerband. It's pretty amazing to be able to get out into gear, just off idle, and then just let the gear do the work instead of doing all the pedaling balancing the gas and clutch to avoid bog. I honestly LOVED my T5's 3.35 1st and the 4.10s. I'd roll out at 1500-2k RPM and then go flat on the gas. I cut a 1.83 60' time that way on stock sized (225/50/16) Goodyear All-season tires (link). I've been in the game a long time and I've never heard of anyone do that on that kind of tire. Plus, when you have a cam that bucks below 1,500 RPM, like my e-cam, it's nice to have a very short gear that I can do just 9mph at 1,600 RPM in a parking lot or in traffic.
I have the opposite problem, right now. I have a T56 I decided to use because it was already on the garage floor. Unfortunately, it has a 2.66 1st, and I wanted 3.73s for a couple of reasons (2nd in Auto-X is very important, and 4th on the quarter should put me approaching 6k RPM if I can get my trap speed up to ~128mph. However, 2.66 with 275/40/17s & 3.73s is a DOG! I'm currently launching off of the stock limiter and still struggling to avoid bog. I hope the nitrous and my future build gives me the boost in torque it needs to get the car off of the line without blowing off the tires. If I ever rebuild the T56, I'm going to go with a 2.97 1st gear, for sure.
Last edited:
Hey, by the way, I noticed in your thread about this stuff, you list your transmission's gear ratios stating you think you have a 90, but then the gear ratios you list are for that of an 86.5-89:
The T5Z would have a 2.95 1st. The earlier trans (83-89) has a 7-tooth drive gear. The 90+ has an 8-tooth. So, maybe, despite whatever car it came out of, the trans you have was originally an early WC T5.
| WC T5 '86.5-'89 (2.95 1st for T5Z) | % drop | WC T5 90-93(2.95 1st for T5Z) | % drop |
3.350724638 | 7(83-89) or 8(90+) | 3.350724638 | |
1.992438563 | 40.54% | 1.928166352 | 42.46% |
1.325337331 | 33.48% | 1.287517532 | 33.23% |
1 | 24.55% | 1 | 22.33% |
0.676492262 | 32.35% | 0.676492262 | 32.35% |
The T5Z would have a 2.95 1st. The earlier trans (83-89) has a 7-tooth drive gear. The 90+ has an 8-tooth. So, maybe, despite whatever car it came out of, the trans you have was originally an early WC T5.
@FastDriver thank you so much for your time.
I am no longer sure what year the T5 is ....on one receipt from the transmission shop that rebuilt it in 2012 wrote down 1990. On other receipts I wrote down 1990 on one and 1993 on another....ugh. I've reached out to the guy I bought it from in 2012 to see if he remembers.
Any other ways to know for sure? It's missing the tag plate :-(
I'll look for the casting date...but that is just a ballpark.....not definitive....
I am no longer sure what year the T5 is ....on one receipt from the transmission shop that rebuilt it in 2012 wrote down 1990. On other receipts I wrote down 1990 on one and 1993 on another....ugh. I've reached out to the guy I bought it from in 2012 to see if he remembers.
Any other ways to know for sure? It's missing the tag plate :-(
I'll look for the casting date...but that is just a ballpark.....not definitive....
I'm not too smart on part numbers. So, barring a search on Stangnet, or maybe Mike @Mustang5L5 would know. I know he's built a couple. But, either way, popping the Driven gear out is just jacking up the driver's side, taking out 1 small bolt and then pulling out the speedo cable from the trans. The year's not exceptionally relevant. Even the 2nd & 3rd gear ratios are so close, it's virtually impossible to tell the difference. You're talking about 2-3% difference in just those two gears. I just wouldn't worry about it, and further, I would assume it's a pre-90 if you have the 7-tooth drive gear.
Speedo gears are usually changed. Any pre-90 T5 i've done gets the newer gear. Short if pulling the top cover off and reading the cluster gear number, hard to tell
Similar threads
