tfbmiata

HI all - just a question to my fellow track day buddies. Anyone run both a torsen and welded diff and could compare/contrast them? I've noticed replacement torsens going for $900+ but open diffs are in the $200 range.

The question is coming up b/c it seems every track day I have my 6 speed and 3.9 final are annoying geared with 5+ turns requiring me to shift just before braking and my buddies '00 5 speed is perfect with maybe 1 turn per track like that. I'm considering switching to the same 5 speed but obviously can't keep the same diff without making the gears CRAZY long.

Or is it maybe I'm just approaching the problem from the wrong direction?

Gee Emm

Got nothing to do with torsen or locked.

Got everything to do with the diff ratio.

Change gearbox and you will change gear ratios, we run 4.1s here with six speed, makes them nice and punchy. Big HP turbo cars are a case apart though, but if I am running an atmo car, especially dual duty, 6-speed/4.1 is the way I'd go..

tfbmiata

Interesting thoughts. The issue is the gear ratios/final. Wouldn't the 4.1 final just make the issue more likely to occur by shortening the gears even further? The reason I started the post was to find out about welded vs. torsen as a cheaper way to get a longer set of gears to make the issues with having to shift just before corners less often.

curly

iTrader: (25)

You're talking about two different things.

Changing your shift points requires a rev limiter change, grip change, driving change, transmission change, or final drive change.

Changing between a welded, torsen, or open diff changes how much the wheels are locked together. If you drive in a circle, the outside wheel is spinning faster than the inside wheel. You won't notice anything different while doing this between an open and a torsen. A welded diff will require one wheel the spin on the ground in order to make the turn. This will result in extreme understeer entering the corner, and extreme over steer exiting the corner.

Another factor with diffs is traction. Exiting a corner, typically the inside wheel is loaded less than the outside. If you have enough power to break the inside tire loose, the open will just spin it. The torsen and welded diff in most cases will continue to apply power to the inside wheel, giving you better traction exiting the corner.

The torsen can be bolted to any miata ring and pinion. Typically a 6-spd is best paired with a 4.1 for a slow car/track, 3.9 for a faster car/track, and a 3.6 for really big or really fast car. If you're not occasionally bouncing off the limiter in 6th at your local track, which should be ~135mph for you, you probably don't need a ratio change.

tfbmiata

Hi guys - I'm well aware these are two different things, but they are connected as a result of my logic. I'd like to have less shifts per lap and few times where shifts happen right before braking and am thus considering switch to a 5 speed and 4.3 rear end. The 4.3 rear ends I can find are a lot less expensive if they are open diff. The question I'm asking is if a open diff that has been welded which I can achieve for comparatively cheap has a major impact to things like drivability or life, etc that I'm not aware of because I would rather sell my 6 speed and 3.9 torsen, and then buy a 5 speed with open 4.3 rear end and have it welded for a few bucks if there are no massive differences as far as track days are concerned. The few things I've seen on welded vs. LSD is there is surprisingly little impact, but that doesn't seem right to me and thus why I'm asking the question.

@curly - I didn't know that a torsen could be easily moved to a different diff, but I've never cracked one open and dollar for dollar seems like if there are no differences, might be better to just get into the open diff-welded side of things. If I blow a diff at some point, I'm not looking for a $900+ version.

Hopefully that makes sense. I appreciate the responses so far. I was obviously not clear enough in my first post.


EDIT: Wanted to quickly mention that at sebring there are 3 to 4 turns I'm having to hover at redline for and at road Atlanta I believe there were 3 as well. I also really dislike the 4th to 5th shift in my 6 speed as even though I've done a rebuild kit from treasure coast, I seem to quite often find the "corner" between 5th and the slot for reverse so it sort of gets stuck.

Gee Emm

You are.

Q1. Do you have a traction problem in the corners?
No? you don't need to touch the diff centre.
Yes? you need to do something to stop the wheels spinning in the corners.

Q2. how do I fix a corner traction problem?
The cheap way is do what we Dunnunda call a CIG diff - weld it. That has handling consequences. Alternatively, fit an LSD - books written on that subject, search is your friend (hint: why do you think that people pay big money for an LSD?)

Q3. Too many gearchanges?
Ever hear of a rev limiter? That's what you use if you are going to lose more time gear changing than you save. Of course, you don't HAVE to sit on the rev limiter, you can just hold revs under that point. Or short-shift early, gives you more time to do the gear changes in comfort.

Q4. No, I need another fix for the gearing, what are my options?
First up, lift your rev limit. Use another 250-500 revs, maybe only in selected gears at selected points where needed most. Second, change your wheels/tyres to change your final drive ratio.

Q5. Nah, not sexy enough.
Okay, break out the spreadsheet, look at the alternative gearboxes and their ratios, look at all the final drive ratios available, and start calculating speed in gears for the combinations. Compare with current gearbox/final drive. Or, experiment with different combinations in the car. Or, talk to people you know running similar cars, and see what they are running and how it works for them. Start with whoever holds the lap record at the tracks/competition you run, or is at least a podium placer.

As to whinging about a $900 diff, you have taken up an expensive hobby/sport. Get used to tipping money into it. If you can't/won't, make sure you are having fun, because the tinware will be scarce.

Out here we had a bloke running in the stock class at State-level supersprints - with great success, shelves groaning with the tinware - fastest laps in class, first in class, first in class and category. The money he spent on brakes and tyres was (relatively speaking) eyewatering though, not even running a standard car was cheap. But it was a damn sight cheaper than us running in the modified classes . As a $$/kg of trophies, he was so far in front of the rest of us it was stupid.

It is all about choices, and their consequences.

thebeerbaron

iTrader: (1)

Your logic is flawed. Read, re-read, understand, and internalize what Gee Emm and Curly have said. They're right on the money.

To shortcut to your ultimate question without getting sidetracked by understanding why it's the case, a welded diff has no place in trackable Miata. You'll spend far more time, money, and aggravation working around it than you would eating ramen for a month to afford a Torsen. You'll be faster with an open diff than a welded one and you'll teach yourself fewer bad habits. Don't do it.

Also, it's extremely unlikely that you'd "blow up" the valuable part of a Torsen. With some caveats that are beyond the scope of this thread, the Torsen center you buy now should outlast the rest of your car. The most likely scenario is that you crack the aluminum part of the diff housing, a relatively cheap replacement item. Anything else is exceptional or makes the $900 Torsen seem like small potatoes.

tfbmiata

Thanks for answering my question. While I appreciate everyone's responses and they were damn sure informative, it was frustrating not to at least get an answer to the question I post. I understand this is an expensive hobby, however there are some of us out there which are clinging on to the hope that we can just barely afford it and still stay involved in it. It's really not super helpful to talk about how expensive things can be or are for people who are struggling to spend what they can and cut corners where possible in order to continue to do the hobby they love. Again, I appreciate everyone's help. The folks who responded who didn't actually answer my question still taught me a lot and that's awesome. You guys have a great community here and I'm happy to pop in and out of it.

Gee Emm

A couple of final points before I check out.

You may be surprised to find that short-shifting doesn't lose you much/any time compared to the alternatives of running on the limiter and a rapid shift up/down again. In fact, it might even be faster.

You can throw money at the car, but it is the driver who makes it go fast (see above re short-shifting). If you are concerned about bang-for-the-bucks and going faster, your best investment will be in a lap timer. Get one where you can sit at home/pits and compare laps/lap time, and use it to put together 'calculated' laps - the device tells you your best theoretical lap, being the product of the best individual sectors you have achieved. Then look and see where you made those best sectors, why they were the quickest. Same with slow laps, what made them slow.

Good luck.

tfbmiata

Great advice! At the moment, I'm mostly concerned with figured out ways to push the car which don't end up with me in the wall. While that clearly overlaps with lap time, ultimately, my PBs are just personal victories and lap time doesn't really matter. The short shift idea is a great one and one I naturally did, but each HPDE event I had a coach they jumped all down my **** on that. Two out of 3 coaches were miata dudes trying to get me to ring out every last rev and bang it off the limiter until the turn was ready. I just got to the point where I'm starting to use a lap timer with track addict and a garmin 10hz GPS so I think over the next few track days I'll start to be able to actually hone in on paying attention to that.

Arca_ex

iTrader: (2)

To answer your original question, welded differentials suck for road courses because they induce unwanted understeer on corner entry. There's a reason why people buy LSD's in all types of different cars instead of just welding their open diffs at a significantly lower cost.

Keep the 6 speed and change to a 4.1 or 4.3 rear end ratio. Play with a gearing calculator and you can see how it will affect you at particular tracks. It's not going to be perfect at every track.

https://kpower.industries/pages/gearing-calculator

tfbmiata

While combing the fb marketplace I found a used 5 speed for a $100. I may try that with my 3.9 final drive. Gear calculators show it super long by comparison and I keep my torsen. I have 2 issues with the 6 speed and its that most corners seem to require a shift just before braking and the actual shifter feel is vague despite having just done a shift rebuild. If this 5 speed feels the way my buddy's did it will fix both of those issues. I've yet to actually hit the same track multiple times at full speed so I won't have a lot of track history, but I'll keep the 6 speed around in the event I want to try that out. Eventually I will likely do some type of FI as I get bored (haha) with the miata's straight line speed and from another thread that's weirdly attached to the bottom of this one, it looks like a lot of people like the 3.9 final drive with 5 speed combo.

EDIT: https://www.miataturbo.net/suspensio...weight-104540/

Arca_ex

iTrader: (2)

Okay stop what you're doing and just drive. Focus on driver mod and consumables. I can tell you right now that as you get better and faster or even just change to better tires among other things, these shift points that you are complaining about will move drastically. Tinkering with transmissions and differentials when you already have a solid setup is a massive waste of effort when you have admitted yourself that you have limited seat time on these tracks.

Keep driving and keep progressing as a driver and these issues you think you are having will sort themselves out as you learn.

tfbmiata

I'm absolutely a tinkerer/overthinker and this is probably the best advice in the thread.

turbofan

iTrader: (1)

100% the best advice in the thread. You're not nearly at the level where you need to be making mechanical changes to the car to adjust shift points. I wouldn't really recommend such a thing until you're racing.

One of the most common problems I face when instructing is that novices shift WAY too much. They brake, downshift, downshift, downshift, blow the apex even though they're going 20 mph too slow into the corner cuz they're so focused on downshifting.

If you have a corner where you're having to upshift right away on corner exit, chances are you're overslowing and have no business being in that lower gear anyway. If you have a shift that's frustrating you, get rid of it and focus instead on carrying appropriate entry speed, hitting the apex, getting on throttle earlier, etc.

Moving to a 5-speed will make the problem worse, not better, since your gears will be even further apart making it so you spend more time at the wrong RPM.

emilio700

iTrader: (3)

Separate topic, but related. One drill I used to have students do to learn to maintain higher min speeds, carry more entry speed and hit apexes more accurately was to drive the whole lap in one gear. That forces the driver to carry momentum. The new driver will often go faster in one gear than they do by over focusing on shifting.

The more power and grip you have, the higher diff ratio needed. The NB 6 speeds has great track ratios, nicely spaced. Higher rev limiter allows a lower final drive.
A few of the cars we have built over the years:

2400 lb PTE race car on 205 Hoosiers, 146whp 8500rpom redline. 5spd x 4.875
2200lb STU race car on 205 BFG R1, 180whp 9200rpm redline 6spd x 4.3
2200lbs PTC race car on 205 Hoosiers, 170whp 8500 rpm redline, 6spd x 4.3
2300 lbs S1 race car, 220whp, 7400rpm rev limiter, 6spd x 3.9
2300 lbs time attack, 400whp, 7800 rpm 6spd x 3.6

tfbmiata

Is there a safe rev limit over 7200 that the stock nb2 motor can rev to? I've been considering a switch over to megasquirt already for the fun of tinkering with tuning and custom dash so that might be the icing on the cake. Most corners another 200 to 300rpm would probably get me there. Though someone mentioned before, short shifting may not even be a net time loss.

emilio700

iTrader: (3)

Define "safe".

Healthy stock BP can survive a few trips to 8k before something breaks. Or regular trips to 7300.
Maintain good oil viscosity with thicker synthetic oil and a cooler. Keep fresh valve springs in it, they wear out. Heavy duty valve springs are good. Epoxy throttle shaft over plate screws, they fracture.

Load on main bearings is both torque (cylinder pressure) and inertia (rpm). I don't know the math but something like 6000rpm at 300whp might be the same psi on the mains as 7800rpm at 160whp

thebeerbaron

iTrader: (1)

Stop. Go back a few posts and re-read what Arca_Ex said.

You may have the itch to spend money and tinker, but try, try, try to put it off. An aftermarket ECU is a slippery step. First you spend the money on the ECU, then you spend time and money farting around with wiring and the custom dash, then you need to find someone local to tune it, pay them a good deal of money to do it, you look at the power gains you didn't achieve, then you start thinking about throwing parts at the engine now that you have an ECU...

Pardon my ignorance, but not knowing where your car is in terms of maintenance and wheel/tire/suspension/brake/safety updates... if you really have money burning a hole in your pocket, let's start looking at those.

Edited to add: in addition to buying more track time, of course!

tfbmiata

I've had almost all of that stuff touched. About the only thing I'm dealing with maintenance wise at the moment is a leaky rear main which was supposed to have been done by a shop that did my clutch but clearly wasn't as the oil is still coming out of the weeping hole and I have a very slippery clutch. At the moment I'm about half way through removing the 6 speed to get to the rear main leak and replace the clutch with a locally found act 6 puck, heavy duty pressure, and fidanza lightened flywheel (just came as part of the deal).

• Koni yellows w/ gc springs
• FM front and rear sways
• Sport Discs front and rear w/ hawk blue pads and motul 660f fluid, ss brake lines
• Hard dog m2 roll bar
• CX racing drop pan w/ 5 point harness and bucket seats
• 300 treadwear continental extreme contact sport (I picked this because they can be used for rain and dry whereas the 200 treadwear versions of just about everything are terrible for rain)
• oil pressure, oil temp, water pressure water temp gauges with audible alarms for bad min/maxes

I understand I need to focus on track time. At the moment, I'm about a month in between each track session. This is a hobby I'm mostly obsessed with at the moment and so my brain doesn't just go into zombie mode in between each track day I get to do. Each time I have 30 days between the sessions to evaluate what sucked and what went well and how to fix that for the next track day. I wish I could go more often, but my full motion VR based racing sim has to do instead as I'm a family man and that much time away from the kids will simply result in a fast tracked divorce! I appreciate everyone's comments here for sure and the points about staying simple and focusing on the driving are not lost, but they are just not everything either. I'm happy to continue to take everyone's advice!

Also if anyone is in the southeast region (Florida), i'd love to meet up for a miata bro track day!

EDIT: Also, who do I owe 3 cats to and how do I keep losing 'em?! -3 cats already!