Galt

I'd like to know if I could get a shop to make a custom final gear for me, in the 2.7:1 or 2.9:1 range.

I have a TII rear end with a clutch LSD.

(Don't tell me this is a bad idea, it's not for a rotary engine, it's not even in an RX-anything)

MmSadda

iTrader: (2)

Ask a shop that does transmission work. If it's not in an RX-anything, or a rotary powered car, let alone an FC, why did you post this here instead of in general automotive?

Galt

Because the part in question is for a Turbo 2 FC RX-7 rear diff. That part was on 2nd generation specific cars.

jgrewe

iTrader: (1)

I'm sure you could get something made but would it be worth the $1000 it will probably cost? That's just a guess, it will probably be higher. I would look into something Ford that you can buy just about any gear you can dream of.

Contact Houseman Autosport they do custom stuff.

Galt

I don't plan on breaking this T2 diff (about 400whp on that I've heard), it's already welded in. I have limited transmission options with the tranny I have, I can either buy a quaife gearset for 4000$ or get a six speed transmission and a lower rear end, for around 1500-2000$ if the rear end does cost 1000$.

jgrewe

iTrader: (1)

Just curious, what ya building?

MmSadda

iTrader: (2)

I'd like to know this, too. Sounds strange.

I know you said it's welded in, but if you could undo that, I believe there's some kind of Ford rear end that mates up with the TII tranny/driveshaft quite nicely. That's IIRC, tho.

Galt

Just working on a Miata. The six speed would give me a nearly unusable 1st with the 4.1 I have now (not that the first 2 gears have traction right now).

A 2.7 would be really nice with a six speed for some cruising. The quaife would be awsome but it's just darned expensive.

I sent an email to that custom shop, thanks for the point out.

Omixeo

iTrader: (1)

Theres a really good differential shop here in Tucson. You can give them a call, they're called Tucson Differential, they have a really huge shop, they can probably help you out.

Black91n/a

Still, that's really low. Most 6 speed Miata guys want 3.6's or dream of 3.3's. A 2.7 is a lot lower. I'm not sure if you can fit a big enough pinion gear in the space available to achieve that.

Why not go with a 5 speed? You can get the quaife gears for them and there's a tall gearing option. It'll be durable with 400whp, whereas the 6 speed won't be as much so, and they've got terrible shifting from what I've heard.

Here I was thinking maybe you were building something diesel, hence low rpm, hence tall gears.

Galt

I understand the gearing is low. I referenced that in my original post

I'm asking if this is possible. Do you know or are you as unsure as I? That's why I'm posting this thread.

As referenced earlier, cost. As I referenced earlier, I don't plan on breaking the RX-7 rear diff, so I won't be doing 400whp. They don't have terrible shifting, sometimes as good, often not quite as good.

If you think anything under 4000 rpm on the freeway is low, we're coming from different fields. As in my original post, I know this is low, I know what I'm doing.

Black91n/a

I'm familiar with Miatas, but 2.7 is much lower than what they ever seem to talk about. No I don't think less than 4000rpm on the freeway is low, but have you done the calcs and are you sure this is what you really want? Even with 300whp or whatever (400 won't come close to killing a TII diff btw), being lower in the rev range means you'll be making less power and flowing less exhaust to spool a turbo, so you'll be needing to go into a lower gear a lot more often in order to get acceleration, especially with a turbo sized for big power. If you've got a smaller turbo and/or shorter gearing then you'll be able to access a little boost to push you up hills and get you some acceleration.

I was really trying to say that I doubt that there's enough room to go that low on the gearing. I just don't think it'll be possible because the pinion will need to be about an inch larger in diameter than stock, and there's probably not a half inch that you can take out of the pinion gear thickness without compromizing it's strength.

Maybe larger rear tires is a reasonable alternative. You could at least get something wider than is available in something approaching a stock Miata diameter.

Galt

Done the calculations dozens of times. A 2.7 with the proposed setup would put me at ~2600rpm freeway, still high enough for a 4cyl.

I'm aware of how gearing affects effective torque. I don't plan on spooling while crusing on the highway, and if I want to accelerate I have 5 other gears. My car with me in it, will weigh hundreds of pounds less than any RX-7 (even an SA/FB) and will have enough displacement to cruise with no issue. The actual reason for a low final ratio is the first gears. If I were to hook up the six speed to a 3.3 rear end, I'd be in the same position I'm in now IE 2 useless first gears. Therefore, the final drive with a 6 speed should be much lower than 3.3.

Thanks for the info here. I'll need to find out who does know how low I can go. If insufficent, I'll go the quaife route, but that will take alot longer to get the money.

I'm already adjusting for the largest rear tires commonly put on a Miata, and going taller would compromise suspension and COG unless I pulled out a torch and made a new rear end. I'd love to fit 285/30/18's all around, but I don't know if that's possible, practical or advisable.

I understand what you're saying, I understand what I'm doing, that's why I said such in the original post. I just need to know if this is possible or not.

Thanks for the link to the Tuscon place, sent them an email as well.

RETed

I agree; I question what exactly you're trying do to?

Sub-3.0 rear ends are not used on anything short of monstrous V8's making huge amounts of torque (and hp).
You mentioned "4 cyl.", so I question why you want such an ultra low rear end ratio when your torque production is questionable?
I know you mention "400whp", but on a 4-cylinder, it's means low torque and boost?

What about when you're not in boost?

If you're trying to get a comfortable cruising RPM, why not just mess with the top gear with the transmission?

400hp is going to explode any Mazda 6-speed transmission.

You sound like you want your cake and eat it too.
This is not possible unless you spend the money for it.

What lower ratio options do the Miatas have?
The rear diff should hold out after the trans blows up.

Non-turbo FC's come with a 3.909 rear end that might be an option...


-Ted

turboeric

Actually, many 6 speed Miatas use the 3.909. http://www.flyinmiata.com/tech/gearing.php

Galt

Please read my orignal post. Please read the post where I've explained myself.

Per my original post, I'm not asking if this is a "Good Idea."

I'm asking if this is possible.

Info from Miata.net:

Topic: Is the six speed transmission really stronger than the five speed?
Response: "Yes. Simple answer. How much stronger is where the debate lies. No one to my knowledge has destroyed a 6 speed with less than 300 RWHP, and I only know of failures above 450 RWHP. Where as plenty of 5 speeds litter the landscape just north of 250 ft/lbs of torque.

Mark"

If you have any information to add or a shop for me to contact, I'll be grateful.

turboeric

A 5 speed with 3.909 gears and 235/40x17 tires (will fit an NB Miata - just) will get you the gearing you're looking for. (2630 rpm @ 60mph) I'm running a 5 speed/3.909 combination in my 220 rwhp/205 ft/lb Miata with no problems. With 300+ hp, all bets are off 'though.

Galt

Don't have an NB Miata, have more than 220whp, as well as most likely having a car that weighs 300-500 lbs less than yours. You have taller tires that I can't properly fit and less power, meaning I need a higher gearset, and I can't use the stock 5 speed unless I change the transmission regularly (and break down all the time because of it). I know my stock Miata parts options, a five speed won't cut it, a six speed has a stump pulling first gear. So as I said earlier, I need either a six speed or a quaife, and I'm asking here to see if I can use the six speed to save money.

RETed

Is it possible?
Of course it is.
Throw enough money at ANYTHING, and it's always going to possible.
Throw enough money at a Yugo, and it'll go faster than you and out-corner you.
That's a stupid question to be asking.

Is it FEASIBLE?
No.
That's my point.
You're asking for a custom set-up that's going to cost a LOT of money.
You're already stated you're too cheap to drop that kinda cash.
Bottom line, no - this is a waste of time - yours and ours.

Custom rears ends with that kinda ratios are used by drag racers who run Chevy or Ford rear ends.
This means live axles and archaic suspensions (versus your already double wishbone).
This is the CHEAP option.
I doubt you would even consider this.

Thus, it means you NEED to go with a CUSTOM set-up.
CUSTOM = EXPENSIVE

Ask any competent drivetrain stop and flash $10,000 in cash.
I'm sure they will be willing to do whatever you want to.
In the meantime, this thread is wasting our time, period.


-Ted

Galt

This was a very simple question. Can I or can I not have a 2.7 or 2.9 R&P cut for a Turbo2 rear end. What you're saying about Yugos, live rear axles, all that is just a waste of time. If the answer to the original question is a "No" all you need to say is that one word. That's why I specificly said in my original post not to talk about "Is this good or not" and I got dragged into it anyway.

Just a yes or no. Simple enough. Cutting a new R&P is not a 10,000$ job. Please stop making pointless general statements about yugos, how much I can spend, live axles or the drivability of the ratios I talked about.

Thank you to the people that linked me to the shops. I've contacted both.

turboeric

Have you looked at these guys? http://www.monstermiata.ca/ They're using T-bird rear ends behind small block Fords. That setup may provide more options.

Galt

I sure have. I don't want to be swapping out my entire rear end again, It's already in there, already set, don't want to spend the money again. I know they have lots of options, but the cost would make it equivilant to a quaife (as well as alot more work) so I'd rather just go that route.

Black91n/a

I doubt that going with a custom rear end gear will be cheaper than going with the quaife gearset, and I wouldn't bet on it being possible to get gearing that low in the TII case.

Fattony

iTrader: (1)

can you put a 3.90 out of a na fd on a TII?

RacerXtreme7

iTrader: (2)

No such thing as an N/A FD. If you meant N/A FC into a TII FC the answer is no, unless you swap the entire 3rd member (case and axles) but then you'd be weakening your car and limiting your power output.

~Mike..........