Turbo 1.8 NA, 240whp, 7.5 Ford rear, what gears?
 

Hey all! I picked up a '97 NA Miata, and I'm trying to sort out what gear set I want to swap to. The car is on 12 psi, currently makes 240whp. It has a Ford 7.5 rear end, currently with 4.10s in it. With the torque this car makes, I don't see any reason to run around at 4,000 rpm at freeway speeds, as well as first through third gears being practically unusable. So, I'm going to step down the gear ratio, but I'm unsure exactly what I want to run. I'm in between a 3.73 and probably a 3.55. I've researched and seen people saying that under 18 psi you want a 3.73, but I'm not sure that a 3.73 will drop my freeway rpm all that much, and would give me a little more headroom for more power later. Conversely, I don't want to go too long of a gear and put too much stress on the motor trying haul around too long of a gear. I just don't want to do the one and then wish I went the other way. What are your thoughts? I'm all ears, thank you! :)

240whp
180torque

What's wrong with the 4.10? Can't use the first 3 gears? Why not? Put a better tire on it, i hooked with a 195 tire, a little less HP and 4.10 gears.

First - is this is a street car or race car?
Second - is the engine built? Do you plan to run more in the future?
Third - is it on the stock 5 speed or 6 speed?

Not enough smileys need moar

You aren't making enough horsepower for the 355 gears. use the 373.

Are you running Walmart MayPop tires or something?

I wasn't aware that psi was a direct correlation to rear end gearing.... unless you're talking about tire pressure?

With how little power you're making, i'd do like... a 3.9. Maybe a 3.73 if you're feeling especially froggy.


Sincerely,

Someone who makes more power than you yet manages to dead hook 1st, 2nd, and 3rd with a 6spd and a 4.10.

This forum is spicy, I like that :)
Sorry about that, I had a feeling missed a couple of pieces of information.
-The car is a street car that may see some track days, but primarily a street toy.
-It's a 5 speed trans.
-While I'm not under the impression that the car is terribly fast, what I meant with the torque comment is that it's got enough bottom end that a little less gear isn't going to make it call on it's face. But I hate driving around at 4,000 rpm on the freeway at ~75mph. Also, I live in Las Vegas, and the streets are fairly greasy (my c6 z06 goes sideways at WOT till 150mph, even my bolt-on 135i spins through the top of third)
-At this point, the car is on a stock block. Whenever it decides to check out, I'll build it bigger and better.

I'd do a 3.55 and a Miata 6-speed to match. Gears should be similar to what you have now with an extra cog for cruising. The 6-speed also has shorter drops between gears so the car should be a little faster.

Funny you mention that...

I was just in LA about 3.5 weeks ago. My car had no problems hooking. I'm betting you have other problems.


Anyways, the Miata motor is perfectly happy turning those RPMs. If for some reason it bugs you, i'd suggest the 3.73 at the most. Going further will start to suck when it comes to the bottom gears if you're only making 180wtq.

I did 7500 miles of this in 3 weeks and it wasn't a big deal. Do i want a 3.9 or a 3.63? Sure. Is the 4.10 ruining the car? Nah.

https://www.miataturbo.net/attachmen...ine=1375385111

Lets see upgraded the diff that can easily handle north of 300ftlbs, left the transmission that asplodes at 250ftlbs.

https://www.miataturbo.net/attachmen...ine=1375447923

I didn't build the car smart ass, I just picked it up as is. Nice try.

Doesn't matter either way if he's only making 180ftlbs. I can only imagine how slow that thing is.

It might be slower than your car, which is slower than my other cars. Your point?

The point is that it's going to be almost unenjoyable going much lower than a 4.10 numerically.


What sort of turbo is on this thing that it's making 240whp/180wtq? That's really bizarre and uncommon, and stupid.


I don't know why we're bringing my car into this. It's not relevant, nor do you know what it is. Get your e-thug on though, hotshot. Cum in my ass.

GT3571R on low boost

his point is you're wasting your time asking the wrong questions.

what you should be researching is a transmission upgrade, then a motor upgrade, and only after all that you should be considering changing the fd

I don't think he said how many torques it makes. I just assumed it was 180 because he claimed 240hp. And we all know the horsepowers count.

get a proper transmission in there, then build the engine, then turn it up ALL THE WAY and only then go to a low fd like 3.55 or whatever your lowest option is

I think the lowest option for the 7.5 is in the 2s the normal stock ratio s like 3.03 or 3.31 or something like that.

LOL.

So it's YOUR fault. :bowrofl:


If you're making 240hp and 180ftlbs, you're doing it fucking wrong.

I'm using a 3.23 on my NA.

I think i'm going to make about 300hp and 150ftlbs.

Should be super awesome. I can hardly wait to hook 1st gear on the streets of LA.

Multiple people have gone on about how slow it must be, how I'm not making any power, etc. I recently bought the car as is, I know it makes 240w, but the guy didn't have a tq number. I'm not an idiot, this is my slowest car, but also my favorite :) even more so than my c6z and the others. I wasn't throwing out my car's specs trying to big-time anybody or seem like I think I'm making a bunch of power. I threw out the specs for the sake of getting some accurate info, and people are trying to bang on me left and right like I don't know how to build a car. Flame away, doesn't matter to me anyway. Thank you to the people with the good info guys :)

How do you know it makes 240whp if you bought it from a guy that didn't have a torque number?


Iono, i'm still sticking with my original 3.9 or 3.73 suggestion, though i'd really take a LONG hard look at why you're having traction issues.

I don't live in LA, I live in Las Vegas. If you're going to troll, be a troll with strong reading comprehension ;)
The guy I bought the car from had it dyno'd a couple years back when he had the megasquirt tuned. He couldn't remember the torque number, just the hp. I'm not worried about it as I'm going to dial a few things in on the car and then start working for some more power as things break. The traction issues are due to the greasy streets of Las Vegas as stated earlier.

Dammit, my bad. Either way... find out why it's not hooking. That shit's weird, and wrong. It's not due to the greasy streets of Vegas unless the entire city has been covered in an oil spill in similar quantities of the famous Exxon Valdez spill since the last time i was there with my Miata.


So you don't actually know how much power it's making. I'd say step one would be to dyno and/or log it and see what the fuck it's doing.

Mine doesn't hook even in 2nd with a 5spd on 12" wide tires. Oh wait......mine only weighs 850lbs in the rear. :bowrofl:

Seriously though, what tire are you running? Don't forget tire height has a direct affect on gearing and drive rpms. My guess is you'd be very happy with 3.55s if you went to a 6spd. With the 5spd you probably want to go 3.73s for drivability even though it won't drop your cruise rpm a lot.

I running about the same power level and felt the same way at first about the gearing. got used to it pretty quickly though. the motor doesnt seem to mind it and the fuel economy is still ridiculously good compared to my wankel. not sure why you're having traction problems 1-3 though. as long is its in a straight line and you don't dump the clutch, it maintains traction no problem. lousy tires maybe? I've got the 4.1 lsd btw.

This. My V8 Miata is 279/308 TQ and I have 3.73's in an 8.8. I could go to the 3.55's pretty easily with my torque but it's fine.

I want to echo the people talking about tires. I had some (old and hard) all-seasons on my car last year and I can see where you might be coming from. Once I put on some summer tires on the car it was a totally different ball game.

Also, another recommendation for the 6-speed.

The right diff ratio not only depends on his motor's output and which tranny he has, but what he is looking for.

Couple of points.

Comparing the 5 speed and 6 speed, the gearing of 1st through 5th are very similar, if the 6 speed is mated to a new diff that is 19% taller. So automatically if the OP thinks the 4.1 with the 5 speed is too tall, then a 6 speed with a 3.44 will be too short. (wrt gear spacing).

Some people say "use a 6 speed with a 4.6 diff and start off in 2nd gear". That's not the same, because then you effectively get a 5 speed with super-close spacing. That's fine if you like super close spacing, but super close spacing with a turbo is slower because you spend more time between gears shifting, than in the gears accelerating.

Note that the percentage the RPM drops at every upshift gets smaller and smaller as you go up in the gears. The reason for this is as you go faster you spend more time in a given gear before you upshift. This is why a 6 speed with a 4.7 diff (and taking off in 2nd gear), is not the same as having a 3.6 and using 1st gear.

In my case I thought the 5-speed with a 3.9 rear was perfect. Far, far better than the 4.3. This was at 10-12 psi. When the 5 speed blew up I installed a 6 speed, and now at 15 psi the resulting gear spacing is annoying as fuck. The RPM drops between gears are too small, and if I skip shift it's too much. With the 6 speed, to get my old ratios back, I need a 3.3 rear, which is nonexistent. A 3.6 will get me halfway there, and for the expense, I think won't be enough of an improvement.

For the OP, a 5 speed with a 4.1 will have the same 1-2-3-4-5 spacing as a 6 speed with a 3.44. So if he upgrades to a 6 speed, he needs to go to a 3.1 rear to feel an "improvement".

Well I can dead hook in 1st with 212ftbls... on 275s with just over 1000 lbs over the rear.

*cough* T5z *cough*

I agree, 5speed w/3.90 is perfect. for a street car.

/\ This right here folks.

I want a t5z with the v8r rear kit. Or my 6spd with the v8r rear kit.

OK I'll bite, WTF is a T5z?

Its the latest and strongest T5, it replaced the World Class T5 for that title.

I suggested either a t5 or t56 a while back and some of you bit my head off.

come back in another year and cry it about something no one remembers more

YES SIR!!!

Maybe he's running an open not LSD that's why no traction!?