*raises hand*

local kid sheared his 6th gear clean off the shaft

had crappy all season tires too

 

Bryan/FAB9

 

Looking at the gear ratio's, the RX7 transmission matted up to a 4.3 rear end wouldn't be a bad option at all. Now if you had a Miata that came with the 6 speed 3.909 rear end it would be pretty steep gearing!

If you are making 500 HP I don't see the RX7 transmission gearing with 4.3 rear end being an issue.

Keith

 

I would have pointed to the 3.9 or the 3.6 for the RX7 tranny. The FD tranny with a 4.3 is like having the 1st 3 gears from a 6 speed with a 4.10, then the 4th from a 5 speed, and a highway gear.

 

FAB9

If you give me a new 6 speed I'm sure I'll be able to break mine in short order.

 

The RX7 transmission with a 4.3 is like having the 1,2,3 of a 6 speed with a 3.636, not with a 4.1. 4th is a 1:1 gear, so it is the same no matter what rear end, and 5th will be a highway gear with what ever rear end you pick.

Stock 6 speed with 3.636 rear end at 7000 RPM (best combo for 6 speed)
1st 34.7
2nd 57.6
3rd 79.4
4th 103.9
5th 130.6
6th 155.0 and 80 mph = 3600 RPM

RX7 TII with 4.3 at 7000 RPM
1st 34.8
2nd 60.1
3rd 87.0
4th 121.1
5th 168.4 and 80 mph = 3300 RPM

RX7 TII with 4.1 at 7000 RPM
1st 36.5
2nd 63.0
3rd 91.3
4th 127.0
5th 176.6 80 mph = 3200

If you put the 3.636 gears in there with the RX7 transmission you are going way tall. If car was making enough power you would top out at 200 mph!

 

Not every Miata out there is a race car you know.

 

topping out at 200 sounds perfect for a 500+ hp miata.

 

Oh absolutely. Our cars are so stable and planted past 100.

 

But almost all of the cars breaking 6-speeds are

 

 

I don't get it. Whats wrong with the RX7 T2 gear rations?

 

On the street? Nothing. But when every tenth of a second matters on track, the drop from 2nd->3rd->4th is too wide. Compare the TII 2nd-3rd-4th-5th to the 6-peed's 3rd-4th-5th-6th, the 6-speed has much closer ratios.

If you can find a circuit racing gear set for it like this Our Website

But at that point it's probably cheaper to get one of the custom gear sets that will fit into a Miata transmission (5 or 6 speed) so I don't know how promising that is as an option.

 

but does the drop matter if I'm still on 400ftlbs torque curve? In my mind wide rations with good torque = less shifting = quicker

 

Torque doesn't make you go fast, horsepower does. And even if you make 400ft-lbs from 4000rpm to redline, it's still gonna be faster at higher RPMs.

 

Thrust math beggs to differ. If you have 400ftlbs, perfectly flat from 4000rpms to redline you're going to accelerate at the same rate from 4000rpms to redline. If you change gearing to keep you at higher rpms, then you're going to have better mechanical advantage on the ground and more thrust because of the gear ratios not the fact that you're at higher rpms.

 

Can we not use EBC to make a flatter HP curve?

is the point that I am missing that if you can get a bunch of low mid you should already have it?

Dann

EDIT: Leafy just because you explained it in a long winded way doesnt make you righter, thats what he was saying regardless, I think.

 

Then what about with 4.875 R&P? I do have those also

 

4.8 seems excessive. If i were to do it with a BP, i'd go with a 4.3 or a 4.1 with the knowledge that you should be making enough power to shred 6spds on the regular.

MFactory® Competition Products - Gear Calculator





But this.... this is my jam right here.

 

TQ and good gearing wins races. The thing is, that is almost the same thing as saying HP wins races.

The V10 F1 cars made fairly pathetic TQ next to say a Viper. But since they revved to like 17K, they could use gearing that would have a Viper topping out at 40 MPH. IIRC the rumor was that they would run 9s pretty easily, with only 300WTQ AFAIK

tl;dr The key is to have good TQ multiplication at all times. Having relatively wide gearing splits is not automatically a bad thing if you have the TQ band to match, and you get good multiplication from an aggressive rear gear. That TQ band has to be flat and extend to high RPMs. You can then stay in TQ, run decent TQ multiplications (aka not having to get into lower multiplication/high gears early on), and not have to shift so often either.