Hi, my friend and i were talking tonight about doing a PP N/A motor for his street car someday, our power goals would be anyware from 250-300hp off the bottle.

we also would want to swap a closer gear ratio set (1-3) for obvious reasons.

here is how i broke down the "distance" between each gear:

"final gear ratios w/ 4.1 final drive:

FC box

1st: 14.25:1

1-2 split: 6.04

2nd: 8.21:1

2-3 split: 2.61

3rd: 5.60:1


FB box

1st: 14.85:1

1-2 spit: 5.98:1

2nd: 8.96:1

2-3 spit: 3.14

3rd: 5.82:1


94-97 Miata box:

1st: 12.86:1

1-2 split: 5.12

2nd: 7.74:1

2-3 split: 2.29

3rd: 5.45:1"


I dont know what miata RXgirl's gear set came from (they list two differnt ratio sets; one for 94-97 and one for 99, i could find nothing on the 89-93). it looks like to my mathimatical eye that the FC actual has the closest or least amout of change in 2-3 change (only 2.61 rotations), but from testimonial from RXgirl per her thread, this cannot be. where did i foul up mathimaticaly.

Thanks!

PS: Where do PP'ed engines usual make their power? we would like to see it make max power @ or just below 9krpm.

 

Edit, the Miata has the closest 2-3 (only 2.29 vs 2.61 of the FC)

i read on a couple other threads that GSL-SE gears (FB/SC) have closer gear ratios for 1 thru 3, but according to Mazdatrix they have only a closer 1-2 and a farther 2-3 then the FC.

 

I was like holy ******* **** at those gear ratios than I realized its the compound ratios, not the simple ratio of each gear set.

 

so i can use the miata tranny on my fc???would have to change the bellhousing right?

 

Theres a write up on here, someone put the gears into an FC case I believe, the input shaft has to be machined.

 

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yes, you have to machine the input shaft down. You swap the miata gears into a NON-turbo case, they will not work with the "R" code trans of the Turbo FC/FD cases....

what were you going to say arghx?

if you want the gear ratios by themselves, just devide the compound gear by 4.1

 

Lol yeah I understand compound and simple ratios, they were just on my exam .

I was wondering but can you just swap the speed gears onto the input and output of the R code tranny...And the countershaft? Though why would someone do it they're probably about the same strength as the NA gears.

 

i'm guessing the shafts are differnt diameter (thats why "R" trans is stronger then N/A), so i wouldnt think so.

 

Probably I was just thinkin about it though.

Have you ever driven a Miata before? They're at like 3000 rpm at 80 km/h.. I would imagine they're at 4000+ on the highway which probably just drains the fuel...luckily they don't cost much to fill up and they still get fairly good mileage.

 

that has to do with the final drive (IE axle gear) and the OD gear (5th gear in miatas/rx7s)

as long as you leave the OD and final drive alone you wont change the crusing rpms

 

i'm wondering if you can swap just the actual "gears" off of the miata shafts and put them on the N/A shafts....

 

If you're going to have 250-300hp "off the gas", which I guess would mean a bunch more on, then you should probably be looking at a TII transmission, since you could easily kill an NA transmission with that power, especially if you're drag racing it or being hard on it in any way.

The gears themselves in the TII box are bigger, it's not just the shaft size that's different.

 

not really a bunch more, maybe 75-100 (i guess that could be a bunch, depending on what you think).

the Nitrous is still up in the air, we want to see how the car "goes" after we get a PP motor built and dialed in.

because i have a feeling the engine is going to be peaky and its going to be more of a street-autox car anyway. so i think we are probobly going to stick with the N/A boxes (unless we break all 4 he has laying around lol)

 

for some reason i feel like we are talking about n/a transmissions like they are disposable camera's in this thread.

disposable transmissions. ROFL