I was just wondering if anyone on the board has done the above or a combination of any of those aspects? I was thinking that if/when I do my bp project that going with a very tall gear (4.85's) would compensate for a lot of the lost torque down low. I also shouldn't lose much top end (over stock) due to the fact that the motor is making a lot more power and spinning up to much higher rpms. So, anyone done this?

 

Going with a very SHORT 4.875 rear gear compensates for no low end torque. It allows the motor to spin up to it's powerband quicker. You'll get GOBS more topend with this motor and intake. Of course getting it quiet enough for the street takes away power and EFI & the gears ain't cheap. And MPG sucks too but damn it is fun!

-bp-

 

Don't go with that high of gears. I have that set in my 83 and I hate it passionately. Way too much gear. It might work better if I had a nice set of 26" tall slicks or just some taller tires. I cruise at 75 at 5000+ rpms.

My rx7's motor used to be in my rx3. Stock REPU carb, full exhaust, and big extend port with a massive exhaust port. It ran high 13's. The same motor in my rx7 with the same setup, the only difference is the rx7 tranny, rear gears, and some added weight and I doubt my car would run 15's right now. The gears are horrible. Might be good for an autox car, but otherwise, you rip through the revs too fast. This is just my personal opinion and experiences, but I don't recommend them to any street car owner.
steve

 

DriveFast7, I'm by no means an expert when it comes to rear gearing but I thought it was considered a tall gear because the ring was bigger to get the ratio up. Is it the other way around--do the make the pinion smaller?

I realize that it is a lot of gear but this car probably won't even be close to a daily driver and you have to remember that the motor will be capable of reaching atleast 8500 rpms. If money allows it might hit 9500 or so.

 

LISTEN TO THIS MAN!!!

 

Direct, have you gone with the 4.85's in the past as well? I guess it all boils down to what the person in question is tolerable of. BTW, what is the stock gearing in the manual fb's?

 

No. I have driven 4.44's - and While it was quick, the high RPM constant "drone" sound sucked.

 

It'll probably come down to how often/where I end up driving this thing. If it never hits the freeway high gearing shouldn't be much of an issue.

 

true, indeed ... but you will also need a helluva lot of low end to make it worthwhile using it on the street or track as well ...
when i had my '83, just switching from the 3.91 to 4.08 SE rear, i noticed a difference in the RPM/sound at a steady cruise ... though it was not annoying by any means, it WAS notcieable. my point is that a 4.8xx is bound to be crazy.

listen to Directfreak and Flamin' NOS

 

Hrrmmm, maybe a 4.44 would be more reasonable. I really appreciate all of the input guys.

 

4.44 is the best gear for the street IMO. Really makes a big difference in acceleration while still providing reasonable cruising rpm. I'm usually pulling around 3400rpm at cruising speed on the highway.

4.8 is probably a bit too high (numerically) but there's no way I'd go lower than a 4.44. It's not like I'm trying to set a land speed record or anything.

 

If you don't like the freeway drone of 4.875 and still want the short gearing, put a tall 5th gear in your tranny. 2nd gens had .711 or so 5ths compared to your approx .81 5th gear and they will fit. The taller 5th will reduce rpms in that gear. This is an OLD trick.

Or go 4.444 for streetie stuff.

 

Drivefast, that is very helpful. I was just wondering if there were any other tranny options that would allow for better 5th gearing. Does anyone have any idea what 5th gear is for the TII tranny? I was thinking that swapping out for a stronger tranny might be a good idea either way.

 

Yeah, sure. Change 5th gear in 5 minutes flat. No prob.
That is going to be a Pain in the freakin @$$. Not even counting the money aspect.

By the way, the Best FB combo EVER for highway cruising, was the bone stock 1985 GSL-SE.

Swapping for a TII Tranny will only be a better ratio than a regular FB, but not an SE.

For THE Absolute best low RPM cruising, an Second Gen GXL tranny would probably be best, to an rear end..


So according to these numbers, my TII Tranny and SE rear end would give me a final drive ratio of 2.931, slightly worse than my stock configuration, but worth it for the strong tranny.

Also note that the tire size, diameter will have the same effect as changing the gears, so a rim/tire combo will yield better cruising RPM as well.


US SPEC MAZDA DRIVELINE RATIOS

*** FIRST GENERATION ***
……………………………………………………………….…….………………………………..AXLE..FINAL.TIRE......TIRE..ENGINE
VEH.. YEAR. 1ST.. 2ND...3RD.. 4TH...5TH...RATIO RATIO SIZE……....RPM...RPM @ 60 MPH
RX-7. 79-83 3.674 2.218 1.433 1.000 0.825 3.909 3.227 185/70-13 892...2878
RX-7. 83-83 3.674 2.218 1.433 1.000 0.825 3.909 3.227 195/60-14 891...2875
AUTO. 84-84 2.458 1.458 1.000 0.720 N/A...3.909 3.909 185/70-13 892...3487
GSLSE 84-84 3.622 2.186 1.419 1.000 0.758 4.083 3.097 205/60-14 878...2719
RX-7. 84-84 3.622 2.186 1.419 1.000 0.807 3.933 3.175 185/70-13 892...2832
RX-7. 85-85 3.622 2.186 1.419 1.000 0.807 3.909 3.156 185/70-13 892...2815
GSLSE 85-85 3.622 2.186 1.419 1.000 0.715 4.077 2.914 205/60-14 851...2480
RX-7. 85-85 3.622 2.186 1.419 1.000 0.697 4.444 3.099 205/55-14 910...2820

*** SECOND GENERATION ***
……………………………………………………………….…….………………………………..AXLE..FINAL.TIRE......TIRE..ENGINE
VEH.. YEAR. 1ST.. 2ND...3RD.. 4TH...5TH...RATIO RATIO SIZE……....RPM...RPM @ 60 MPH
Base. 86-91 3.476 2.002 1.366 1.000 0.711 4.100 2.917 185/70-14 855...2494
GXL.. 87-91 3.476 2.002 1.366 1.000 0.697 4.100 2.859 205/60-15 841...2404
Turbo 87-91 3.483 2.015 1.391 1.000 0.719 4.100 2.948 205/55-16 828...2441
Conv. 88-91
GTUs. 89-91 3.476 2.002 1.366 1.000 0.758 4.300 3.261 205/55-16 828...2700

*** THIRD GENERATION ***
……………………………………………………………….…….………………………………..AXLE..FINAL.TIRE......TIRE..ENGINE
VEH.. YEAR. 1ST.. 2ND...3RD.. 4TH...5TH...RATIO RATIO SIZE……....RPM...RPM @ 60 MPH
(FD). 93-95 3.483 2.015 1.391 1.000 0.719 4.100 2.948 225/50-16 829...2444



Man, you're not gonna believe how long it took me to get those aligned and looking right on the screen..

 

You guys are making me want to go and get gears for the 83'. I've never done that before....do I just go and get some 4.44's and slap them in or what?

 

i had 5.13 gears on my stock 12a ... with a header..... nothing could touch me till 80mph!!!! the gears got hot though.... anything over 60 miles in distance..... you would smell the gear oil ....and sucked tons of gas....best upgrade for the money .....

 

Thanks for those numbers DirectFreak!

I guess I really should be considering getting rid of the open differential before jumping up the gear. That'll only lead to bald tires! Or should I say bald "tire"

 

Check this out: http://www.hitman.hm/ported.htm

He's making 178rwhp off of an efi 12a with nothing more than a mild street port. Makes you wonder what kind of power can be had with efi + bp. I bet, with a setup similiar to his, you could make 200rwhp off an extended port.

 

bump for last post

 

That thing is pretty cool. It's hard to believe he's still running a water-to-oil oil cooler

 

Yeah, he has a very nice setup. He has me considering just going with an extended street port. If I could make around 200rwhp with that and keep it streetable I would be in heaven. What do you guys think an fb with that kind of power and a gear would run in the quarter?