Johnny_Cracker

iTrader: (1)

Looking for guys with any personal experience running a 4.77 final ratio...

I'm soon to pull the 3rd member and am considering my options while it's out.

I can locally source the front diff from a proper year Sportage and do the swap covered in other threads. My main concern is that I'll be geared too low (numerically high) and be screaming at highway cruising speeds. I don't think this ratio would be available from Mazdatrix though if this was the case.. I run an SE with the stock 4.07 ratio and slightly larger than stock overall wheel diameter.

My goal is to make it an as quick as possible NA non-DD street car and occasionally autox.

I'm not concerned about having a high top end, just enough for good local road cruising and occasional highway travel. Quick acceleration is what I'm after

Siraniko

iTrader: (13)

My RX-3s old set-up was a kia 4.77, miata internals on a FB trans housing and 13-B big streetport/48 IDA. It was fun on the street but sucked on the freeway. At 85 mph, the rpm was around 6500 and screams, sounded like, dont go any faster or it will come apart so do speak. But I have since downgraded or settled with a 4.44 (plus Im now running a 13-B bridge). Im happy but i occassionally miss the 4.77 on the street.

Carl

iTrader: (2)

Sometimes have a Kia 4.77 in my ITA car. In 5th gear above 6500 rpm, the driveshaft shakes like crazy. I am not convinced it is the best way to go. I put the stock 3.9 back in for upcoming WRL and SCCA races at Texas World Speedway at the end of May.

Carl

peejay

Love mine. What do you want to know?

Johnny_Cracker

iTrader: (1)

Thanks again to Siraniko and Carl for the advice. You guys have helped me out before and it's always much appreciated


Hi peejay, my main question I suppose is what's the highest streetable ratio suitable for my SE. At first I was considering the 4.77, but am now considering the 4.44 thanks to the input from Siraniko and Carl. Do you have your car set up mainly for autocross or is it mostly street? Do you have any vibration issues like Carl mentioned?

I'm hoping for a "bolt-in" upgrade path similar to the 4.77 kia swap so I won't have to go thru setting up pinion depth. ..Not sure I could set up a pinion myself just yet. Backlash, diff preload and rebuilding the clutch pack I should be able to handle however.


Siraniko, is the 4.44 you now run from the 87-88 B2600 4x4 and is it a "bolt-in" or would I have to swap out pinion and ring into my existing differential?

Thanks guys

Siraniko

iTrader: (13)

My set-up is for canyon run and occassional street race. The 4.44 is from a kia also (same as b2600 front diffy). I actually have 3 complete pumpkins: 2 small axle diffy (4.44 and 4.77 for RX-3), takes less than 2 hours to swap and 1 large axle diffy with 4.44 for my SA (converted to 84-85 front/rear suspension).

The front diffy is open/no lsd. It will work on large axle FB without any modification. have seen this done but no hands-on since i like to have a lsd.

Im actually looking for S2000 4.30 gears to experiment.

85TIIDEVIL

iTrader: (2)

If the car is winding out to much on a highway cruise just put a taller tire. Nitto drag radials on stock SE rims solved that problem for me.

peejay

The driveshaft harmonic happens at about 5300 driveshaft RPM. That is about 80mph with original gearing/tires. With the 4.78 and stock tire diameter, this is about 65mph. You can't really cruise at 65, just higher or lower.

The other downside is that the fast driveshaft eats the transmission's tailhousing bushing. Mazda Comp used to sell a hardened yoke and a roller bearing setup which required extensive transmission modification to use. (Weld up the OD at the end so it can take the larger bore, and reboring the housing after finding center again since welding will warp everything all to heck) but this stuff is NLA.

My car eats maybe three transmissions for every tailhousing bushing that gets wiped out, so while it is a problem for me, it's not the biggest fire that I have to put out.

As far as actual engine revs are concerned. If you have an early 12A trans, then swapping to 4.78s is like driving with the 3.91s and 4th gear. Mazda sold many thousand SAs with four speed transmissions. If you have a late 12A trans or any 13B trans, the 5th gear revs will be somewhere between your current 4th and 5th. 4.78 sounds like a HUGELY SHORT GEAR OMG but in reality it is only 22% different. It's not like going from 2.73s to 4.11s in your Chevelle.

I don't really do any city driving. I rallycross and take long highway trips.

project7s

iTrader: (5)

Cool, thanks peejay for explaining the 4:78 gear on the highway. I've been thinking of using them as well, but didn't know if I could still drive out on the highway or not.
My only knowledge with gears is in my cutlasses one has 3:23 and my other has 3:91 both with 3 speed autos, and no way I can drive the 3:91 car on the highway.
I think I'll go with the 4:78 in the 7 now, sounds like I should be fine.

Carl

iTrader: (2)

PeeJay is right about 4.8 in 5th being about the same as 3.9 in 4th. 80mph is about 4400rpm with 4.8. I just did 21 hours of >4000 rpm driving from Houston to San Diego in my Miata. It is little wearing, but 21 hours is kind of wearing anyway.

My somewhat negative experiences with the 4.77 are in a race car going 100-120mph. A lot different than street driving or autocrossing.

project7s

iTrader: (5)

Yeah I could not imagine driving any 7 for that long lol.
I just use mine as daily driver which I only live like 6 miles from my work. But I do go to tenn. Every year which is about 250 miles away one way, that's about the extent of my distance I drive.
I think it sounds like I should be safe with the 4:78, would you agree as well?
Oh plus I use a gslse trans so my 5th gear is a little higher

peejay

My rallycrosses are 2-5 hours away from home, and I've twice driven the RX-7 to Nationals (once to Tulsa, once to Omaha, 975mi and 800-ish mi) no problems. First Tulsa trip the car returned 24mpg average, breaking in the new bridge port engine on the way to the event. Omaha trip, the engine was really worn out and I was towing a tire/tools trailer, I only got 16mpg there... was a little pissed off at that The trailer really sucks fuel economy.

project7s

iTrader: (5)

Thanks guys, makes me feel better about it.
That's awesome peejay you got 24mpg, Is that a full or half bridge, 6 or 4 port?
You actually answered something else I was wondering, is would this be a good gear for any bridge port engine but since that's what yours is I'm guessing that's a yeah.

peejay

Actually I think the bridge port would be happiest with a 3.6 final and an FC trans. It really likes to be loaded and hates to be spinning.

project7s

iTrader: (5)

Hmmm I never would have thought of that, thought it was like in v8 world when you put a bigger cam in you need more gear to make up for the low end.

peejay

I've found the opposite with V8s too...

The issue is not how much power it makes, the issue is how well the engine wants to run. When you have high overlap whether it is a big cam with a tight lobe center or a bridge/peripheral port engine, they don't like to run at part throttle. Even with an FC transmission and 215/70R15 tires with the bridge port, the engine isn't loaded down enough on the highway to run smoothly. Brapping down the highway at 75mph sounds like a neat idea until you figure that half the fuel going into the engine is going right back out again unburned.

I've played a lot with ignition timing and air/fuel ratio and there is a kind of unhappy medium where fuel economy is optimized, you either need to retard ignition timing or richen the engine to get best economy. I've tried pulling a ton of timing so I can run near stoich, and I've tried giving it best timing and then covering up the bucking with more fuel (sometimes 12:1 under cruise), the happy medium for my engine seems to be stock timing settings, which means the engine doesn't like to run any leaner than 13-13.5:1 under 50-60kpa cruise. Funny thing is, go up hills so vacuum drops (kpa goes up to 80-85 or so), and the engine is perfectly happy running at 15-16:1.

So taller gearing is needed to load the engine down, it really doesn't like running at much less than WOT, and tuning is mostly a case of trying to convince/bribe the engine to run at part throttle. Richer makes for better economy because the engine isn't misfiring despite choking on its own exhaust gases, misfiring is always worse for ecomomy than adding a bit more fuel.

j9fd3s

iTrader: (3)

the 99-05 miata 5 speeds are 4.30 also

Carl

iTrader: (2)

I believe the the Miata 3rd member bolts right into the GSL-SE (or large axle GSL) axle housing. You might be able to find the Miata 3rd member at a junk yard for $300-$400 with the torsen in it. I have not done it, but I believe it bolts right in. I have put a miata torsen in a kia housing with 4.77 gears. Direct bolt-in no need to reset the pinion depth.

Carl

j9fd3s

iTrader: (3)

i think you're correct.

the 94-97 miatae, are 4.10.

the 99-2005 get a 4.30 with the 5 speed, or a 3.9 with the 6 speed.

the S2000 uses the Mazda gear set.

peejay

The S2000 also has 29 spline axles, not 26 or 24. So you don't get to use its fancy differential, just its gearset.

All series 3 have the 26 spline axles, not just the disk brake cars.

Johnny_Cracker

iTrader: (1)

Awesome stuff guys.. thanks for all the goodness!


One thing in particular I'm hoping to clarify is which year Sportage I need the front diff from for my "big axle" SE. The writeup I found about this says that a" (front) Kia Sportage 3rd member 94, 96-01 model year" is what is needed. Can anybody confirm this before I go and get the wrong one?

I'm curious because why not the 95 model year??? Also these years don't coincide with generation breaks either . First gen Sportage was supposedly from 93-04. Here's a snip from the http://en.wikipedia.org/wiki/Kia_Sportage
"First generation (1993–2004): The first generation Kia Sportage was developed with a Mazda Bongo engineering base platform. It shares many mechanical components such as the engine, transmissions (early versions), and differentials with the Mazda line of vehicles".

So I'd expect the front diff from this 93-04 to be what I'm after, especially as the wiki reinforces the fact they share diffs from Mazda vehicles.

...I know one of you guys can school me on this!

Siraniko

iTrader: (13)

Low end will be more sucky. With my bridge, i played with 3.70 (best if you want all top end), 3.90, 4.10, 4.44 and 4.78 and settled with 4.44.

For the upcoming WHIV, I will switch back to 3.70 since its a 300 mile trip from LA to Vegas. A few years ago, i drove my RX-3 (13-b streetport) to WHIV with 3.70 and it was a blast at 6am. Interstate was empty and no cops

j9fd3s

iTrader: (3)

i think that may be right, but Kia didn't put the 4.77's in every year, some of them use something different. the gear sets were actually cheap new as well, but the parts books didn't give you the ratio, so you're kind of on your own there.

i know Mazda had their act together in the 93-04 time frame, but Kia didn't, they came to the US went out of business and got bought by hyundai.

Siraniko

iTrader: (13)

On top of my head, the early sportage had 4.44 while 95+ were 4.77

Johnny_Cracker

iTrader: (1)

Got one from a local u-pull it yard over the weekend.

I found and reviewed the 95-02 KIA SPORTAGE FSM so I knew what to do once I got to the yard.

I had good luck for once... the second Sportage I checked had the steering linkage, hubs and half shafts removed. All I had to do was unbolt the driveshaft and remove the 3 bolts mounting the axle allowing the axle assembly to rotate forward and down for easy removal.

Once the axle was removed it was easy to remove the output shaft and then pop the 3rd member off. (kia fsm group 50B-22). Dividing Ring gears by pinion gears confirmed I had the proper 4.77 unit.

All it cost me was $62.50 including admission to yard and about 1.5hrs. Ring looks fine and there's no play in the unit. Rotation is nice and smooth too. It didn't appear to be leaking fromt the pinion seal, but I suppose I'll find out eventually. I'll of course be spec'ing and swapping the LSD from the 7 into this thing.

Hooray!