4.10 vs 4.3 in 20B N/A FC

[Christopher W.]

I got a 90" model TII rear end to go in my GTUs. Didn't bother with the S4 because I am thinking about a Guru diff. I want a Torsen not interested in Kaaz or the like. I want quiet and smooth operation. Depending on how it acts with the stock TII rear I might even stay with stock TII viscous lsd. Looking to make in the 350-380hp. Well, I was going to try to stay with the n/a for weight saving by cryoing the stub axle. I think there is a lot of debate how much the n/a can handle.

I decided to go ahead and get a TII rear and not risk trashing a perfectly good low mile GTUs rear.

I was always excited about the 4.33 gearing with the n/a rear. As best I can tell this rear has a 4.10 gear. This car is for all real purposes a street car. I don't see speeds over 150mph being that important.

My question is how much of a real difference is there, real and perceived?

Does anyone think you really get through the gears that much quicker?

What would some of you guys do?

I am leaning toward putting in the 4.3...

[Roen]

You might break the Torsen with that much power and the added torque of the 3 rotor. I would still test it and if that doesn't work, there's always the viscous. How's the condition of your viscous LSD though? How many miles?

You can do the math, the 4.33/4.10 = 1.056 so 5.6% increase in acceleration and a 5.6% penalty in top speed.

Though, it'll feel quicker, because you spend less time in the low end.

Which 4.3 R&P are you getting? I think Mazdatrix's or Racing Beat's is a 4.375:1.

[Christopher W.]

I edited my first post because I wasn't sure if we are talking about the same thing. The stock n/a 4.33 rear end is coming out for sure. I bought a 90 TII to go in. The TII rear has 85,000 miles and is getting a good check tomorrow. I was saying I might just keep the TII stock diff in and see how it goes. If I upgrade I was thinking about the Guru Torque Biasing Differential.

As for the R&P I was probably getting Mazdatrix. Racing Beat's is 525.00. I haven't spoke to Mazdatrix yet. Their website is getting upgraded or something and don't know the price yet. I have dealt a lot more with Mazdatrix.

Thanks Roen, that formula puts in a more tangible perspective. I think the 4.3 is what I want.

[Roen]

If your engine produces too much power, you may want to look at the ATS Carbon clutch-type diff. Can hold more power, and feels more like a torsen than your normal metal clutch packs. Downside? $$$$$$$$$$$$$$$$$$$$$$$$$.

[josh18_2k]

a 99+ FD torsen should handle the power. they're cryo treated and whatnot.
any FD torsen should be fine with the power also, but if you run slicks its only a matter of time.

[Christopher W.]

I bought the R&P from Racing Beat today. It was about $40.00 less than Mazdatrix. I sure wish I had an AutoX under my belt for prices from Mazda Comp. Last time I did an AutoX was like 1985 in a 240Z.

I don't know about the ATS Carbon Diff but I have spoken to Carbonetics about theirs. They said it is much quieter than the metal ones but there is still some noise coming from it. I don't really know how to quantify that statement. That's something I am quite a ways off from having to deal with...

[gmonsen]

Christopher... The Torsen can handle the power. I have a 20b NA in an FD and am using the stock diff. If you are going for better acceleration, I understand the choice. But you should probably also run the speeds in gear for the wheel tire combination you have in relation to the driving you're going to do. In other words, if you're on the streets, where is 40-50 mph? Is it in second? How high in rpm? Where is 65-90 and how much room in gear do you have over and under that? I actually went the other way with the 3.90 R&P because of the speeds in gear for my driving.

Gordon

[BLK FC3S]

Stock TII rear here and putting 366hp 357tq to the ground. No problems so far. I'm also only running small stockish tires though. If I had more traction or went to the track, I dunno if the stock rear would hold up or not.

[Phoenix7]

yes. You'll go through the gears faster but not fast enough to actually make the rear end cool enough to use.

80mph in my TII GTUs = ~3600RPMs
80mph in my 4.30 GTUs = ~4000RPMs


I don't really see a huge difference even at lower RPMS and flying through the gears.

and seriously, you don't want to hear the car chill at 4000RPMs+ on the freeway when you're cruising (80-90mph).

*note, I haven't driven my TII in a while so my numbers will be slightly off.

[Whizbang]

yea a 4.3 isnt a huge jump from a 4.1. Not the 4.78s i am putting in my GSLSE that originally has 4.0, that is another story.

[Christopher W.]

Too late now... I took a S5 TII rear and put in a S6 diff with new S4 stub axles. It has the new 4.3 ring and pinion.

This is a purpose driven car, not a car I will be driving to work. Well, I work at the house but you know what I mean. I might drive it 5k a year.

I am not too worried about 4k at 80mph. And also if it is annoying or anything I will change it out.

Since the car is a GTUs, I like the idea of staying with the 4.3. Here are a couple of picts...

By the way, I won't be doing any drag launches.

[Phoenix7]

very cool. the increased torque of the 20B and the 4.3 gears. How soon till she's on the road?

[Christopher W.]

Maybe by Spring... Logan at Defined Autoworks has some R&D still to do before we move forward. I have a couple more months before I will be ready to get the car to him.

[Phoenix7]

cool, I love seeing others projects! Keep it up man.

[gmonsen]

It seems to me that so many people with high horsepower cars keep going for shorter gears as a way, I suppose, to accelerate faster. This is an area where I am less technically knowledgeable, but have some experience.

Higher ring and pinion gears help leverage less powerful motors. When you have the kind of power available with 20b motors (500-700+whp), you do not necessarily need higher gears. In fact going with lower ring and pinions will probably get you through the quarter quicker, though this depends a bit on the transmission. I think Carlos (CLR) runs a 3.73 ring and pinion, for example, and I can name a few others, if you give me a minute.

If you have the kind of hp and torque that these motors can produce and use the higher gears (4.1 and 4.33), you run into several issues. You get tremendous wheelspin that costs time and is hard to control and you also have to shift 3-4 times instead of twice. I think that's why the guys running in the 9's use taller gears.

I use the 3.90 rear gear, though for a different reason. I have the Quaife close ratio gear set and want more time in gears, plus, 5th gear is 1:1 instead of 0.8:1. Anyway, I just jumped in here and there may well be other reasons for considering the 4.33 gear.

Gordon