Hey guys, I'm about to build up my 3 rib diff and was debating which set of gears to go with. I have 1-7/8 longtubes nd will be doing a fast 92/92 with the additional of a 238/242,112lsa cam nd eventually ported 243s. I know as far as drag racing and such the 4.10s would be very beneficial. Only thing I'm skeptic of is how will it be in autocross/roadracing with more shifting. Also I like to cruise around at like 80mph will it be taching too high? Ive looked at all the gear calculators and I'm aware of what it will be...I'm just looking for first hand expedience of people that driven them. All my f body buddies are swearing by the 4.11s since we have the double overdrive.

 

I would say it depends if you have a Z or coupe/vert. Given that you are asking about a 3 rib I'll venture to say you've got a Z. The gearing in the trans makes a big difference between the two. In a coupe/vert I would go with 4.10s. In a Z I would go with 3.90s. I recently upgraded my diff with 3.90 gears at the same time I put a new cam in (224/232 114lsa) and we also did a little work on the stock heads. I absolutely love the gears with this set up. Someone else will have to chime in about the autocross/roadracing feedback as I only drive mine on the street, but with true Corvette spirit.
My car flat screams off the line and I'm in the power band whenever I need to be. I've never felt like I have to let the engine build power. It's just there when I want it. No spinning up the engine to get there.
Luckily I live in a small town and the LEOs aren't everywhere because my new favorite thing to do on my nightly honey-do errands is miss a turn just so I can pull a U-turn and fishtail coming out of it.
Good luck with your decision and if you decide to get your diff built I highly recommend Rick Kim with RKT56.

 

Good guess, but I got lucky with the 3 rib in my coupe! Plus I'm going with a much larger cam lol. But your setup sounds real fun, how's high speed cruising?

 

When I'm over 70mph I can certainly say I hear the exhaust. Part of that could be because I'm running lth with no cats and a GHL cat back, but it doesn't bother me. To be honest, I've never really looked at the tach when I'm cruising over 70 to see exactly what rpms are spinning at a certain speed. I know I'm over 2k at interstate speeds, but I don't think of it as being excessive.

 

Lol I hear your pain, arh lt catless x, b&b bullets

 

I have a similar setup to you, and I am wondering the same thing when it comes to gears. I wonder if my FRC has the 3 rib

 

99? Single rib

 

For MM6 trans, I would recommend 3.90's for all around, 4.10's for max 1320 runs. 4.10's would be too much for the track/auto cross, ask me how I know.

BTW all C5 come with 3 rib diffs starting on 2002. Some late 2001 models came with 3 ribs also.

 

Hey Rick- On C5Zs, isnt the final drive ratio same as 3.90 due to the tighter trans gears on the MN12 that have 3.45 gears out back or is that a myth?

 

Yes, it is very similar to having a MM6/3.90. Not the same but very close.

 

Drag racing and autocross / road racing are three different things.

the most common diff for road racing / track days is the stock 3.42

and of course if talking real road racing, then you have tech rules to follow. But for just track days the 3.42 is just fine.
a few ppl have gonig to a 3.73. The 4.10s or 3.90 was just way too much shifting, and the car was speed limited to about 145-147 mph on the longest straights. ( red line 4th gear )
Plus with the 4.10s or 3.90s the trans and diff would heat up much more then normal so the trans and diff coolers where needed. plus a big arz oil cooler for the engine too.

What may be a an other option which more guys do is take out the MN12 and replace with an MN6 trans. plus brass shift forks.

the 2-3, and 3-4 comb in the MN6 is a better gear ratio then the 2-3 and 3-4 combo of the MN12 for a road course.

the MN12 2-3 gear is too low for most road course, and the 3 to 4 combo is too wide between the gears.

Or just a close ratio box of the GM motorsports box or the ZR1 ratios with the 3.73 rear gear. That will keep your engine right in the sweet spot for torque and HP. Then again, big dollars and big coolers are needed. ( What the hell put in dog rings gears for no lift shiting )

dont forget a clutch too. the stock GM clutch is OK but not great. the Spec II seams to be the most popular for road course guys.

Like any modifications, deep pockets are a blessing or a curse.

Good Luck on that

80 mph cruising I am in 3rd gear occasionally 4th . never 5th