ZL1 RDM differential 3.73 or 3.23 gears selection - for turbos

[dreksnot]

LS3 M6 (6-speed), twin turbos, 3.73

I've been told by "they" that I should raise my RDM gears from 3.73 to 3.23 and I'd get lower 1/8 and 1/4-mile ETs. I've also ran some "benchracing" software and on paper, it confirms it. But you know hypothetical and real life are two different animals.

What say ye? Anyone with this/these gear(s) experience?

[DaFisch]

yeah, you'll hook better with twins, not spin through as many gears. have you done any trans mods?

[swiftkart]

I'm sure it will help the twins spool up better from having more load on them from moving the car instead of spinning the tires.

[dreksnot]

Originally Posted by DaFisch

yeah, you'll hook better with twins, not spin through as many gears. have you done any trans mods?

I am spinning all the way through first gear with my drag radials. I build about 1.5psi boost on the line with my 2-step. I'm guessing I can build more with the higher gears if I need to by killing some timing.

I have no trans mods.

[JakeW1990]

You need to take into consideration that you have a stage 3 cam and dropping from 3.73 to 3.23 is going to leave a sour taste in your mouth in 1st gear and low rpm cruising. Load is good for turbos, bad for cams.

[stevieturbo]

What size tyres ? What rpm range ? What trap speed ?

And are you managing the 1/4 in 4th gear at present, or shifting to 5th ?

Taller gears can help for sure in most cases, but dont go too tall if you dont have the power to back it up.

[dreksnot]

Originally Posted by JakeW1990

You need to take into consideration that you have a stage 3 cam and dropping from 3.73 to 3.23 is going to leave a sour taste in your mouth in 1st gear and low rpm cruising. Load is good for turbos, bad for cams.

At first, I had awful bucking and surging below 2,000rpms. I've dialed most of it out with fueling and airflow (still have timing to play with) but still contend with clutching in parking lots below 11mph (1,500rpm). If I switch to 3.23 then that ups me to 13mph for 1,500rpm. Doesn't look like much but going that slow in a parking lot is huge. At highway speeds and low rpms, the cruising has been just fine and am well aware that I'll drop 180rpms at 55mph (from 1370 to 1187) in sixth gear. Might lug and have to downshift back to fifth for 1749rpms. Oh, the dilemma.

[dreksnot]

Originally Posted by stevieturbo

What size tyres ? What rpm range ? What trap speed ?

And are you managing the 1/4 in 4th gear at present, or shifting to 5th ?

Taller gears can help for sure in most cases, but dont go too tall if you dont have the power to back it up.

Ran 315/40R18 DRs last year but going to use 275/44R18 this year. My redline is 6,700rpm and I'm trapping 11.2sec at 127mph (5,700rpm in 4th gear - my peak RWHP). Looks slow but that was at a DA of 7,551ft at Bandimere (Denver).

The "calculator" says I could knock off a 0.1sec and add 4mph in the 1/8th, and 0.1sec faster but lose 2mph in the 1/4-mile times.

[JakeW1990]

Originally Posted by dreksnot

Ran 315/40R18 last year but going to use 275/44R18 this year. My redline is 6,700rpm and I'm trapping 11.2sec at 127mph (5,700rpm in 4th gear - my peak RWHP). Looks slow but that was at a DA of 7,551ft at Bandimere (Denver).

The "calculator" says I could knock off a 0.1sec and add 4mph in the 1/8th, and 0.1sec faster but lose 2mph in the 1/4-mile times.

I wouldn't sacrifice that drivability for 1/10. I'd rather take the passenger seat out,buy a smaller/lighter battery, and have 2-3 gallons of fuel in the tank. There's you 100lbs and 1/10 of the quarter and drivability is still good. Lol.

I'm in the same boat. The struggle of getting a ZL1 rear end and it being 3.23 or 3.73... ��

Tbh, if you're at 5700 rpms in 4th, you've still got another 1k to go. 3.73s are going to get you to the end faster than dropping gears because you haven't shifted into 5th yet, granted you have the right tires to hook. I can see having to shift into 5 causing you to lose time, but who's going to complain about going 145+ in a 1/4? LOL.


800+ hp and only trapping 11.2? Get you some skinnies and radials! I ran 11.5x at 464hp. You should be in the 9s!

[dreksnot]

Originally Posted by JakeW1990

800+ hp and only trapping 11.2? Get you some skinnies and radials! I ran 11.5x at 464hp. You should be in the 9s!

Fun thing, but uninformative, about the corrected RWHP is that it looks immense. My correction factor is 1.33, so take my 804 and divide by that to get my actual RWHP. A measly 605 in this thin air. But the corrected looks more interesting.

I'm so serious about racing that I leave my subwoofer in the trunk, still have my stock suspension albeit BMR sways (stock alignment), and I enjoy my heated seats and sunroof. Hell, the track is pretty strict so I really can't run full out else I'd be below the 11.5sec ET threshold and I'd get a finger shaking in the face warning me to slow down, or don't come back until I get a rollbar. Would have to do the Drag-n-Dash at the end of the night to see what the car would really do. I'd bet my best time would be 10.9sec with my 4,300lbs heap.

[Unreal]

I would never gear down like that. Unless you are dead hooking now.

[dreksnot]

Originally Posted by Unreal

I would never gear down like that. Unless you are dead hooking now.

Nick - are you saying don't 3.73 to 3.23 or the other way around? I have 3.73 now and spinning like a banshee.

[Taco Time]

Why would you go from a 315 to a 275 if you're already spinning? Why not drop to a 17" wheel? (I don't know, I'm just asking.) would that not be any help?

[dreksnot]

Originally Posted by Taco Time

Why would you go from a 315 to a 275 if you're already spinning? Why not drop to a 17" wheel? (I don't know, I'm just asking.) would that not be any help?

Good question! The 315/40R18's were Nitto NT05R. Just wouldn't hook. I've had recommendation to a little skinnier and taller, and in an M&H. So, better tire, taller but skinnier. We'll see. And my Welds are 18's. I could try a 17 but $$$. Figured the spinning couldn't get any worse.