Bersaglieri

iTrader: (13)

Well I swapped out my 4L60e for a full manual 4L80 and now I'm going to a 9" I am putting together in place of my 3.73 geared 10 bolt. Knowing the 4L80 has different gearing [2.48/1.48/1.0/.75] I've notice that my seat of the pants torque feeling is lacking a bit and with the added 9" strength I want to go bigger.

I used some basic calculations to determine 1st gear torque multiplication, for instance:

My old setup with a 4L60E and 3.73 geared 10 bolt: 3.06 x 3.73 = 11.41
My new setup with a 4L80 and 3.73 geared 10 bolt: 2.48 x 3.73 = 9.25
My 4L80 with 4.11 gear option: 2.48 x 4.11 = 10.19
My 4L80 with 4.56 gear option: 2.48 x 4.56 = 11.31

As you can see it would take 4.56's to get me where I was with a 4L60E and 3.73's. What do you guys think? I have a set of 4.56's laying under my bed, so it seems logical. But I'd have to move to a taller tire since my M/T's are 26" currently and I'd be running out of RPM's in the 1/4. Although its easy to change gears in a 9" carrier so I could easier to 4.11's down the road. Just wanted to see if anyone has done this. I figured the TH400/TH350 crowd might have some input too.

I know your not supposed to over gear too much with juice, but how would you gear if spray were to be factored in?

-Dustin-

ALLBOTTLE

iTrader: (13)

4.56's are going to kill your top end and 3rd gear be incredibly short. i don't know if you drag race but you don't want to have to shift into OD at the track.

4.10's will be short too, a 3.89 will prob be your best bet.

Bersaglieri

iTrader: (13)

Yes I drag race, obviously the car is being setup more for the drag than not and I am aware I dont want OD at the track. 4.56's look like they would bring me through at 115ish, but if I upped the tire diameter to 28 it would be closer to the mid 120's.

I think I'd have a hard time going lower than 4.11's simply to offset the extra weight and power loss. 4.11's with a 26" tire bring will carry me to the mid to high 120's.

I appriciate the comment, keep em coming.

-Dustin-

ALLBOTTLE

iTrader: (13)

that MPH is without any converter slip, depending on the stall and who makes it its not uncommon for an off the shelf converter to slip 10% up top.

chrismorales75

I'd add more gear and the taller tire, worse case you can always add a bigger cam and get a little more rpm out of it, either way I say it's a win win =)

EPP

iTrader: (22)

I wouldn't worry about your first gear ratios, as the nitrous will take care of that. Figure on what rpm you want to be crossing the finish line at with your tire diameter. If you're adding a decent shot of nitrous, your mph is gonig to be fairly high. I'd also go with a 28" tall tire to get you more contact area, plus they shock the surface less. Bob

Bersaglieri

iTrader: (13)

Wells its a relatively large cam already, CC306 on stock heads for now and these figures are calculated revvin to 6800, cant go much higher on the stock PCM.

Been talking to you on the phone Bob about the 9" Housing. When I get measurements on the axles I'll be ordering one up.

So you guys think 4.11's are too high also? Or should I go with 3.73's again?

-Dustin-

EPP

iTrader: (22)

Thats cool, thanks! I'd personally do 3.70 gears as it sucks when you're bouncing off the rev limiter through the traps. Bob

Bersaglieri

iTrader: (13)

Using this wonderful utility I got this information. http://www.f-body.org/gears/

4L80 + 4.11 + 26" Tire
RPM 1st 2nd 3rd 4th
6300 48 80 119 158
6400 49 81 120 161
6500 49 83 122 163
6600 50 84 124 166
6700 51 85 126 168
6800 52 86 128 171
4L80 + 3.73 + 26" Tire
6300 53 88 131 174
6400 54 90 133 177
6500 54 91 135 180
6600 55 92 137 182
6700 56 94 139 185
6800 57 95 141 188
4L80 + 4.56 + 26" Tire
6300 43 72 107 142
6400 44 73 109 145
6500 44 74 110 147
6600 45 76 112 149
6700 46 77 114 152
6800 47 78 115 154
4L80 + 4.56 + 28" Tire
6300 46 78 115 153
6400 47 79 117 156
6500 48 80 119 158
6600 49 81 121 161
6700 49 83 122 163
6800 50 84 124 166

I plan on trapping in the 120's N/A next season, and possiblt adding nitrous to the mix later. So 3.73's are going to have me pretty low RPM wise in the 1/4 when I cross. 4.56's are going to require a taller tire to keep out of OD. Although 4.11's seem like they'd be great with my current 26" tire with an upgrade to 28" when using Nitrous.

Thoughts?

-Dustin-

ALLBOTTLE

iTrader: (13)

What converter are you using?

Findout from the manufacturer what the typical slip is on the converter. If you get an NA converter it will slip more when on the bottle.

Bersaglieri

iTrader: (13)

Vigilante 3200 Single Disk. Not sure on the slip %.

-Dustin-

Bersaglieri

iTrader: (13)

How would I adjust the speeds using the slip percentage on the converter? I am running 4.11's now and the car acts like it wouldnt mind more gear, just gotta see how much I have left at the end. I have more RPM at the end of the track to play with. I shift between 6500-7000.

-Dustin-

supernaturalta

iTrader: (6)

If your slip percentage is 10%, I'd say you multiply your rear ratio by 1.1. 4.11 x 1.1 = 4.521, so if your converter slip percentage is 10%, it's like you have 4.52 gears.
Are your M/Ts slicks or drag radials?

Bersaglieri

iTrader: (13)

Now I am on Hoosier 26 x 10 x 15 slicks. Thanks for the explaination, I was wondering where you deduct the 10% from.

-Dustin-

Sunset'01Z

iTrader: (10)

you will add 10% rpm to the speed at which you pass through the traps. I would go with the first option, 3.73's and 26" tire to start with, and step up to a 28" tire if need be when you see what the car does with nitrous.

supernaturalta

iTrader: (6)

OK. Slicks will grow a little in the top end (not like a Top Fueler, but they'll grow a little), having the effect of running a slightly taller (lower numerically) gear. That's something that probably needs accounted for. Maybe someone who has those can comment on that.