Rear Gear Decisions

Howdy guys,

So I'm trying to decide on gear ratios for my car. I was originally solid on 3.25 b/c i thought 3.55 were too low. Well, i just found out they make 3.40 gears and that has my interests peaked. So i would like your alls input on what would you do, 3.25 or 3.40?
What I have:
•2V 1980 head, headers, 256H Schneider cam, dual headers, DUI.
•1985 SVO WC T5. 4.03, 2.5, 1.5, 1, .83
•25.9 inch tires, may be going to 25.6 inch.

1 worry:
I'm jumping up from a 2.8 gear, so the teeth on the output shaft of the tranny might need to be swapped as the speedo gear might not be enough. I really don't want to have to yank the transmission.

My driving situation:
Daily driver, mainly around town. Gets on the highway semi frequently doing 65ish for about 10-15 mins. Occasional long drives.

Specs:
@65 in 5th:
3.25=2220 RPM
3.40=2322

@15 in 1st
3.25=2549 RPM
3.40=2666 RPM

Its funny looking at this compared to my 2.8, with that I'm doing about 2000 at 70 lol.

I know the numbers arent a whole lot different but it is a decision that has to be made. I feel like the 3.4 may be a little more fun but I want to make sure I'm optimizing the gearing for my I6 since gearing is crucial to make them as fun as possible.

Thanks a lot,
Ryan

I might not B da best guy ta ask - I'm a kinda gross person
What I mean by that is I don't notice until B I G differences come inta play.
The chicks say "Chad! That's not very nuanced." At your age I had alota fiats
and alfas. I didn't really notice a difference until there wasa 500 + rpm change.
.25 to .40 seems like a pretty small change. I wouldn't over think 1 that small.
I guess its like choosing an exhaust note, pretty personal (never got a 6speed -
same reason, nother OD? nother few 10ths?).

Now the 2.xx to 3.20/40 THAT makes a difference. Look at that 'gear calculator' I sent ya.
At least the one that has the 3 colors ("upper /mid'n/ lower") It had may B 4 or 5 ratios in the middle -
the lower - poor gas MPGs but 'peppy'; the upper - good MPGs but 'wimpy. I usually pick oneada 4 or 5
'middles' that are more on the 'peppy' side.

The guy I wrk for just ripped out his 383 and put ina 12v. After we rigged up the turbo and auto transmis we took
it (he asked me 2B there)for a test drive. After all that wrk he did he wuz just happy it wuz finally on the rd. I hada
tell him the 4th gear wuz not comin n at the right spot. After, he rigged upa switch (to bring it in properly/manually) he
smiled in agreement. Soooo...may B its just something in the back of ur mind, something U just feel aint right? May B the girls
will smile on me now? "Oh Chad! Now that's nuanced!" HTH~

It comes down to where your comfort level is rpm wise at your chosen cruising speed. The .83 OD is the limiting factor. I would drive the car at the various RPM's of the 2 combos and see what feels right to you for the rpms of whatever speed you expect to cruise at 90% of the time, whether that is 60, 65, 70 or whatever. 90% of my highway driving is at 60-65, sometimes 70. With the 8" rear end? If so you can always swap in the old 2.8 for road trips and go with a 3.5 or 3.4 for daily driving. I wish I would have just kept my old 3.25 9" chunk and bought the 3.7 instead of having the ring and pinion gear changed just in case I wanted to take a really long road trip or cross country. And price wise it makes sense as well. With .67 OD and 25.5" wheels the 3.7 works really well for me daily and keeps highway at a reasonable level. Something to think about. Put a drain in to if you go that route.

Since you have a 4.03 first gear i would go with the 3.25 gear.

X2 on the 3.25 rear gears.

With the 3.40, and definitely with the 3.55, your 4.03 first gear would be useless.
You'd be shifting out of first at low MPH. Now, if you live in a hilly area, it would be beneficial
to have the lower gearing.

Alright guys, i was kinda leaning towards the 3.25 after talking with you all and realizing that first gear would become almost useless. I went ahead and ordered an 8 inch center from Quick Performance. Here's the build:

8 inch center
Posi LSD 28 spline
New Nodular Iron
Billet yoke
Aluminum alloy bearing support
3.25 gears
Drain plug

This is officially pretty sick now. Thanks for the input guys!

What kind of oil should I run?

Ryan

LS may require specific additives, some take 75w-90, others GL4, 5, etc. Make sure U have this info from the supplier.

Do U know how to break in? No red - hot conditions on this 1.
Most of this is gotten frm the manufacturer (or retailer):
"Drive 15 to 20 miles, stop 1/2 hr, 20 min til cooled, do so 2, 3 times. No tire shredding 1st 100 mi, no towing.
Change oil at 500 mi, look init for unusual chunks. Fillings (very fine) R expected. 1st towing has a sim break-in."
HTH - C manafact &/or retailer

When I had mine rebuilt and ring and pinion swapped I was given a specific break in procedure and advised to use mineral 80-90 type. Then switch to synthetic after a certain number of miles but mine is standard not posi. You may need an additive. I can't remember the details. It was something like drive it at moderate speeds, like 30-40 for 1/2 hr then park it and let it cool, then something else, then after x miles swap to synthetic. But like I said, I don't recall exactly. Ask the mnfr if it doesn't come with instructions. I also installed a magnetic drain plug in my rear end while I had it apart. An 1/4" pipe plug w/ a pipe tap would be fine as well. Don't tap all the way, just deep enough, remember they're tapered.

Btw, Since you'll have to pull the axles anyway it may be a good time to replace the bearings and axle seals if you haven't already.