for a compare my '79 was changed by a prior owner from the stock 3:55 to 3:08. With the 3:08 at 3000 RPMs, I'm at 75MPH with 255/60's. That's versus your 60MPH at the same RPM. To me with that engine, 3000 RPMs on the highway is high enough. The 3:55 must be spinning at over 3500RPMs at 75 MPH, which is a lot of wear on the engine I would think but fine for those who don't drive much highway.

 

How do I know what my first gear is? I have a Borg-Warner Super T10.

 

I tested it last night. I got three turns plus an 1/8+- so it's either 3.08 or 3.07. The real question is how much more pull would I get upgrading to 3.55. If I can't smoke the tires now will these gears do the trick? Also, is there any way to test the tach? I always felt I was running high. My speedo is off by 5 to 10mph but at 75 on the speedo I'm turning 3500rpms. Something is not right.. How do I find out what it is?

 

Just rotate the tires or differential.
Count the rotation of the input yoke or drive shaft.
3:08 = 3.08 revolutions of the drive shaft or input yoke to one rotation of the wheel...and so on.

Gears make all the difference. If you ever want a powerful cam you need 3:55 or better. plan for the future mods now. :steering:

 

Just saw your above post...girlfriend came in naked while I was typing....sheeeeesh.
Took a little extra time to type :lolg:


[Modified by 81ZZ4, 7:23 AM 3/4/2003]


[Modified by 81ZZ4, 7:27 AM 3/4/2003]

 

That's what I was thinking but if I'm turning high tach numbers now I won't be able to go over 60mph without red lining.. Any idea what could be wrong. The tach and engine sound seemed right..

 

When I had the Original trans in my 81...TH350C
I changed the rear to a 3:55. at 6,000 rpm I think I hit around 125 or 130 with the convert. locked. Your tach or speedo is way off...
At 70 mph I was around 3500...my speedo gear was off..but in this area is close. even with a 4:56 gear you could still hit 90 or so before red line

 

Koz

This is general info. which may help you. About 3.55 is a typical manual trans. stock rear ratio. Autos are typically stock about 3.08 as there is slip in the TQ. Neither will put it close to redline at highway+ speeds.

PS L-48 badly needs more CAM!

:cool:

 

I counted the gears.. 43 and 14 = 3.07 rear.. 3.0714285714285714285714285714286 for you math guys.. :D

No one really answered the question of how much difference the 3.55 gears will make.. Spin tires much easier.? Feel a little more pull in the seat? Worth the money?

 

Yes, you'll DEFINITELY feel it! It'll multiply the torque by 15% more (3.55 divided by 3.08 = 1.15) than it is now! And, you should NOT 'run out of motor' at highway speeds. For instance, the '77-'79 4-speed Z28's, with basically the same motor, tranny, and tires (225/70R15), had 3.73:1 gears as STANDARD EQUIPMENT! I'd guess your 1/4 mile ET will drop by 2 tenths or so, too. I saw an earlier comment, saying 3.90s are a 'direct swap'; Drive Train Specialist told me that in the '80-'82 Dana 44 rears, up to 3.73s are a direct swap, but 3.90 & lower need a different carrier. Not trying to argue; only passing info along...

 

Yes you will spin tires with more ease. Feel more snap when you hit gears.
More fun when you drive. 3:08 is a mild gear. A cruiser type.

 

Have you done any exaust work on it yet?

 

Spend the $300 bucks toward Nitrous. You will definely spin the tires with a 100 shot. :reddevil

Note: That the my car in the sig was a 3:08's at one time. But with several mods.


[Modified by Budman78, 1:02 PM 3/4/2003]

 

I have emissions so I've replace the cat with a high flow cat but kept it basically the same.

 

You will get a BIG difference with true duals and good hi flow cats.

 

My 60 foot times went in the toilet with my 3.73's in my 1980. Behind a ZZ4 and 700R4, 3.73's are way to high. I get nothing but tire spin in the first 2 gears.
I am going back to the 3.08's when I get time to do so.

 

Youll definatly feel a difference in launch and acceleration with a swap from 3.08 to 3.55. Another good idea to boost that would be a stall convertor. I put in a 2500rpm convertor and it alone with no other mods took 4 tenths off my ET.

I stand corrected that 3.70 is the lowest for the 3 series in 80-82. I now remember my gears being advertised for years 68-79. Thanks for the correction.

 

OK let me see if I can answer that question as well as add a litle more food for thought on this subject.

First I have a 1980 with L48 and BW Super T10 and form what I can determine I have a 2.88 first gear. Now comes the fun part, the reason I said to stick with the 3.08 rear end is; somewhere there is an optimal gear ratio for drag racing, launching etc. Anything too far over this ideal ratio and you will just smoke the tires and you might as well start in second gear and too far below this ratio and you will not launch very well.

Some time back someone posted this to be ( I am not sure of the exact numbers ) I believe between 8.5 amd 10 or thereabouts. You get this final ratio by multiplying your first gear by your rearend. Someone with a 3.70 rearend could get by with a first gear between 2.3 and 2.7 witch is why they are so popular as the Turbo Hydra-Matic 350 and the Turbo Hydra-Matic 400 have first gears of 2.52 and 2.48 respectively.

Now you run into a bit of problem when you combine a 700-R4 tranny that has a first gear of 3.06, the result is a combined ratio of 11.3 and you can see why B Seery posted this:

QUOTE/ My 60 foot times went in the toilet with my 3.73's in my 1980. Behind a ZZ4 and 700R4, 3.73's are way to high. I get nothing but tire spin in the first 2 gears.
I am going back to the 3.08's when I get time to do so./QUOTE

I could be a little off here on some numbers but the theory behind this sure makes a lot of sense hopefully the poster who first posted this ratio thing will chime in. :D

BTW 3.08 and 2.88 = 8.87

Double BTW I have 3.08's




[Modified by MotorHead, 6:12 PM 3/4/2003]

 

I think that BSeery's REAL problem was 'lack of traction', be it too small a tire, or not 'sticky' enough, not necessarily 'TOO MUCH' gearing. I offer my '79 Z28 as an example. A 400 HP 355" SBC, THM400 w/ 2.75:1 1st gear, a 10"/2400 RPM converter, and 4.10:1 rear gears (2.75 x 4.10 = 11.275:1), sitting on 26" x 8" McCreary street- tires. It hooked, CONSISTENTLY, running 13.50s @ 103+, winning 8 races of 43 starts, and one Points Championship, over two seasons. IMHO, the 3.73s aren't the problem; you may want to try something other than EAGLE GTs or BFG T/As. It 'may not' be the best ride in every-day driving, but it 'should' hook good enough, with both the gears AND the converter, to run 'quick ETs'. Good Luck!!!

 

P.S.- I installed TCI Extra-Low gears in the THM400, hoping to ensure the 3700 pound Z28 could run in my local 12 & 13-second bracket. When I added the 8"/4500 RPM converter, I had to add 28" x 10" EAGLE 'Dragway Specials', and 4.56:1 rear gears to offset the 2" height increase. The Z28 runs 12.80s @ 106+ MPH, launching @ 4000-4500, shifting @ 5800, trapping @ 6300, on SUNOCO 94.