Which gears do you think will give me the best performance, 3.42 or 3.73 for my 305 TPI? I don't care about saving gas, I'm willing to sacrifice gas for performance. My engine is bascially stock (very few mods). I have heard that 3.73 is overkill for the engine because of the rpm range, anyone agree? Is there much difference in performance bewteen the two? I need some help making a decision. Thanks.

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1992 Z28 (305) TPI.
160' stat, Accel 8mm, Accel Cap & Rotor,
Flowmaster high-flow cat-back.

 

Definately go with the 3.42 gears. The 3.73 will get you out of your powerband too fast. Go with 3.42 and start going crazy with mods.

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TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph

"Speed kills, wanna live forever, drive a Ford."

 

i have 3.42's with my 86 305, and i get through 1 2 3 in the 1/4.
just as i go through the traps(@14.6 94mph) i should be hitting OD,
3.42 would be best for you

 

If your building a 1/4 mile car, then you want to optimize your gears so you are crossing the finish line at the end of your torque peak in drive (1:1 ratio gear).

If you want a stop light to stop light car, then a bit high gear is better.

Remeber the TPI is torque, and to make use ot the torque, you need to use a lower gear.

3.42 would be a good all around choice. 3.73's are a bit higher, but can certainly work. Try to plan around a package.

What gears do you have now? 3.23 or 2.73? If you have 3.23, then you will not see much gain, but if you have the 2.73, then you will feel something.

Mark.

 

I have 2.73s right now. If I go with 3.42s, will I need to re-calibrate my speedo? What will I need to do?

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1992 Z28 (305) TPI.
160' stat, Accel 8mm, Accel Cap & Rotor,
Flowmaster high-flow cat-back.

 

On my Iroc, 305, I'm right at 5,ooo RPM (5,500 RPM redline) as I cross the line in fourth gear (manual tranny). I have the 3.42 rear, and the "hotter" cam. I love the 3.42 gears, I was tossing the idea of getting higher gears a while back, but like you was advised agianst anything bigger than the ones I have now. They told me there was no point in going from 3.42's to 3.73's.

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"Clear your mind, relax, and float downstream."

 

Yes you will need to recalibrate your speedo. GM should be able to help, although it depends on who you get.

Check out my link to speedo gears. Its from a GM book in 1986, so it has the borgwarner gears, but you can use the 3.45 ratio.
http://home.epsb.net/~mstrembi/speedogears.jpg

Mark.

 

I agree that it depends on what you want. I'm running 4.10's and I've beat cars that were much more powerfull than my T/A. I know street racing is not "cool", but if a hot car lines up with you at a light, what are you gonna do? I race them. I've beat 4th gen Zee's and T/A's, 300 hp Mark 8's, Cobras, and all types of lightweight imports. People are shocked when I tell 'em it's a 305! Wait until I do the mods! On the street, low gears are for me.

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1989 Trans Am, 305 TPI 5-speed, T-Tops(love 'em),4-wheel disc

 

Thanks Mark. That chart really helped. I know what I need to get now. What are your recommendations for a manufacturer to purchase from? Also, will I get that "whining" noise with 3.42s? Thanks.

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1992 Z28 (305) TPI.
160' stat, Accel 8mm, Accel Cap & Rotor,
Flowmaster high-flow cat-back.

 

Manufacturer ... GM of course. Speedo gears are not much.

You should get NO whining from any gears, if you do, they are installed wrong or wore out. I am running 3.73's on my S15 and they are quiet as can be and they even have a ton of miles on them.

S15 you say ... well ya, my F-body turned into something practical when the family began, but hey it's TPI, WS6 steering, and what ever else finds it way there.

Mark.

 

Also, traction becomes a problem with the 3:73's. Getting out of the hole with the 3:42 will be much easier. I have 3:23's in my 89RSconvtZZ4TPI and I love them but I do wish I had 3:42's

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Rob P
89RSconvtZZ4TPI
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

Hate to say it, but me too. I have 3.42's in my '87 IROC (305TPI/A4) and they are just about perfect. I'm going through the traps at the end of the 1/4 mile just past the engine's horsepower peak (4000 rpm). Highway mileage may have gone down 1-2 mph, but I can use OD around town more so city mileage is better.

As Mark_ZZ3 said, you shouldn't have hardly any gear noise, although I've heard that some aftermarket gears are worse than others. I have GM gears in mine, and all I have is a faint whining on decel between 40 and 25 mph, none above and none below those speeds. The shop re-set the backlash or whatever a few times to get it to that point, but I barely notice it now.

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Greg Westphal
'87 IROC 305TPI/A4

 

Cool. Thanks a lot guys. I know what to do now. Can't wait to put em in. One more thing, since I'm going from 2.73s to 3.42s do have an idea on how much better my 1/4 mile time will be? Thanks.

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1992 Z28 (305) TPI.
160' stat, Accel 8mm, Accel Cap & Rotor,
Flowmaster high-flow cat-back.

 

Do have a chart for 6-speed bw with 3.42 and 255-50-16's[2.97-1.94-1.35-1.00-.84-.62 ?

 

I dont know guys. I had 3:42s stock with my car. I replaced it in the summer time with 3:73s and I LOVE the difference. The most noticeable difference is when I'm in 3rd and pound it. The car MOVES. I was also told not to go with 3:73s. "Pointless with a 305TPI blah blah blah". But I can tell you the majority of the people who tell you not to get them probably don't have a 305 TPI with 3:73s like I do. I actually HAVE the combo and I can tell you I love them. My 3:42 posi is sitting in my garage and it's staying there.

 

Guys, from personal experience...going from 3.42's to 3.73's, and then backwards to 2.73's....I'd strongly suggest 3.73's again. Look at my sig..we have almost identical cars, as far as performance stock goes. I'd advise you to take advice from the guys on this subject that have a similar car to yours...not an 82 berl with a 400 in it or an 87 2.8 liter.

I'm not trying to be a richard, but it seems to be a good point, so you can more accurately judge what your performance gains will be.

I gained performance and gas mileage with all my mods. When I went back to 2.73's my gas mileage started to suck extremely bad. What I'm trying to say is that the 373's put my engine at rpm's it liked to be at in any situation.



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1992 Texas DPS B4C 1LE FE2 5.0/5spd:
Intake and Plenum Ported
Fully Ported Corvette Heads
TPIS Tricks ,No Smog Pump, NOS FI Fuel Pump
K&N's Adj. Fuel Pressure Regulator
Alston SFC's, Energy Supension Hyperflex system
MSD 6AL, SLP 1 3/4" SS Headers
3.73's with 275/55/16's out back...blew those now 2.73 one legger
My complete back seat
encompases my RF tunes...

Currie 9" on the way with 3.70 gears

Adam

 

Ohhh...one more thing....

I totally agree with formula....

and I was running mid and low 13's with the above combo, and getting 20/25 mpg

 

I want to make the right choice here. Anyone else have a testimony?

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1992 Z28 (305) TPI.
160' stat, Accel 8mm, Accel Cap & Rotor,
Flowmaster high-flow cat-back.