# Gear Ratios



## dahd11 (Feb 25, 2011)

First, let me say I have read the sticky 3 times, thouroughly.

Currently I am running 2.73 gears in my stock 68 GTO/400, with a 4 speed transmission. I am scheduled to get these gears swapped out in three weeks. I have already bought 3.73s, but after reading the sticky on Gear Ratios, I want to be able to drive it both on the highway and have some power in town, so I am changing directions and really think I want 3.23s or 3.55s. The problem with my current gears is that I own a muscle car and it will not smoke the ONE tire. (I have bought an EATON posi 3 series carrier to go with my new gears.) 

My goal is not for the car to smoke both tires forever, but I would like for it to chirp them a little bit, and then set you back in your seat. (That is what a muscle car is right?) This car will not be raced, but it feels like a dog right now with these gears and I don't like it. If you have experience with these gears, and have an idea what effect they would have on this car, please help!


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## Eric Animal (Oct 28, 2007)

Split the difference....3.36......3.55 is a little stiff for long highway trips, although it is a great gear ratio for a 4 speed GTO


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## geeteeohguy (Feb 2, 2008)

My favorite gear for a 4 speed GTO is a 3.23. My own 4 speed '65 has a 3.36, because that's the tallest gear I could use with my carrier. 3.36 gears are ok...mine cruises 65-70. That said, my heavy, low compression, TH400 '67 GTO convertible has a 2.56 limited slip and it FRIES the tires. Something is wrong with your tune or combo. Seriously wrong. The tallest gear Pontiac put in their 4 speed GTO's was the 3.08. A 2 series gear with a 4 speed isn't the greatest, so yeah, you should re-gear. But get the engine checked out!


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## GTO JUDGE (May 14, 2005)

Last October I swapped out 4.10's for 3.55's. Car drives and tachs great. Plenty of power and get up and go.


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## BearGFR (Aug 25, 2008)

dahd11 said:


> Currently I am running 2.73 gears in my stock 68 GTO/400, with a 4 speed transmission. ...
> 
> The problem with my current gears is that I own a muscle car and it will not smoke the ONE tire.


Have you tried this formula?
1) Depress clutch pedal
2) Select first gear
3) Tach to 3000-3500
4) Side-step clutch pedal and simultaneously...
5) ...Bury the loud pedal



Bear


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## nyte_ryder67 (Feb 18, 2011)

I have a 3.55 on mine and it will cook the tires at the drop of a hat. It's great for crusin' around town or going on a country cruise. 2500 rpm at about 50-55 mph. rpm's do get a little high on the interstate though, 3500-4000 rpm @ 70-80 mph. I have a TH400 3-spd auto. trans so my set up is differant than yours. Sometimes I wish that I did have a higher gear, like a 2.93 mabe, because gas is starting getting expensive again. Hope this helped.


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## dahd11 (Feb 25, 2011)

BearGFR, you are right on. I baby all of my cars, and would feel guilty popping the clutch. My friends insist I do, but it is my baby... I am almost 100% certain it would light them up like that, but I don't want to do it that way. And frying my tires off is not what I want either.


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## Instg8ter (Sep 28, 2010)

:agree with GeeTee check your tune, that car should not have a problem barking the tires from a get even with the tall gear.


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## dimitri (Feb 13, 2009)

Richmond gear has a fun calculator you can play with. Give it a speed and rpm it will calculate gear ratio. You need to know the diameter of your rear tires.

RICHMOND Street Performance Calculator


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## BearGFR (Aug 25, 2008)

dahd11 said:


> BearGFR, you are right on. I baby all of my cars, and would feel guilty popping the clutch. My friends insist I do, but it is my baby... I am almost 100% certain it would light them up like that, but I don't want to do it that way. And frying my tires off is not what I want either.


Ohhhh tayyy... I wasn't advocating the procedure, necessarily - just offering a solution.  I'd have a tough time doing that on a regular basis myself.

Bear


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## xconcepts (Jan 4, 2009)

I have a full housing with 3.23 gears that came off a 66 that I didn't/couldn't use. I'd sell the whole thing for 100 shipped. link


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## dahd11 (Feb 25, 2011)

OK, my car is running night and day different. I did a couple things and they both helped equally. Thanks to lars and the sticky he provided on tuning your car, the first thing I did was bend the accelerator back. WHOA! I don't think the secondaries were ever opening. The other adjustment was the timing. When I first got the car it was set at 6. I then advanced it to 12 and it ran a little bit better. The next time I said what the heck and bumped it up to 18. And WOW! The guy I bought it from said he was messing with it to get it to run better, but he admitted he was not a mechanic. I am guessing when he put the distributor back on he did not get it stuck in there right, so it may only be advanced 10 degrees or so, but I don't really want to mess with it because it is running perfect. Also these 2.73 gears now feel amazing, but I am probably going to go with 3.55s and not the 3.23s because my friends are begging me to go with the 3.73s. Still not sure...

Thanks!


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## BearGFR (Aug 25, 2008)

dahd11 said:


> but I am probably going to go with 3.55s and not the 3.23s because my friends are begging me to go with the 3.73s.


Good deal! Glad to hear it's better. If your friends are Chevy guys, ignore them. They don't understand the power band of a Pontiac and the torque it makes down low.

Fr'instance. The 461 I built for my 69 makes 493 peak HP, but the real story is the torque - it makes 540 lb.ft. at a measly 3200 RPM. I've got 3.50's in it because that's all it's going to need - and even with those I'm just _hoping_ I'm going to be able to get it to hook...

Bear


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## geeteeohguy (Feb 2, 2008)

It all depends on how often you drive the car, what KIND of driving you do, and what you are expecting from your car. When I was a teenager, and gas was 51 cents a gallon for leaded premium, and the speed limit was 55mph, I thought the 3.55 gears in my '66 GTO were great. I drove that car everywhere, buzzing along at 55 mph, sucking cheap gas. As I got older, and time went by, and the new cars got overdrives and the speed limits went waaaay up and road noise went waay down, 3.55's lost their charm. 3500-4000 rpm at 70mph wasn't any fun. Mind you, this was daily driver/commute car 100 miles a day, not "fun" driving. I changed my '65 gear to 3.36 in 1990, and it works very well with the 4 speed. It runs "like a GTO", and is cruisable. I personally would not run 3.55-3.73 or shorter gear because I don't require one for the kind of driving I do. Pontiacs tend to do better at the strip with a low 3 series gear, do to traction problems and huge torque. I can't believe some of the et's guys are getting with 2.56, 2.73, 2.93 gears. Really impressive. As always, build it the way you want it. I've been driving mine constantly since the '70's, and have found that 3.36-3.23 works for me with a 4 speed and 2 series gears are great with an automatic. Gas is skyrocketing, but I drove my '67 160 miles on Sunday, and got about 20mpg. Your mileage may vary!


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## dahd11 (Feb 25, 2011)

I have to say I was extremely shocked at how hard the 2.73 gears were pulling yesterday. Maybe I will go with the 3.23s. I am so confused right now...


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## geeteeohguy (Feb 2, 2008)

3.23 is my all time favorite pick for a 4 speed GTO. Can't go wrong there!!


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## BillGTO (Oct 16, 2009)

With a good tune and a steady pedal, I get 18.5 mpg on my 67 with the HO and 3.55's and 4 speed. (keeping the speed around 62, though!)


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## judgelover (Jan 1, 2017)

3.35 rear end will get you the quick take off and still can cruise


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## WillGeo (11 mo ago)

geeteeohguy said:


> My favorite gear for a 4 speed GTO is a 3.23. My own 4 speed '65 has a 3.36, because that's the tallest gear I could use with my carrier. 3.36 gears are ok...mine cruises 65-70. That said, my heavy, low compression, TH400 '67 GTO convertible has a 2.56 limited slip and it FRIES the tires. Something is wrong with your tune or combo. Seriously wrong. The tallest gear Pontiac put in their 4 speed GTO's was the 3.08. A 2 series gear with a 4 speed isn't the greatest, so yeah, you should re-gear. But get the engine checked out!


I agree with geeteeohguy, the 2:56 limited slip I had in my 68 Firebird, with 400 engine and TH400 transmission would smoke rubber if I stepped on it and it would also get me up around 140 on the highway (yes, I brought it up there one time) and I would be doing around 5000 rpm according to the hood tac! If your GTO is a dog with a 2:56, then it is something else.


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## AV68 (Aug 18, 2021)

I have 3:55's with a TH400 and its great around town, a 2 hour trip at freeway speed does wear on me though, but 99% of my use is around town cruise stuff so 3:55's are perfect
3:55's with the 4spd would be a great combo


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