66 GTO; Change Rear End Ratio vs Overdrive

[Robert G. Smits]

66 GTO 389, 4 speed with 4.11 rear end ratio.  Would like to turn this into a better touring car.  Considering changing the rear end verses going to a Gear Vendor.  Thoughts and recommendations appreciated.  Looking for the best solution, not necessarily the cheapest.  Thanks

[Terry Bond]

Unless you buy a rear end assembly that's already been rebuilt and guaranteed, you will need to disassemble and check everything anyway.  Once you start unbolting things, you'll end up with a lot of "might as well" things you should do while it's apart.  I recommend just replacing the gear set and carefully inspecting everything, that way you'll know it's done to your standards and meets your requirements.  Is it a Safety-trac (posi) rear end?  I bet your 4:11 is a replacement gearset anyway.  My 67 is a 3:55 and that was special order.  Share a pic Bob, sounds like a great car.

Terry

[padgett]

AC cars came with a 3.23 & is a reasonable touring gear. Or find a Trimec and save the fragile (small shaft) Muncie.

 

I have a 3.55 4 pinion in the Judge and keep looking for another gear at anything over 50.

[Robert G. Smits]

I will try to post a photo.  This is a nicely done (clone), 1500 miles since restoration and engine rebuild,  Headers and 2.5" exhaust with H pipe, 068 cam.  I found this one while looking for a real one and couldn't pass it up as I was looking for a driver with no interest in showing it.  Scheduled for Vintage Air this winter

Edited September 13, 2019 by Robert G. Smits (see edit history)

[Robert G. Smits]

I have the same experience as padgett.  I start looking for a higher gear around 45 and at 60 i'm no longer having fun.  Does anyone have any experience with a Gear Vendor in a muscle car?  Back in the 90's I towed all over the country towing a Classics using a 30 ft Airstream, 454 with RV cam, Banks headers and Gear Vendor.  I loved it

[Pfeil]

I'm the original owner of this 69 H-O LeMans. In 1992 I built the car over for Grand Touring. ( brakes,suspension and steering modified, engine- a H-O 455 with a 068 cam. )  I run a 10 bolt 3.25 Safety Track. At 70MPH I'm at 3100-3200 RPM which is way high rpm for cruising. I also have a 2.56 ten bolt Safety Track and a 3.08 ten bolt Safety track. These rear ends were cheap to pick up at the local Pick You Part and relatively inexpensive to rebuild. Remember this; these BOP 10 bolt rear ends are different from the Chevrolet 10 & 12 Bolt types. They are stronger and have a larger diameter axle than the Chevy. Rear ends are easy to swap out in about twenty minutes. The LeMans while not built for drag racing runs a 12.37 @ 113mph with the 3.23, and still a respectable mid-low 14 second quarter mile with the 2.56 Posi. Times may be different but most people can't tell by the seat of the pants, in fact some people think the 2.56 is faster because just when they think it's wound out at 105MPH I shift to third gear. The gratifying part about the 2.56 is it's 24MPG car on the HYY. BTW the car weighs 4050

 

Edited September 14, 2019 by Pfeil (see edit history)

[padgett]

You realize you are heretical ? My 1972 tow wagon had a 3.07 "economy" axle. 3000 rpm at 70 was common then thanks to short 14" tires. What you really have is a resto-mod already.

 

Since my 3.55 is a 4 pinion posi, think I'll keep it but would like to swap in a five or six speed manual with a lot of OD in top. 2000 rpm at 70 is a sweet spot for a gas engine with lotsa torque.

[cheezestaak2000]

back in the day, some fool challanged me in my 1965 GTO. we came up to a stoplight and i nailed it. went about 50 feet before i came to a sudden stop. towed it to the shop and removed the diff cover to find all of the bolts in the 4:11 posi unit resembling poorly made pretzels. $100 bucks later, i had a tempest rear assembly with 3:06 gears in there.took all of an hour to do. i've done differential overhauls and they are only a little less painful than getting poked in the eye with a sharp stick. had some amazing top speed after that swap

[Robert G. Smits]

Thanks for all the replies.  Because of the 1st gear ratio I am afraid that a 2.56 to 3.06 ratio will require excessive clutch slippage off the line.  Would work much better with an automatic in my opinion.   Any thoughts on a Gear Vendor?

[padgett]

After assembling a Corvair transaxle on the back of a trailer at the track (removed all synchros and made it a crash box, time was limited and spares lacking) any 10 or 12 bolt GM is a piece of cake, even a 4 pinion posi.

 

Most common sudden stop was the lockscrew in a 12 bolt shearing off.

 

ps you mean you have a close ratio Muncie - 2.20:1 1st ? That should be a large shaft. M21 (M22 was also close ratio but later. Was known as the "rock crusher" not so much for strength but the straight cut gear SOUNDED like it was crushing rocks. I'd still just go for a Tremec or Richmond with a long OD top.

Edited September 13, 2019 by padgett (see edit history)

[Pfeil]

19 hours ago, padgett said:

You realize you are heretical ? My 1972 tow wagon had a 3.07 "economy" axle. 3000 rpm at 70 was common then thanks to short 14" tires. What you really have is a resto-mod already.

 

Since my 3.55 is a 4 pinion posi, think I'll keep it but would like to swap in a five or six speed manual with a lot of OD in top. 2000 rpm at 70 is a sweet spot for a gas engine with lotsa torque.

 

 It's not a resto mod. It's a street car that's been modified so that I can drive it on the track. They are known a Grand Touring cars. With just a few parts changes the car can pass as stock even though internals, especially steering and suspension,  most of which come right out of the GM parts bin anyway appear to be your every day Pontiac GTO, LeMans or Tempest parts. 

Edited September 13, 2019 by Pfeil (see edit history)

[Pfeil]

4 hours ago, Robert G. Smits said:

Thanks for all the replies.  Because of the 1st gear ratio I am afraid that a 2.56 to 3.06 ratio will require excessive clutch slippage off the line.  Would work much better with an automatic in my opinion.   Any thoughts on a Gear Vendor?

 

If you would like to go with a 2.69- 2.93 rear, you can get yourself a wide ratio 4 speed. They are cheaper than the ever so in demand close ratio. The wide ratio has a deeper 1st.  and can easily be rebuilt. That would be the cheapest and fastest way to solve your problem.

[Robert G. Smits]

Thanks again for the replies.  Pfeil I like your solution.  

[padgett]

Guess I am confused, why not just get a five speed with .67 5th and be done with it.

 

Is this a good place to mention that back in the first fuel crisis a common conversion for a Goat was to add a BW OD to a Saginaw 4-speed, just needed to drill one hole.

[Pfeil]

5 minutes ago, padgett said:

Guess I am confused, why not just get a five speed with .67 5th and be done with it.

 

 

 I guess you are confused because you already said this in your first post.😉

[Marty Roth]

9 hours ago, Robert G. Smits said:

Thanks for all the replies.  Because of the 1st gear ratio I am afraid that a 2.56 to 3.06 ratio will require excessive clutch slippage off the line.  Would work much better with an automatic in my opinion.   Any thoughts on a Gear Vendor?

 

Bob,

 

Considering the torque and horsepower of your car, in my opinion neither the 2.56, nor the 3.06 would require excessive clutch slippage, and highway driving pleasure would be much improved. I cannot comment on the Gearvendor unit, but seriously considered it for the 1914 Buick before having Rempco make a 3.31 ring and pinion to replace the factory 4.08. The Buick never required sl;ipping the clutch, and is far, far less powerful than your "Goat". 😉

 

PS: with new differential gears there are far fewer parts to fail, and you can cruise those West Texas interstates with the big boys.

 

See you "down the road".

[padgett]

OK fagedaboudit.

[Pfeil]

45 minutes ago, Marty Roth said:

 

Bob,

 

Considering the torque and horsepower of your car, in my opinion neither the 2.56, nor the 3.06 would require excessive clutch slippage, and highway driving pleasure would be much improved. I cannot comment on the Gearvendor unit, but seriously considered it for the 1914 Buick before having Rempco make a 3.31 ring and pinion to replace the factory 4.08. The Buick never required sl;ipping the clutch, and is far, far less powerful than your "Goat". 😉

 

PS: with new differential gears there are far fewer parts to fail, and you can cruise those West Texas interstates with the big boys.

 

See you "down the road".

 

Uh Marty, it's "TIGER". And to a Pontiac guy "GOAT" has two meanings. 1. a derogatory word to a Pontiac owner. 2. Something a Tiger would probably eat.😉

Edited September 14, 2019 by Pfeil (see edit history)

[Pfeil]

7 minutes ago, padgett said:

OK fagedaboudit.

You REALLY are confused.

[Marty Roth]

9 hours ago, Pfeil said:

 

Uh Marty, it's "TIGER". And to a Pontiac guy "GOAT" has two meanings. 1. a derogatory word to a Pontiac owner. 2. Something a Tiger would probably eat.😉

 

 

No disrespect intended,

I don't recall hearing that before.

I've had several Pontiacs - and an Oakland,

and my brother had an almost brand new 1964 GTO convertible-

389, Tri-Power, Fenton Mags, Wide Ovals,

it was silver with a black convertible top-

I was really disappointed when he sold it just before signing up with the Navy Band, and didn't offer it to me first.

[alsancle]

4:11 is awesome for drag racing and horrible for driving around in.   I was running factory 3:55 and that was fine around town but not great on the highway.

 

Swapping in the 15 inch wheels in back with oversized tires will help.

Edited September 14, 2019 by alsancle (see edit history)

[alsancle]

GOAT vs Tiger?    As the proud owner of a 69 GTO 400/4 speed Vert in HS and College (I wanted the 66)  at well as a 68 we always referred to them as GOATs.   Have never heard anyone call them a Tiger.    Or do I misunderstand the conversation?

[Buffalowed Bill]

Going to 15" wheels is about the equivalent of gearing up one gear set. Even if it is not intended to be a permanent arrangement it would give you a good idea of how you would like the next gear up. 

[Pfeil]

1 hour ago, alsancle said:

GOAT vs Tiger?    As the proud owner of a 69 GTO 400/4 speed Vert in HS and College (I wanted the 66)  at well as a 68 we always referred to them as GOATs.   Have never heard anyone call them a Tiger.    Or do I misunderstand the conversation?

 

 In 1959 my dad placed a SO order on a very special 59 Catalina. 389 4 bolt main solid lifter Tri-Power hand built in the Pontiac toolroom to be raced in AS/A. This engine was one of the type of engines that was built for NASCAR teams and Drag racers. Later on I got my IHRA license at the age of 14 I raced the car in FS/A. I remember when the production 64 LeMans GTO's started showing up at the drag strip and street races. The term GOAT seemed to come from the MOPAR, but later all the opposition brand guys used it in verbal jousting about this new Pontiac. In this jousting of the new kid on the block ( the opposition) they switched the letters around to inexactly say GOAT. This was meant to rattle the GTO owner as in the old term "getting someone's goat". Unfortunately that moniker stuck with the GTO. For three years Pontiac advertising struggled with GTO Tiger theme to make sure it's nickname was the tiger. Uniroyal tire made special red line tires for the GTO and the tires were called TigerPaws. Later the term TIGER was applied to all Pontiac's which you can see in the last picture I posted with a GTO next to a Pontiac Catalina 2+2 

 

Just a FYI, The first time the word Tiger was ever mentioned was in a 1963 Pontiac Tempest add. In 1963 Pontiac re-cored the 389 engine to make it lighter, Pontiac also came out with a small bore version of the 389. The engine was called a 326. In 1963 the engine was really a 336, in 1964 it became a true 326. Anyroad this add for the Tempest had a picture in the middle of the street with a Tempest coming at you and one going away in the opposite direction. One of the Tempest had the 195.5 " ( half a 389-slant 4 engine) the other with a 336. The add said something like " can you tell which Tempest is the TIGER.

 

BTW this verbal jousting was not special to Pontiac guys. The nicknamed for FORD was " Found on the road Dead " and

"Fix Or Repair Daily".

Edited September 14, 2019 by Pfeil (see edit history)

[alsancle]

You learn something new everyday.   My HS days were 78-82  and Goat was never used a a pejorative.    The Tiger thing did not seem to stick.

Edited September 14, 2019 by alsancle (see edit history)

[padgett]

The correct pejorative was "Garbage Truck Option". And don't forget "put a tiger in your tank" (the loop attached to the gas cap).

[Pfeil]

19 minutes ago, padgett said:

 (the loop attached to the gas cap).

 

Did it now??? That would be tail dragging.

[Pfeil]

43 minutes ago, alsancle said:

You learn something new everyday.   My HS days were 78-82  and Goat was never used a a pejorative.    The Tiger thing did not seem to stick.

Ah, The young ...so sad. Pontiac advertising did their best;

 

 

Pontiac GTO Tiger Under the Hood Commerical 1965 - YouTube

 

 

1966 Pontiac GTO "Tiger" TV Ad - YouTube

 

 

1965 Pontiac GTO Tiger Commercial - YouTube

 

 

[misterc9]

In 1970 or so ESSO had a promotion " Put a tiger in your tank " to promote their gasoline. They handed out tiger tails to hang out  of your gas tank.

[Pfeil]

20 minutes ago, misterc9 said:

In 1970 or so ESSO had a promotion " Put a tiger in your tank " to promote their gasoline. They handed out tiger tails to hang out  of your gas tank.

They bought all the leftovers for when G.M.'s President made Pontiac give up the Tiger theme after 1966, They also made Pontiac give up it's Tri-power, a symbol of Pontiac power that Pontiac had used since 1957.

Pontiac's new GTO theme for 1967...……"THE GREAT ONE" 

Edited September 14, 2019 by Pfeil (see edit history)

[padgett]

Well sorta. Rochester was pushing the QuadraJet as the answer to everything. Originally 750cfm later there was an 800cfm variant with larger primaries.. And the tiny primarys and metering rods gave a lot better mpg than the 2GC (center carb) of the tripower. Besides the "small center" (pre-1966) was only about 170 cfm while the 1966 only used the large center and properly tuned gave about 900 cfm.

 

Now I know the C&D comparison test showed the QJ outperforming the tripower but it was partly 400 vs 389 and partly Milt being under strict instructions for the QJ to be faster. Believe it or Don't.

 

ps the tails were available in different lengths. Mine is the long one. Have several complete A & B body tripowers (might need linkage)…. somewhere.

Edited September 15, 2019 by padgett (see edit history)

[JACK M]

Back to the original question.

Does a Chevrolet manual tranny work on a Pontiac like this? It would seem to me that they would but what do I know.

If so, look into a five speed from an S-10, They may not be real stout but you did say on the cheap.

[JACK M]

My apologies, I reread and discovered that I misread the "not the cheapest" part.

I still suspect some GM guys here would like to comment.

[Pfeil]

14 hours ago, padgett said:

Well sorta. Rochester was pushing the QuadraJet as the answer to everything. Originally 750cfm later there was an 800cfm variant with larger primaries.. And the tiny primarys and metering rods gave a lot better mpg than the 2GC (center carb) of the tripower. Besides the "small center" (pre-1966) was only about 170 cfm while the 1966 only used the large center and properly tuned gave about 900 cfm.

 

Now I know the C&D comparison test showed the QJ outperforming the tripower but it was partly 400 vs 389 and partly Milt being under strict instructions for the QJ to be faster. Believe it or Don't.

 

ps the tails were available in different lengths. Mine is the long one. Have several complete A & B body tripowers (might need linkage)…. somewhere.

People with Tri-power really didn't care about mileage especially since gas was so cheap and if they were concerned they could have bought a Tempest with a 1bbl. OHC SIX.

   The G.M. ( Ed Coles ) ban on multi carburetion hit Pontiac hard. Oldsmobile had finally got it's 3- 2bbl. setup going for 1966. Olds fans lost the J-2 option after 1958 and now after the real car guys at Olds finally got their way with the stuffy old Olds hierarchy the 14th floor ( Ed Cole and his peers ) took it away from them. Buick lost it's 2X4 system as well. Everyone knows Ed Cole has a couple of his baby's over at Chevrolet and guess what? Chevrolet was allowed to keep multi carburetors on the 427 Corvette and also his beloved Corvair. What a corporate political move. Bunkie Knudsen, Pete Estes and John DeLorean ALL had problems with Cole.

 

I have also seen the Pontiac Tri-Power test. But if you perform a apples to apples test ( not a 389 tri-Power against a 400 QJet ) the Tri-power comes out ahead with a 400 against a 400.And I have seen that test.

Pontiac enlarged the 389 to 400 and the 421 to 428, change the valve angle and went to open combustion chambers, straighten the intake runners and install larger valves to get the same HP. THAT's HOW THEY MADE THE SAME HP as the 389 Tri-Power with a 400.

Edited September 15, 2019 by Pfeil (see edit history)

[padgett]

GM always played games with HP ratings. In your example the tripower Corvette with solids was rated at 435 hp. But the "for racers only" single quad  L88 was rated at 430 (5 hp less just like the Z28 and the SS-350). In reality the L88 was more like 550 hp. And then in 1967 Pontiac had three different ratings for the same 400 depending on whether in a Firebird, a GTO, or a 2+2.

 

For GM the magic words were "not available with AC" for a really interesting engine.

 

ps in 1985 I was getting 22 highway mpg from a highly tuned SBC with dual quads, at least that is what my Prince On-Board Computer said.

 

MBATR the four speed Muncie bolted the same way (4 bolts) for all GM lines. What was different was the number of splines on the input shaft where it engaged the clutch disk and the bell housings depended on the engine. And yes the S-10 had a five speed but AFAIR the max torque was much less than even the 305 V8, is another item I have somewhere (think I know which pile though).

[Marty Roth]

14 minutes ago, padgett said:

ps in 1985 I was getting 22 highway mpg from a highly tuned SBC with dual quads, at least that is what my Prince On-Board Computer said.  

 

The computers in our 2000 7.3 Diesel Excursion, and the 2006 Avalanche 8.1L always lie.

WE have the correct size tires,

and the speedometers and odometers on both are dead-accurate with our Garmin GPS,

yet both claim 14 - 18% better mileage than my carefully calculated numbers show.

This has been verified, not over a sigle tank, but over many tens of thousands of miles.

Numbers of actual miles driven, divided by actual gallons used =  true MPG

Edited September 15, 2019 by Marty Roth (see edit history)

[Ben Bruce aka First Born]

On 9/12/2019 at 4:32 PM, Robert G. Smits said:

66 GTO 389, 4 speed with 4.11 rear end ratio.  Would like to turn this into a better touring car.  Considering changing the rear end verses going to a Gear Vendor.  Thoughts and recommendations appreciated.  Looking for the best solution, not necessarily the cheapest.  Thanks

 

 Robert, I don't have as much power as you. Having said that, here is my experience.   My 1950 Buick came with 4.10.   I changed to a 3.36.  It could still use a higher ratio for hwy.  In town driving sucks!  If I had it to do over,  and as you have said, cost matters not, an overdrive of some sort would have been used.  There should be several options for the Pontiac.

 

  Good luck.

 

  Ben

[JACK M]

12 hours ago, padgett said:

MBATR the four speed Muncie bolted the same way (4 bolts) for all GM lines. What was different was the number of splines on the input shaft where it engaged the clutch disk and the bell housings depended on the engine. And yes the S-10 had a five speed but AFAIR the max torque was much less than even the 305 V8, is another item I have somewhere (think I know which pile though).

 

Then I suggest a Tremec, Pretty sure they can supply bolt on and up to six speeds.

I have their suggested T-5 behind a 472 cid 525 hp crate Hemi and have had zero problems.

I say suggested because I make tons of torque and they advised that this one will handle it.

Sounds like you may have to swap out a clutch disc.

[alsancle]

How about a hone drive?  That would be period correct!

 

http://hone-o-drive.com/hone-o-drive/

[carbking]

17 hours ago, Pfeil said:

P

 

I have also seen the Pontiac Tri-Power test. But if you perform a apples to apples test ( not a 389 tri-Power against a 400 QJet ) the Tri-power comes out ahead with a 400 against a 400.And I have seen that test.

Pontiac enlarged the 389 to 400 and the 421 to 428, change the valve angle and went to open combustion chambers, straighten the intake runners and install larger valves to get the same HP. THAT's HOW THEY MADE THE SAME HP as the 389 Tri-Power with a 400.

 

Tests often show what the tester wishes to show; and that is certainly true with the tripower.

 

Pontiac paid Carter to sabotage the AFB on the mid-60's Pontiacs in order that the standard 4-barrel engine would not out run the more expensive tripower!

 

Of course, the tripower wins the "open hood racing" contests until such time as one looks at a dual quad  

 

As far as the original gear question; not my ballpark, no comment.

 

Jon.

Edited September 15, 2019 by carbking (see edit history)