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Old 08-04-2010, 08:57 PM
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choosing a pontiac rearend gear?

my 72' firebird has a 2.78 gear in it, i want to come up a little bit just to get a little more umph, what would be a good gear, but also let me still drive on the highway at 65 in a reasonable rpm range?

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Old 08-04-2010, 09:10 PM
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Depends on if you have a 400 or 455 and how radical the engine is. The 400 can make good use of a 3.23 up to a 3.73 on the street, I'd not use more than a 3.23 for a 455 street machine unless max acceleration was the object.
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Old 08-04-2010, 11:06 PM
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I vote for 3:42's Right between 3:23 (good milage) and 3:73's (not so good).
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Old 08-04-2010, 11:14 PM
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Currently its a 350 but im going to put a 455 in it. So your thinking about a 3.23?
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Old 08-04-2010, 11:39 PM
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Quote:
Originally Posted by AndersonRacing44
Currently its a 350 but im going to put a 455 in it. So your thinking about a 3.23?
I had a 12-bolt w/3.31's and a decent 455 Pontiac in a '81 Camaro and it was the best all-around street machine I've ever owned. Not the fastest, but the most flexible. Ran 12's w/the shifter left in "D", shifting out around 4800 RPM. Idle around all day in heavy traffic w/o a whimper. Used a 4777 Holley. Regular fuel. Could have welded the hood shut.

So, w/your 8.5" corporate rear end, the 3.23's w/the '55' engine would be my choice.
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Old 08-05-2010, 06:25 AM
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The 3:23's were standard with the 400 GP's in the late 60's and early 70's.
They kind of made up for the lower numerical ratio of the TH400 first gear compared to the TH350. Their good all around gear's for either the 350 or 455.
I also had a 73 Lemans that came with a 350/th350 and 3:73's and later on switched the 350 for a 455 with the same TH350 and gears. You could defiantly tell the difference with 105 more cu. in. in the power dept. and the fuel mileage. 15 mpg was the best I could get even with a little 600 Holley and headers. Unless your going to the drag strip every weekend I would stick with the 2:73's or 3:23's for street/hwy use.

After my last post I had to re-think the 3:42's as I had those in a 65 cat 2+2
with 4 speed Muncie and 421 tri-power. They worked very well but that was with a manual tranny.
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Old 08-05-2010, 07:38 AM
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Man, how I loved the Big Pontiacs- especially the Bonneville.

My Father had a '61 Bonneville 421 4-speed. Instead of dual fours, it had a Tri-Power along w/a McKellar #11 cam and 11:1 CR.

By the time the '63 13:1 CR big valve 421 engines were out, our '61 was pretty tame (on paper, at least), but actually ran decent for it's size. It never had enough rear gear, but because it was a DD (EVERY day!), that was a price that was paid.
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Old 08-05-2010, 08:22 AM
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I know what you mean Cobalt. The 65 I had was rated at 376hp and even hot rod mag claims that was under rated. I wooped on a 69 roadrunner 3 times in a row once. Poor guy just couldn't understand why he was getting beat after having it dyno'd at 400 hp by a big ole poncho. He came over to my pit looking at the car and asked me where the 4 sp came from. He had no clue! Even when I opened the hood the wow factor set in with the 3- 2's. he couldn't believe that it was stock and that I had to have something in there I wasn't saying. He was really pi**ed off.
That's one car I let get away I wish I had back.
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Old 08-05-2010, 10:42 AM
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69 Firebird 400

If you have a 421,428 or 455 engine, a 3.42 is the best compromise between acceleration and cruising with either an automatic or manual transmission. The so called "anti-pump up" hydraulic lifters will pump up and float the valves about 4700 RPM and the engine will fall flat on it's face when the engine RPM is raised in relation the MPH. Solid flat tappet cams will raise the RPM range before valve float, but solid lifters require engine and oiling modififations that are not for part timers. In 1963, Pontiac installed a 3.42 rear end in all 421 Pontiacs as standard equipment, regardless wheather the transmission was a manual or automatic. All other gear ratios were optional for 1963 Pontiacs equipped with a 421 engines.

Example:
In 1971, I broke the 3.36 open rear end and bent the driveshaft in my 1969 Firebird 400. The Pontiac Zone Office in Dallas approved the replacement of the rear end gears, gear case and driveshaft with a 4.33:1 ratio, 4-pinion Safe-T-Track gear case, and a new driveshaft. What is unusual is that the Zone Office manager knew I was drag racing the car. The 3.36:1 rear end broke soon after mounting a pair of Goodyear 11" wide x 30" tall 9.00 x 15 wrinkle wall slicks. After the dealer installed the 4.33 gears, STT gear case and driveshaft, I found that the OE hydrulic lifters floated at 4500 RPM in every gear and the engine fell flat on it's face.

A month after the dealer replaced that equipment, I installed a Crane Z300 solid flat tappet camshaft with Chevy solid lifters and kissed the 50,000 mile drive line warranty goodbye. After blowing the stock clutch disc, I replaced it with a Schieffer 10-1/2" Rev-Loc clutch and a Schieffer bonded and riveted disc. I finally got my Firebird 400 in the low to mid-13s (avg. 13.30) after replacing the OE valves and valve springs with BB Chevy L88 valve springs and Ram Air 4-valves in 1969 #48 Ram Air III heads and 428 HO exhaust manifolds. Unfortunately, I spun-out OE rod bearings on two occasions trying to drive the pontiac engine like it was a Chevy. In the last rebuild, I replaced the Crane Z300 cam with a Melling Ram Air 4 hydraulic lifter cam, using the now extinct Pontiac-Oldsmobile Melling JB-951R Ram Air 4 limited travel hydraulic lifters. I also replaced all the OE cast iron rods with resized and polished stock cast iron rods using ARP rod bolts. The hydraulic lifters and the ARP rod bolts solved the rod bearing problems.

The moral of that story is that the end gear ratio will determine what other modificatins to the engine and drive line will be required.
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Old 08-06-2010, 12:23 AM
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thanks for the replys!
yea 455, stock cam, and a quadrajet from a 454 BBC

I just happen to have a ford 9" with AFCO rear disc brakes on it laying around so i was thinking that since I used to work on super stocks that all had them. plus gears are everywhere for those.

also its a M-22 4-speed with a vintage McCloud pressure plate and lightweight clutch disc.
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Old 08-06-2010, 05:23 AM
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Heat

If you install lower gear ratio such as a 3.90, your engine will run hotter at normal highway speeds. Pontiac called 3.90, 4.11 and 4.33 rear end ratios a "Performance Axle" option and the cooling system was not capable of cooling the engine if the vehicle was equipped with those ratios. Those gears were meant for drag racing and not for "freeway flying" or sustained high speed. My '63 Pontiac Catalina 421 HO had 3.64:1 cogs with a 455 CI engine. The engine was the original 421 HO block bored and stroked using a 455 crank. I never had a cooling problem idling in summertime city traffic or drigning a 80 MPH on the highway, however, my Catalina did not have A/C. A great modification to the heads and block in order to prevent overheating is to drill two 5/16" steam holes in each block deck between the center cylinders with two matching holes in each head using the head gasket as a template. Drilling the steam holes was a NASCAR modification because Pontiac never did it to the production engines.

I never addressed the overheating heating problem with my '69 Firebird 400 after I changed the rear gears from 3.36 to 4.33. For that reason, engine overheating prevented driving the Firebird on a public road or highway at a sustained speed over 45 MPH in the summer. I had to trailer the Firebird to sanctioned drag strips. Which as it should be I suppose.
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Old 08-06-2010, 06:35 AM
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Quote:
Originally Posted by AndersonRacing44
also its a M-22 4-speed with a vintage McCloud pressure plate and lightweight clutch disc.
That's cool.

But you know- truth be told, the strong suit of a Pontiac engine is it's ability to make a good amount of torque over a relatively wide RPM range. This means to us that if not for the difference in strength, a wide ratio box would be better suited to a Pontiac engine unless it is highly modded to run w/a narrow power band, IMHO.

Also, the wider gear spread allows a milder rear gear to be used, w/o any compromise to acceleration through the gears.
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Old 08-06-2010, 07:28 AM
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McLeod clutch

I had a McLeod 40 lb. steel billet flywheel with the starter ring gear moved 0.700" rearward and a 11" 3-lever style pressure plate behind my 455 in the '63 Pontiac Catalina. I only used a McLeod 11" 3-lever Borg and Beck style pressure plate because a 11" diaphragm pressure plate would hit the OE cast iron bellhousing. Those OE pontiac bellhousings were designed for 10.5" pressure plates. A 10.5" diaphragm pressure plate would fit with not problem.

I installed a 2,350 lb. McLeod 3-lever 11" Borg and Beck style pressure plate for a Chrysler Hemi because of the lower pedal effort. All high performance GM versions of the Borg and Beck 3-lever style pressure plates are 3000 lb. and 3200 lb. ankle breakers. That kind of brutal clutch pressure is totally unecessary except for a dump truck and only serves to wear out the clutch linkage and your left leg in a passenger car. If a 2,350 lb. clutch is good 'nuff for a 426 Hemi, it is good 'nuff for a Pontiac.

I found that lower static clutch pressure permits faster and smoother power shifts when using a Borg-Warner or Muncie 4-speed. Those are not the smoothest shifting transmissions even with a Hurst Competition Plus shifter. One missed power shift with the accelerator nailed to the floor can cause expensive engine damage. If I had to lift my right foot to power shift, the tri-power linkage would cause the engine to lose 500 to 1000 RPM before I could get back into the carburators. I prepared a 750 CFM Edelbrock AFB 4-barrel on a vintage Edelbrock 4-barrel intake manifold. That carburator would have had much better performance than a old-school Tri-power with progressive linkage. Unfortunately, never got a chance to get a time slip with the 750 CFM 4-barrel carburator before I sold the car a few months ago.
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Old 08-06-2010, 07:37 AM
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They had a medical name for high pressure clutch users, it was called "clutchinitis" where the left leg was noticeably larger the right one!
After reading that, I did the math and put a real heavy return spring on my brake peddle.
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Old 08-06-2010, 08:26 AM
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Springs

My '63 Catalina was equipped with the factory HD clutch linkage that was designed for the factory HD Borg-and Beck style 3-lever clutch. However, the OE 3-lever HD pressure clutch in 1963 was only rated at 1,800 lb. The aftermarket high performance 2,800 and 3,200 lb. B&B pressure plates are descendants of the old GM HD truck clutches that are designed for better holding power at low RPM. .

The 1963 Pontiac HD clutch and clutch linkage option included a heavy "over-center" assist spring under the dash. However, when I first tried a 3,200 lb. Zoom 3-lever clutch with the OE HD clutch linkage, the adjustable pushrod broke in half and the z-bar lever broke off. I reinforced the Z-bar as you were supposed to do,sinstalled Hurst hardened steel shifter bushings in the z-bar linkage holes and installed a Mr. Gasket HD push rod designed for a 55-57 Chevy. I got rid of the Zoom 3,200 lb. 3-lever "truck" clutch. I would have certainly used a high-cone diaphragm pressure plate if the 11" version of that design would have fit in the bellhousing. A high-cone diaphragm pressure plate has better holding power than a 3,200 lb. Borg and Beck pressure plate. I successfully used a 11" Hays high-cone diaphragm pressure plate in my '66 GTO with a 10.5" Zoom 5-spring bonded and riveted clutch disc. (The Hays clutch disc hub springs and part of the lining material fell out on the floor when I removed the clutch)

The small disc/large pressure plate set up worked even better than I expected. The 10.5" clutch disc used with a 11" pressure plate deforms the disc just like grabbing a womans breast. The smaller disc has less centrifugal inertia and has a smoother release for power shifts.

In 1971 -73, I had a Zoom 3,200 lb pressure plate and it worked fine in my '55 Chevy 2-door sedan with a 455 Pontiac engine. So, I thought that was the clutch to use in my '63 Catalina. It appears to me that the '55 Chevy clutch linkage was stronger than the original HD clutch linkage in the '63 Catalina. I never had a problem with the Chevy linkage but I could not sit at a traffic light for 3 minutes with the clutch depressed so I had to shove it out of gear every time I stopped.
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