# B.O.P. 10 bolt question



## danthepontiacman (Jul 5, 2008)

here we go again with yet another question regarding a mod i want to make to my tempest, i like my top end but i plan on adding air to the car, it has 2:56 gearing and acoding to my phs papers had it had air it would of had 2:59 gearing but i dont know where to even find gearign that high or if anybody makes it. i think chevys had 2:73 gears and i was wondering if A. anybody makes theme and B. will thay fit in my current chunk or or would i have to change that to? ive noticed the chunks you buy say what geas will work with each one so im wondering about the original one. the other thing im wondering is i keep reading contadicting info from diffrent places regarding if my rear is a 8.2 or a 8.5 so any help from you guys and girls would be great.:cool


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## 05GTO (Oct 6, 2004)

*8.2" rear end used 64-71 for the Tempest/GTO.*









*8.5" rear end used 70-81 GTO/Firebird.*​


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## geeteeohguy (Feb 2, 2008)

Dan, your 2.56 will be fine with AC. Most AC cars had 2.73, 2.93 or 3.08 gears. 2.59 is not an option and was not made for these cars. You can leave it as is or put 2.73 gears in your present carrier. For 2.93's thru 3.23's, you'll need the 3-series carrier. I'd leave it be if you like the way it drives now. I put 2.56 gears in the back of my '67, and in central CA, where it's pretty flat, I'm loving the 19+ mpg at 70-80mph I'm getting!


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## danthepontiacman (Jul 5, 2008)

ok thanks its a 8.2 i can tell nwo by the way the cover is shaped. well the phs showed the 2:59 in the gear lineup but idk maybe that was fo a full size car o something, i used ultimategtopicturesite.com's top speed calculator and 3:08 is to fare for my taste i liek haveing top end, with a 2:56 is like 150 mph and the 2:73 is like 140, i was just looking to inprove my take off a small potion while still keeping long legged gears in it. im glad to know if i deside to put the 2:73's in it that thay will go but the next question is who has theme? and will originals from a chevy work? ha dang what is your 67? and how you geting 19 mpg? what kinda carb and ignition are you useing? id kinda liek to get 18-20 on the highway here!


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## heyman (Jan 15, 2010)

Be easier to go out and find a rear out of a early 70-72 Monte Carlo they would give the 2:73 your looking for, and it would be a lot cheaper and better then swapping gears in your present rear, 2;56 vs 2:73"s you would notice the difference


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## heyman (Jan 15, 2010)

just for reference, that 38 Pontiac you see to you left, has 2:29 posi in it, 75 mph tach 2 grand, have like a 28 inch tire on the back, on paper the car should do like 190 at 5 grand, RIGHT, but on the highway have gotten 23 mpg


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## topfuel67 (Dec 23, 2008)

There are tons of cheap B.O.P. peg leg rear ends with the 2.93 gear in it. If your car is a 66, make sure to get a 64-66 (early 66) rear. 67 and up will bolt up, but its a headache. The 2.93 is a great rear for highway and take off. Also, do you have a th350? Its a direct fit over the 2 speed auto. The th350 gives you a first gear, where the 2 speed is similiar to a th350's 2nd and 3rd gear.


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## danthepontiacman (Jul 5, 2008)

ok cool and my 66 was amde late in the model year so do i still need the 64-66 one? cool i wasint awair monte carlos had that gearing but then again i know alot more about pontiac then chevys. its got the 2 speed auto and i know its a direct fit but i want to keep the car has original has i can so id kinda liek to keep the 2 speed. wow a 2:29 where the heck you find a gearing that high? would the 70-72 Monte Carlo 10 bolt mount or would i need to just use the gears out of it?


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## topfuel67 (Dec 23, 2008)

The tranny swap is so easy in these cars. You can easily find a nice running one for about $200 in the recycler, craigs list or even here. The swap could easily be done in a few hours. Keep the 2 speed tucked away. If you leave your current rear end you'll gain the low end gear of a 2.80-2.90 rear end and still have your 2.56 top end.


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## geeteeohguy (Feb 2, 2008)

Dan, I'm getting 19+ mpg hiway with the original 400 engine, turbo 400 trans, original Quadrajet carb, and original points distributor. Bone stock except for a set of 87cc 455 heads for lower compression (around 9:1). The 2:56 puts my RPM at 75 mph at 2450, and I'm turning 3000 RPM at 92mph. If the car stayed on the road, the theoretical top speed would be 158mph. It starts to float pretty good around 130, and the speedo pegs at 120. I don't think it's streamlined enough for 150+. With my old 3.55 gears in a '66 I had, it turned 3000 RPM at 60 mph!!!


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## Too Many Projects (Nov 15, 2008)

For the little difference in gearing you are talking the expense isn't worth it. Geeteeohguy dropped his almost a complete revolution to see a change of 550 rpm. You're talking .17 revolution with the 2.73. It isn't going to change the rpm more 70 which isn't going to net any mileage or performance improvement.
Spend your money on a more worthwhile and rewarding modification.:cheers


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## danthepontiacman (Jul 5, 2008)

yea thats why i want to keep highway gears, im trying to get it to be peppyer without doing much mods to it and keeping the highway gears so ill have a high speed top end that way at 70 when i go to pass somebody it just zooms but it already does that but it be nice to make it peppyer on takeoff, do you think the carb,cam and msd would be the way to go there? or just a msd o just a cam and Q-jet, my car once got 17 miles to a gallon with a bunch of trips to my grandmothes house witch is 10 miles away, surely with the small primarys on the q_jet i can get closer to 18 or 19 and my car already has 9.2 compeshion so i got it made there. yo realze how geat a milige that is you geting? i mean for a 60's midsize car (fullsize by todays standeds) with a v8 and that much power to do that, i think some fods got like 8 and some chargers got like 13 on the highway and you in something just has good geting almost 20


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## geeteeohguy (Feb 2, 2008)

Dan, one way to increase your performance "off the line" would be to mothball the 2 speed auto trans you have and install a three speed (turbo 350 would be fine). You would get a much lower ratio first gear, which would help your take-off , a close ratio shift to second gear, and when it hits third gear, the same killer top-end performance. Your fuel mileage would increase a little due to the better gearing requiring less throttle tip-in off the line. If I had a two speed GTO or Tempest (and I have had 'em), I would switch over to a three speed. That said, the two speed's are a strong, durable unit, and worth keeping with the car for value's sake.


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## Too Many Projects (Nov 15, 2008)

geeteeohguy said:


> Dan, one way to increase your performance "off the line" would be to mothball the 2 speed auto trans you have and install a three speed (turbo 350 would be fine). You would get a much lower ratio first gear, which would help your take-off , a close ratio shift to second gear, and when it hits third gear, the same killer top-end performance. Your fuel mileage would increase a little due to the better gearing requiring less throttle tip-in off the line. If I had a two speed GTO or Tempest (and I have had 'em), I would switch over to a three speed. That said, the two speed's are a strong, durable unit, and worth keeping with the car for value's sake.


This is THE single most effective mod you could do to improve performance while maintaining top end and fuel mileage. Adding the lower 1st gear is the same as lowering the rear axle ratio but you still have the benefit of the 2.56 in top gear. The TH 350 is a 2 speed with 3 gears instead of 2. It is dimensionally identical and bolts right in with no mods other than an appropriate shifter. There are thousands of them available and are a tough, dependable trans. With a mild shift kit, it would stand up to anything that 326 could throw at it, even if you built the 326 with the HO cam and 4 barrel. I know you've said you want to keep it original but this is a very smart, economical suggestion by geeteeohguy who has been around and repaired/modded them for many years. Put the original trans under the work bench and enjoy the 3 speed.:cool


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## 66tempestGT (Nov 28, 2009)

:willy::willy::willy:


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## danthepontiacman (Jul 5, 2008)

but the fact the car has its orginal engin and tansmission is what amkes it diffrent i cant take that away from it but anything i can do without emoveing the original engen or tanny will be ok i just like haveing something diffrent, if i wanted to go with what most people go with i would just drop a 400 in it with a nice 6 speed behind it but im thinking ill try a Q-jet and maybe a came andor the msd with the multiple spark thingy and see if it will give it a kick. if the dang gearvenders overdrive wasint so high id put 3:55 gears in my car and put the od behind the 2 speed and still be able to maintain my top endand then i could keep my 2v but still put the msd and cam in it and i would have something diffrent but im not paying $2500 for that when i can get a od gm tansmission for $1200 thats crazy


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## danthepontiacman (Jul 5, 2008)

the two speed is a must keep but any carb cam gearing or ignition stuff i can do would be great! its just the dan thing has only had one rebuild in 44 yeas and is always shifts smooth and the car has never ever been babyed the hole time its been guned and everything and the tansmission fluid is so clean you can barely see it on the stick


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## geeteeohguy (Feb 2, 2008)

:willy:


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