276 rear gear

Brian W · 2022-07-12T15:43:32-0400

Hello everyone ,
New guy here . Im new to the Hellcats, and pretty much any drive trains newer than 1990. Question for the masses. Ive picked up a low mileage drivetrain out of a 2017 , has a mild up grade with pulleys and injectors. Supposed to be about 800 hp.It has the 8 speed automatic transmission. Anyway im putting this in a 71 Roadrunner. My question is how well do you think a 276 rear gear ratio will work for this ? My understanding is it is a 262 from the factory. I dont see a 262 available for a 8.75 rear end. I want to be able to drive this everywhere reliably . Any help would be appreciated. Thanks

Xylander · 2022-07-12T16:03:47-0400

The difference between a 2.62 and a 2.76 is very minor. Your actual final drive ratio is also going to depend on your tire size. Lots of classic muscle cars run tall sidewalls, if that's the case, then your final ratio is going to be lower than a 2.62 anyway.

NoScat · 2022-07-12T16:28:57-0400

Brian W said:
Hello everyone ,
New guy here . Im new to the Hellcats, and pretty much any drive trains newer than 1990. Question for the masses. Ive picked up a low mileage drivetrain out of a 2017 , has a mild up grade with pulleys and injectors. Supposed to be about 800 hp.It has the 8 speed automatic transmission. Anyway im putting this in a 71 Roadrunner. My question is how well do you think a 276 rear gear ratio will work for this ? My understanding is it is a 262 from the factory. I dont see a 262 available for a 8.75 rear end. I want to be able to drive this everywhere reliably . Any help would be appreciated. Thanks

Will be just fine. Can imagine you will have lots of fun opening the hood on your car to reveal that motor. Guarantee you will hear “I wasn’t expecting that!” Many times!

SickToo · 2022-07-12T17:19:29-0400

All depends on tire. I would go with 3:23’s and a 29.5-30” tire. Your car is 1000 pounds lighter than hc but unless you spent boxes of cash on suspension/aero it’s not gonna be super stable at 200 mph. Where you want to go that fast anyways?

MJS73 · 2022-07-12T17:27:08-0400

It probably had a 2.76 open rear end from the factory if it had a 489 case 8¾". Get a 3.55 Sure Grip and add a Gear Vendors overdive. That's what I did in my '73 Challenger.

moparjim · 2022-07-12T17:28:53-0400

The car will be fine with the 2.76 gears.
You won't need more gear as that will just make you crazy looking for traction. Especially if you are keeping the 8sp . If not then yes add more gear.

SickToo · 2022-07-12T17:40:52-0400

I never saw a 8 3/4 come with that ratio and posi from the factory

Just throw a good 323 pumpkin in it. Doesn’t have to be 489 case. 742 is fine. Prolly never break 741 on street but I would stay away regardless

sleeper_redeye · 2022-07-13T01:48:39-0400

Pics of the 71 please

NoScat · 2022-07-13T02:00:49-0400

Vezconsumer said:
Pics of the 71 please

1970 but my birthday is November…

MJS73 · 2022-07-13T14:43:03-0400

SickToo said:
I never saw a 8 3/4 come with that ratio and posi from the factory

Just throw a good 323 pumpkin in it. Doesn’t have to be 489 case. 742 is fine. Prolly never break 741 on street but I would stay away regardless

You're right, there was no 2.76 Sure Grip, it was an open rear end.

Brian W · 2022-07-13T16:36:15-0400

SickToo said:
All depends on tire. I would go with 3:23’s and a 29.5-30” tire. Your car is 1000 pounds lighter than hc but unless you spent boxes of cash on suspension/aero it’s not gonna be super stable at 200 mph. Where you want to go that fast anyways?

I dont need to go 200

Would like it to be a nice street fighter, but able to drive it where ever I would like to go .

Brian W · 2022-07-13T16:41:08-0400

MJS73 said:
You're right, there was no 2.76 Sure Grip, it was an open rear end.

Actually I would need to check the fender tag to see what is in the rearend. Im only saying 276 because the gear set is available and I know the HC has the 262 in it

Brian W · 2022-07-13T16:45:06-0400

Vezconsumer said:
Pics of the 71 please

Doesnt look like much right now, just put quarters on it . Car is stripped and in primer without the front end parts. But I will post a picture of the car when I bring it into the shop and start working on it.

Brian W · 2022-07-13T16:47:36-0400

moparjim said:
The car will be fine with the 2.76 gears.
You won't need more gear as that will just make you crazy looking for traction. Especially if you are keeping the 8sp . If not then yes add more gear.

Thanks moparjim. Im thinking keeping the driveline as close to the HC configuration. Should be plenty fast enough

SickToo · 2022-07-13T17:45:05-0400

Don’t go by a tag. Look at the last three numbers in the casting and see how many times you gotta spin the pinion to get the drum to go 360°. If both drums go same direction it’s posi

moparjim · 2022-07-13T17:47:00-0400

Brian W said:
Thanks moparjim. Im thinking keeping the driveline as close to the HC configuration. Should be plenty fast enough

Don't forget if you keep the 8 SPD the first gear is 4.71 vs maybe a 2.6 if you used a th400.
Looking forward to more info on the build.

SickToo · 2022-07-13T18:24:51-0400

Don’t forget high gear is .67

Get tire under car before choosing ratio

2fast4u · 2022-07-14T08:10:44-0400

Most sure grips were 3.23 for the RR, I did make a 2.76 sure grip in my 70RR for hi speed runs in So. Cal many years ago...4 speed would be at 1700rpms at 90-100.

Slidd · 2022-07-14T10:46:56-0400

I thought the 69 Polara Police 440 Magnum used the 2.76 to get the 150 mph top speed but for CHP anyway, they used the 3.23.

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2fast4u · 2022-07-14T12:28:24-0400

I believe the pursuits had the 2.76...

276 rear gear

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