Mopar 8 3/4 VS 8 1/4

Phillip marvetz · 10-06-2009, 10:26 AM

Can I expect a gain in ET buy switching from one to other if using the same gear ratio? How about overall weight?

John Dinkel · 10-06-2009, 10:58 AM

8 1/4 will be easier to break.

treessavoy · 10-06-2009, 11:12 AM

I broke an 8 1/4 with a warmed over slant six and a 4 speed but it was not a posi unit. With a locker and aftermarket gears it might live behind an automatic but in my opinion it's not worth the weight savings,

JimR

Jim Wahl · 10-06-2009, 12:18 PM

Not worth the trouble! You *will* break the 8 1/4 ! Jim

Todd Boyer · 10-06-2009, 02:17 PM

I read a long time ago that Bob Lambeck ran an 8 1/4 in a Duster 360 stocker but I don't know how long it lasted...

Eric Merryfield · 10-06-2009, 02:38 PM

Quote:

Originally Posted by Todd Boyer

I read a long time ago that Bob Lambeck ran an 8 1/4 in a Duster 360 stocker but I don't know how long it lasted...

Does anyone or did anyone make a spool for a 8.25? I don't think so, but I could be wrong. If you do go the 8.25 route, you will have to get the right suregrip unit to fit your application. I have a NOS one in the garage since I bought two for my warlock just in case I needed it.

Axles are another concern here too. Not sure how strong the factory original units were/are after 25 and more years.

Eric

magnumv8 · 10-08-2009, 03:38 PM

With the limited choices of ratios for the 8.25 if the optimum gearing for your combo turns out to be between those ratios and it is available for the 8 3/4 then the latter would be the rear assembly to use....I think that any small benefit (if there is one) in performance with the same ratios in each would be overcome by the flexibilty of the 8 3/4.....

D L Rambo

magnumv8 · 10-06-2009, 08:50 PM

I've run an 8.25 for years and never had an issue with it 12 sec.vehicle....over 1000 passes with the original suregrip and 4.56 gears (they are getting replaced now)..... Moser made me a set of alloy axles when I first built it and recently I picked up a locker for it for the rebuild....I guess the the main issues would be axle retention and the fact that you can run a little shorter driveshaft with the 8 3/4 allowing more rpm before driveshaft issues....

Phillip marvetz · 10-07-2009, 12:50 AM

I have been using the 8 1/4 all season with out any issues and I'm sure it is plenty strong enough for what I use it for, I'm wondering if the 8 3/4 is more efficient or not. I don't really have any concerns about the ease of gear changes, Is it worth the hassle of changing the hole assembly ET wise?. Hey John, have you swapped out the rear in the mirada yet? Any one have a phone number for Loge? Sound's like he would have experiance to give me the right answer.......

GTX JOHN · 10-07-2009, 03:27 AM

Sold the Mirada to North Carl. family.. beleive they are still running the 8.25 with no problem. I would research gear availablity ... have not seen any gears past 4.50 since 1980. Mopar in its race seminars did not encourage us to run then in high HP stockers even in 1970's.

10-06-2009, 10:26 AM	#1
Phillip marvetz Senior Member Join Date: Oct 2008 Location: Lynden ,WA Posts: 820 Likes: 0 Liked 3 Times in 3 Posts	Mopar 8 3/4 VS 8 1/4 Can I expect a gain in ET buy switching from one to other if using the same gear ratio? How about overall weight?

10-06-2009, 10:58 AM	#2
John Dinkel Senior Member Join Date: Nov 2005 Location: Pinckney, Michigan Posts: 507 Likes: 399 Liked 263 Times in 68 Posts	Re: Mopar 8 3/4 VS 8 1/4 8 1/4 will be easier to break. __________________ John Dinkel 3295 STK

10-06-2009, 11:12 AM	#3
treessavoy VIP Member Join Date: Feb 2009 Location: Dunnellon,FL Posts: 1,103 Likes: 0 Liked 4 Times in 4 Posts	Re: Mopar 8 3/4 VS 8 1/4 I broke an 8 1/4 with a warmed over slant six and a 4 speed but it was not a posi unit. With a locker and aftermarket gears it might live behind an automatic but in my opinion it's not worth the weight savings, JimR __________________ Jim Rountree

10-06-2009, 12:18 PM	#4
Jim Wahl Veteran Member Join Date: Jan 2002 Location: Central Florida Posts: 5,844 Likes: 666 Liked 683 Times in 129 Posts	Re: Mopar 8 3/4 VS 8 1/4 Not worth the trouble! You will break the 8 1/4 ! Jim __________________ Jim Wahl....NHRA #2239 S/SS - IHRA # 8 Stock, D2 Stock Champion (forever I guess) 2019 Baby Gators Stock Champion 2009 NHRA D2 National Open Stock Champion 1982 NHRA D2 West Palm Beach LDRS SS Runner Up Past President, Southern Stock / Super Stock Association.

10-06-2009, 02:17 PM	#5
Todd Boyer Senior Member Join Date: Feb 2004 Location: Saint John NB Canada Posts: 561 Likes: 30 Liked 6 Times in 5 Posts	Re: Mopar 8 3/4 VS 8 1/4 I read a long time ago that Bob Lambeck ran an 8 1/4 in a Duster 360 stocker but I don't know how long it lasted...

10-08-2009, 03:38 PM	#7
magnumv8 Member Join Date: Feb 2009 Location: Coraopolis, Pa. Posts: 172 Likes: 0 Liked 0 Times in 0 Posts	Re: Mopar 8 3/4 VS 8 1/4 With the limited choices of ratios for the 8.25 if the optimum gearing for your combo turns out to be between those ratios and it is available for the 8 3/4 then the latter would be the rear assembly to use....I think that any small benefit (if there is one) in performance with the same ratios in each would be overcome by the flexibilty of the 8 3/4..... D L Rambo

10-06-2009, 08:50 PM	#8
magnumv8 Member Join Date: Feb 2009 Location: Coraopolis, Pa. Posts: 172 Likes: 0 Liked 0 Times in 0 Posts	Re: Mopar 8 3/4 VS 8 1/4 I've run an 8.25 for years and never had an issue with it 12 sec.vehicle....over 1000 passes with the original suregrip and 4.56 gears (they are getting replaced now)..... Moser made me a set of alloy axles when I first built it and recently I picked up a locker for it for the rebuild....I guess the the main issues would be axle retention and the fact that you can run a little shorter driveshaft with the 8 3/4 allowing more rpm before driveshaft issues....

10-07-2009, 12:50 AM	#9
Phillip marvetz Senior Member Join Date: Oct 2008 Location: Lynden ,WA Posts: 820 Likes: 0 Liked 3 Times in 3 Posts	Re: Mopar 8 3/4 VS 8 1/4 I have been using the 8 1/4 all season with out any issues and I'm sure it is plenty strong enough for what I use it for, I'm wondering if the 8 3/4 is more efficient or not. I don't really have any concerns about the ease of gear changes, Is it worth the hassle of changing the hole assembly ET wise?. Hey John, have you swapped out the rear in the mirada yet? Any one have a phone number for Loge? Sound's like he would have experiance to give me the right answer.......

10-07-2009, 03:27 AM	#10
GTX JOHN VIP Member Join Date: Jun 2009 Location: Boulder City, Nevada 89005 Posts: 2,728 Likes: 2,783 Liked 2,462 Times in 694 Posts	Re: Mopar 8 3/4 VS 8 1/4 Sold the Mirada to North Carl. family.. beleive they are still running the 8.25 with no problem. I would research gear availablity ... have not seen any gears past 4.50 since 1980. Mopar in its race seminars did not encourage us to run then in high HP stockers even in 1970's.