In your opinion(s), roughly how much horse-power can the original 78 rear axle handle without crapping out. Im not interested in drag racing it but maybe some spirited acceleration from time to time. Is anyone here using the original rear with a v8 swap? Thanks for any and all input!!
Hi Jimmy!
The stock rear axle is a very strong item...
I'm not sure if you are running a 3.9:1 or a V8 3.07:1 axle. It does not really matter because all of the internals are the same apart from the cw&p ratio. What I mean is the items are all the same strength and both axles use the same shafts.
I have found the breaking point of the stock MGB shafts on my car at the drag strip. I run a 280 ci (4.6 litre) engine in my B. She only runs 200hp nasp because I have built it for nitrous use. If i launch on the drag strip with 150hp of nitrous the shafts will let go as I'm hitting them with 350hp and 450 ft/lbs of torque in an instant. This is with hot slicks that wont slip. But if I drop that to a 120hp hit they dont break. But they will start to twist after a few good hook ups.
On the dyno I have pulled many times a chunk over 400hp with 550 ft/lbs and the shafts are ok because the hit is quite soft with the rear wheels already up to a good speed before nitrous activation.
If you are running a 3.9 rear end with a decent V8 and good tyres on the road then expect the occasional left front wheel in the air when you gun it if the tyres will hold :)
This is my car with all MGB V8 stock rear end pulling off the line with 100hp of nos as a fixed hit with another 200hp of nos coming in over 1.5 seconds on MT slicks.
It looks cool. But since then i have done a few mods to convert the wheel lift into forward motion so i can pull easy 10's on the 1/4 mile.
http://www.youtube.com/watch?v=uiDVhKpwxVM
I should also add that I have now had copy shafts made by Moser so I can hit the launch harder this year. The new shafts will be fitted next week and i am told that I will have trouble breaking these??
My intention is to hit the moser shafts with 400hp off the line and then work it up to 500hp in 2 seconds.
I will post up results on this forum when i hve more data.
Perry, Welded diff or spool?
Hi jim!
Stock V8 axle with the spider gears welded together and a slight bead of weld from spider gears to diff cage. Small enough to be easily ground off if a gear cracks :)
Regards
Perry
Perry, Cool car! Did you check out any more info on a Powerglide?I had an idea for the rear axle. I could have the Moser axles splined to 28 spline Ford like the 7.5 and 8.8 or 7.5 Chevy 28 spline and use a mini spool or 4X4 locker for the street.
I was able to break the pinion gear, and strip off several teeth off the ring gear with a fairly stock original engine in my '67 B. I drove my car pretty aggressively on a nearly daily basis, but this axle had roughly 170k miles on it, and i'd say the failure was fatigue over time, and the lash probably being out of adjustment due to worn parts. I replaced the axle with another wire wheel unit out of a much lower mileage car (70k miles). I still plan on running an original axle behind my 300hp 5.0 with no other power adders. I'm hoping the diff will last.
Here's an entertaining video of the broken parts in action:
http://www.youtube.com/watch?v=TDoouuzHYxk
and some pics of the damage:
(http://i219.photobucket.com/albums/cc254/cjsteak/IMG00626-20100707-2013.jpg)
(http://i219.photobucket.com/albums/cc254/cjsteak/IMG00639-20100707-2020.jpg)
(http://i219.photobucket.com/albums/cc254/cjsteak/IMG00640-20100707-2020.jpg)
(http://i219.photobucket.com/albums/cc254/cjsteak/IMG00635-20100707-2018.jpg)
(http://i219.photobucket.com/albums/cc254/cjsteak/IMG00633-20100707-2017.jpg)
(http://i219.photobucket.com/albums/cc254/cjsteak/IMG00631-20100707-2016.jpg)
New axle! :)
(http://i219.photobucket.com/albums/cc254/cjsteak/IMG00641-20100715-1647.jpg)
(http://i219.photobucket.com/albums/cc254/cjsteak/IMG00651-20100718-2015.jpg)
The spider gears are the weak point. But, I ran one behind a blown (16+ psi Eaton) 215 for a long time before the R&P began to growl.
JB
Ring and pinion damage from spider gear shrapnel !!!
I've been lucky so far. I broke 5 spider cogs in the last year but luckily only one small chip on the big ring.:)
Chris, I hope you are using spline fit minilite type wheels and not wire wheels with you 302!