Rear Axle Ratio Difference

[Old Moparz]

Just wondering what I can expect, acceleration & performance wise, going from an open 7-1/4" rear with a 2.73:1 ratio, to an 8-3/4" with a 3.23:1 sure-grip? I just got the rear axle housing back from the shop over the weekend, & will be swapping it soon. I got the A-Body 8-3/4" rear & had them put the sure grip in it, new bearings, seals, etc., & it's for my '71 Scamp which has been out of commission for a while. It has a 318 with a 4V set up, 10.5:1 pistons, headers, & has run a best of 15.20 with the 7-1/4" in it, but I was hoping this thing should get me into the 14's maybe.

Anyone know if this rear end set up should do it? Not that I'll lose sleep, it's just that the old rear was making noise & I couldn't see putting money into it being a 7-1/4".

Thanks, Bob

[phat69charger]

I always use this to compare what you have now to what it can be: http://users.erols.com/dmapes/GEARCLC.HTM

[firefighter3931]

It should 60ft a lot better with the suregrip. The improved gearing will get it into it's powerband sooner which will help acceleration significantly. You'll need to work on traction but i don't see that combo having problems getting into the 14's. You should notice a descent improvement in straight line acceleration. 

Ron

[Old Moparz]

Thanks for the heads up. 

I had figured the car would do better, but have never done a swap like this & was just curious as to what the results might be. It's not solely for the track, but I had made a couple of runs in the past to see what it could do. Maybe I'll try again this summer at Englishtown to see how much of an improvement there is. It has a 904 trans which doesn't have too many miles on it, so the 727 will stay on the shelf for now.

Next thing on the list is to have the driveshaft shortened.

Bob

[Lightning]

quick question: what kind of numbers is your engine producing?

[Old Moparz]

quick question: what kind of numbers is your engine producing?

I have no idea, but when I got the 318 rebuilt I had it done so it was streetable, could run on 93 or 94 octane, & I managed 15 to 16 MPG on the highway. I can dig out the machine shop bill & scan or list the parts on it, but not at the moment.

[sext7366]

Yeah you'll be in the 14's, switched my 383 from the 2.76 to a 3.23 posi, and it is definately quicker...I would think it would easily push your time down in to the mid to high 14's.

[Old Moparz]

Mid 14's would be pretty cool for a measly 318 with a holly 600.

Found the receipt & had the following work done years back. I still have the A/C set up on the car too.

8 Pistons
Ring Set
5 Main Bearings
5 Cam Bearings
HV Oil Pump
Roller Timing Chain Set
Direct Connection Cam #4452761
Gasket & Seal Set
8 Exhaust Valves
16 Pushrods
AK 5000 Headers
Edelbrock Performer Intake
Holley 600
-------------------------------------
Clean Block & Replace Plugs
Bore & Hone Cylinders 030
Clean & polish Crankshaft
Balance Pistons & Rods
Valve Job, Clean & Assemble
16 Bronze Guides
8 Exhaust Seats   
Resurface & Mill 025

[firefighter3931]

Hey Bob, that sounds like a nice solid street engine.    Just curious about the cam...any specs on that grind ?

Ron

Edit: Ok, i found the specs for Pn 4452761

268/272 advertised
228/232 @ .050 lift
110 lsa
.450/.455 lift
Nice cam....that motor will definately respond well to more gear. 

[Old Moparz]

If I don't run into any set backs, (Like that never seems to happen, so why worry?) I'll make sure I update what I am doing with the car & how it runs. I've been on the interstate running side by side with 2 other cars that just pulled away from me as I ran out of top end. One was a 440-4V Superbird, & the other was a '69 Bee with a nice 426 Wedge in it. I did think about trying to make a few more HP, but I think I'll leave this one alone & save that for my Charger with the 440 later on.

Thanks for the bits of info, Bob   

[firefighter3931]

I've been on the interstate running side by side with 2 other cars that just pulled away from me as I ran out of top end. One was a 440-4V Superbird, & the other was a '69 Bee with a nice 426 Wedge in it.
Thanks for the bits of info, Bob   

You're welcome Bob.

Maybe you should challenge those B-bodies at the track and whip em there ! 

Ron