My GVod is .78, and into an A-body, it only needed a few hammer swings to get the clearance it needed; IDK about your Fifth
But I gotta say with an automatic, I highly recommend the A500/A518. And the reason is because of the .69overdrive. This will allow you to run absolutely any rear gear you want to. So if you optimize the rest of your combo for street work, then you can let the .69 od claw your say 4.56s back to a sane 3.15, and 65=~2550 in loc-up. Badaboom
Do you need 4.56s? Probably not, so that makes it even more attractive.
Let's say you just wanted to be quick to 60mph.
The quickest you can get to 6, is by going thru your power peak twice, and ending on the power peak the second time. With a given engine, you can do no better.
Ok so with an A500 the ratios are; 2.74-1.54-1.00-69
and 60 mph with say 4.30s, and 27" tires in 1.54 second gear , would be 4936 at zero-slip, say 5200 at 5%. and say the plateau is 300 rpm so you can pick a cam to peak 200 to 300 rpm sooner And I get About a 212@.050. That's a pretty small cam. Could be about a 262 advertised. and, these 4.30s will cruise at 65=2210.
Ok but say you want to go faster.
So with 4.56s now,the rpm at 60 mph is 5235@zero-slip so say 5500 at 5% slip, and the cam could peak at -300=5200. That would be two sizes bigger or a 224@.050, which could be a 268advertised. See how easy this is? And with the 4.56s your rpm at 65 mph will be ~2540 in OD
Ok but say you are going for mpgs WITH performance, and you already have a stock 5.2 Magnum.... with its factory 250/264/110 cam in it. Well first thing to do is to retime the cam to in at 106 to make some serious pressure. Then, from what I have researched, that cam is a puny 182/194 @.050. so it's gonna run like an old LA318 as to advertised, which makes it peak at about 4200rpm, and the 110Lsa is gonna give us 400 rpm so you are gonna want to hit 60 at no more than 4200+400+200= 4800. Enter the math; and 3.91s come up; which cruise at 65=2180 in loc-up. Easy peasy.
Ok I know what your thinking, you can't split gears with the Mopar TFs. Well with these gears, as described above, there is no need to nor opportunity, in a two gear run to 60. Besides, the ratios don't split the best when you do.
If you bolted a GVod onto a an A999, you would get 2.74-2.14-1.54-1.20-1.00-.78od ...GVs in red
and the splits are; .78 -.72-.78-.83-.78 into overdrive. Hey that looks pretty good.... right?
But think about it;
at the top of 1.54 second gear, you are doing 60 mph. Now on the split from 4800 @60 mph your Rs are gonna drop to .78 =3744(with the GV).... but using direct the Rs fall to 3116. Hey that looks good too right? That looks 657 rpm better.
But go look on your power curve, how that little Magnum cam works is this; there is very little power difference over that 657 rpm. So you are paying $$$$ for very little gain in splitting, and you still have to get out of the OD unit into third, which cannot be done under power, so you are gonna have to lift, and when you do, ouch, any or most of the gains you made in that 657 rpm are instantly lost in the lifted-foot out-shift. daymn.... So now all the GVod was good for is the 1-2 split plus cruising.
As to the 1-2 split, forget about it, cuz 1) you still have to deal with the lift-foot out-shift, and 2) the tires are gonna be smoking into second gear anyway, cuz your starter gear is 2.74x3.91=10.71, plus about 10% or more in the Tc =11.78; So there you go; 4800 into second comes at 36 mph with tires blazing.
OK so what about with the bigger cams?
Same problems but with even more gear like 4.30s and 4.56s, traction in first gear at WOT is impossible... so all that extra power just goes into tirespin and an earlier mph upshift.
So what's the answer?
IDK, my tires spin to 80mph and higher, and they are 295s so bigger tires, by themselves are not the answer. When you solve that,cheaply, lemmee know.
One thing I can tell you is this;
For a streeter, limited by a 65mph speedlimit, big-power is just bragging rights. oh and let's not forget
big fun
until it isn't any more.
Like when you get pulled over, or crash, or the engine blows up, or something breaks. My engine broke a lotta things.
The most fun you can have is the right amount of power at the right time,.... and with a given engine,that always leads to the right gear at the right time, with a fairly flat torque curve. However, when cruise rpm is not an issue, and you have two full gears to play with from zero to sixty....there is never a shortage of power even with a decent 318. Some of my best memories involve a factory stock 318LA from 1973 with just a 4bbl and headers........ and radical for street, gears. Like 4.30s behind an A999 and no overdrive. Yeah 50@2670 wasn't the best,lol, but thru the gears was POW!, wicked.
Ok here comes my point
Since I like the A500/518TFs so much, and they have proven themselves over and over, do this; just get yourself a second HD rear end for your car and bolt yourself some big-number rear gears into it, and see how you like it. The only thing that the A500 will give you beyond this incredible kick in the azz, is a cruiser gear. Then you will be able to tell right away if the A500 is in your future. And you will be so impressed with that slug of a 318 under your hood, that you may decide to leave it alone .......... at least for a while. It already has the right cam for 3.91s. And if you put some better springs on it so it can reliably rev to 5000 plus, then I see 4.10s.= 4940@5% slip =60 mph, yessiree.
The rear gear is the whole purpose of running an overdrive, so why not just start with it! Then you'll know if spending the money on the A500/518 is gonna be worth it........... to you.
Those od-TorqueFlites are not bolt-ins, I'm sure you know that, but the crossmembers are now being fabbed up for us, which makes the job so much easier, and usually cleaner too,lol.
Happy HotRodding
