What gears would work best w/A518?

[randy73]

Tranny has a .69 OD and I have a 3.23SG, I have been reading and am wondering if 3.55 or higher would be better for all around performance.

Car has a 340 and will be at some time modified with turbo(s), cam is slightly better than stock now and will change when/if I put the turbos on. It currently has a forged bottom end bored .030 w/ported eddy heads.

Not looking to be a stoplight warrior, just looking to make the most of what I have, both top end and bottom end.

[cdr]

Tranny has a .56 OD and I have a 3.23SG, I have been reading and am wondering if 3.55 or higher would be better for all around performance.

Car has a 340 and will be at some time modified with turbo(s), cam is slightly better than stock now and will change when/if I put the turbos on. It currently has a forged bottom end bored .030 w/ported eddy heads.

No looking to be a stoplight warrior, just looking to make the most of what I have, both top end and bottom end.

A518 is .69 over drive, for the turbo 3.23 ,3.55 is good, non turbo 3.91,4.10

[randy73]

Tranny has a .56 OD and I have a 3.23SG, I have been reading and am wondering if 3.55 or higher would be better for all around performance.

Car has a 340 and will be at some time modified with turbo(s), cam is slightly better than stock now and will change when/if I put the turbos on. It currently has a forged bottom end bored .030 w/ported eddy heads.

No looking to be a stoplight warrior, just looking to make the most of what I have, both top end and bottom end.

A518 is .69 over drive, for the turbo 3.23 ,3.55 is good, non turbo 3.91,4.10

Thanks, will edit to correct.

[c00nhunterjoe]

I run 4.88s without an overdrive.... if i had overdrive..... i would run 5.13s.... but thats just me, and i am crazy, and thats ok too.

[Troy]

Define "best". The A518 is essentially an A727 with an OD unit attached to the tail. The first three gears are the same. Basically, the A518 will drive just like the A727 until the OD kicks in. The only difference will be lower RPMs at highway speeds.

You didn't say what size tires. The stock tires were ~26" tall. The popular rear tire these days is a 275/60-R15 which is about 28" tall. This effectively makes 2.76 gears act like 2.55, 3.23 gears act like 2.98, 3.55 act like 3.28, 3.73 act like 3.44, 3.91 act like 3.61, and 4.10 act like 3.79. Again, the first three gears will behave similarly to any factory automatic with the larger tires. The OD ratio will be on top of this adjusted ratio (so your "standard" 2.76 becomes 1.76 in OD and 4.10 becomes 2.62).

RPM @ 60 mph:
2.76 gears, A727, 26" tire = 2,140
2.76 gears, A727, 28" tire = 1,987
2.76 gears, A518, 26" tire = 1,473
2.76 gears, A518, 28" tire = 1,368
3.55 gears, A727, 26" tire = 2,753
3.55 gears, A727, 28" tire = 2,556
3.55 gears, A518, 26" tire = 1,900
3.55 gears, A518, 28" tire = 1,764
4.10 gears, A727, 26" tire = 3,179
4.10 gears, A727, 28" tire = 2,952
4.10 gears, A518, 26" tire = 2,194
4.10 gears, A518, 28" tire = 2,038

I have had 3.91 and 4.10 gears with non-OD transmissions and 28" tires and still couldn't stand them on the highway. I don't race so the first gear acceleration doesn't affect me. However, as you can see, it's a drastic drop with the OD and the car would "lug" I think with anything numerically below 3.23 - maybe even 3.55. As you can see, the OD makes a 4.10 equivalent to the garden variety 2.76 these cars mostly came with.

Troy

[Kern Dog]

Thanks Troy, that was a nice gesture...doing the math and all..

[Troy]

Thanks Troy, that was a nice gesture...doing the math and all..

Pointless for me as my cars only see 60 mph twice - on acceleration and deceleration. I typically cruise at 75+.

But I can tell you the outboard carbs on my Six Pack open around 3,100 RPM (haven't nailed down the 4bbls yet) so that's my main metric for determining gearing and tire height. The gas disappears a whole lot faster after that point!

Troy

[randy73]

Mine will be a cruiser and I would like to open her up and mess with newer cars, also your tire size was perfect, as I have 275's on her now.

[Troy]

I was just thinking that my numbers are likely off by a little because of the inherent "slip" of an automatic transmission (although I assume this can be mitigated on the A518 or late A727 with a lockup converter). The regular A727 RPM will likely be a bit higher than what I listed. Almost all my cars are 4-speed so I just do the math straight across.

Troy

[randy73]

Thanks Troy, you always have good info.

[randy73]

I run 4.88s without an overdrive.... if i had overdrive..... i would run 5.13s.... but thats just me, and i am crazy, and thats ok too.

You must must be a red light warrior.   

[c00nhunterjoe]

I run 4.88s without an overdrive.... if i had overdrive..... i would run 5.13s.... but thats just me, and i am crazy, and thats ok too.

You must must be a red light warrior.   

I dont drive the highways, and never cared to even when my 69 had 2.76s in it. Way too many crazies out there for the classics to tango with. On the 4.30s and a 28" tire i did make several trips from home to cabelas which was about 150 mile highway trip. Cruised at 70 the whole way, got 4 mpg. Lol. But i cruise comfortable at 60-65 on our main roads in both cars. The 63 has 5.13s in it with a 32 inch tire. Keeps up with traffic just fine for me.

https://youtu.be/EmFknw4UmDY

[Kern Dog]

You burn a quart of gas per mile? Holy shit !! 

[c00nhunterjoe]

You burn a quart of gas per mile? Holy shit !! 

If i kept that engine at 50, it got 13 mpg. I think that was about 2200, 60 was 3000, 70 was 3500. I didnt build it for fuel economy. I built it to be badass. Lol.

[John_Kunkel]

I'm so spoiled by OD that, when my tach nears 2000, I look for another gear.

[c00nhunterjoe]

Lol, mine is skipping off the cam til almost 4k. 2k is almost idle.

[Kern Dog]

You burn a quart of gas per mile? Holy shit !! 

. I didnt build it for fuel economy. I built it to be badass. Lol.

I wasn't trying to insult you, I was just surprised!

[c00nhunterjoe]

You burn a quart of gas per mile? Holy shit !! 

. I didnt build it for fuel economy. I built it to be badass. Lol.

I wasn't trying to insult you, I was just surprised!

No insult taken.  My foot is heavy. I drive the cars to have fun. 

[Ghoste]