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Best Ratio?
https://slantsix.org/forum/viewtopic.php?t=52422		 Page 1 of 1
Author:  vynn3 [ Thu Jun 20, 2013 1:53 pm ]
Post subject:  Best Ratio?
I have a beat-up, junkyard 4-speed that I'm planning to rebuild for my Swinger. The gears look pretty bad, so I'll likely be replacing the cluster gear, and Passon has all three ratios (2.47, 2.66, and 3.09). I'm trying to figure out which ratio would work best with my combo: a mild long-rod 225 with the Erson 270 cam and 9.3:1 compression, 3.91 gears out back with a big 27" tall tire.

I don't want first gear to be useless, but I also want the car to be fun and "peppy" out of the hole, too. Would the 2.66 gear be the best all-around compromise?
Author:  DusterIdiot [ Thu Jun 20, 2013 2:14 pm ]
Post subject:  Ideally...
Ideally, the first gear ratio for a spirited launch drag race or "beating the light" in town :roll: is 10:1....so if you went for a 3.09...a set of 3.23/3.55 would work well for that range (in my car with 4.56's and the 3.09 1st gear I shift to second while crossing the crosswalk before entering the intersection), 2.66 would be great for a 3.91 and is on the riding edge of being granny for 4.11's (unless moving a heavy car like a Charger...) 2.47 is good for 4.11/4.56/etc. Having an Overdrive 4th gear would also will help keep the gas prices down with 3.91-4.11 gearing, your 27" tire is effectively making your 3.91 rear seem like a 3.73 rear compared to running the 3.91's with the 25.6" R14 stocker size tires.

Buying a whole new gearset and countershaft gear cluster is definately not going to be cheap! :shock:

I would also suggest in the near future that you bump up the compression on your build to at least 9.5:1 SCR the 270 duration really comes on in the upper-9 to 10 range and has it's torque band a little lower than the 280/270 so it will come in sooner.

One of the mopar boards used to have a nice Excel spreadsheet that allowed you to change the tranny ratios, tire sizes, and see what the rpms would be at certain speeds, and determine the speedometer gear needed to support the combination, sadly I don't remember which one had posted it.

-D.Idiot
Author:  Doc [ Thu Jun 20, 2013 2:15 pm ]
Post subject: 
Look at start off ratio & highway RPMs at your driving speed.
With your stated combo, you will have a 10.4 start-off ratio and the engine will be turing 3163 RPMs at 65 mph.
The start-off ratio is pretty good but rpms at freeways speed is somewhat high.
DD
Author:  Dart270 [ Thu Jun 20, 2013 7:21 pm ]
Post subject: 
I would go 2.66.

Lou
Author:  DusterIdiot [ Thu Jun 20, 2013 7:24 pm ]
Post subject:  Lol...
Quote:
I would go 2.66.
It's funny, while researching T-5 trannies to put behind the slant, I eventually settled on the 5.0L mustang and Cobra T-5 as being the
good one, since it had the 2.66 ratio (good for 3.91/4.11), and a
nice OD to couple to it for mileage...too bad the boxes cost $700
at the junkyard, it's a perfect match end to end in ratios.

-D.Idiot
Author:  vynn3 [ Fri Jun 21, 2013 5:48 am ]
Post subject:  Re: Lol...
Quote:
Quote:
I would go 2.66.
It's funny, while researching T-5 trannies to put behind the slant, I eventually settled on the 5.0L mustang and Cobra T-5 as being the
good one, since it had the 2.66 ratio (good for 3.91/4.11), and a
nice OD to couple to it for mileage...too bad the boxes cost $700
at the junkyard, it's a perfect match end to end in ratios.

-D.Idiot
Yeah, that's what's turned me off from my own T-5 transplant. I've got the bellhousing, but I always figured I could find a $300-400 Mustang trans when the time came. I've been looking casually for the last year or so, and had no luck.

Over the years I've (slowly) collected an A-833 out of a '74 Dart, an aluminum slant bellhousing, and the conversion input retainer to make them play together. I've also ebuilt a pedal box for install, but haven't put it in yet. Still have a lot more parts to gather, like everything clutch-related. I may try to rebuild the A-833 myself, but it seems a bit daunting. Guess it depends on how cheap I can get it done professionally.

Since I have to replace gears anyway, I'd like to get the Passon Overdrive gearset, but can't afford the $1900 yet. I'll have to see how much the stock set will be and compare the two (plus the extra expense of a custom 18 spline clutch). In the end it may end up costing me as much as a T-5 conversion. But at least there's no fabrication involved. :)

As always, thanks for the input, guys!
Author:  Dart270 [ Fri Jun 21, 2013 6:15 am ]
Post subject: 
Hm. Then only 1st gear ratios I have seen for 5.0L and Cobra Mustangs are 3.27 and 2.95, with the latter being the "hipo" and aftermarket trans option. That is what I have in my car. You can get a BRAND NEW T5 for about $1250 from Summit or similar, which is pretty nice if you can handle that cash. Way better than buying/finding parts for 833s IMHO.

Lou
Author:  vynn3 [ Fri Jun 21, 2013 8:03 am ]
Post subject: 
Quote:
Hm. Then only 1st gear ratios I have seen for 5.0L and Cobra Mustangs are 3.27 and 2.95, with the latter being the "hipo" and aftermarket trans option. That is what I have in my car. You can get a BRAND NEW T5 for about $1250 from Summit or similar, which is pretty nice if you can handle that cash. Way better than buying/finding parts for 833s IMHO.

Lou
Unfortunately, the Summit/Ford trans is up to $1600 these days... :(
Author:  Dart270 [ Fri Jun 21, 2013 2:06 pm ]
Post subject: 
Good to know. I guess I bought the first one in 2003, so 10 yrs later...

Curiously, the T56 has not gone up much at all. I bet another source would sell you a good T5 for ~$12-1300?

Lou
Author:  DusterIdiot [ Wed Jun 26, 2013 2:12 pm ]
Post subject:  My bad.
Quote:
Then only 1st gear ratios I have seen for 5.0L and Cobra Mustangs are 3.27 and 2.95
That was my bad, I looked at my notes and the T-56 comes with the 2.66 first, the cobra/5L are the 2.95 boxes. :oops:

I know I was comparing both for a while, a local junkyard I know had a couple of the T-56 boxes in the $1000 range, but if they are out of a late corvette fo'gettaboutit...

-D.Idiot
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