Preparing for a possible 727 to 5 speed swap. I am looking at SST and I was quoted the TKO 600 which has ratios of 2.87, 1.89, 1.28, 1.0, 0.64.
Their other option is the TKO 500 with ratios of 3.27, 1.98, 1.34, 1.00, 0.68.
I am not ashamed to admit that I know next to nothing when it comes to this so any advice would be appreciated. Would the 600 be better for my needs?
71 Demon, 340, 3:91, 28 in rear tire. Most all of my driving will be highway with possibly a track day once or twice a year. I recently swapped an open 3:23 rear for the 3:91 with sure grip. I love the difference on the low end but cruising is pretty brutal at 3k rpm at close to 60 mph.
Thanks.
The splits are;
600: .66-.68-.78-.64od
500: .61-.68-.75-.68od
The 500 works well with a smaller engine or one with limited torque off idle, or allows about 13% less rear gear.
Say you are a streeter with a stock 268 cam and you love the 3.91s. So your current trans has ratio of 2.66-1.91-1.39-1.00 and splits of .72-.73-.72 . With your current 3.91s the final drive ratios are 10.40-
7.47-5.43-3.91. For a streeter, it's the first two ratios that count. That 268 cam wants to be shifted at about 6000 maybe 6100. with the A833. At the shift, the Rs will drop to 72/73% so from 6000 to about 4350, for a powerband of 1650, centered at about 5175. This will get you 60mph @ 5600 with 27" tires, just about perfect for a streeter with a stock 340. So then it follows that you want your new trans to be about the same. So the we take the target 7.47 second gear ratio and divide it by the new second, say 1.98 and you come up with the proper rear gear for it, which is 3.77. Rounded down to 3.73s.
For the
TKO 500 with ratios of 3.27, 1.98, 1.34, 1.00, 0.68. Now the new final drives with the 3.73 gear and the 500 are;
12.2-7.39-5.00-3.73-2.54.
Now lets look at those other ratios. The 12.2 is an excellent drag-race starter, and a fabulous first gear for a teener. It's a bit much for a 360 tho. And a 340 is right up the middle. But I like the 61% 1-2 split. Now the hiway gear at 2.54 will bring the Rs up to 80=2524 with 27s. That's pretty sweet. Except the 65 =2050. And the 268 cam is not known to get good fuel economy down there. What I do is rev the engine up in Neutral and measure the rising manifold vacuum. The last RPM when it stops rising, that is the first rpm that the engine is finally becoming efficient. From there it will linger for a while, then begin to drop again.With a 268 cam in a 360 this occurs at about 2200, so 2200 is probably the best cruise-rpm for it. Ima thinking in the 340 the cruise Rs might be about 100 rpm higher. That puts you at a minimum cruise of 2300 in terms of fuel efficiency. And with 2.54s this would be 70mph. So you're in the ballpark.
Then the other two ratios. The 5.00 ratio is good for 98@6100 in the 1/4, and the 3.73 is good for nothing except getting into od,lol. So that's all about the 500. So this is a poor choice for drag racing a stock 340, cuz you never get into 4th. To be able to use 4th, you might need 4.30s and that would kill the starter gear. So bad trade.But it's a great trans for a streeter that hits 98 in the quarter.
Now lets take a look at the 600 which has ratios of 2.87-1.89-1.28-1.0-0.64.
To get the same second gear of 7.47, you'll need 7.47/1.89= 3.95s, rounds to 3.91. Which you already have. So the road ratio are 11.22-7.39-5.00-3.91-2.50..
So the the starter gear will be 3.91 x 2.87=11.22. This is a very nice street starter gear; so we're 2 out of 5.
Next is the cruiser gear; 3.91 x .64= 2.50 and 2200=71 mph just about perfect, so 3 out of 5.
The 5.0 is the same as the 500, and the 3.91s are the same as you currently have. That 5.0 btw is a great passing gear at 60/65 where the Rs will drop right into the peak-torque zone at about 3880
This trans also has better ratios for a streeter going weekend racing, cuz the 4.30s will drive the starter gear to only 4.30 x 2.87=12.34, very nice. (Too much for street IMO, but great at the track). And those same 4.30s are good for 108 at 5800ish. And if you must know,those 4.30s will cruise with a FD of 2.75 which I really like. It makes 65=2220,lol; 80=2730
So you're probably thinking,that I'm thinking,that the 2.87 low is the way to go.... and for a street 340 you'd be right; with anything 3.91 or bigger, that's what I'm thinking.
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