Black68Vette

Ok, here is the listing of choices on gears in the ROD

http://www.richmondgear.com/cat/rod2.html

So what does it mean? I'm at a complete loss. I'd like the 27/31 master drive set, probably the 39/20 first (4.11 rear), the 30/29 4th, the fifth :) and the 25/52 6th I think.. the second + third seems to make no sense (as its 2 gears? so how is it one ratio?) and I'm no sure if the master drive set is just openly selectable on it... Anyone give a hand?

Cookwithvette

Wow! That's one confusing chart. Looking through Summit one day with way too much time on my hands I made a spreadsheet using the gear ratio sets offered by Summit and rear gears available for the stock 'vette carrier. It gives final drive ratios in each gear. I can email it to you if you'd like. Afraid I'm no help with the link though.

Black68Vette

Sure, send it on down! and thanks!

zwede

With a 4.11 rear you want the 27/31 type tranny so you can get the 0.62 OD.

With such a deep rear I'd look at the following ratios:

1st: 2.77.
2nd: 1.88
3rd: 1.46
4th: 1.19
5th: 1.00
6th: 0.62

You may even want to step down to the next set:

1st: 2.24
2nd: 1.67
3rd: 1.36
4th: 1.19
5th: 1.00
6th: 0.62

However, 3rd and fourth will be very close.

Bob Turner

I just emailed you a gear ratio spreadsheet as well.....

Check it out and let me know what you think of it. I created it a few years ago...

Bob :cheers:

Rockn-Roll

The rightmost columns are the input/output spline count. For example my muncie Input/output are 22/37 which is standard for early C3's with Muncie trannys, except for the M21 which is I believe is a 22/31, but don't quote me on that. I think you CAN get a clutch kit that will fit the 27 spline input, plus get an output yoke that will fit the 31 spline output; however, I have heard that the output yoke is too long...or too short...or something like that, be sure to check.

What you are doing is basically engineering the gears. Here's how I can help...with some theory to put you on track. Let's look at the extremes then narrow our focus. Let's say our hypothetical engine gets a dyno chart that is a nice bell curve (yeah right) with horsepower maxed at 300HP @ 4500RPM then falls to 250HP at rev limit of 6000RPM. Looking back across the chart we see that the horsepower curve is also at 250HP @ 4000RPM.

OK, ideally we would want a tranny with about a thousand gears so that when shifted at 4500RPM each gear will be running at max HP. The problem is that it's a "manual" tranny and a human can't shift that fast...and my 1.4Ghz Pent 4 would be stressed to get that done as well if it was connected to a robot. So, we need to space the gears so they can be shifted by a human...which includes working the clutch too (hopefully depressing clutch pedal BEFORE shifting to the next gear). Then the thought dawns on us...why not just use one gear then there would be no shifting! Well, first we need to get the car rolling...and at around 500RPM this engine has like 350FTLB of torque but only like 60HP, so several minutes later all the rubber is gone off the tires and there are two holes in the concrete where your tires were spinning and you've gone nowhere.

OK, back to our horsepower curve. The drop from 6000RPM to 4000RPM is a 66.667 percent drop in RPMs, thus we need gears that reduce 66.667% each time they are shifted. Why do we want to drop down to 4000? Because we are taking the engine to near the rev limit to maximize the amount of time the car is accelerating instead of being shifted, and when we shift it is wise to maintain the HP for the new gear to avoid loss of traction, etc. due to undesired torque applied to the tires upon dropping the clutch with the new gear in place.

OK, now we know what we want...we did the math...in a street application we don't want to use the rev limit...too risky...but we still want to drop down to the lower RPM that has the same HP. So for this example we want close to a .66 difference in gear ratios.

Let's look at the Richmond chart at the 22/37 spline column and arbitrarily select 3.04 as the 1st gear cause we already have a 3.55 rear end so we don't want a granny gear with the 4.41 that's for sure, or we'd be changing gears before we get up to 30MPH, and we'd be getting up to that speed in just a second...too fast for manual clutching/shifting without risking a dropped clutch!

OK, using 3.04 as the 1st gear gives us something to work with. We know that the next gear needs to be 66.667% smaller which would mean:

3.04 * .66667 = 2.027 or let's call it 2.03

From the Richmond chart there's that number falls between two of the gears, a 2.13 and a 1.99. Also note that Richmond includes the 3rd gear in that section, so let's look at the 66.667% reduction from both of those:

2.13 * .66667 = 1.42
1.99 * .66667 = 1.33

Heck, just what I feared...with our rear end Richmond just doesn't have a 2nd-3rd gear combo that fits our engine...well...duh...Richmond makes these trannys for newer applications that usually have something between a 2.5 or 2.9 rear gear cluster. If we don't want to get another rear end then we should try a different 1st gear...let's try the 3.28...then the math:

3.28 * .66667 = 2.18

Hey, we could try a 2nd gear of 2.22 (which is fine cause we really don't want to wait until we hit the rev limit in case we go over it) so using 2.22 we get:

2.22 * .66667 = 1.48

OK, the closest is the 1.57...let's see what Richmond has for 4th:

1.57 * .66667 = 1.05

Hmmm...the closest is a 1.24...maybe a bit too close, but servicable and 5th is dead locked at 1.0, but we would have liked a 5th gear of .83, but heck, we will be going 120MPH at rev limit with the 1.0 so what the heck. Then of course our 6th gear would be nice at .67, but the .74 will do OK.

Anyway, you see how the math works...you might want to try the 4.06 1st gear if you have the 3.08 rear end, or you might just like that extra torque for wheel burning if you have the 3.55 or larger.

Here's what I came up with for my Richmond selection (if I ever scrap together the tickets)

      &nbs p;      &n bsp;            % &nb sp; final drive
1st Gear  3.04            &nbs p; 10.792
2nd Gear 2.22    0.73 &n bsp;  7.881
3rd Gear 1.99    0.90 &n bsp;  7.0645
4th Gear 1.24    0.62 &n bsp;  4.402
5th Gear 1.00    0.81 &n bsp;  3.55
6th Gear 0.76    0.76 &n bsp;  2.698


As you can see, I'll be short shifting from 2nd to 3rd, then from 4th to 5th, but in 6th I have a possible 160MPH at my rev limit of 5300RPM...not bad going from a limit of 120MPH with my current 4 speed.:)

Aw heck...I made this a long post. :eek: I guess I could have just mentioned that you only have to look at the last two columns and select the column that works with your splines. :crazy:


[Modified by Rockn-Roll, 8:46 PM 4/8/2002]