TomCat39

Hi gurus and all.

I did some digging and found MistaBone (aka transzex) posted a nice post on D-Series with the actual teeth counts of the D trannies.

From that I compiled the following table:

Gear/Ratio	Teeth	Trim and Years
1st gear:
3.250	39/12	all
2nd gear:
1.762	37/21	cx/dx/lx/vx (92-95)
1.900	38/20	ex/si (92-95)
3rd gear:
1.066	32/30	cx/vx (92-95)
1.172	34/29	dx/lx/hx (92-00)
1.250	35/28	ex/si (92-00)
4th gear:
0.853	29/34	cx/vx (92-95)
0.909	30/33	dx/lx/hx/ex/si (92-95)
1.066	32/30	cx/vx (92-95)
5th gear:
0.702	37/26	all non si (92-00)
0.750	36/27	sol si (93-95)
Final drives
3.250	65/20	cx/vx 92-95
4.058	69/17	dx/lx/ex? (88-00)
4.250	68/16	ex/si (88-00)

Then from ecomodder California98Civic posted a condensed version for all the generations of which I pulled the 5th gen from which added a little clarity on the SI 5th gears and the final drives:

Year & trim level	OEM engine code	VSS / Speedo gear	OEM wheel / tire	1st Gear	2nd	3rd	4th	5th	Reverse	Final Drive
1992-1995 Civic DX LX / Del Sol S	D15B7	1026rpm=60mph (VSS) / 90.6mm (Speedo)	175/70-R13 (DX&LX)	3.25	1.761	1.172	0.909	0.702	3.153	4.058
92-95 Civic Si/ EX / Del Sol Si	D16Z6 VTEC	1026rpm=60mph (VSS) / 90.6mm (Speedo)	185/60-R14 or 175/65-R14	3.25	1.9	1.25	0.909	0.750 Si Hatch & Del Sol Si / 0.702 2dr & 4 dr	3.153	4.25
92-95 Civic CX/VX	D15B8 (CX) D15Z1 (VX)	1026rpm=60mph (VSS) / 90.6mm (Speedo)	165/70-R13	3.25	1.761	1.066	0.853	0.702	3.153	3.25

Now I'm not the swiftest guy on the block so I was a little confused when I first saw this. What I gathered is the closer the ratio on the gears is to the final drive ratio, the closer it is to a 1 to 1 setup. i.e. First gear on all and the final drive of the USDM CX at 3.250. This cancels each other out and makes it a straight 1:1 so it's pretty easy to go? Then as the ratio on the gear drops it's becomes a higher and higher ratio taking more power/speed to turn etc?

Am I understanding the operation correctly on how the gear ratio to final drive ratio works?

The reason I'm trying to understand is I have had the CDM CX/DX (USDM DX) tranny in my car for some time and recently I dropped in the CDM SI motor and tranny and I've notice a small fuel efficiency drop of about 3-5 mpg. As well as highway travel in these parts tends to be over 3000 RPM where before I was closer to 2500 RPM for the same speed.

I have another big bearing D transmission I can open up and rebuild and I would like to change 4th and 5th gear.

I know I have a final drive of 4.25 68/16 and I do not know the 5th gear of the spare tranny while the one in the car is the coupe so is the 0.702 37/26.

The 4th gear in the car is already the DX Ratio but I would like it to be the same setup as the DX gear in a DX final drive. So 0.702 4th with the 4.058 final drive. Then do the same idea for 5th but shoot for a CX/VX gear with CX/VX final drive.

How do I figure out the 4th gear ratio I need with the 4.25 final drive ratio that would equal the 0.702 to 4.058 setup?

Trying to understand but struggling in the process. Please help oh masters of the transmission ratios, I definitely could use it.

TomCat39

Digging some more as I didn't have any luck catching a guru's attention, I found this excerpt on wikipedia that may be the piece I was missing:

So with that it appears my current transmission 4th gear has a total ratio of 3.86325:1 while the regular DX (CDM CX) transmission has a final ratio of 3.688722:1. Taking that, to find the same ratio on a final drive of 4.25 it appears I need a fourth gear ratio of 1.15216. To get this I divided the final drive of 4.25 by the DX final ratio to the engine of 3.688722.

And also looking at the ratios of the gears themselves, it looks like the closest thing would be a DX 3rd gear set with it's ratio of 1.172. I think I might be finally understanding the match behind all this... Please correct me if I'm wrong.

Are alternate teeth gears available aftermarket from say Synchrotech? Say like D series 37/32 teeth which comes out a ratio of 1.15625?

TomCat39

I wish someone would be kind enough to show the error in my math. I think it is wrong.

Looking at the list for the 92-95, the 4th gear is starting the overdrive ratios except on the USDM CX/VX.

So taking the final motor ratio of the DX 3.688722 and dividing it by the final drive ratio of my current tranny I get an overdrive ratio of 0.8679. This seems to be more in line with the table. So stock gears, the closest is the 4th gear from the CX/VX to get me close to the desired results of the DX/LX 4th gear motor ratio with the final drive of 4.25.

Or so I think. So now I'm thinking the more ideal teeth for 4th would be 32/37 on the final drive of 4.25. This (if I finally have my math correct) will result in a final motor ratio of 0.8649 x 4.25 = 3.6757.

It's not exactly the same as the 4th of a DX transmission but it looks to be pretty close.

I would like to know if I got my head wrapped around this correctly, finally. Here's to hoping.

If I have my understanding straight, then I can work out 5th gear for my desired results and begin sourcing parts.

94EG8

4th gear is easy enough, you can use one from either a DX or VX trans depending on just how long you want it to be. 5th is harder unless you happen to have the lower Del Sol? 5th (some Si trannies had a DX 5th, some have an Si 5th, it seems to have depended on what they came out of) Long 4th with a short 5th doesn't really get you anywhere.

MFactory makes custom gearsets but generally aftermarket gears will be shorter not longer. People looking to save money on fuel typically aren't looking to buy gearsets valued at more than a lot of the cars they're going in are worth.

TomCat39

By the sounds of your reply, I finally got the math right.

I understand it's more money than most would put into the car, but that is also typically how it goes building a car for oneself typically. Rarely do you see what you put into the car even with most these classic muscle cars. Unless it's your business (Gas Monkey Garage anyone?) us hobbyists almost always throw way more money into it than we can get out of it. On the other hand, we get a car pretty much exactly as we want it.

For me, since I've started with the SOHC motor and plan on dumping a bit into it for this long term build, I would like a pretty specific tranny. SI 1st, 2nd and 3rd, then DX 4th and VX 5th. This too me, fits the street build the best for a daily driver and a city happy car. Usually the custom gear demand is for drag so of course shorter is better there but sucks ***** for any sort of highway driving.

Anyways, thanks for the tip, after I can then work on the Y8/B7 minime build that I am going to definitely dump waaaay too much money into, but should be fun.

TomCat39

Now that I believe I understand the math, I sat down and came up with what I believe to be the ideal custom gear sets for the CDM SI 2D (Coupe) manual transmission. The same principles can be applied to B series transmissions with the greatest of ease (or any manual transmission/differential combo really).

The table below is the break down of the actual transmissions (SI, DX and VX) and the modified gear sets to get as close to the same results with reasonable gearing selections:

Actual			Engine Ratio (Total Ratio)	Modified			Engine Ratio
Gear/Ratio	Teeth	Trim/Years		Gear/Ratio	Teeth	Trim Result
1st gear:			SI 2D	1st gear:
3.25	39/12	all	13.8125	3.25	39/12	all	13.8125
2nd gear:			SI 2D	2nd gear:
1.9	38/20	ex/si (92-95)	8.075	1.9	38/20	SI	8.075
3rd gear:			SI 2D	3rd gear:
1.25	35/28	ex/si (92-00)	5.3125	1.25	35/28	SI	5.3125
4th gear:				4th gear:
0.909	30/33	dx/lx/hx/ex/si (92-95)	3.86325 SI 2D	0.864864865	32/37	DX (Taller)	3.675675676
			3.688722 DX	0.868421053	33/38	DX (Shorter)	3.690789474
5th gear:				5th gear:
0.702	26/37	92-95 2D/4D SI	2.9835 SI 2D	0.536585366	22/41	VX/USDM CX (T)	2.280487805
			2.2815 VX/USDM CX	0.538461538	21/39	VX/USDM CX (S)	2.288461538
Final drives				Final drives
3.25	65/20	cx/vx 92-95		4.25	68/16	92-95 CDM SI
4.058	69/17	dx/lx/ex? (88-00)
4.25	68/16	ex/si (88-00)

I did trial an error on the actual teeth counts until I found combos that came pretty close to the same engine ratio as the original transmission set up.

Hopefully this info helps someone in the future.

Cheers

Addendum: Heard back from Synchrotech. Custom gears sets require a minimum order of 30 gear sets per custom gear at $250 USD a set so minimum cost of $7500 to order a custom gear set as of September 26, 2016. Also there is a tooling charge of approximately 10,000 dollars per custom gear design. So to get 2 custom gear sets you would be looking at 60 total gear sets and 2 tooling charges totalling out for $35,000 USD.

tony_2018

Is it possible to use the vx final drive in the si tranny? That might lower your rpms a bit but if you have to climb hills you'll be downshifting alot.

TomCat39

I was looking to keep the performance final drive of the SI and just mod the highest gears for highway cruising.

I can just put my DX transmission back in if I want a the lower ratio final drive.

Was looking for the best of both worlds as city driving, your rips rarely go past 3rd gear and 4th and 5th are usually just for highway/freeway cruising.