21 replies to this topic

[evilGearhead]

whats the gearing difference between the 85 si tranny and the 86-87si?

ive got an 85 , with 13s and on the highway, ive noticed that it runs alot more revs than my 87.

so whats the differences? is one tranny better than the other?

[jsgprod]

There is no difference in the gearing. It 's the tire size that causes the different RPM. That's also a big reason the "85 Si out- accelerates the '86-'87's.

[squareback]

Yeah, and the 100 pounds less weight doesn't hurt any either . . .

Mike

[CRX8Grand]

There is no difference in the gearing. It 's the tire size that causes the different RPM. That's also a big reason the "85 Si out- accelerates the '86-'87's.

i beg to differ...

I had a 87 SI tranny on the SAME diamiter of tires then after that blew up I put in a 85 and it was noticably shorter in 3-4-5... 1st and second seemed the same...

the final drive is shorter... i forget the accual measurements though... I think someone knows....

the GEARS are the same, but the final drive is different.

[jsgprod]

According to the factory manual I got when I bought my '85 Si it came with a 4.428:1 final drive ratio. The DX has a 4.26:1 ratio and the HF has 1 4.06:1. Those are the ONLY factory final drive ratios ever used in the (2WD) five speed. This was also verified by the '86 Si manual I later purchased.

I also have three Si gearboxes from my first '85 an '86 Civic Si, and an '87 we did a swap in. The final drive ratios are the same in all of them.

Is it possible that the ''87 you blew up had the wrong gearbox in it when you purchased it? Or did you buy it new?

Not trying to be smart but I've been racing these since 1986 and been inside the gearbox many times.

[CSPCRX]

When I bought my 86 SI in 1992 it had a goofed up trans. It was an SI case but the gears were from an HF. You could down shift the thing to 2nd on the freeway. Hard to believe the previous owner didnt notice the differance. So jsgprod might be right.

[balladeSports]

Now what I've heard is the 85 si had the DX finnal drive 4.27 but had shorter gears 1st-5th. as for the 87 CRX si it has a 4.40 final drive with the regular 1st-5th gears.
Civic Wagon had short 1st and 2nd
Most of the 3rd gen Civics has the same 4.27 finnal drive.

[EPcivic]

I agree with balladeSports. There is a difference between the 85 Si and the 86-87 Si, but it results in almost identical effective ratios. I've got the exact numbers on my other computer, but it's sitting in pieces on my floor right now so I can't post them. I have both an 86 and 85 Si trannys in my garage right now, and I've counted gears on both of them.

The 85 has the taller FD, but has shorter gears. The end result is that they're nearly identical, but not quite.

-Chris

[IamNOTaRicer]

I've got two '86 Civic Si's. One built in late '85 and the other in mid-'86. The earlier car does carry a slightly higher RPM in 5th than the later car. If I remember right, it's somewhere between 200 and 300 rpm. The tire diameter wouldn't really effect the revs at a given speed, as the speedometer is driven directly from the transmission, before the tires have a chance to make a difference in the equation. A different tire diameter would change your actual speed, but not your indicated speed...

--Danny

[jsgprod]

I guess I was wrong after all, I went and checked my two manuals a little closer.

FWIW, here are the gear ratio differences for the Si from 85 to 86.

85; 1st_2.916 2nd_1.764 3rd_1.181 4th_0.846 5th_0.714
FD_4.428:1 (I know this is right, I've counted the gears)

86; 1st_2.916 2nd_1.764 3rd_1.192 4th_0.866 5th_0.712
FD_ 4.400:1 (I still think this is questionable)

I'm pretty sure I took the final drive out of the 87 and it was a 4.428 gearset also. Not absolutely certain now.

Jay

[balladeSports]

ya this is what I always thought

85; 1st_2.916 2nd_1.764 3rd_1.181 4th_0.846 5th_0.714
FD_4.428:1 (I know this is right, I've counted the gears)
86; 1st_2.916 2nd_1.764 3rd_1.192 4th_0.866 5th_0.712
FD_ 4.400:1

keep in mind 13's with 175/70/13's are almost the same diameter as 14's with 185/60/14's
so their almost the same. Just a longer 1st and 2nd

[Rampage]

Okay, I did some technical research (somewhat)

First, lets get this right, 175mm tires with a 70% aspect ratio translates into a 12.5cm sidewall height, which is 4.8 inches, times two for both sides, equals 9.6 inches, plus 13 for an overall wheel height of 22.6 inches. Still with me?

Putting that number, along with the 85's ratios, and calculating a 6500 rpm redline, using the Houseman gear ration calulator, here are my findings:

Speed at Max RPM MPH / Km/h
1st: 34 / 54
2nd: 56 / 90
3rd: 84 / 135
4th: 117 / 188
5th: 138 / 222


Next, 185mm tires with a 60% aspect ratio translates into a 11.1cm sidewall height, which is 4.4 inches, times two for both sides, equals 8.8 inches, plus 14 for an overall wheel height of 22.8 inches. Make sense?

Putting that number, along with the 86's rations, and so on and so forth, here are my findings:

1st: 34 / 54
2nd: 57 / 91
3rd: 84 / 135
4th: 116 / 186
5th: 141 / 226

In conclusion: It seems that these are identical, assuming the ratios are indeed correct.

Afterthought: I did an 87 Si Tranny swap on my 86 DX, and didn't notice any particular difference in gearing. As far as I remember, the regular gear ratio for these particular trannies is 4.100, so I put that into the 86's ratios instead of the 4.400 ratio as posted, and here is what I got:

1st: 37 / 59
2nd: 61 / 98
3rd: 90 / 144
4th: 124 / 199
5th: 151 / 243

1st gear is right, topping out at 60 km, 2nd and 3rd are too tall, but 4th is right, becuase I was a smidge off of redline in 4th doing 195....

Anybody want to try and back these numbers up? Next time I go for a drive I am going to test my car out for top speed in each gear at redline... and report back with my result. Then when I get the Si out I will do the same.

Anyone with an 85 Si want to do the same?

Finally, give me the formula for determining gear ratios and I will go and open up my 87 Si tranny and start counting teeth....

Cheers,
Mark

Edited by Rampage, 14 April 2004 - 02:37 AM.

[jsgprod]

Mark,

The formula for figuring gear ratios is division. Just divide the number of teeth on the driven gear (countershaft) by the number of teeth on the driving gear (mainshaft). That'll give you the ratio for that gearset.

If you want to know the overall gear ratio, just multiply the ratio of whatever gear you're in by the final drive ratio.

As for the FD ratio in the DX's sedans and (2wd) wagons all I’ve ever found, in both the gearboxes and in the manuals, was a 4.266:1 ratio. Which is what is in my Houseman gearbox at this moment, until I change it for Daytona, need to install the HF ratio for that, (Thanks, Shadowboy). Which in the 49 state models was 4.066:1.

I was quite shocked last night when I saw what the 86 manual listed as the FD ratios for the Hi Alt and Cali models (of the HF only) 3.5:1 and 2.95:1 respectively. They also had completely different gear ratios from any other model and even the 49 state HF.

Learn something new everyday.

[rexsk8er]

huh thats awesome, i thinkn my hf is a cali modle..... is there any sure-fire way to tell? im going to be selling the engine soon so if it is would you be interested in the tranny???? sorry for gettin off topic



sean