9 replies to this topic

[Andy69]

OK, time to back off and reassess this whole thing.

 

My 1987 CRX si is used exclusively for autocross, mostly in SCCA local regions. 

 

The problem I have is that 2nd gear is too short - according to my GPS speed (a Dual WAAS enabled 10hz bluetooth), it topped out at 54 mph, which on national style courses often creates sections where I hit the rev limiter.  Rev limiter or upshifting, either option makes me slower than if I could just stay in the same gear.

 

I picked up what I thought was an HF, but I think it's a California HF - GPS tells me top speed in 1st gear is 44 mph.  That's way too tall, and creates the same problem I had before only it's 1-2 rather than 2-3.  I'm going to check the ratios this afternoon to be sure.

 

The transmission I replaced I thought was a 1987 Si, but using a MPH calculator, I come up with 48 mph in 2nd gear but my GPS speed for the top of 2nd is 54.  The closest to that speed at the top of 2nd is a regular HF, so I'm working on the assumption that the old trans is not an Si but a 49 state HF.  It's apart, so I can check the ratios.

 

According to sources I've been able to dig up, the 1985 Si transmission has the following ratios, which are different than the 86 and later Si

 

1: 3.30

2: 1.99

3: 1.35

4: 1.00

5: .79

FD: 4.428

 

According to the MPH calculator (spicerparts.com), that will have a 42 mph second gear and a 62 mph 3rd gear.  While most people like to autocross in 2nd, I think, if those ratios are correct, I can spend most of my time in 3rd with maybe an occasional drop to 2nd.  While not an ideal solution, it seems like a better solution.  I have an 85 Si transmission apart, so I can confirm ratios for that too.

 

Thoughts?

[Andy69]

OK, got the info from the transmissions I have in the garage.

 

The 85 Si (only went to 4th gear on these):

 

1: 2.916

2: 1.764

3: 1.181

4: 1

FD: 4.428

 

I don't know what those ratios are in  the last post, but my old 85 Si trans does not have them.

These were confirmed by counting the teeth.

 

The 87 trans I took off is from an Si

1: 2.916

2: 1.76

3: 1.192

4: .866

FD: 4.40

 

The one in the car is definitely a California spec HF.  I could only count engine vs wheel revolutions so I don't have the same data but figuring out the same numbers using the gear tooth count for the others it seems to fit.

 

Using the MPH calculator, I came up with the following for top speed in 2nd at 6500 RPM

 

85 Si: 52

87 Si: 52

Ca HF: 90!!

49 state HF: 60

 

Looks like I need a 49 state HF, which is what I thought I had.  Next time check the ratio first!!!!!  Save yourself some work!!!!!

 

I don't have a regular HF transmission, but what I DO have is a Ca HF and an Si ring and pinion.  Swap in the Si ring and pinion (which would require disassembly of the gear stack), and I'll have a car that can do 60.2 MPH in 2nd gear.

 

Now, this would be a technical violation of the SCCA Solo rules, which are quite clear when they state you cannot mix and match subcomponents of assemblies, that the entire assembly (transmission, engine, etc) must be swapped. BUT, it would convey no performance gain, so, ethical grey area even if it's technically violation.

[1985 CRX SI]

I trust the factory service manuals more than what is posted on the internet. 

[CSPCRX]

All the solo cars I had or helped with had SI transmission. The hf gears are so tall it will work against you.

[Andy69]

All the solo cars I had or helped with had SI transmission. The hf gears are so tall it will work against you.

 

Interesting.  I've been working on this assumption:

 

"Get the tallest legal second gear that the update/backdate allowance grants you. Even for a low-powered car, a top second gear speed less than 60mph is not going to cut it on national-level courses."

 

https://www.scca.com...street-prepared

 

What was the reason for sticking with the Si transmission?  Is the 49HF not really that great of a choice?

[CSPCRX]

gear ratio because HF gears were to long. car just doesn't have enough torque to pull the longer gears affectively.

[crxracer87si]

What about changing the final drive ratio granted this will move your 1-2 shift as well but there maybe a sweet spot in there from another stock FD with si gear ratios. Hondas have proven time and again that they are the chevy of imports and if you have two transmissions just sitting on the floor it wouldn't take much to see if it fits

Edited by crxracer87si, 05 September 2018 - 12:43 PM.

[Andy69]

What about changing the final drive ratio granted this will move your 1-2 shift as well but there maybe a sweet spot in there from another stock FD with si gear ratios. Hondas have proven time and again that they are the chevy of imports and if you have two transmissions just sitting on the floor it wouldn't take much to see if it fits

I could. It would involve disassembling the gear stack, but as long as you get the right length on the drive gear or whatever it’s called and the matching final drive gear you can make a variety of combinations the factory never made.

However, the SCCA Solo rules state that assemblies must be swapped in as a unit. While anyone who doesn’t drive a CRX wouldn’t notice, if I were to show up at a National event with a car that does some mph in second that was not achievable with factory transmissions, chances are another CRX driver will notice. It’s a long shot but I’m trying to stay in the rules


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[PuddleSkipper]

gear ratio because HF gears were to long. car just doesn't have enough torque to pull the longer gears affectively.

I second that, but if you really want to try one let me know, i have one i was going to just pull the 5th gear off of

[Andy69]

OK, season is over, time to sort out the transmission.

 

I'm going to see what I can mix and match to put together a transmission with a favorable 2nd gear.

 

I tore into my spare 85 Si 5 speed.  What a mess!!!  The guy I got it from said 4th and 5th gear were not working.  Messing with the shifter, seemed like maybe there was a problem with the forks inside.  There was a problem, alright.  4th and 5th were SMOOTH.  And I mean. smooth as in no teeth AT ALL.  And the bottom magnet was buried in a mountain of sludge consisting of oil and finely ground metal shavings.  Needless to say all the bearings are shot so the only thing usable is the case.  That's ok, that's all I really need as I have the original 85 trans with a bad case.