So I have a spare 91 CRX Si transmission in the garage for my CRX and was thinking of getting creative with it. It has a rebuilt OBX LSD in it which could use a new home. After replacing the mainshaft bearing on the Insight, I noticed how similar the two transmissions are internally, so I wanted to know whether the parts were interchangeable. What I found was a little disappointing, because I wont be able to use most of these parts, but I know what parts we can use!
01-05 Civic EX 5 speed
If you had one of these transmissions as a donor, you'd have pretty much all the parts you need, here's the parts diagram of the bell housing from our car and the civic:
Notice the needle bearing that supports the counter shaft has the same dimensions. The mainshaft bearing has the same outter diameter, as does the mainshaft oil seal. These two parts would need to be ordered for the civic and installed into the insights bell housing. Once that's done one should be able to take the differential, main/counter shaft assemblies with the insights shift forks, and drop them into the insight transmission. Also, D series differentials are all compatible with the Insights 5 speed. This would allow the car to make a turn from a stop without frying one tire like it loves to do with these little Bridgestones.
notice the Honda Civic HX has the exact same gearing as the mk1 Insight.
The gearing I'm thinking about is:
First 3.143
Second 1.870
Third 1.241
Fourth 0.970
Fifth 0.757
Final Drive 4.412
This would make 5th gear slightly longer than 3rd is right now. This would obviously have a negative affect on mpg depending on your speed. But if someone were looking for a relatively inexpensive way to get more performance from their Insight without adding any more HP to the engine, this would be the obvious way to go. Gearing being much closer means much less wear on the synchronizers. You also wouldn't have that drastic drop in acceleration when you get into 2nd gear which is the main reason I'm toying with this idea.
Here's the speed at redline for the new gearing vs. stock:
Stock:
1st:36 2nd:71 3rd:114 4th:146 5th:176
Civic EX gears:
1st:29 2nd:49 3rd:73 4th:94 5th:120
So I have a spare 91 CRX Si transmission in the garage for my CRX and was thinking of getting creative with it. It has a rebuilt OBX LSD in it which could use a new home. After replacing the mainshaft bearing on the Insight, I noticed how similar the two transmissions are internally, so I wanted to know whether the parts were interchangeable. What I found was a little disappointing, because I wont be able to use most of these parts, but I know what parts we can use!
01-05 Civic EX 5 speed
If you had one of these transmissions as a donor, you'd have pretty much all the parts you need, here's the parts diagram of the bell housing from our car and the civic:
Notice the needle bearing that supports the counter shaft has the same dimensions. The mainshaft bearing has the same outter diameter, as does the mainshaft oil seal. These two parts would need to be ordered for the civic and installed into the insights bell housing. Once that's done one should be able to take the differential, main/counter shaft assemblies with the insights shift forks, and drop them into the insight transmission. Also, D series differentials are all compatible with the Insights 5 speed. This would allow the car to make a turn from a stop without frying one tire like it loves to do with these little Bridgestones.
notice the Honda Civic HX has the exact same gearing as the mk1 Insight.
The gearing I'm thinking about is:
First 3.143
Second 1.870
Third 1.241
Fourth 0.970
Fifth 0.757
Final Drive 4.412
This would make 5th gear slightly longer than 3rd is right now. This would obviously have a negative affect on mpg depending on your speed. But if someone were looking for a relatively inexpensive way to get more performance from their Insight without adding any more HP to the engine, this would be the obvious way to go. Gearing being much closer means much less wear on the synchronizers. You also wouldn't have that drastic drop in acceleration when you get into 2nd gear which is the main reason I'm toying with this idea.
Here's the speed at redline for the new gearing vs. stock:
Stock:
1st:36 2nd:71 3rd:114 4th:146 5th:176
Civic EX gears:
1st:29 2nd:49 3rd:73 4th:94 5th:120
Great detective skills in pulling all that together! You understand the top speed in gear is theoretical, I think we top out around 112 or so.
Given that the whole reason d'etre of the car is fuel economy, why would you want to do such a drastic swap? You are essentially running the car in what amounts to about 3rd gear, which will kill fuel economy. What, 20-25%?
If that is the case, there are any number of cars out there that would be very competitve rides with the lower mpg.
Now, if you want more performance, how about either the thread about getting more power out of the electric motors, or better yet, slap on a turbo!!
An extra 40 hp or so should make the car a scream, and you can actually make better use of the long gearing since you will have a bunch more power (torque) to pull the tall gearing in the higher gears.
Or maybe you can find a compatible 6 speed? With closer gearing, you would see some small improvement in acceleration times.
Or perhaps a change in the diff, about 10-12% stiffer might help acceleration with only a very modest hit on mpg. Again, the extra torque might help offset the slight additional fuel of the increased revs.
If you do any of the above, make sure to post pics and share!
Regards,
Jerry
__________________
2004 MT Silver Bullet
West Palm Beach, Fl.
Great detective skills in pulling all that together! You understand the top speed in gear is theoretical, I think we top out around 112 or so.
Limited electronically, aerodynamically, and by the rating on the tires. Each of those things can be addressed, but who buys an Insight to do >112mph?
First gear is plenty low enough for my needs, especially when your battery is above freezing. I have no desire for a gear lower than first.
Before you decide to go forward with a gear swap, drive around for a week or two without touching 4th or 5th gear, including a highway trip. 75mph would be 4000RPM, and I wouldn't want to listen to or subject my engine to that for hours on end.
I took a look around the internet for gears that are taller than the Insight's, but I haven't found anything. The stock 2560RPM at 75mph is fine, but I have my doubts about the stock 1360RPM at 40mph. I feel like I have way too much displacement / too many revs when I'm lean burning at 35-45mph.
I posted the top speed in each gear just for comparison purposes. No need to drvie around for a week like that. Get comftorble on the highway and then click it into 3rd and try to get lean burn, it wont happen... No matter how much you let off the throttle. Either way, this was to represent how you could make the car faster without the need to add more hp. So if you do this modification in addition to turbo or the MCM hack, the performance gains would be huge.
I agree 1st gear is perfect, I wouldn't want to make it any shorter, but its a necessary evil if you want the other gears shorter. 2nd really is way to long IMO... MotorWeek even stated when doing their 1/4 mile test that acceleration drops dramatically when you get into 2nd, and it does more so than just about any other car i've driven.
If I was using the car mostly in the city, I would do this tomorrow, but since I bought it for my 100 mile round trip commute to work, I wont be doing it anytime soon. If I come accross one of these transmissions as a freebe tho I might have to find a spare insight transmission to see what this can do compared to other mods.
The engine can take 4000rpm at light load for as long as you would want to leave it there. Remember these gears are from another Honda and they're all known for their reliability. As short as these gears are, they're still not as short as the gears in my S2000, which is over 4k rpm at around 70...
It would be great if there was a .4 or .5 fifth gear we could find to get our great highway performance and the acceleration I'm looking for from 1-4. I'll post up if I find anything interesting.
You can get lean-burn in 3rd on the highway, you just can't be going over I think its 55mph. Whatever the same RPM is that kicks out lean-burn at 78mph in 5th gear. I think its somewhere in the 2800-3000RPM range but I pay more attention to the speed I'm at and the hill I'm approaching before trying to downshift and snag lean-burn again. ...I'm not entirely sure its the correct technique or if I should just be sticking with a high gear and adding more throttle, seems it probably is roughly the same gas mileage either way with similar engine loading but I figure the higher engine speed is probably not the best plan and I've been playing with my strategies lately.
...chilling on the highway with lower gears and a ~3000RPM limit on lean-burn would be pretty lame. I think being able to get 78mph that we can get out of lean-burn at 75mpg or so in the right conditions is pretty sweet for highway cruising though.
Very interesting post. Those gear ratios sure would make the Insight fun to drive! Of course, at the expense of fuel economy. Could you only change 1st through 3rd gears and leave 4th, 5th stock for highway use?
I think my main goal next time my transmission goes out will be to simply beef it up. There is no excuse for the input shaft bearing problems. The synchros..eh, it happens.
Any input on how to fix those problems? Has anyone tried to tackle them with a performance transmission shop or anything?
The main shaft bearing has the same internal diameter, but smaller external diameter when compared to d series transmissions. Take a look at the dimensions in the parts links I posted. Really nothing you can do about that except change it when it starts to fail...
The main shaft bearing has the same internal diameter, but smaller external diameter when compared to d series transmissions. Take a look at the dimensions in the parts links I posted. Really nothing you can do about that except change it when it starts to fail...
Oh, we'll see about that. The bearing doesn't have to come from Honda. I *WILL* find a replacement that is robust enough to handle the thrust loads of engine and regenerative braking(at least, I think that was the conclusion as to the cause of their premature failure). It shouldn't be hard, unless there is something uber special about the bearing.
I will comb every last bearing manufacturer's catalog until I find one!
Fortunately I had mine replaced about 55,000 miles ago, so it should have plenty of life left.. But I had to replace it at 100k, only 14k after buying the car.. which was a bit of a shock.
Well then, while you're combing, see if you can find a needle bearing that's 30x59x20. If I could find that bearing I could use the counter/mainshaft assembly from that spare CRX transmission. Honda doesn't have a bearing with those dimensions. That would be awesome since crx tranmissions are much cheaper.
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Short Gear Ratio / LSD 5 speed
I *WILL* find a replacement that is robust enough to handle the thrust loads of engine and regenerative braking(at least, I think that was the conclusion as to the cause of their premature failure). It shouldn't be hard, unless there is something uber special about the bearing. 
