Gear ratios

[Unkle Crusty]

Hi guys.
I have an 83 XS400 Seca DOHC. 6 speed motor was tired. Installed a 5 speed Maxim motor that is now running sweet.
My question. Can you direct me to the gear box ratios. I am mainly concerned with the top gear ratios in each engine. That will help me with my final drive selection.
Getting 8150 revs in 5th at the moment. Could the other DOHC riders give me their final ratios, front and rear sprockets, and maximum revs in top gear.
I can get 10,000 in third and fourth.

Thank you. Unkle Crusty*

 

[Unkle Crusty]

Maybe I will reply to my own thread.
I have checked the manual, and I have checked past posts.
Back in about 009 the question was asked about 16 and 17 tooth sprockets, with 35 rear.
I had already deduced that the Maxim and Seca had different final drive ratios, based on the the Seca using a 16 tooth front, and the Maxim using a 17. But I was not sure about the rear sprocket on the Maxim. Still do not know, as no replies.
A review of the bike when new, said the Seca hit red line in top, 6th, while nudging 100 mph. Found that useful link on this site. Also found and appreciate the link to the Mikuni guide.
Still curious about what revs you other guys are getting in top gear, either a Maxim 5 speed, or a Seca 6 speed.
60 mph at 6000 is a common them / guide that I will check on my next ride.
I am nudging 90 indicated at 8150. Might be some guys do not want to run their bikes at WOT in top for a while, as it is a bit over the speed limit. However on I5 south of here with a 75 mph limit, lots of folks are doing 90.

Unkle Crusty*

 

[xschris]

The reason why you can't red line in top gear is because your bike wont make enough power to do it. With a lower gear ratio it can. But as you add a taller ratio you need more power to keep moving the weigh.

 

[16VGTIDave]

Stock Maxim gears are 16 x 35.
Stock Seca gears are 16 x 38.
The Maxim has a "wide" ratio 5 speed gearbox.
The Seca has a close ratio 6 speed gearbox.
The Maxim has a 130/90-16 rear tire.
The Seca has a 4.10S18 (120/90-18?) rear tire.
Both bikes have effectively the same overall drive ratio.

On my Maxim, I tried a 17 tooth CS sprocket and found it dropped the revs by about 500 RPM for a given gear/speed. And this didn't work for me, my riding style, or the roads I ride. So I changed the rear sprocket to a 38. This resulted in the engine revs increasing about 250 RPM above stock for a given gear/speed. The top speed has not changed, because the engine is still making the same power. I just get there a bit faster is all. And I don't have to downshift nearly as much.

The downside of having 17/38 gears is added weight from the larger gears and more links in the chain. The upside is reduced gear and chain wear, less friction and noise, and the ability to accelerate briskly. Some people whine that the engine is buzzy at highway speeds. To that I respond: "Then why did you buy a 400 twin when you obviously want a 1300 V-twin?

 

[Unkle Crusty]

The reason why you can't red line in top gear is because your bike wont make enough power to do it. With a lower gear ratio it can. But as you add a taller ratio you need more power to keep moving the weigh.

I am very much aware of the forces involved, having done numerous sprocket changes at the tracks, on a variety of bikes, with a variety of fairings, or lack of.
What I asked for, was what you guys are using, and the results you are getting.
My bike is limited by wind drag, created by the extra gear. I also am doing my tests sitting in an upright position.
I have already stated I will be making carburetor stacks and trying again. Also I will likely try different air filters.
I am also not wearing one piece leathers, which is likely what the original tester was wearing.
I also said, after I have made the changes I might lower the over all ratio to get more revs in top gear. But that will be after the changes, and I may not change the gearing at all.

Unkle Crusty*

 

[Unkle Crusty]

Stock Maxim gears are 16 x 35.
Stock Seca gears are 16 x 38.
The Maxim has a "wide" ratio 5 speed gearbox.
The Seca has a close ratio 6 speed gearbox.
The Maxim has a 130/90-16 rear tire.
The Seca has a 4.10S18 (120/90-18?) rear tire.
Both bikes have effectively the same overall drive ratio.

On my Maxim, I tried a 17 tooth CS sprocket and found it dropped the revs by about 500 RPM for a given gear/speed. And this didn't work for me, my riding style, or the roads I ride. So I changed the rear sprocket to a 38. This resulted in the engine revs increasing about 250 RPM above stock for a given gear/speed. The top speed has not changed, because the engine is still making the same power. I just get there a bit faster is all. And I don't have to downshift nearly as much.

The downside of having 17/38 gears is added weight from the larger gears and more links in the chain. The upside is reduced gear and chain wear, less friction and noise, and the ability to accelerate briskly. Some people whine that the engine is buzzy at highway speeds. To that I respond: "Then why did you buy a 400 twin when you obviously want a 1300 V-twin?

Great Dave, this is good.
I am running 17 35, Maxim 5 speed motor in a Seca. I will study the rear tyre, and double check the sprocket sizes. I have a 16 CS sprocket but thought it might be too big of a change. So was thinking of going up a couple or three teeth on the rear.
Meanwhile i will study your post carefully.

Thank you. Unkle Crusty*

 

[Unkle Crusty]

Did not know about the rear tyre size difference between the Seca and Maxim.
Dave, do you know if a 38 rear sprocket is readily available?
I will do the 6000 revs at 60 test likely on Thursday. May also try the 16 on the front just for a reference point.

Thanks. unkle Crusty*

 

[16VGTIDave]

38 tooth rear sprockets are still available. JT sprockets makes them and they are still stocked by some suppliers. Took less than a week for me to get one about a year ago. This page lists all the bolt on sprockets available for DOHC bikes. JT for some reason lists a 37 tooth rear sprocket for the Seca, but the factory manual calls for a 38 tooth.

 

[Unkle Crusty]

Sweet.

Thank you. Unkle Crusty*

 

[Unkle Crusty]

Just checked Deep Purple. Rear tyre is 110/90 18, and the rear sprocket is the stock Seca 38. Not the 35 as I reported earlier.
I will take off the side cover in a few days and check the front sprocket. If it is a 17, I will change it to the 16 I have. Will also grease the clutch mechanism.
I find 1st 2nd and 3rd, arrive quite quickly, with a bigger gap to 4th and 5th.

DP is running real sweet with 122.5 main jets, the rest the same as yours. This with the EMGO filters directly on the carbs. Having the local ( on my Island ) machinist turning down some PVC pipe next week.

DP was bought specifically for the winter months, and is doing good work. I have bar guards, leg guards, rear top box, saddle bags, and a large tank bag. I also often have a large bag across the back of the seat. Will have to figure out how to post a picture.

I also have a 79 XS11, and an SV1000 Suzuki. Have an Inder side car for the big Yami. that does the truck work. I do not drive a car.

Unkle Crusty*

 

[Unkle Crusty]

Did the test today. 6000 revs gets me closer to 65. So that fits with the 500 rev difference that Dave mentioned.
I am getting about 8150 revs in top gear which is just above the maximum torque at 8000. The front sprocket change to a 16 should get me around 8650 revs which is closer to the maximum horsepower at 9500. So the potential for a small amount more top speed should come from the smaller front sprocket.
If the foam filters require larger main jets, that in turn will create a small gain in power.

Thanks for the help so far guys. I am enjoying the bike now that it is running quite well.

Unkle Crusty*

 

[Unkle Crusty]

Swapped the front sprocket to the 16. Dropped about 500 revs as Dave reported. 6000 at 60, so should also be 7K at 70, 8K at 80 and so on. And the red line, 10,000 at 100 as reported in the original test.
That gets me to thinking about the fellow in Germany who reported 115 at 10,500. Makes me suspicious. Same top speed as claimed for a 68 hp Norton Commando. Mine only did 108.

Unkle Crusty*