Gearing

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BamBamTheAprilia
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Gearing

Post by BamBamTheAprilia » Sat Oct 22, 2016 6:15 pm

Ok Chaps , here goes !!
My TRX is on standard gearing currently producing 72BHP measured on a dynojet dyno. I'm going to be racing it next year.
The problem I have is this flat out in top gear it's showing 125 mph on the clocks and 7750 rpm, 2 things to note it is a Japanese Market bike with the KMH clock converted to MPH by a speedo cable converter and I think I am getting clutch slip .
Now I was expecting it to get nearer to 135 mph , I have FCR41 to go one this winter and a Race pipe from Michaela which will lift the bhp to somewhere between 85-90 bhp ( at a guess, although in reality the lower figure is probably nearer the mark )
Now I have looked everywhere as I would like to raise the gearing to take advantage of the extra power on tracks like Silverstone.
So the question is has anyone managed to do this ? If so how , as I can't see anyway to fit a reduced tooth sprocket at the rear with the existing carrier . Maybe this is a question for Cobba ?

cobbadiggabuddyblooo
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Re: Gearing

Post by cobbadiggabuddyblooo » Sun Oct 23, 2016 6:00 am

Even with FCR's you'll probably make peak horsepower about 7500rpm and maybe hold it to around 8200rpm with exhaust more so designated for top end power. Your overall peak torque will be up plus it may not be as peaky too and plateau a little more around that 6500rpm Mark.
You'll more than likely find your 220kph by going down 1 tooth on the front because you'll find you have a slightly wider power band.
You'll gain better acceleration with 1 tooth lower in the front and the wider powerband with FCR's will allow you to run it up to 8500rpm.
If you look at most of the guys dyno charts with FCR's and free flowing pipes ,forget the outright numbers but look at the power and torque curves and RPM. They are all much as much just slight variations in certain rpm ranges due to choice of exhaust or intake set up.

You'll gain a little more by finding cooler air hence why I made up a simple but effective air box/ heat shield. An alloy sheet sitting between the rubber inlet manifolds and FCR's and sides made from 3mm rubber that are braced inside with alloy plate then bolted to the frame tubes encloses the FCR's under the tank with only cool air fed in from under the front of the tank.
If just doing track work just run bell mouths with no filter because there is less restriction.
Running a Ramair twin sock filter on the bell mouths will rob about 2 HP because it sits right on the bell mouths. The reason why I just built a larger filter sitting under the front of the tank where the air is drawn in as it allows the bell mouths to draw on a lot more free air with no restriction from under the whole tank area.
Enclosing the FCR's also pressurizes the fuel bowls if there are any gains in inlet pressure too.
Last edited by cobbadiggabuddyblooo on Sun Oct 23, 2016 11:50 am, edited 2 times in total.
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cobbadiggabuddyblooo
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Re: Gearing

Post by cobbadiggabuddyblooo » Sun Oct 23, 2016 6:11 am

Go into gear commander site and look at your options.
17/ 41 rear may be another good option as it's close to using a 16 front/ 39 rear and still give you the option to run a 16 front 41 rear for tighter track days on other circuits.

You can see what I mean when you look at the gear commander options I placed on my rebuild threat a couple of days ago. Gear choices of 16/40 17/40 16/41 17/41.
You have the freedom to place in your tyre size , shift your peak rpm around and choice of sprockets.
Hence why I changed the peak horsepower up to 9500rpm compared to 7500rpm in std trim.
I'm just lucky enough to have peak HP around 8500rpm and able to hold that to close to 9500rpm.
So if you find a dyno chart with a similar intake and exhaust set up that your looking at, look at the torque curve and where the peak HP is and if it holds it or just starts to drop off to set your peak RPM on the gear commander.
Theoretically you'll gain about 1 HP by running a 520 chain and sprocket set up due to less drag.
Pay that little extra for a top quality chain and you'll find you'll get around the same life as a 525 pitch.
All these little gains start to add up with cooler air and chain pitch. Suspension and weight is a priority too.

http://www.gearingcommander.com/

Just looked at std specs and custom set up with a 16 tooth front.. Are you sure it's not a 16 tooth up front already????
Anyway here is the link for you...
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cobbadiggabuddyblooo
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Re: Gearing

Post by cobbadiggabuddyblooo » Sun Oct 23, 2016 12:27 pm

Here is my old dyno chart with FCR's, bell mouths and ramair twinsock with a stepped header 2 into 1 large bore with a 57mm outlet can as a reference .
3 runs
1st with std FCR set up
2nd with 1 clip leaner on the needle which improved lower rev range
3rd run with the tea strainer/cap in the end of the can removed which made me loose a little down low but gain a touch more up top.

Image
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BamBamTheAprilia
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Re: Gearing

Post by BamBamTheAprilia » Wed Oct 26, 2016 1:14 pm

Cheers for all the info Cobba !
It was on 16/39 setup when I bought it , recently bought new chain and sprockets all standard gearing ( 17/39) . I'm struggling to find 520 pitch sprockets to fit both front and rear. I have been on the JT sprockets site and gone through their catalogue . The XTZ750 Super Tenere ( 750cc TDM lump) runs 520 pitch , the front sprocket is available in 14-18 teeth sizes , just no joy finding a 520 pitch rear to fit . Have you got any suggestions as to where I might get hold of one ?
I was looking at adapting a standard airbox to fit the FCR's and setup a forced induction system .
On another note one of the tracks I will be racing at is Aintree which has an 800m straight. You enter the straight in top gear almost flatout because of the way beachers corner is setup, hence the need for more top speed. Aintree is about 2.4km long has 3 rights 1 left and the lap record is around 55 secs for 1000c in line four ( A friend laps it in 1:20 on a 200cc single ). So one of the things I am trying to avoid is over revving the engine as it is on std rods , which I believe suffer from stretching?
By the way tried Arias UK for some 878 pistons they have never come back to me :( :(

cobbadiggabuddyblooo
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Re: Gearing

Post by cobbadiggabuddyblooo » Wed Oct 26, 2016 1:48 pm

I think I had an early 90's xr500 Honda rear sprocket that had the same pattern and I just had to enlarge the bolt holes by 2 mm on the sprocket so easy fix. Suzuki k6 and some r6 front sprockets will work too, but double check on the JT site as it was a few years ago I tinkers in this with the TRX std rear wheel.
If you force feed or ram air into the box you'll need to pressurize the fuel bowls to the same pressure hence why it's easier to place the carbies in the chamber too .
If your looking at changing pistons to a higher compression above 11.1 and larger capacity you'll have to start looking at longer duration cams otherwise your pumping loss comes into play and most of the power gains are lost.
Capacity and duration go hand in hand too.
8500rpm is pretty safe on std rods if piston weight is kept standard or even better less...
If you finally get in touch with Arias their office in the US will have all the specs for the 878 pistons and weights are about 5 grams less than std or for a few $$$ more you can safely take 25grams from their total weight to help ease the load on the rod caps at higher revs and compression.
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Ragnar
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Re: Gearing

Post by Ragnar » Sat Nov 05, 2016 11:54 am

As far as i know the R6 Front sprockets are interchangeable, but you'll need a Little spacer so the chain Runs in a straight line.

He Can provide you a complete 520 Chain Setup which Fits the TRX, Even with Aluminium rear sprocket and light Front sprocket: http://www.rennservice-grimm.de
Just send him an Email and ask for it...

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