Low End Torque

Don,
One can change the rear wheel belt sprocket from the International 61 tooth to a 70 tooth sprocket (Standard sprocket used on earlier Big Twins sold in the US). The belt will need to be changed also.
There are vendors of different ratio transmission sprockets also. Most Harley shops have the information you need and access to the parts.
FYI: There is no "Cheap" fix.

Lonnie
Northwest Sidecars

What exactly do you consider reasonable? Unfortunately, performance is expensive.

As mentioned above, changing out the sprocket will increase your low-end torque at the expense of decreasing high-end Hp.

Other options include:
A big-bore 95" kit will add approximately 10 ft/lbs of usable torque at the rear wheel across the power-band. At my local dealership, this kit costs approximately $1000 installed.

A fuel-injection controller + high-flow mufflers and air-cleaner will also add approximately 10 ft/lbs but this will be closer to the mid-range of the power band. Again, expect to spend approximately $1000 for this upgrade. If you choose to only add the fuel-injection controller like you talked about above, you'll at least be able to richen the fuel mixture which will help but not as much as doing a complete intake / exhaust job. Harley ships their bikes running very lean to satisfy the EPA. The FI controller lets you "fix" this 🙂

A final option is to put in a cam designed for low-end operation (like and Andrews 21N).

Keep in mind all of these will decrease your gas milage and all three will require an ECM remap or fuel injection contoller like the power-commander.

Changing the final drive gearing will not change the torque produced by the engine at all. Changing the final drive grearing wil allow you to start from a stop with less clutch manipulation etc. though. If you are now okay with starting from a stop then possibly learning to run in lower gears for a given speed may work okay. If you lower the gearing because you are running out of steam in the higher gears fine but it is not a real substitute for more power to begin with.
Many , expecially american riders, tend to short shift their machines rather than let th ebike be happy in the gear it is in. Sometimes a variation in riding (shifting ) style once a hack is added can make a lot of difference.
To take an already expensive stock bike and add more dollars to it to increase power is not uncommon with some brands. Possibly beaing able to ride one that has already been tweaked woudl be a good idea.
No sidecar rig IMHO will ever have too much power. The question is how much is enough and what will it cost. Smokey Yunick used to ask : " Speed costs money how fast do you want to go?"

Originally written by Donald Fox on 6/7/2007 10:56 AM

I would like some advice on increasing the Torque on 04 Road King/w Spalding Sidecar.I have a reccomendation to do an expensive engine job?(this I don't want to do)Change some sprockets (this I know nothing about)or install an electronic commander spark,fuel etc control(I have installed these on Chevy Surburbans and they work very well)anybody have any ideas at reasonable costs?Thanks Don Fox

The 2004 Road King has 3.15:1 gearing overall. The rear belt has 32 Tooth at the countershaft and the rear sprocket has 70 teeth. thus the rear ratio is 2.1875.

The primary ratio with a stock 25 tooth motor sprocket and a 36 tooth clutch shell sprocket is 1.44:1. A change to a 24 tooth motor sprocket (P/N 40264-85A) and a 37 tooth clutch sprocket (P/N 37846-99A) will give you a 1.54:1 primary ratio for a 3.37:1 overall ratio taking into account the rear belt ratio. These two parts are fairly straightforward to change and can be bought online for $350 not counting labor. They will only work up to 2006 models on the FL's.

While the new gears will not increase torque per se, they will change your Road King into a good sidecar bike by making your existing torque more available to you. I did the change on mine about two months ago and the difference is remarkable. You will still be able to cruise economicaly at road speed and your fifth speed will be much more usable.

By the way, the stock 88" motor is an excellent engine for a sidecar. It has excellent torque from 1500 rpm on up and is almost seamless up to road speed.

Any engine modification you will do is going to make your bike less useful for sidecar work. For example, a change to 95 cubic inches will raise the compression ratio and require a change to the mufflers and air cleaner to make the extra power available.

At the same time, to get the maximum torque and hp increase from your possible modifications will certainly require changes to the EFI map to prevent a lean mixture (unless you have a carburetor where you could change jets more easily). It costs even more for a Harley Map download or Power Commander or other unit. It's possible that your machine could also incur more engine heat and detonation as the result of this change as well.

Any change of cams will also increase the rpm at which the torque begins to increase to a useful level. Generally speakling you would get more horsepower and torque but it would only be from 2500 rpm on up. While it would be fine for a solo machine, this is not something you want to do with a sidecar. Dollar for dollar, a simple gear change will do you more good than any other modification.

Happy Trails.

the most important thing to understand is this - if you dont understand in detail what you are being sold it will most likely NOT do what you want. you need max torque below 4000 rpm. high sales numbers obove 4000 rpm wont do any good [ie the chart they use to sell you the parts]

1 - nearly all performance modifications availiable in the aftermarket are to get more hp at high rpms to go really fast - and many of them will lower the power below 3000 rpm - so let the buyer beware

2 - the stock manifold is proven via the dyno charts to be the best manifold for tourqe - dont change it.

3 - if you dont want to spend much more than 1000$ then a gearing change is your only option and that will cost near a grand since the belt has to be changed as well & that is a really big deal to the uninitiated.

4 - for each model year - the police spec engine is the highest torque performer - copy that.

5 - fuel injected harleys respond better to a sert than a power commander - however a good sert tech can be hard to find - you get what you pay for. random download that "might work" or put it on a dyno with a sert and actually get something you already paid for - your choice.

your cheapest bet is to run in a lower gear when possible

the 96 basically is 88 cyls with the 103 crank and cams near what a 95 police bike has.

if you had unlimited cash the current 103 [ for the 96' bikes] or the 110 both have a torque curve that is really just right for a sidecar - but the 96 is just fine.

what everybody says is true - it can have as much power as you want and go as fast as you want depending on the cash you want to spend.

but the only things that will get you more torque without taking the engine out and apart is gear changes. you do have options on gear changes - there are smaller engine sprockets and larger wheel sprockets - you have to decide how much torque you want and how much you want to spend and if you want to just guess or put it on a dyno and tune it properly.

Originally written by timo482 on 6/10/2007 6:50 PM

the most important thing to understand is this - if you dont understand in detail what you are being sold it will most likely NOT do what you want. you need max torque below 4000 rpm. high sales numbers obove 4000 rpm wont do any good [ie the chart they use to sell you the parts]

1 - nearly all performance modifications availiable in the aftermarket are to get more hp at high rpms to go really fast - and many of them will lower the power below 3000 rpm - so let the buyer beware

2 - the stock manifold is proven via the dyno charts to be the best manifold for tourqe - dont change it.

3 - if you dont want to spend much more than 1000$ then a gearing change is your only option and that will cost near a grand since the belt has to be changed as well & that is a really big deal to the uninitiated.

4 - for each model year - the police spec engine is the highest torque performer - copy that.

5 - fuel injected harleys respond better to a sert than a power commander - however a good sert tech can be hard to find - you get what you pay for. random download that "might work" or put it on a dyno with a sert and actually get something you already paid for - your choice.

your cheapest bet is to run in a lower gear when possible

the 96 basically is 88 cyls with the 103 crank and cams near what a 95 police bike has.

if you had unlimited cash the current 103 [ for the 96' bikes] or the 110 both have a torque curve that is really just right for a sidecar - but the 96 is just fine.

what everybody says is true - it can have as much power as you want and go as fast as you want depending on the cash you want to spend.

but the only things that will get you more torque without taking the engine out and apart is gear changes. you do have options on gear changes - there are smaller engine sprockets and larger wheel sprockets - you have to decide how much torque you want and how much you want to spend and if you want to just guess or put it on a dyno and tune it properly.

As I outlined above, no belt or rear sprocket change is necessary.....only a pair of front sprockets on the 2004 model. The same primary chan is used. About $350 for parts and no labor cost if you can do the work yourself. It's about a four hour job.

In the Screamin' Eagle catalog Harley-Davidson offers a compensator sprocket/primary chain kit that was designed for racing. It will increase your rpm at any given speed (and any gear) by about 400 rpm vs the stock compensator sprocket. It provides greater torque multiplication due to the changed ratio, which will do exactly what you want as long as you are willing to live with the fact that the engine will be revving higher at any speed compared to stock. The speedometer accuracy will be unaffected. The price of the kit was around $130.00, if memory serves. You'll also need a primary cover gasket and an inspection cover gasket, as well as a quart of fluid. It can be installed within a couple of hours fairly easily. If you pay a dealer to do it your total with parts and labor should be around $325.00, give or take.

Originally written by Bueller on 6/11/2007 5:15 PM

In the Screamin' Eagle catalog Harley-Davidson offers a compensator sprocket/primary chain kit that was designed for racing. It will increase your rpm at any given speed (and any gear) by about 400 rpm vs the stock compensator sprocket. It provides greater torque multiplication due to the changed ratio, which will do exactly what you want as long as you are willing to live with the fact that the engine will be revving higher at any speed compared to stock. The speedometer accuracy will be unaffected. The price of the kit was around $130.00, if memory serves. You'll also need a primary cover gasket and an inspection cover gasket, as well as a quart of fluid. It can be installed within a couple of hours fairly easily. If you pay a dealer to do it your total with parts and labor should be around $325.00, give or take.

I've considered that kit. The main problem with it is it's only suitable for racing, not for the road, not even with a sidecar.

Leaving the clutch at 36 teeth, and changing the motor sprocket from 25 to 21 teeth is a major drop. The overall ratio would then be 3.75. That's entirely too much. It's a19% change in gearing. Top speed and fuel economy would be impacted in a major way.

The motor sprocket and clutch change I've outlined above is the best way to change gearing for a sidecar usage on a Harley FL.

timo482 wrote:
>>...snip...what everybody says is true - it can have as much power as you want and go as fast as you want depending on the cash you want to spend.
but the only things that will get you more torque without taking the engine out and apart is gear changes. you do have options on gear changes - there are smaller engine sprockets and larger wheel sprockets - you have to decide how much torque you want and how much you want to spend and if you want to just guess or put it on a dyno and tune it properly......<<<

One other possibility if such a thing is avaiable it to try a lower profile rear tire. If there is something out there it will lower the final rear end gearing where the rubber meets the road.
Also , please note that in my previous post the question was asked if starting off from a dead stop was an issue. If it is then lower gearing will help out. If it isn't an issue then possible just staying in the lower gears by adjusting riding style can do wonders, even if it is not the overall best case scenario.

That is true, changing the sproket doesn't change the torque of the engine, but it does change it at the rear wheel, which is where it matters.

Also, putting in the Andrews 21N (like I suggested) moves the power-band down, not up as someone else suggested. This cam is designed for HEAVY bikes like riding two-up and riding with a sidecar or trailer. Yes, most cams are designed for high-end power, but not the one I suggested.

Finally, moving an 88 to the 95" kit does not increase the compression ratio. This kit uses larger pistons, not stroking to increase displacement.

The original poster was requesting information regarding increasing pulling power for his Harley rig with low cost.

Changing cams would also require a different air cleaner, mufflers and EFI tuning equipment. Porting the heads would also be a good idea....more cost all around.

In any case, changing to a modified cam usually raises the torque start point. If the cam you are describing is the Andrews 21, their own material states that the torque point for that cam starts at 1,700 rpm. A stock Harley TC 88 has usable torque starting at 1,400 to 1,500 rpm.

The 95" changover will raise compression. Same size combuston chamber with larger pistons. Stock compression is 8.6:1 and the 95" changeover typically gives over 9:1.

A gearing change is a lot cheaper.

Originally written by gnm109 on 6/12/2007 3:51 AM

The original poster was requesting information regarding increasing pulling power for his Harley rig with low cost.

Changing cams would also require a different air cleaner, mufflers and EFI tuning equipment. Porting the heads would also be a good idea....more cost all around.

In any case, changing to a modified cam usually raises the torque start point. If the cam you are describing is the Andrews 21, their own material states that the torque point for that cam starts at 1,700 rpm. A stock Harley TC 88 has usable torque starting at 1,400 to 1,500 rpm.

The 95" changover will raise compression. Same size combuston chamber with larger pistons. Stock compression is 8.6:1 and the 95" changeover typically gives over 9:1.

A gearing change is a lot cheaper.

....................................................................
The following is in general terms only.
Typically advancing the cam timing (not the ignition) will bring the torque curve down the RPM scale. Whether this is easily done on a Harley Is unknown to me.
Increasing the bore with the obviously larger pistons will only increase compression ratio if the pictons are the same design from wrist pin to the top surface. Many times piton designs for larger bores are modified to retain stock or near stock compression.
Larger bore will not increase torque the same as more stroke will.
True Compression ratios are affected by cam design as well as piston shape and combustion chamber size.
More back pressure in the exhaust may increase low end torque over straight pipes or various aftermarket exhausts.
If the stats given for the change in RPM that the andrews cam produces it is only 300 more revs. If there is an increase in torque that is significant this is a small price to pay unless the low bottom end is killed altogether which is doubtful.
I would think that a final gearing change may be the first plan of attack followed by the andrews cam if more 'umph' was desired down low. Unless advancing the stock cams is doable. Pipes should be evauluated as well
Then of course there is always the Triumph Rocket 3 🙂

Originally written by claude #3563 on 6/12/2007 3:25 AM

Originally written by gnm109 on 6/12/2007 3:51 AM

The original poster was requesting information regarding increasing pulling power for his Harley rig with low cost.

Changing cams would also require a different air cleaner, mufflers and EFI tuning equipment. Porting the heads would also be a good idea....more cost all around.

In any case, changing to a modified cam usually raises the torque start point. If the cam you are describing is the Andrews 21, their own material states that the torque point for that cam starts at 1,700 rpm. A stock Harley TC 88 has usable torque starting at 1,400 to 1,500 rpm.

The 95" changover will raise compression. Same size combuston chamber with larger pistons. Stock compression is 8.6:1 and the 95" changeover typically gives over 9:1.

A gearing change is a lot cheaper.

....................................................................
The following is in general terms only.
Typically advancing the cam timing (not the ignition) will bring the torque curve down the RPM scale. Whether this is easily done on a Harley Is unknown to me.
Increasing the bore with the obviously larger pistons will only increase compression ratio if the pictons are the same design from wrist pin to the top surface. Many times piton designs for larger bores are modified to retain stock or near stock compression.
Larger bore will not increase torque the same as more stroke will.
True Compression ratios are affected by cam design as well as piston shape and combustion chamber size.
More back pressure in the exhaust may increase low end torque over straight pipes or various aftermarket exhausts.
If the stats given for the change in RPM that the andrews cam produces it is only 300 more revs. If there is an increase in torque that is significant this is a small price to pay unless the low bottom end is killed altogether which is doubtful.
I would think that a final gearing change may be the first plan of attack followed by the andrews cam if more 'umph' was desired down low. Unless advancing the stock cams is doable. Pipes should be evauluated as well
Then of course there is always the Triumph Rocket 3 🙂

Usually increasing bore will increase compression in a Harley engine. The people who make pistons are not in the business of making low compression pistons. Most people are looking for 10.5:1 when they make such changes and that's where the market lies.

Cam timing can be advanced on some cams that have the proper keyway design and that would increase torque to a certain extent. Ignition timing on the late Harleys is controlled by the ECM and you need an aftermarket ignition and/or a Screaming Eagle Race Tuner device or equivalent to change it.

Again, all of this is nice and certainly possible. Changing cams, pipes, ports, air cleaner, and EFI equipment to control the different mixture is about a $2.500 expense.

The original thread had to do with inexpensive changes.

WOW what a bunch of information and all sounds good,I am a novice rider this is my first bike and I love it.I am at the age where speed is not an issue,I just want something that is nice and feels good like it is doing it's job.I have (since my first response to this, started to practice riding every day) I am learning that riding in the lower gears a little longer feels right and the shift at the right time is OK.I like the idea of the Sprocket change and I will persue that if I don't find that practice riding in various gears satisfys me.THANKS TO ALL YOU GUYS FOR THE WONDERFUL RESPONSE>DON FOX