Boost torque across rev range

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crashcourse

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So, I've finally convinced myself I can afford to make some performance upgrades. Basically, I don't need go-for-broke top end. I just want a little extra torque in as wide a range as I can get. I also realize that just bolting parts on willy-nilly probably won't get me what I want - I have to select a system of parts that work together.

Now, with torque being the primary goal, I am constrained by cost (I would like to spend less than $300), looks (this is my stock '81 special, and I don't want anything too far from that), and noise (I ride a lot with my wife, and she's not a fan of really loud exhausts).

So, I was thinking of doing XSJohn's airbox modpaired with aftermarket filters (UNI or K&N) and replacing the stock exhaust with mike's commando 2-2 system or a system from Gordon Scott.

What I haven't found is any data on how the commando system boosts performance. I know Gordon Scott does excellent work. Has he made a stock-looking, torque-boosting system for anyone on here? If I bought from Gordon Scott I'd have to get the pipes chromed; how much would that cost me?

Any suggestions for me, keeping in mind my performance goal of increased torque with mostly stock looks and volume? Would this combination of mods (of course, I'll rejet appropriately) get me what I want? Or, is there something of similar cost with better results?
 
I assume you want low end torque and mid-range power. A good running stock XS has great torque for only 650cc. The very best, bar-none, no-compromise easy increase in overall torque is a 750cc kit. The kit doesn't meet your budget. You could try increasing displacement and compression with 700cc pistons. Increasing displacement and/or compression is a time honored way of getting a torque increase across the entire rpm range.

Many of the common power mods result in mostly upper end power.

Tom
 
Reading between the lines you aren't necessarily looking for dyno numbers but seat of the pants feeling? Something that will pull a little easier and quicker(meaning getting to road speed) when two up?
 
weekendrider said:
Reading between the lines you aren't necessarily looking for dyno numbers but seat of the pants feeling? Something that will pull a little easier and quicker(meaning getting to road speed) when two up?
Click to expand...

While I would be curious about numbers and the shape of the torque curve, what I'm really looking for is a little easier pulling for two-up riding. I could change the rear sprocket, but I do occasionally take the bike out on the freeway, and I don't want to have to rev super high to keep up with traffic.

And neither of us are very big people, so it's not like I really need the extra oomph. So let me ask the question a different way: would commando mufflers push my power higher up in the rpm range, or keep it pretty close to the stock feel?
 
Put a 36 tooth sprocket on the rear. It will make a big difference on how the bike feels (torque). Yes, its best for around town and back roads; however, you can still drive it on the expressways..................will be about 4100 to 4200 rpm at 100 km/hr (62 mph).
 
The commando system is supposed to increase power in all rpm ranges. I like how it looks and sounds. I would say close to stock feel. Maybe a little more power in the upper mid range than stock. Work well in the lower RPM also.
 
crashcourse said:
So, I've finally convinced myself I can afford to make some performance upgrades. Basically, I don't need go-for-broke top end. I just want a little extra torque in as wide a range as I can get. I also realize that just bolting parts on willy-nilly probably won't get me what I want - I have to select a system of parts that work together.

Now, with torque being the primary goal, I am constrained by cost (I would like to spend less than $300), looks (this is my stock '81 special, and I don't want anything too far from that), and noise (I ride a lot with my wife, and she's not a fan of really loud exhausts).

So, I was thinking of doing XSJohn's airbox modpaired with aftermarket filters (UNI or K&N) and replacing the stock exhaust with mike's commando 2-2 system or a system from Gordon Scott.

What I haven't found is any data on how the commando system boosts performance. I know Gordon Scott does excellent work. Has he made a stock-looking, torque-boosting system for anyone on here? If I bought from Gordon Scott I'd have to get the pipes chromed; how much would that cost me?

Any suggestions for me, keeping in mind my performance goal of increased torque with mostly stock looks and volume? Would this combination of mods (of course, I'll rejet appropriately) get me what I want? Or, is there something of similar cost with better results?
Click to expand...
........................hi if you look up the aussie xs650 site ,,,,there,s a guy thats building himself a super fast xs650,,, with fuel injection ,,,re- designed gearbox etc.etc etc. its well worth a read ....regards oldbiker
 
Couldn't he also retard the timing a few degrees for slightly better low, mid range? It will take away some from the top end but should make it better for what he is looking for. Lollipops in the exhaust could help also, combined with a bigger rear sprocket. Going up a few teeth isn't going to kill beltway rpm, but will raise it a few hundred.
 
If you go with the Uni pods, then the xsjohns air box mod won't be needed. I'm running a stock header and Dunstall repros on the '83 and what I believe is a close to, if not, mikes Commando system on the '77. 18/32 gearing and wouldn't change a thing. One up 90percent of the time......exhaust is so much better than stock, either way. May switch one of the bikes back to stock gearing just for the comparison.
 
RatyXS said:
Couldn't he also retard the timing a few degrees for slightly better low, mid range? It will take away some from the top end but should make it better for what he is looking for. Lollipops in the exhaust could help also, combined with a bigger rear sprocket. Going up a few teeth isn't going to kill beltway rpm, but will raise it a few hundred.
Click to expand...

Can timing be changed with the stock TCI? I read that xsJohn pressed the cam sprocket off the cam, moved it, and pressed it back on. Is this the only way to change the timing?

And I forget, does retard mean to make spark occur later or earlier?
 
The XSJohn cam change was in conjunction of doubling up on the head gasket for lower compression.......moving the TCI pickup clockwise will retard the timing. If you decide to move the pickup, it's a good idea to mark the stock location before hand so's to be able to set it back if you need.
 

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I've thought about porting, lowering compression, and retarding timing. That all may be in the future. For now at least, I'd like to not take apart the engine until it needs to be fixed. I'm not confident I could put it back together and have it run as well as it does now.
 
What carbs you got, what has been done to them? Are they synched? Jetting spot on for your altitude? Provo is mile high country, stock lowland jetting would be hairy lean rich...
What compression are you getting? Has the ignition been upgraded? pamco pete ran some experiments and got improved performance with stronger spark and "better" plugs.
The point here is that the cheapest AND best "upgrade" is getting the stock setup to it's peak performance. And if you don't do these FIRST other "performance upgrades" will be fruitless.

What are your "ride" parameters? If it's an in town-ish bike. bumping the rear sprocket up a couple of teeth will do just what you want for about $100 all up.
Doing all this is the best performance money available and a world of education.
do as it is and after on the dyno, report back we'd love to see the results.
 
Hi Gary,

Rethink your jetting. Higher altitude has less air so lean stock jetting will richen at higher altitude.

Hi John (Ratty),

Retarding timing will absolutely kill low end torque, even more so at higher altitude.

Hi Crash,

Lowering compression will reduce torque, even more so at higher altitude.

Tom
 
Crash, you asked a simple question that went unanswered--will Commando muffs reduce low end torque?

Answer--no, they won't, if you're installing them on OE headpipes. If you install 1-1/2" single wall pipes, the torque peak will move up the rpm range due to the larger ID of the pipes, but likely not enough to notice if you tune the carbs properly.

You will not get increased torque by lowering compression.

Apart from getting turned around on altitude and jetting (glad somebody besides me gets dyslexicated once in awhile), gggGary has summed up just where you need to start.
 
Okay, glad we have a consensus on changing timing.

I've felt that the jetting is pretty good. It starts easily, even in the mornings or after sitting for a few weeks. If anything, its a little rich, but I'll check the easiest things first.

If I buy the headers sold with the commando complete system (mine are in rough shape), would they be the 1-1/2" single walled pipes?
 

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