No dyno available and I'd like something more objective than seat of the pants. I'm running stock exhaust on my 351 and am looking to buy a 300klx exhaust and a Four Stroke Works header (the guy who makes them lives close so I'm going up to his shop Sat.)

As on person pointed out after he put on his slip on: he thot it was faster but that couls just be subjective cause it was louder.

I'm thinking a roll on at a fixed rpm, shift the same place and look at top speed or time between two points. I do have a stop watch I could probably tape to the handle bars.

Suggestions?

 

Lacking a dyno that's going to be tough to positively, absolutely qualify your results. Another odd thing is that an increase in something like a 1/8th mile or 1/4 mile performance on pavement might not be a good indicator in how the bike will perform off road where low end torque increase might be more important than a little top end power at the expense of torque. Timed runs on a dirt track can be a little fuzzy at times, because everything you do on each run has to be exact to qualify a performance increase. And we know how hard that can be sometimes. Additionally, sometimes just making the powerband broader instead of just increasing peak power can be just as big a performance benefit. So much depends on how and where one rides and what type of power gain will give you the most return. A nitrous bottle strapped on the luggage rack might give an unholy increase in power, but it probably wouldn't be that great for trail riding...though drag racing from the Tastee-Freeze against that guy on the Vespa scooter might be a hoot.

Unfortunately the butt dyno is still a real and applicable guage of useable power increase for a rider with some experience. You make some mods and go ride...preferably somewhere you ride frequently. How easy was the climb up that last gnarly hill? How much did I have to slip the clutch? How fast and hard does it pull out of slow corners? How easy is the front to loft over that big ledge now? Do you still have to rev the engine to the moon to get any speed, or can you short-shift a bit more? The list goes on. If you have a small section of trail that you ride frequently, you could time enough runs to probably get a decent qualifier, but it would take quite a few. Unless a rider is new to the sport, I think most of know when a modification has produced real results...good or bad. The best thing about performance mods is that we don't really have to produce a dyno sheet at the end of the process. If we are honest with ourselves, we know whether that big bore kit, rejet, pipe change, new carb, or whatever doo-dad we installed actually did any good. Now, if you race for a living, you wouldn't be messing with a KLX anyway for hardcore performance gains. All we have to ask ourselves, "is this bike more fun to ride now?"

 

Oh gosh that's a hard one. Very subjective and lots of variables. Even dynos aren't 100% objective because little things change between runs.

Nothing wrong with seat-of-pants testing, in my opinion, because we are massive parallel processing supercomputers. But you must encode what 'before' was in your brain, or go back to before conditions sometimes to recalibrate, do a lot of 'after' iterating build convincing data, and try to keep from being fooled by the primitive side of your brain, with vibration, noise, or tribalism (since I spent money on this mod, it must be better). Ultimately, the bike either runs really well or it doesn't, and only you have to be satisfied.

About pipes, making more noise will definitely throw off the evaluation. One reason loud pipes and lowered gearing are popular is the increase in noise and vibration fool that more primitive parts of our brain into thinking we are going faster. Loud pipes are hated by many - including me, and I'll never spend another dime on them.

I have a KLX300 muffler and header. The only difference between the 250 and 300 headers is the exit diameter. The KLX 300 header has a bigger exit to fit the 300 muffler. Mine muffler came without the baffle, because some spud removed and lost it. Exited to receive my new setup for my 330, I fit it and was sorely disappointed to lose power on the low end. The bike ran like crap and did not respond well to jetting changes. I use the low end and midrange a ton, so if the bike only runs great WFO I consider the mod a failure. I took it off the 300 pipe for months, put it up for sale, and got a CRaiglist scam email. Pissed off, I thought I'd give the pipe one more try, this time making a very quiet baffle from a section of steel handlebar. The bike then ran better than the stock setup, and it wasn't irritating to me or others.

If you do run the 300 muffler, I strongly suggest not pulling the baffle out. If you don't have one, make one.

Be interesting to see what the larger volume header will do.

 

I have a steep 2 mile hill by my house that puts a huge load on the little 250. In stock form it struggled to gain speed in 4th gear and would lose speed in 5th. After all the mods it will now pull in 5th and barely maintain in 6th.

So the butt dyno told me I gained a lot of power, but also the performance up the hill told me I gained some power.

Also, now if I goose it in 1st gear the front tire will come up. Wouldn't do that stock either.

 

I went from the 250 to a 351 bore for more power. It worked.

Look here http://www.advrider.com/forums/showthread.php?t=107591&page=291

at post #4357 then post #4364 page 291, then go to page 294 Post #4402.


I will be going back to see what the new carb does.

I can copy and paste if you want. It worked for me.

David

 

As said, hard to get an accurate sense of a power gain w\o a dyno and excluding seat of the pants. I know when I ride, I can tell the difference in power charactersitics on how the bike reacts to terrain....like the hillclimb mentioned. Higher gear held through woods sections, not running out of steam where it would before, even handling could suffer from an infusion of power. Don't discount your butt.

 

Get your hands on one of these



It says that it's not intended for the acceleration on bikes, but I think they mean sport bikes.
I have been meaning to make a little bar mount for mine and try it, but just haven't gotten around to it.

I think I paid $25 for it.

 

There's also a way to record the spark plug with and audio recorder and use a software to analyse it.
Here's one http://jcdperformance.free.fr/powerdyn_me_uk.htm
I think there's other one too.
I've never tried it.

 

That's interesting...I have one of those somewhere. It still is up to the person to ride exactly the same on each run though. I know the readings would be off if not level.

 

A dyno is only a small part of all of this and if I do one it would be more to check the afr thru the revs, more so than the numbers it provides. It's really real world riding that matters in the end, great big show off type numbers mean nothing if they aren't achieved in the range where the bike opperates. So at best all things must be considered. This is a good reason to only do one mod at a time and see if you gained or lost in an area that matters. It's like the powerbomb I put on I really don't know if I gained any total hp but it pulls the front end up with almost no effort now so it is something I would strongly reccomend for a stock to stage 1 or 2 bike as my result were desirable either way.