decreasing the stroke?

[cals400ex]

i am looking for a good power mod for my 400ex. many of the people i talk to with the strokers say they rev slow and aren't intended for higher speed drag racing. i am looking for something with great power in 3rd-5th gear. low end power isn't a huge concern. has anyone decreased the stroke to make a high revving bike? i am not really sure what my other options are. i am not buying a 450. i want this to be as fast as the 450's in a drag. i am not that far behind now, but some work does need to be done. thanks

[K_Fulk]

1 guy I know that races tt destroked his crank 1mm and used a 91mm piston . Said it worked great and kept him under 450cc.

But hardly anyone does it.

[wilkin250r]

I've never heard of anybody destroking the crank for higher revs. Personally, I think you would be better off increasing the stroke and gearing it accordingly. A CR250 will rev higher than a CR500, but there ain't no way the 250 will beat it in a drag. Like the old saying, no replacement for displacement.

True, the stroker cranks tend to lose power in the upper RPMs, but I think that is largely due to balance and vibration issues. If you want a high-revving drag motor, first off, talk to a profesional, but that almost goes without saying. I think you'd be better off with the biggest bore you can get on the stock stroke, and then get your crank and motor balance with the larger piston. Anything off-balance or any vibration will kill your power in the upper RPMs.

[INFANTRY RACING]

i don't know who told you that but i guarentee you my powroll 4mm stroke and 13:1 comp piston motor dosen't rev slow. thing blows away crf and yfz hybrids and has great power bottom to the top.

[cals400ex]

i forgot to mention, i will only want 11:1 compression. you guys may be right, stroking might be the best option. i was going to have GT Thunder do the work, just so you know the builder. i know one individual who runs a powroll +6mm with a 87mm piston. he said he would never stroke another motor of his again. he mentioned it was quick but nothing too impressive. i also talked to another individual who ran a 88mm piston with a 6mm stroke and he mentioned in a drag race his regular 426 is just as fast. the stroker just does way better in the woods, which i don't care at all about. this one was built buy a builder that uses the same work as laz at gt thunder. he mentioned he loved the stroker, but he was a woods racer. he told me not to do it for what i want. i realize a 12.5:1 or something like that may be great. this isn't going to be used for strictly racing. i will be playing a bit on it. reliability is a concern too, so i want to stick with 11:1. boy, i am not sure what i want to do. :confused:

[INFANTRY RACING]

mines all motocross no drag except leaving the gate. i would stick to the 4mm stroke with a heavy duty rod. then run a 416 piston at whatever you want. i really like my setup. i ran a stock cam with a lectron carb. ported head, and hetrick exhaust and the thing ripped. the powroll setup uses a good ad and even comes with a new bearing on the pressed side. all thats required is a little skirt maching for 30 bux. for 550 it's a good imvestment.

[44oEX]

I have a 500ex bore/stroker and it runs great. I say that is the best way to get the most power.

[cals400ex]

for $550, what all do you get?

do you use a custom piston? or did you just change the rods length?


i plan on getting a heavy duty rod with it. also, why do you recommend the 4mm stroke over the 6mm stroke?

[K_Fulk]

4.0mm STROKER WITH POWROLL ‘TOUGH ROD’

425cc with stock piston, 440cc with 87mm piston, 460cc with 89mm piston

PISTON KIT IS NOT INCLUDED WITH THIS STROKER

This stroker utilizes our super-strong ‘Tough Rod’ (with your stock pin and needle assembly).

The shorter rod allows you to utilize any 400EX piston kit (piston skirt may need to be shortened) and does not require any case or gear modifications.

INCLUDES: New Powroll Tough Rod. Stroke work done on your crank.

REQUIRES: Your crank pin and needle assembly must be good. Non-Powroll pistons will need modification to skirt.


copy and pasted from there site

[wilkin250r]

For high revs and top-end, I think you're best bet is big-bore, stock stroke, and balanced crank. Balance is the key to high revs. It's the whole reason stroker motors lose their top end.

[chad502ex]

if you build an engine with a longer stroke it will develop more torque because of the greater leverage with the longer rod on the crank.

if horsepower is your prime goal, then it is better to build an engine with a large bore and short strock capable of turning high crank speeds.

torque is an expression of the amount of work the engine can develop, and horsepower is the ability to do work in relation to time.

torque wins races!

wilkin is correct about balancing being the key to a stroker being to be able to output high R's.

bore/stroke ratio is "key" too! it comes to a point where the bore becomes too big and then the engine become a slug. In my opinion, it's finding the perfect bore/stroke ratio in every stocker that provides maximum output.

just my thoughts.

chad502ex.com

[cals400ex]

thanks for the help. i just got done talking to laz and he honestly came out and told me that i shouldn't buy a stroker without driving one first because there is a good chance it isn't going to be what i want. i don't mind stroking it or balancing it or going with a larger bore but i want a gain out of it. if i am going to put that kind of money in i want more power for my style of riding. it seems like there isn't much more i can do that will fit my riding style or it may be hard to find the "proper" setup for the bore and stroke. :confused:

[INFANTRY RACING]

i think a 4mm strokes good. i would stay away from any more than that

[wilkin250r]

Let's face it, the 400EX is not a drag bike. And any mods you do to it generally decrease the upper RPM power.

If you want a rev monster, you certainly don't want to stroke it, but I don't think you need to go so far as to de-stroke it.

[cals400ex]

i guess it doesn't have to be a rev monster but i don't want to put 1K in the motor and it be slower for my style of riding (3rd and 4th gears are really important and a good top speed would be nice too). i really don't know how much larger i can go on the bore and still be safe and provide gains that i am looking for. i mean, if stroking with lower gearing would provide what i am looking for, i would consider.

[wilkin250r]

I don't think the particular gear will matter much. The stroker won't change your gears, obviously, it will change your RPM region.

What is your particular riding style? What RPM range are you typically running in? Are you typically screaming near the rev limit for extended periods of time?

[cals400ex]

i do a lot of dragging with my buddies. it is nothing like in professional races or anything like that. however, i ride with a few yfz's so i need a bit more out of this bike. when riding, a aftermarket rev box is manditory for me. i am above the stock rev limit. so i would say when i am racing, yes, i am at 9,000 + rpms. however, it isn't like i race the whole time i ride but i would like the power to be there when i am racing. it seems like chads 502 runs pretty good. maybe i should go a route like that. i don't need to be a decked out yfz when dragging. if i can run with a piped one, which is pretty quick, i will be happy. i am wanting to spend 1K or less and i believe i can get mickeys kit for that. if this will make more power than my bike at much lower rpms, that should be fine. all i need is to be quicker. if i need to change my sparks pipe to a more torque pipe or my TC cam to a different one, i am willing to do that.

[chad502ex]

Originally posted by cals400ex
it seems like chads 502 runs pretty good. maybe i should go a route like that.

Better than "pretty good"

cal, what i've learned from a stroker is this...

when you get a stroker you'll have more power from the start to pull out front if you stay in the peak of the powerband and not over-rev. once you over rev the stroker the 450's will pass you because can they generate equavalent hp but only faster than a stroker because of the shorter stroke. If you get a stroker, you will have to gear for top end cause more torque will generate more low end power (torque) on the engine.

advantage: strokers increase low end power to pull you out front first, and strokers have enough power to permit and pull through a higher gear ratio than your competition(higher gear ratio more top end speed). win on first point, win on second point, win on raceday!

torque wins races if you know how to use the torque and not the hp of the stroker

hope this helps cal.

chad502ex.com

[wilkin250r]

I hate to be the bad guy, but I don't think $1000 will give you really what you are ultimately looking for. It will certainly make it better, but not "great".

I got my big-bore 340cc, and it vibrated like a mofo. I had gobs of low-end (even with a mid-top end pipe) and could beat anything off the line, but I couldn't stay out in front because I had NO power in the upper RPMs. So I went with taller gearing. Same problem, I still couldn't stay out front. I eventually went too tall on the gearing, and when I downshifted, I dropped out of my powerband.

My point is: balance is the key to high revs and high horsepower.

Don't get me wrong, torque is great. A high HP motor with no torque sucks. But even with all the torque in the world, you NEED to be able to rev it out a little.

Personally, the 502 sounds great. But if you're going to spend a thousand bucks on a big-bore/stroker combo, I sincerely advise you to spend a few extra hundred and get the whole thing balanced together. It will greatly increase your upper RPM limit, and probably add 10hp to your peak. You will retain all the great low-end torgue, AND be able to rev it out further and be all that much faster.

[chad502ex]

Originally posted by wilkin250r
I hate to be the bad guy, but I don't think $1000 will give you really what you are ultimately looking for. It will certainly make it better, but not "great".

I got my big-bore 340cc, and it vibrated like a mofo. I had gobs of low-end (even with a mid-top end pipe) and could beat anything off the line, but I couldn't stay out in front because I had NO power in the upper RPMs. So I went with taller gearing. Same problem, I still couldn't stay out front. I eventually went too tall on the gearing, and when I downshifted, I dropped out of my powerband.

My point is: balance is the key to high revs and high horsepower.

Don't get me wrong, torque is great. A high HP motor with no torque sucks. But even with all the torque in the world, you NEED to be able to rev it out a little.

Personally, the 502 sounds great. But if you're going to spend a thousand bucks on a big-bore/stroker combo, I sincerely advise you to spend a few extra hundred and get the whole thing balanced together. It will greatly increase your upper RPM limit, and probably add 10hp to your peak. You will retain all the great low-end torgue, AND be able to rev it out further and be all that much faster.

tisss, you not the bad guy wilkin. most of the time, your advice seems to be sound

i agree with most of what you say,... especially spending $1000. $1000 won't get you to the end of the rainbow. my point is there is nothing like a stroker! if your going that direction, be sure to do it all the way or its not worth it

BTW: the 502 was balanced and trued with its custom piston, and it still hasn't lost a race either. sorry to gloat here- just clarifying its speed

[wilkin250r]

Rev limit and upper RPM power are the reason the YFZ, although smaller in displacement, is better than the Raptor.

Like I said, don't get me wrong, torque is good. But when you can also rev it out, THAT is when it it becomes truly potent. It's the entire claim to fame for the YFZ motor and why it has been so dominant.

[cals400ex]

what does this "balancing" involve? do they need to do that when the whole motor is together or how do they accomplish this? do you think a 4mm stroke would be better than a 6mm stroke because it may want to rev a bit higher?

[chad502ex]

Originally posted by wilkin250r
Rev limit and upper RPM power are the reason the YFZ, although smaller in displacement, is better than the Raptor.

Like I said, don't get me wrong, torque is good. But when you can also rev it out, THAT is when it it becomes truly potent. It's the entire claim to fame for the YFZ motor and why it has been so dominant.

yes, very true. we are talking same but different language...

lets say that my 502ex pushes 46hp peak, which it does, and a 450 pushes equal 46hp (very reasonable with pipe and cam mod); and both racers stay on the peak of their hp as much as possible in race, then what else remains to win the race? rpm or torque?

502 78ft/lbs of torque vs. 450 38ft/lb of torque

would 11500 rpm on 450 engine make up that difference on 10400 502?

i don't think so especially since most power curves fall off in that rpm range.

[Kennethyfz450]

Originally posted by chad502ex
yes, very true. we are talking same but different language...

lets say that my 502ex pushes 46hp peak, which it does, and a 450 pushes equal 46hp (very reasonable with pipe and cam mod); and both racers stay on the peak of their hp as much as possible in race, then what else remains to win the race? rpm or torque?

502 78ft/lbs of torque vs. 450 38ft/lb of torque

would 11500 rpm on 450 engine make up that difference on 10400 502?

i don't think so especially since most power curves fall off in that rpm range.

78??

[chad502ex]

Originally posted by Kennethyfz450
78??

:D

[wilkin250r]

Originally posted by cals400ex
what does this "balancing" involve? do they need to do that when the whole motor is together or how do they accomplish this? do you think a 4mm stroke would be better than a 6mm stroke because it may want to rev a bit higher?

It's difficult to say, it's getting a little beyond my expertise.

I know that you can get a crank balanced against a larger piston, but I'm not sure of exactly HOW far this can be taken, and how effective it becomes with a stroker. They may also do modifications to the counterbalance and other engine components. What you really need to do is talk with a proffessional.

When they build high-horsepower automotive motors, they weigh all the rods, pistons, rings, clips, and so forth. They are slightly concerned with the actual weight, but far more concerned that they are all the SAME wieght and matched. Vibration is the death of the upper RPM power.

Still not convinced? Get a small electrical motor and a 9v battery. Attach some off-balance weight to it and fire it up, and see how it performs. Then, add even more wieght to balance it. Even though you add more weight, it will rev much faster. I first discovered this at a young age when they came out with motorized Legos.

[wilkin250r]

Originally posted by chad502ex


502 78ft/lbs of torque vs. 450 38ft/lb of torque

would 11500 rpm on 450 engine make up that difference on 10400 502?



If your motor is still making power in the 10k range, I am extremely impressed.

[frosti108]

this thread is starting to make me want a 502 like chads got...

78 ft/lb :eek2: :eek2: :eek2: :D

[chad502ex]

Originally posted by wilkin250r
If your motor is still making power in the 10k range, I am extremely impressed.

well, the power in the 10k range falls off just like the 450's do, but not as much.

my peak power is ~7k rpm and most 450s peak is ~8k rpm

power at 10k rpm for the 502 falls off to about 22% compared to most 450's where their power falls to 50% of peak

22% of 46hp is still 35hp at 10k rpm for 502
50% of same 46hp for 450's at 10k rpm is only 23hp

but, then you get into hp/weight ratio being that my 502 feels like riding a tank compared to my 450.

the thing is even with all the power on the 502, i don't want nothing to do with it anymore. when i ride it it feels like i'm on the back of a dinosour. heh!

[frosti108]

well chad id gladly take that dino off your hands whenever you please :)

[chad502ex]

Originally posted by frosti108
well chad id gladly take that dino off your hands whenever you please :)

frosti you have a PM!

[cals400ex]

this may be a bit off subject, but i have another question. is is common when lightening a flywheel to be slower in a drag race? just curious because i lost probably at least 3 bike lengths when dragging. the lightened flywheel does great at lower rpms but won't rev as high as before. i would recommend it for trails and such, but not really high rpm riding.

[wilkin250r]

That sounds absurd. A lightened flywheel should not effect upper RPM power or rev limit at all.

The lightened flywheel is removing rotating mass. This should increase acceleration. Rotational motion is very similar to linear motion. Imagine two bikes, identical motors, but one bike is 100lbs heavier.

Who has the faster top speed, the heavy or the light one? They should be exactly the same, right? Same motor, same rev limit.

But who would win in a drag race? The lighter one, obviously. The power/weight ratio is better, so acceleration will be better.

Same with a lightened flywheel. It's rotational power/weight ratio. Your top speed (RPM) shouldn't change, but your acceleration should be better.

[cals400ex]

i don't know that top speed changed. it may not have. however, i know i am slower getting there. i contacted laz at gt thunder and he said when "powershifting" a bike with the lightened flywheel will be slower. i am not sure what he considers powershifting. i always use the clutch but of course shift quick at high rpms. i am not sure.

[MIKE400EX]

The engine with the lighter flywheel will get pulled down a little farther when shifting but should recover quicker. Once you're off the line I can't see the lighter flywheel being slower when accelerating.
One thing to think about though, and I'll leave this up to you Wilkin......since I have the flu and am in a "fog". The 400ex flywheels are zero balanced from the factory (checked that). Since they are an assembly sometimes Honda has to bring the balance back within spec by drilling lightening holes/dimples in the outside. Seems that when everyone lightens them, that band of material is machined off in a lathe - along with the balancing holes. Now the flywheel becomes out of balance (again). Since I have yet to see someone re-balance the flywheel afterwards, maybe yours cal is to the point where the out of balance condition is affecting top end HP. I have personally seen flywheels from the factory with 0 and as many as 6 lightening holes. Just a thought.........

[cals400ex]

it is funny that you mentioned that. i just contacted a place that balances flywheels. i am considering sending my stock one and my lightened one there. i can tell you it doesn't rev as high. i can always tell when my bike is faster/slower. i drag my buddy all the time and our bikes are pretty close. it was to the point that i was beating him by at least 3 bike lengths. then all i did was add this flywheel and now he beats my by 1/2-1 bike length or so. there are really no other factors. we were on hard pavement so traction wasn't an issue. neither one of us messed with anything else on our bikes.

[MIKE400EX]

Cal, If you have an adjustable timing light, compare the timing of the two flywheels. A little difference there could set you back a few lengths. Also, did your Buddy make any changes to his quad?

[400sEXridr]

what are the bore and stroke on a 502

[MarkyNark]

My 2 cents on how to quicken a stroker ...

A light piston, light and balanced flywheel and quick accelerating cams with some decent head work (porting and larger valves) will help a ton. The 4mm strokers by Powroll are all built properly to be as quick as they can, but they do need some help. A stoker will never out rev a similar sized bore only motor, but they key, as already mentioned, is how you use the power. Proper gearing to ensure you are in the power band at all times during a race is also key. I'll probably get a tach to help me with that. Other things that can help with quickness in rotational mass is lighter rear wheels, lighter axle, lighter tires, lighter sprockets and chain.

When I had my 13:1 440, I had no problems going up against 440 strokers. They simply could not rev up fast enough against me in a dune drag.

While I am still breaking in my 460, (stroked 440) I do have a nice power band forming. My hope is that, with the aid of the cams, and lighter piston and flywheel, that I will not lose any of that top end quick rev. If I do, I'll have to start thinking about a titanium axle and lighter chain and sprockets.

[cals400ex]

i definately don't want a stroker if i will be slower. :p



mike, no changes were made to my buddies quad. to be honest with you, my buddy has a timing light but i would't have a clue how to use it or even do what your saying?? i don't know if it is adjustable either.

[chad502ex]

Originally posted by 400sEXridr
what are the bore and stroke on a 502

91 x 77