Ok I was just thinkin about this
I used to have a 1986 XR50 a few years back when I was livin on my P's farm, and that thing hauled ***. I had my neighbor across the road pace me on his FZR and I got up to about 55 mph before he pulled away. That thing was probably about 50 lbs heavier than a stock xr50 and with my fat *** on it, it still moved quick, and it was completely stock. It seems to me that if you put an 88cc kit on an XR50, it should fly, but from what I can tell, most of you people with the bore kit aren't going that fast, with the exception of Silver Surfer, he has that **** on lock! What is the difference? Is it gearing? With 88cc's you should be going at least 45mph, like I said, my 80 would do about 55.

 

1986 XR50? Did you pick that one up in your delorean?

[just playing around]

 

did you pick that one up with your delorean...thats a good one...nyuck nyuck nyuck...lol

i think he had an 80 though...and i can't see an 86 xr80 going 55, i had an 82 that i swear went about 35, and last weekend i ran all over about three crf70's it was horrible.....and i bet my bike is a 4x mph bike...maybe high 30's, but i dunno
it's got an 88cc kit with sprocket...

 

88 dont and **** to you speed, gotta regear to change speed.

 

that is false, xidium.

 

Then why does every single speed calculater never check power? Only ones are quarter mile or distance times. Horsepower adds acceleration. The only reason bigger bikes are faster is because the extra power allows them to gear for more top end will still having more bottem end than smaller bore bikes.

 

ok here it goes. im sick of reading about how 88s make u have more MPH. that is a FALSE statement. Xidium is 100% correct.

im using all generic numbers here. lets assume u can rip down the road while on the rev limiter (lets say 10,000 rpm) on yer stock fiddy at exactly 35 MPH. say your buddy who has an 88 kit and all stock gearing rips down the road next to u (also on the rev limiter at 10,000 RPM). the 88 kit will get to the destination alot quicker, but will never exceed 35 MPH because they both have the same...

...tire size
...gearing
...RPM

these are the factors that determine MPH. NOT HORSEPOWER. if 2 bikes are both spinning their engines at 10,000 RPM and they have the exaxct same gear ratios and tire sizes, u tell me how one bike will have more MPH than the other. it wont happen.

thats y its a good choice to install a 4 speed or at least a bigger front sprocket with an 88 kit. it has more power to turn that gear and get u going alot quicker. the change in gear ratio will get the speed u are after.

heres a speed calculator i found on the web real quick..
http://pw1.netcom.com/~sgalaba/mph.htm
no where does it ask how much horsepower u are making. punch your numbers in and see what comes up...

i used 80/90/10 as the tire size since thats a common street tire size for a fiddy.
transmission gear ratio for a 3 speed in 3rd gear is... 4.83:1
final drive ratio is your rear sprocker devided by the front... 2.64:1 (stock)

 

yup I think I go with fab5 and xidium on the speed

and laugh along with buick..... ....delorean.....

 

Actually, stock every except enigne the stock might be faster, because the smaller bore allow it to rev higher. Im not sure on that but it bmght be true.

 

O yea, this is the one I use http://members.tripod.com/sidecase/calc1.htm

 

remember it's piston speed, not bore......
i think a lot of people look at the classic 383 and say, well, that bigger motor can't rev that high so big bore motors can't rev as high, but the 383 is a stroker not just a big bore...
and i think the weight of the piston, in this case is kinda negligible, but i'm not sure...

 

I wasnt sure so Im wrong.

 

All of you are right and all of you are wrong.....

I believe a xr80 going 55 mph is extremely possible

my friend's son 8 years old, has gone 55 mph on his 01 XR70

Second

We'll use the dyno to show top speed caomparisons since we have been doing it for a while.

My Z50 Stock ..... ..........................................34mph 14 front 37 rear
My Z50 With 88cc Big Bore no cam stock carb......30 mph 14 front 37 rear

A big Bore's drag WILL contrary to popular belief kill some of you bike's top speed. We have proven it..... I didn't believe it first either but its true. Perhaps its the fact that a 49cc can rev quicker and faster because of the small piston.

Now you take your stock Z50 and change your gearing say to a 15 front 35 rear which I'm running...... THE MOTOR ISN'T GETTING ENOUGH FUEL FROM THE STOCK CARB at the "theoritical" top speed of the new gearing to get you up there ESPECIALLY IF YOU ARE A BIG PERSON. The BIG BORE WILL STARVE OUT OF FUEL. THATS WHY THE 20mm CARBs are so popular.

We went to a 15 front 35 rear setup with a ported 50cc head and 20mm carb....no cam.......my bikes top speed on the dyno went up to 46 mph......

We then go up to a 70cc head and mild race cam....same 15 front 35 rear gear setup....my top speed jumps up to 56 mph......why ......partly because of the cam WHICH ALLOWS THE MOTOR TO REV A LITTLE HIGHER but mostly becuase that motor is getting FUEL. IT IS BEING FED.

FUEL DELIVERY....REMEMBER THAT...is what gets you top speed..........
Gear selection is also important but when pushing a xr50 top speed but fuel delivery is KEY. Our bikes don't make enough horsepower to say gearing is the limiting factor.

Believe what you want about gearing........ FUEL DELIVERY

Second example

We did 2 more big bores no cams, stock carbs

Duc-Man's Z50..........15front 37 rear 72cc BIG BORE ......38 mph top speed
Craze INC's Z50..........15front 37 rear 88cc big bore ....... 35mph top speed

Both were dynoed on the same day so weather conditions weren't a factor.
72cc kit made 3.6 peak hp
88cc kit made 3.8 peak hp

 

Something else you need to take into consideration...weight of the rider

 

thats a given


....and by the way Matt aka900Fury.....your **** will be on lock as well as soon as my guy gets done with it.

:YEAH

 

Surfer just pointed out to me today that I made an error in my first post: I used to have a 1986 xr80!!!!!! Not a fiddy. I was drinkin and postin again-no wonder all you fools made fun of me! And it WAS FAST

 

i gut a 03 xr50 88 kit 1 up in front 2 down in back my **** crews :YEAH

 

now try it with a 30 tooth rear sproket
and hang on
1 tooth in the rear is worth 4 in the front
not good for bottom end but way sweet for top end

 

and dont forget a 70 has bigger wheels
14 / 35 8 inch wheels 46 mph
and thats pretty darn fast on 8 inch wheels

 

hey, whenever you do a 70 head you gotta get a bigger piston right?? well, how much is a head and piston?? and where can you get them cheap??