How much rpm and horse power

R

Ryans822

New Member
#1
#1
Hello,

I have a predator non hemi 212cc engine that has a billet rod, billet non adjustable flywheel, straight pipe, mod 2 camshaft, and a free flowing wannabe k&n filter that I opened the jet a little for. I removed the govenor. I was wondering approxamently how much rpm this set up is running and hp?
 
LSCustoms

LSCustoms

Moderator
#2
#2
If I had to guess, I would say a little bit over 6.5 hp...

but on a serious note, youngengines has a thread where he upgraded the carb and some other minor mods and posts his hp/tq numbers. he details what he did in that thread...

more important than the number, how does your motor perform? if you did not change the springs, then i would say you would run into prob before you get up there in rpm... one thing you can do, is grab an rpm gauge they are pretty inexpensive depending on the one you choose...
 
R

Ryans822

New Member
#5
#5
LSCustoms said:
sweet, not sure on the mod2, but my isky cam'd motor rev pretty high... but youngengines posted hp numbers in his thread
Click to expand...
I checked that thread out it helped me out a lot.
but the motor performs great! the main reason I posted this was to figure the rpm out for re gearing but I think you might be able to tell me my answer. right now I have a 10tooth clutch going to a 20tooth jackshaft sprocket then a 10tooth jackshaft sprocket too a rear 50tooth rear sprocket. it runs a little under 50mph right now and the take off speed isn't exactly sluggish but the front wheel doesn't want to come off the ground at all. what im wanting is to slow down the top end to about 35-40mph and have a lot more torque so the front wheel wants to come up. I was thinking about putting a higher tooth sprocket on the first jackshaft and seeing where that got me before putting a 60tooth on the rear. also now that I have most of the normal mods to make the motor handle these high rpms what would you suggest next? im running the stock carb is there a good upgraded carb that will help out a lot?
my main uses are for offroad in the woods climbing hills ect..
 
LSCustoms

LSCustoms

Moderator
#6
#6
toward the end of this vid (9:11) is one of my bikes when i first got it and did a motor swap... the motor at the time was a predator with minor mods, similar to yours but with an isky black mamba cam... had no issue with torque as you can see, the top mph was higher though, prob closer to 45 mph with that gear ratio and as you can see, no prob in the wheelie department... 12t/70t works out to around 5.83 : 1 (different motor now, different gearing)

https://www.youtube.com/watch?v=Y0gwSoFRNdI

at 7:51 in the vid (and right after that), you can see the wheel still came up, with a 12t/54, but the motor has a little more modding to it...

i would think that your jackshaft setup would be more snappy, but maybe im calculating something wrong... my bonanzas gearing is 13t/12t/13t/60t way higher top mph... but i would think if you went with a 60 rear, it would be great torque... im just now getting into playing with my jackshaft gearing on it...
 
LSCustoms

LSCustoms

Moderator
#10
#10
Ryans822 said:
its on a similar set up to the Baja mini bikes but with rear shocks. my rear tire is 19"

youre mini bike flyyyyys man!!
Click to expand...
with your gear ratio, unless im reading something wrong, you should be at 10 : 1, with that tire height (which is around 4.97 feet in circumference), the math puts your bike doing around 45.18 mph at 8000 rpm (not taking into consideration weight etc)... at 7500 rpm would be around 42.36 mph

so if we were to guess based only on the information you gave (if its accurate), my assumption would be that your motor is spinning up to around 7500-8000 rpm :shrug:

if you want more torque, given your top speed goal of 35-40 mph... you have to change the 20t or the 50t to a larger gear... you could change the gear ratio to 12 : 1 (by either going with a 60t rear sprocket, or changing the 20t to a 24t)...

that would put your top speed at roughly 35.29 mph at 7500 rpm and 37.65 mph at 8000 rpm

:shrug:
 
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LSCustoms

LSCustoms

Moderator
#11
#11
and here is what the math looks like, if you want to play with it yourself (i like the gear ratio calculators, but dont mind doing the math myself, also... you can play with the gear ratio calculator if you dont want to figure it out yourself... and then do simple math to get an approximation of your top speed and at what rpm etc, if you want:

gear ratio calculator and speed calculator here:
AGK - Gear Ratio Calculator - Affordable Go Karts

to get your ratios:
teeth on clutch= 10, teeth on input/jackshaft =20, take that and 20 divided by 10 = 2
teeth on output/jackshaft= 10, teeth on rear sprocket= 50, take that and 50 divided by 10 = 5... take the two answer and multiply them together= 10 to 1 final gear ratio for that gear setup

anyhow, your tire height of 19":
[19" times pi (3.14)] divided by 12" to get tire circumference in feet = 4.97 feet (rounded off)

for your rpm, i based that on reverse math and your estimated speed... for rpm you can estimate what your top rpm would be on your bike, or like i said, buy a tach, but plug in the rpm you would like the motor to spin to, or what you think the motor is capable of spinning to... i choose 7500 and 8000... ill show the math for 7500

with your goal of 7500 rpm:
take 7500 and divide it by your gear ratio to get your WHEEL RPM... 7500/10= 750
to get how fast your wheel would be traveling based on its size you take the wheel rpm and multiply that by the tire circumference in feet. 750 x 4.97= 3727.5 is how fast your wheel would be going in feet per minute

take that number and multiply that by 60 to get feet per hour 3727.5 x 60= 223650, this is how many feet per hour you are traveling at 7500 rpm

to break that down into mph divide it by 5280 (feet in a mile). 223650/5280= 42.36 mph (rounded off)

so at 7500 rpm your bike would be traveling approx. 42.36 mph

not that you asked, just felt like typing that to show you i did the math required to make my assumption
 
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