The black mamba jr is a torque / mid range cam. If you shooting for 20HP, then you don't want a torque cam. 20HP is pretty significant, so you don't want any cam that says "JR". You want big daddy cams. LOL
I ran the black mamba jr. it took 26lbs. On a minibike with torque converter (6" Driven), it spun up to 7500 RPM at 55mph and still needed wheelie bars.
The largest cam I ran was the 285 series from NR racing. It was 285-0211. 285 lift.
250 duration. Supposedly good to 7k RPM with 26lb springs, I used 36lb springs and spun it up to 8500 RPM on a minibike with TC (7" Driven). The 285-0611 will make more power at higher rpms, but since I was using a TC, I wanted to keep the RPMs lower. I never got a chance to take it for a top speed run. The bike with engine was stolen. The engine had 28.5mm intake, full port work, 24mm slide carb, 11 :1 Compression Ratio. No idea how much power it made, I hope it was close to 20HP.
For 20HP, you'll need a carb upgrade, head work (bigger valves, port work,...), a pretty good cam, .... Best bet is to find a builder like FHB mentioned and have them put together something for you.
This is the head I got, but I think it was $200 when I got it.
http://www.nrracing.com/product-p/headhemi.htm
And this is the cam.
https://www.nrracing.com/product-p/200cam-285.htm
The Black Mamba SR is close to that 285 I used. BMSenior is 275 lift, 246 duration, 108 LSA - compared to 285 lift, 250 duration 111 LSA.
Something serious might be an ISKY custom 315 lift, 260 duration ... IF you don't care about having 5k RPM clutch engagement. Find a carb, cam, and head that work together. You (or one of us) could guess, or a professional can do it professionally.
---------- Post added at 02:32 PM ---------- Previous post was at 02:14 PM ----------
I'll post this again. It is a very informative post. It should probably be stickied somewhere.
This is the best post I found about Honda / Clone / Predator Camshaft specs.... I shared before, but here it is again.
It originally came from Russel at NR
https://karting.4cycle.com/showthrea...cam-logic-more
"
There are four important numbers on a cam. ICL (intake center line), LS (lobe separation), duration, and lift.
Don’t worry too much about lift. The Honda head (i.e. port design) does not respond much once the lift at the valve exceeds about .350. A .275 lift cam with 1.3 rockers will achieve this. We have spent a lot of time on the flow bench, and unless the head is radically changed you will not see much gain past .350 lift.
Duration is another story. This is how long the valve is kept open. Hondas love lots of duration. We have run as much as 300 at .050, but 260 seems to be a good compromise better power and tractability. As duration goes up, so does the rpm at which max power is made. At the same time idle quality goes down along with low-end torque. An engine with a lot of duration will scream and make lots of power but can be a dog off the corners and/or trying to get started, not to mention idles at 3000 rpm.
Typically 210 to 220 makes for high torque motors that start and stop a lot, use low rpm stall/clutches, and see a wide range in operating rpm. These motors will peak somewhere between 4500 and 5500, and will pull to 6500.
250 to 260 are for the 7000+ motors that don’t see RPM much below 5000.
Needless to say, 230 to 240 cams fall in the middle.
One interesting thing about duration, the smaller the carb, the more duration can help a motor. With small carbs, usually the cam/ports will flow more than the carb can deliver. The only way to improve power is the hold the valve open longer. In other words, where going from a 240 to a 260 cam on a motor running a 28 mm Mikuni will only show a 10% improvement in peak HP, doing the same on a motor with a stock carb can show a 20% improvement.
Almost as critical as duration, is the ICL. This is the intake opening and will range from 98 to 116 degrees. It is also referred to retard or advance in the cam. This determines the where the peak torque will occur. Most cams fall in the 102 to 110 range. FYI: Honda 160s are around 105 and GX200s around 110 from the factory (retarded for emissions).
A cam with a 102 will have power range/peak around 1000 to 2000 rpm lower than a cam with 110 ICL. It will also have considerable more low-end torque and will pull a lot harder off the corners. For very, very small tracks this can translate into significantly lower lap times despite having lower HP. For Boats, winch boarding, rock climbing ATVs, these cams can make huge differences. Depending on the application, it is possible to stall a motor that has a high ICL, whereas advancing the cam produces great results.
At the other extreme, a cam with 114 ICL might peak in the 9000-rpm range. On a large track (1/2 mile) where the rpms never get below 7500, it would be unbeatable. However, you would need a clutch that engages at 5000+ just to get moving. Not always fun for a street toy.
The other important number is the LS (lob separation), which determines the amount of overlap. These will range from 100 to 115, but most cams will be in the 106 to 110 range. As a general rule the lower the number, the more HP, but the with a smaller power band. However, the wider (less overlap) the LS, the more dynamic compression a motor can build. For high compression engines, overlap is needed to bleed off compression at lower RPMs preventing detonation. Anything over 11 to 1 should be using a 106 to 107 LS. For lower compressions, it depends on how wide a power band is desired. If you want a power band of only a few 1000 rpm (typical for oval tracks), then go with a narrow LS, however if your rpm ranges from 2000 to 7000 (road courses), then you may want a wide LS.
The duration, ICL, and LS all work together and changing any or all of these numbers can have a significant impact on how a motor performs.
One final note, what works on the dyno does not always work on the track and vice versa. What works great in a Mini Bike may not be the best for a Kart, a dirt track cam is not going to be the same as a paved cam, etc, etc.
www.nr-racing.com
The part number of our cams tells the ICL and LS. The first number is the lift, the second set is the CL, and the last set is the LS. For example
280 0207 .280 lift 102 ICL 107 LS
252 0607 .252 lift 106 ICL 107 LS
252 0207 .252 lift 102 ICL 107 LS
252 0211 .252 lift 102 ICL 111 LS
274 0607 .274 lift 106 ICL 107 LS"
So i’ve always worked around motors but this is my first motor building i have a ultramax frame for dirt racing and i bought a predator 212cc and i’m looking for some tips to squeeze out 20hp and i would like to know what y’all think i’m running now, i bought the motor new and all the parts i’m slowly getting am i’m breaking everything in at once here are my specs
