Trying to build a 20+ hp predator 212

[Rat]

Don't feel bad.
We thought it was the hot ticket too, til we started testing it against stock cams with the same set up.
But we did learn how to get it to move,

That cam you have MIGHT be a restrictor plate cam from Dover, idk much about em.

They restrict the air flow for plate racing, so they play with cams that are retarded and go up on the ignition timing and carb jets.

Them plate engines have come around quite well in the last few years.

I'm not a fan of retarding a cam like that, but I don't race on a rules track either.

If that cam was straight up (108.5* icl and 108.5* ecl) it would make that 76* ivc change to 72 or 73*, making power come on sooner.

In other words, the intake valve would close earlier and put the air fuel mix under more pressure before the sparkplug fires.

But it's not a bad cam from the numbers I see.

I did some digging, I did get it from Dover! It's a RevPro Stage2 Booster Cam lol.

 

[bob58o]

The (#2) Superman states it is similar to a Dynocams CL3. A cam for racing in stock classes. Perhaps good for certain race classes. If not racing, it’s probably ok if you don’t want to upgrade anything else. If doing a cam swap and not restricted by racing class rules, I wouldn’t consider any CL type cam as an option. You don’t got to go big or go home, but go bigger or stay where you are.

This cam will give slight gains when doing 6000+ RPM, but you give up that power while in the more useable part of the powerband (<6000 RPM).

I like the (#3) Superman Outlaw version. Could probably use 22# springs and stock valve train. I’m not very familiar with the 5.0mm valve stem Predators, but guessing it wold be ok with stock pushrods, rockers, and valves.

• CL3 utilizes the -5 duration check, in the AKRA rule package, by allowing a softer ramp rate on the nose of the cam. This design has shown gains in the 6200+ RPM range with minimal loss in peak horsepower.
• The DynoCams CL3 is legal for the current profile rules for stock classes.
• The lobes are hardened for extra durability, extending the life of this cam.

Specs​

Engine:	196cc OHV Clone, 212cc Hemi Predator
Recommended Class:	Unrestricted Stock Classes
Target (MAX) RPM:	6400-6900
Spring Pressure (In / Ex):	10.8 lbs
Valve Lash (In/Ex):	.003"
Ignition Timing:	32 Deg BTDC

Profile​

	Intake	Exhaust
Open:	29.15 BTDC	65.95 BBDC
Close:	75.58 ABDC	41.55 ATDC
Lift:	.2245"	.231"
C/L:	114.0 ATDC	103.5 BTDC
DUR @ 50:	220.5 Deg	223.5 Deg
DUR @ 200:	82.1 Deg	92.95 Deg

 

[Rat]

The (#2) Superman states it is similar to a Dynocams CL3. A cam for racing in stock classes. Perhaps good for certain race classes. If not racing, it’s probably ok if you don’t want to upgrade anything else. If doing a cam swap and not restricted by racing class rules, I wouldn’t consider any CL type cam as an option. You don’t got to go big or go home, but go bigger or stay where you are.

This cam will give slight gains when doing 6000+ RPM, but you give up that power while in the more useable part of the powerband (<6000 RPM).

I like the (#3) Superman Outlaw version. Could probably use 22# springs and stock valve train. I’m not very familiar with the 5.0mm valve stem Predators, but guessing it wold be ok with stock pushrods, rockers, and valves.

I've got more than enough grunt, and plenty power. I need to replace my degree wheel (age has made it useless) any figure out where to key it to instead of going on guesstimates. It runs great on the stock key, and the 5° key I cut although the cut key has a lot more ambient sensitivity (carb is a little too small but dialed in good anyway)

 

[bob58o]

I’ve always wanted to try advancing or retarding a stock cam by one tooth in the gear. I believe there are 48 teeth.

360 / 48 = 7.5 degrees per tooth.

Advancing a cam with a 112 Intake center line by one tooth would make 112 ATDC into a 104.5 ATDC. Or other way, retarding 106 ICL cam by one tooth would turn it into a 113.5 ICL

I’ve never tried it and not sure if clearancing would be possible.

Just thinking out loud. 104 for grunt and go. 112 to light up the track.

 

[Rat]

I’ve always wanted to try advancing or retarding a stock cam by one tooth in the gear. I believe there are 48 teeth.

360 / 48 = 7.5 degrees per tooth.

Advancing a cam with a 112 Intake center line by one tooth would make 112 ATDC into a 104.5 ATDC. Or other way, retarding 106 ICL cam by one tooth would turn it into a 113.5 ICL

I’ve never tried it and not sure if clearancing would be possible.

Just thinking out loud. 104 for grunt and go. 112 to light up the track.

I've considered that possibility as well but the ramifications of things POSSIBLY going sideways don't justify any potential gains for me.

It's got enough grunt to stand up, and enough get tha F★ck lost that I'm beging to regret not getting a 40 series when I got my 30 because the 3/4-5/8 full package kits were everywhere... now they aren't easy to find among the very abundant 1~3/4 and 1~5/8.

What I'm dealing with ATM is a slightly too small carb (24mm when it should be a 28, but no smaller than a 26) and it will pull the 30 series to 5k before getting pulled back down to 3800-4800 depending on if I flog it WOT.
It's not an FD ratio issue because the 9/56 puts me at 6.22; any lower than that and the nose will become impossible keep grounded.

Time to get a PWK28 I guess.

 

[RefAlpha]

You don't need 20 horsepower to go very fast in a go kart. And you don't need a
.356" lift cam any more than a 28mm carburetor. Do you even know what coil bind is? A stock cam with some ratio rockers and 26 lb springs will deliver good performance, especially with increased compression as I explained in my 1st post. Have you even ever taken one apart? Do you own piston ring compressor.
How about a valve spring compressor. You will also need a 1/2" drive torque wrench, and a 1/4" torque wrench calibrated in inch pounds. If you don't have these tools, you won't get to 1st base in trying to build an engine. I am not a professional engine builder. Just an old man who has been working on and racing different things for more than 50 years, and have built about 8 Predators in the last 4 years. It is VERY easy for me to recognize from your post that you are way too fixated on big this and big that. Buy your engine, get.the aftermarket rod and flywheel, delete the governor, put some stiffer valve springs, jet the stock carburetor and put on a pipe and rvl muffler. Mount it on your kart and drive the darn thing. You will then have the foundation to modify more extensively from there going forward.

If you need any advice or help I can assist. Freshly built a 224 and I can let you know whatever your heart desires.

 

[bob58o]

I’ve always wanted to try advancing or retarding a stock cam by one tooth in the gear. I believe there are 48 teeth.

360 / 48 = 7.5 degrees per tooth.

Advancing a cam with a 112 Intake center line by one tooth would make 112 ATDC into a 104.5 ATDC. Or other way, retarding 106 ICL cam by one tooth would turn it into a 113.5 ICL

I’ve never tried it and not sure if clearancing would be possible.

Just thinking out loud. 104 for grunt and go. 112 to light up the track.

I wanted to correct myself.

One rotation of the cam gear is two rotations of the crankshaft gear. So one tooth on the cam gear is 7.5 degrees but because of the 2:1 ratio of crank to cam, it means 15 degrees of crank rotation.

i realized this a few years ago but then forgot. The joys of getting old and being able to experience things for the first time every time.

So if a cam has ICL of 115, you could install it at ICL of 100 provided clearances and things are accounted for. Not sure why I would want ICL under 102 or over 114 so I suppose that is why it hasn’t be done often.

 

[busted_blocks]

I wanted to correct myself.

One rotation of the cam gear is two rotations of the crankshaft gear. So one tooth on the cam gear is 7.5 degrees but because of the 2:1 ratio of crank to cam, it means 15 degrees of crank rotation.

i realized this a few years ago but then forgot. The joys of getting old and being able to experience things for the first time every time.

So if a cam has ICL of 115, you could install it at ICL of 100 provided clearances and things are accounted for. Not sure why I would want ICL under 102 or over 114 so I suppose that is why it hasn’t be done often.

Are the degrees referencing the cam or the crank? It seems it would indeed advance cam timing by 7.5 degrees, but advances the crank 15 degrees. Since we care about cam degrees (I think anyway) aren't we getting the 7.5 degree cam timing advance we want? That 7.5 means the valves open/close 7.5deg earlier or later. I think you were right the first time. I'm not going to bet you $100 bucks I'm correct though, just giving my 2 cents

Another way to look at it, if I want to adjust the cam timing by rotating the crank shaft gear, I have to take into account the ratio. That means I'd have to rotate the crank gear by 3.75 deg (7.5/2) to get the cam advance of 7.5. Since we are moving the cam directly ahead by 7.5, I don't think the ratio comes into the calculation.

 

[bob58o]

Are the degrees referencing the cam or the crank? It seems it would indeed advance cam timing by 7.5 degrees, but advances the crank 15 degrees. Since we care about cam degrees (I think anyway) aren't we getting the 7.5 degree cam timing advance we want? That 7.5 means the valves open/close 7.5deg earlier or later. I think you were right the first time. I'm not going to bet you $100 bucks I'm correct though, just giving my 2 cents

Another way to look at it, if I want to adjust the cam timing by rotating the crank shaft gear, I have to take into account the ratio. That means I'd have to rotate the crank gear by 3.75 deg (7.5/2) to get the cam advance of 7.5. Since we are moving the cam directly ahead by 7.5, I don't think the ratio comes into the calculation.

If people are talking degrees, they are talking crankshaft rotation degrees. As the crankshaft turns the piston moves up and down. Once per crankshaft rotation the piston reaches its highest point in the cylinder. This is known as Top Dead Center. The piston is at the top, but it got there because of the crankshaft rotating. The crankshaft turns another 180 degrees and now the piston is at Bottom Dead Center.

A 4stroke engine has two crankshaft rotations per “full cycle.”
Intake - piston moves down
Compression - piston moves up
Power - piston moves down
Exhaust- piston moves up

Timing events use crankshaft rotation degrees, mostly relating to when the piston is at Top Dead Center.

So to find 28 degrees before TDC, you rotate the crankshaft so that the piston is at Top Dead Center, then rotate the crankshaft backwards 28 degrees. There are two times the piston is at TDC. Once between exhaust and intake strokes; once between the compression and power stroke.

timing events can be degrees before TDC (BTDC), after TDC (ATDC), before bottom dead center (BBDC), after bottom dead center (ABDC).

The gear on the cam has 48 teeth.
The gear on the crank has 24 teeth.
The crank turns twice for every cam turn.
360 degrees on cam is 720 degrees on the crank.

360/24 = 15 degrees
720/48 = 15 degrees

My brain is mostly a jumbled mess to I wouldnt bet money on my answer either.

 

[busted_blocks]

If people are talking degrees, they are talking crankshaft rotation degrees. As the crankshaft turns the piston moves up and down. Once per crankshaft rotation the piston reaches its highest point in the cylinder. This is known as Top Dead Center. The piston is at the top, but it got there because of the crankshaft rotating. The crankshaft turns another 180 degrees and now the piston is at Bottom Dead Center.

A 4stroke engine has two crankshaft rotations per “full cycle.”
Intake - piston moves down
Compression - piston moves up
Power - piston moves down
Exhaust- piston moves up

Timing events use crankshaft rotation degrees, mostly relating to when the piston is at Top Dead Center.

So to find 28 degrees before TDC, you rotate the crankshaft so that the piston is at Top Dead Center, then rotate the crankshaft backwards 28 degrees. There are two times the piston is at TDC. Once between exhaust and intake strokes; once between the compression and power stroke.

timing events can be degrees before TDC (BTDC), after TDC (ATDC), before bottom dead center (BBDC), after bottom dead center (ABDC).

The gear on the cam has 48 teeth.
The gear on the crank has 24 teeth.
The crank turns twice for every cam turn.
360 degrees on cam is 720 degrees on the crank.

360/24 = 15 degrees
720/48 = 15 degrees

My brain is mostly a jumbled mess to I wouldnt bet money on my answer either.

Yeah I get that the cam rotates 360 degrees and the crank rotates 720. So my confusion is thinking cam specs are cam degree's but they are crank degrees. Which makes my explanation the inverse. If you want to adjust your cam timing 7.5 deg, you have to move the crank gear 7.5 deg. If you move the cam gear (if that was possible) 7.5/2-3.75 degrees.

My confusion was what degrees we are talking about. It makes sense now and I can see how that is correct. Cam specs refer to crankshaft degrees. I'm no longer willing to make that 2 cent bet. Thanks

 

[butterbagz]

butterbagz. You have clearly fallen for the big numbers buz words without really understanding what's going on. I am not trying to be mean, or put you down. I want to try to educate you a little bit. In fact I am glad that at only 15 years old you want to build an engine. Hemi sounds cool and all that, but for the Predator engine that is not the one to modify. The reason is because the valves sit on a angle. So when the valve opens ( lifted by the cam ) the lower edge of the valve is
much closer to the piston. With the non hemi head, the valves sit straight up and down. The whole face of the valve comes down evenly. You can use a cam with much more lift SAFELY with the conventional or wedge head. Most ALL big valve heads or modified heads ( high compression ) are the non hemi style for the reason explained above. Valve to piston clearance. Heads with 32mm intake valves are very expensive, not to mention that the larger valves have a history of burning and melting the seat. A 28 mm carburetor could be used on a very heavily modified engine like in a jr. Dragster, but for a go kart ( even with a highly built engine ) it is way too much. A properly jetted 24mm Makuni flat slide will feed a very built engine. Tone it down a little and build your first one.

Is the wedge head the non hemi?

 

[butterbagz]

@butterbagz
Pancho, speaks the truth. Listen and pay attention.
Start small and work your way up.

Mark, from EC Carbs put together some nice "builds for beginners" that won't break the bank.

Jus looking at the parts combo of each build, I'm sure they will have plenty of power, IF the compression ratio and ignition timing is right.

As his builds get into bigger cams, he gets away from the hemi head. There's a reason for that, jus like Pancho is saying.

Have a look for yourself.
Good luck with your build, .

EC's 2023 Small Engine Builders Guide

Right now I'm going to start at just parts I can remover the governor and as this summer goes on I'll keep adding stuff, what is the wedge head? I assumed the would be a hemi with the angles, bit what else could it be?

 

[butterbagz]

Hey young fella. With a hemi head and a .356" lift cam your valves are going to hit the piston long before the cam reaches full lift. Getting 20 hp will be very expensive. Getting 15 to 16 is quite doable. If you already have a hemi engine, then buy a bare non hemi head to build. If you don't have the engine yet, then buy
the non hemi. The non hemi head will bolt on your engine. Port the head, also mill it .065" to raise compression. You need a flat top piston ( hemi comes with one, ) non hemi you need to buy an after market one. Any cam with more than .310" lift you need extra long valves to prevent coil bind. And with 36 lb valve springs you need stainless steel valves, otherwise you stand a good chance of ripping the heads right off the pot metal stock ones. 26lb springs and a lower lift cam will get the job done. You have been watching too many vroom vroom videos. Educate yourself a little by watching Red Beards Garage. He will show you close up how to build your engine. Then watch his series of videos titled the road to horsepower. He installs speed parts on a predator engine, and after each part runs the engine on a dyno. Letting you know how much power each modification is worth. Value to you is priceless.

I found a guy who has a ported and polished non hemi head for 50$ is it a good deal I'm going to convert the hemi to a non like you said

 

[Rat]

Is the wedge head the non hemi?

Correct

 

[Rat]

A wedge head can achieve better performance by way of higher compression, valve lift, and milling down to further increase CR... but I've also found recently that a Hemi can be nasty on account of better flow geometry.

I prefer to run a wedge. I tend grind the ports out a bit, polish the exhaust (doesn't need to mimic chrome just be very smooth and shiny) to reduce the rate at which carbon can cling, and rough up the intake for the same reason golf balls have all them divots