Cam upgrade question

[Benry]

Hello, Ive recently taken up modifying a predator 212 I managed to find. So far Ive done all of the following: billet rod/ flywheel, governor/oil sensor delete aswell as 22 Lb springs. Would installing a camshaft give more power and higher rpms, it’s currently around the 5500s under load.

and should i get stronger push rods or are stocks ones alright?

 

[BrownStainRacing]

5500 is pretty good, for a mostly stocker.
I've seen alot of guys add a modified cam and go backwards.

There's more to it then jus a cam change.

The stock cam is actually too big for the compression ratio and stock carb. The stock cam was designed to last forever with the stock valve train, when the engine is used as intended, such as utility uses, tillers, log splitters, pressure washers, ect.

It's a slow, lazy ramped cam that's easy on the valve train, and closes the intake valve really late. Getting the intake valve to close earlier will put the air/fuel mix under more pressure, causing more power when the spark plug lights off. Same as would bumping up the compression ratio.

A 1.3:1 stamped steel rocker on the intake side will help the stock cam. Don't worry about the exhaust side, it works pretty good as is.

Theres some small things that'll wake up a stock cam.

Whats compression ratio???
Where's ignition timing set at???
What size carb??
What's installed height on those 22# springs???
Any port work to the head???
Which head???

I run stock pushrods and all the other stock valve train parts with 26# springs at .840"-.850" installed height, with no problems. Jus check for coil bind, and keep an eye on the valve lash.

 

[Oilpan4]

A compression bump going from 8:1 to around 9:1, 4 degree timing advance was a nice wake up for my otherwise stock 4,100rpm gx390.
Everyone who doesn't live in a smog trap (pretty much all of those locations are in California) should run at least 4 to 6 degrees more timing even on otherwise stock engine.

 

[bob58o]

Isn’t the CL series of cams (CL1, CL2, …) basically a stock cam (same lift and duration) but the intake center line is retarded to shift the powerband to slightly higher RPMs?

 

[bob58o]

What do you do with this engine?

Do you drive stop and go?
Do you keep it wide open throttle all the time?
What size tires and gear ratio on what vehicle?

I try to match RPM range of cam with gearing / tire size / vehicle speed for use.

I don’t race, so I try to build “street” stuff mostly. Shorter duration, wider lobe separation (less overlap), intake centerline around 104-108 ATDC

I’ve been curious about this cam for a while for something mild that stays in higher rpm’s most of the time.

Racing Cams and Parts | Aggressive Ramp Cam for 196cc Clone & 212cc Hemi | Cheater Stock Class | CL-CS | DynoCams

Aggressive ramp cam for 196cc Clone and 212cc Hemi engines. Compatible with stock carbs, but requires upgraded springs. Billet rod and flywheel recommended. Hardened lobes for durability, max RPM 7000. | CL-CS

www.dynocams.com

 

[Benry]

What do you do with this engine?

Do you drive stop and go?
Do you keep it wide open throttle all the time?
What size tires and gear ratio on what vehicle?

I try to match RPM range of cam with gearing / tire size / vehicle speed for use.

I don’t race, so I try to build “street” stuff mostly. Shorter duration, wider lobe separation (less overlap), intake centerline around 104-108 ATDC

I’ve been curious about this cam for a while for something mild that stays in higher rpm’s most of the time.

Racing Cams and Parts | Aggressive Ramp Cam for 196cc Clone & 212cc Hemi | Cheater Stock Class | CL-CS | DynoCams

Aggressive ramp cam for 196cc Clone and 212cc Hemi engines. Compatible with stock carbs, but requires upgraded springs. Billet rod and flywheel recommended. Hardened lobes for durability, max RPM 7000. | CL-CS

www.dynocams.com

Thank you for the reply,
The engine runs on a minibike and is more leaned towards a road bike so it stop and go although there are times were it's wide open for a couple of minutes at a time.

It's on 145/70-6 tires so around 13.5 inches.
And the gear ratio is a 10-tooth clutch and 60 on the rear.

I actually made the stupid decision of buying a cam before I even made this post and I coincidentally went with a CL3 cam.
Although I won't have the time to test it out for around 2 weeks, I will update my post with some benchmarks if I remember.

 

[bob58o]

My thought process (is scary) and looks like this.

13.5” Tire is 42.4” Circumference which means the bike would move 3.53’ per crankshaft revolution if gear ratio was 1:1.

Now adding the gear ratio..
60:10 or 6:1 gear ratio means the bike actually moves 3.53’ / 6 per crank rev.

0.589’ per crankshaft revolution.

Now the target rpm range of the CL3 low duration cam is 6400 - 6900 RPM.

6400 RPM is around 43mph.
6900 RPM is around 46mph.

So the cam target range would set you up for cruising at around 45 mph at 6500 RPM (you should currently be around 37mph if at 5500 RPM.

I had a similar sized mini bike and I was able to get to about 52 mph at 7000 rpm going slightly uphill using a black mamba Jr camshaft with gx390 carb on a 212 with torque converter.

 

[Benry]

M

0.589’ per crankshaft revolution.

Now the target rpm range of the CL3 low duration cam is 6400 - 6900 RPM.

6400 RPM is around 43mph.
6900 RPM is around 46mph.

So the cam target range would set you up for cruising at around 45 mph at 6500 RPM (you should currently be around 37mph if at 5500 RPM.

I had a similar sized mini bike and I was able to get to about 52 mph at 7000 rpm going slightly uphill using a black mamba Jr camshaft with gx390 carb on a 212 with torque converter

So after installing the cl3 on my mostly stocker the engine had a cruising range of around 5600-5900 rpm under load (5500ish before cam)

Just recently I decided to also upgrade to a knockoff vm22 and a header pipe and now reving 6700-7000 rpm under load.

Thank for all the help and advice!