Best low-cost cam for low rpm usage on a predator 212?

[JToTheIzzack]

What's the best low rpm cam for a predator?

I'm looking for a relatively cheap can that will give good torque below about 4200 rpm. I plan on upgrading to a billet rod and heavier springs, and hardened pushrods if necessary, but the stock governor is still in place, with the screw backed all the way out to alllow around 4200 +- rpm. What would you guys recommend? I have a wallbro type fuel pump with a stock carb, unrestricted intake and exhaust, 140 e-tube and a full set of jets to play with. I believe I have the #90 in right now on an otherwise stock engine. What would you guys recommend for good low end power, and still somewhat affordable? I understand such a thing might not exist, and I'm still fairly new to nodding these engines. Any help is appreciated, thanks!

 

[Xtreme Yard Karts]

I'm looking for a relatively cheap can that will give good torque below about 4200 rpm. I plan on upgrading to a billet rod and heavier springs, and hardened pushrods if necessary, but the stock governor is still in place, with the screw backed all the way out to alllow around 4200 +- rpm. What would you guys recommend? I have a wallbro type fuel pump with a stock carb, unrestricted intake and exhaust, 140 e-tube and a full set of jets to play with. I believe I have the #90 in right now on an otherwise stock engine. What would you guys recommend for good low end power, and still somewhat affordable? I understand such a thing might not exist, and I'm still fairly new to nodding these engines. Any help is appreciated, thanks!

Most small engine performance camshafts are designed to make power at higher RPM than stock. I'm not sure you'll find an off the shelf cam that will greatly improve your engine at that low RPM. If it were mine, I'd buy a 14cc head (assuming yours is not a Hemi Predator) or shave yours to raise compression and advance the timing 3 or 4 degrees. Both of those mods will increase low end power and probably can be done so cheaper than a cam. Bumping the compression and timing is a trick that has been done since people starting modding these little engines to make them feel more snappy and more powerful.

 

[itsid]

advancing the timing will increase the power in the UPPER RPM band, not the lower..
(that's why cars advance timing dynamically the faster you rev )

a newer ARC flywheel has an 8° advance build in.. adding another 4° is basically stupid I'm afraid.
retarding the timing again by 4° to end up with 4° total advance would indeed help
(flip the key)

the engines as they're meant to run at 3600 rpm come with about the ideal cam layout already..
so all you need is a cam that keeps that and only increases lift and/or duration for a better filling ratio.

'sid

 

[Xtreme Yard Karts]

advancing the timing will increase the power in the UPPER RPM band, not the lower..
(that's why cars advance timing dynamically the faster you rev )

a newer ARC flywheel has an 8° advance build in.. adding another 4° is basically stupid I'm afraid.
retarding the timing again by 4° to end up with 4° total advance would indeed help
(flip the key)

the engines as they're meant to run at 3600 rpm come with about the ideal cam layout already..
so all you need is a cam that keeps that and only increases lift and/or duration for a better filling ratio.
'sid

First of all he said nothing about a billet flywheel, so I assumed he was using a stock flywheel. Advancing his engine 3 or 4 degrees from stock with help at all RPM ranges.

Advancing ignition timing absolutely increases low end power, when talking about moving up from stock. These engines are not built with optimum timing, because they are not built for max power. They are tuned very conservatively to be reliable and to be as easy to crank as possible. Increasing the timing on these engines from the stock setting is basically just correcting the factory retard built in to them. An engine with the factory set 24 degrees (on most of these engines) timing is built to be easy to crank and run all day at 3600 RPM in the hottest climates with no air moving in a most applications.

The ignition timing in cars advances because a standard starter cannot crank the engine at fixed total timing. A lot of drag/race cars using do have locked distributors set from 30 - 36 degrees total timing depending on the engine but also use high torque gear reduction starters.

If these small engines had an ignition system that could start the engine at 6 degrees BTDC and then advance to total timing as RPM rises like an automotive application, you'd see higher compression engines with more aggressive factory tuning and higher HP stickers on them... (ya know, if they still put HP ratings on them)

 

[itsid]

well he talked about stronger valve springs.. running those without a billet wheel is,
how to I put it politely...?
ah 'not recommended'

but keeping the governor isn't as well (even worse in fact).. so yeah .. who knows

keeping the governor at work and maxing at 4.2k rpm
heavier valve springs are pointless
(no valve flutter will occur at those rpms )

it's like installing ceramic brakes if you only go 30mph for 15mins max.

but maybe I just haven't fully understood what his intentions are in the end. *shrugs*

And

The ignition timing in cars advances because a standard starter cannot crank the engine at fixed total timing.

that is not true I'm afraid... not always at least.. my good ol' 914 (may he rest in piece) was very well able to crank up with a heavily advanced timing (more than he could ever advance on his own )
the one thing he couldn't do with such advanced timing was starting to move, he lacked a ton of torque...
but in neutral revved to the moon..
and one time when that ****** screw loosened up on the highway (Autobahn ) he reached unknown speeds (220km/h without problems... 60km/h though !impossible! the engine died!)

Why do I pull that vintage car card here you might ask.. well most of all, because there was no noteworthy electronics involved, a very crude engine, with nothing but a carb (yes I downgraded from fuel injection) and the most basic ignition system there is.. air cooled.
So pretty much a bigger version of those industrial engine we deal with here. (well... better quality I admit )

While I agree that they're meant to run 3600rpm 24/7 in any climate imaginable
I don't think their timing is off by anywhere near 4° for their intended rpms.
mainly because that'd cost power in the rated (3600rpm) band
by a fair amount and who would want a 5hp engine with exactly the same specs as a 6.5hp engine just a different timing in order to have an easier pull on the rope?

I admit IDK for sure, but I highly doubt anyone would

especially not if it's easier to keep the timing alright and just reduce the compression (compression releases are on EVERY cam on a clone...)

Anyways, increase compression (thin head gasket should be enough) and increase airflow (in and out!) that's basically all I'd do for 4200 rpm.

'sid

 

[Xtreme Yard Karts]

I totally agree about not needing stiffer valve springs at that RPM. It is not necessary and will yield no gain in power. In fact, it could hurt performance at that RPM and will increase unnecessary wear on the valves.

On optimum timing, there is a small window of time in the combustion cycle the spark needs to take place in order to produce peak power. When the spark happens too late, power is lost in all RPM ranges. Some of these clones are said to be actually having less than 20 degrees timing when checked in stock form, and that is not ideal. Advancing the timing to correct that will result more power everywhere, in my experience. If it were me, I'd buy keys from 2 to 4 degrees, and experiment with it.

I'll just say this, In my nearly 30 years of building and racing small engines, and I've never seen a stock engine that didn't respond very favorably to increasing the compression and a little bump in timing together - on the bottom end and top end.

I will admit though, I have never (and will never) only turned one of these engines 4200 RPM on a go kart!

 

[Denny]

E-Z-GO retarded the timing on golfcart engines by 4 degrees to clean up the emissions. In turn they became harder to start cold (cranked fine) and sluggish. Giving them back those 4 degrees woke them up. Retarding the timing 4 degrees is a old trick that the American auto manufacturers have used since 1965 along side retarding the cam timing 4 degrees. Again all this is done to reduce emissions at idle and low speeds. Not speculation just fact.

Denny

 

[JToTheIzzack]

Thanks for the replies, didn't mean to start an argument about timing! Anyway, I only mentioned the stronger springs because I had an old tecumseh before my predator that floated and ate an intake valve at stock rpm. Granted, it was fairly old and worn out and, well, a tecumseh. You'd be right in assuming I have a non-hemi motor, and stock flywheel. With no bump in rpm, I don't really want to shell out the cash, and I'll take the risk. When you mention a 14 cc head, do you mean a gx140 head? Again, sorry, I'm pretty new to these little engines. Also sorry for not quoting previous comments, I wanted to address more than one in one reply.

 

[Relativity]

I'm looking for a relatively cheap can that will give good torque below about 4200 rpm. I plan on upgrading to a billet rod and heavier springs, and hardened pushrods if necessary, but the stock governor is still in place, with the screw backed all the way out to alllow around 4200 +- rpm. What would you guys recommend? I have a wallbro type fuel pump with a stock carb, unrestricted intake and exhaust, 140 e-tube and a full set of jets to play with. I believe I have the #90 in right now on an otherwise stock engine. What would you guys recommend for good low end power, and still somewhat affordable? I understand such a thing might not exist, and I'm still fairly new to nodding these engines. Any help is appreciated, thanks!

1 GXC-412-00 Rod Guide Plate $5.20, DJ-1100 Ratio Rocker 1.3 $8.74, MOD2 Grind, Predator Core Dyno Cams $50. Find you some valve springs that are at around 22-24lb.

 

[itsid]

When you mention a 14 cc head, do you mean a gx140 head? Again, sorry, I'm pretty new to these little engines. Also sorry for not quoting previous comments, I wanted to address more than one in one reply.

No, it's an old GX160 head (still being 'cloned' AFAIK)
old, because the new style heads are a slightly larger.

Quoting is unnecessary if you reply to the post directly above you, no big deal.

As long as it's obvious what you're replying to it's completely unnecessary IMHO...

well in fact unnecassary fullquotes (like you see in this thread)
can lead to a ban in some forums, because it's just cluttering up the database, makes it a pain to read the post on a small screen and, it is completely pointless

'sid

 

[OzFab]

Problem solved...