Which would you go? gx390 or gx270

[codeyell0]

I found these two engines for sale for a good price.
MY 196cc smokes. has gotten better but one of the exhaust studs stripped so I was looking at my options rebuild, or see whats out there.

I am assuming the 390 is what the predator 420cc is cloned after?
why are the clones bigger but the same?

I am worried if i go bigger less available parts. But at the same time a stage 3 212 is what 14hp and would cost more than the 420cc

I use a #40 chain now so that should still work on the bigger setup?

 

[itsid]

parts for the hondas should be fairly identical.. both are technically big blocks already,
both ends of the same scale so to speak

And yes'ish the GX390 is the role model for all similar sized clones..
Rato makes both, the 390 and the 420 which you find relabelled as predator at HF.
And many parts are shared between the two.
(keeping the costs down and such)

the bigger combustion volume comes from a slightly bigger bore and stroke (GX390 is 88x64 mm just like the R390 and R420 is 90x66 mm so a two mm increase in both directions )
why? because it's cheaper to increase the bore slightly and save on crankcase material more than you'd need to spend for the increased piston size.. and the crankshaft is likely cut from the exact same blank.

btw rato makes a true clone (196cc);
the 210 (212cc) and a 225cc
as well as the 240 and 270 gx clones and a 440 cc to top out the gx390 case size...

And yes.. the least likely it is an engine gets used for racing, the least likely it is to find aftermarket performance parts for it.

the gx390 is about the most modified enigne right after the true clones
(don't forget: anywhere in the world but the US the 212 is basically a niche product and everyone's going true clone really... very slowly single 212 225s are coming around (thanks to Tilly mostly))

Nevermind.. GX390...
the engine is the base of all mini nascars soem junior dagsters and whatnot,
modded to push up to 45hp
(and no, you can't in your homeshop I'm afraid)

So chances are you'll be able to find whatever performance part you might need.

the smaller GX270 however might prove to be a tad more difficult.
sure some gx240 parts fit, and even some gx390 parts do..
but it's essentially too small for a big block and too big for a small block
to take a noteworthy share of the tuning parts.

great engine, don't get me wrong..
but if you want a good coverage with tuning parts.. the gx390 is about as good as it gets.


#40 is okay.. if you have #41 sprockets I'd recommend swapping to 420 chain though (much much beefier chain, same size sprockets as #41)

'sid

 

[Joe-405]

What are you trying to put it on ? Those engines are quite a bit bigger than the 212 you have now. It may not fit.

 

[codeyell0]

I have tons of room. The 196cc i have now looks small back there.
My thought is if i can get the power from a stock motor that i would spend 100's trying to get out of the 212 might as well go bigger if the price is right.

I would save up and go vtwin if I could only get / find bigger wheels. I'm still looking for hubs.

 

[anickode]

The advantage you'll have going with modding a 212 is top speed. Throw GX390 money at a predator and it'll be a 6000+ rpm screamer.

That gx390 will still only get you into maybe the low 40s ungoverned. It will get you there a whole lot quicker though. They can't spin as fast (valve float around 2400 iirc) and cost a LOT more money to make them rev faster.

If you're talking used engines though, the cost savings is a no brainier on the big blocks.

 

[karl]

They can't spin as fast (valve float around 2400 iirc) and cost a LOT more money to make them rev faster.

Wat

 

[itsid]

pfff!

gx390 valve springs are stiffer than the gx200 ones..
valve float at around 6k (compared to 5-5.5k on a gx200)

an old gx390 has a peak torque of 27Nm @2500 rpms
so MORE than a predator 420 (rato's 440 has 27Nm too)
(newer ones suffer slightly )
but the old cams are still around, and compression can be increased again

And while the increase in moving mass makes it less quickly revving compared to a 200cc,
I would say the difference is essentially not noteworthy at all.

'sid

PS the gx390 is a beast out of the box (older ones preferred.. newer ones can have a rev limiting magneto [3400 or 3800 rpms IIRC])
and finding a good replacement for that can get a bit difficult at times
other than that everything is almost just as easy to find as it is for a gx200

 

[bob58o]

I think it was the small diesel engines that only turned around 2400 rpm or so out of the box. I remember it being an issue when considering clutch engagement rpms

 

[JTSpeedDemon]

I’d take the GX390 any day. Bigger displacement, plus there’s actually a considerable aftermarket parts market for the 390.