Upgrading My Honda

[Branderino]

Hey guys I need your help. I recently finished building a go kart with a honda gx240 motor. I love the power compared to my old 6.5. Well yesterday I was given a gx390 because it was "broken." It ran just fine when I put my carb on it. (gx390 Carb)

So my question is: What parts can I use off of the gx390 to upgrade my 240 and what is involved with the swap.

 

[Kartorbust]

Could just drop the GX390 on the kart instead. Both have a 1" pto, both have big block engine mounting pattern. Though the GX390 is a bit bigger physically.

 

[Branderino]

Could just drop the GX390 on the kart instead. Both have a 1" pto, both have big block engine mounting pattern. Though the GX390 is a bit bigger physically.

Well the main reason I am doing this is because I like upgrading things and the idea of having a go kart with a cam/head upgrade sounds way cooler than just bolting on a bigger motor.

The cart is already too fast for its own good anyways and the 390 would require more fabrication and supporting mods.

 

[Kartorbust]

Understood. Like most I'm in the no replacement for displacement usually mindset. So if the opportunity is there for a larger engine, I'd go for it. Not sure what you'd gain with the 390 cam, might be the same stock but I'm not sure, since looking at NR racing, they sell a cam for GX240, 270, 340, 390 cam and seems to be the same, difference is how aggressive the cam is, and that's it.

 

[Whitetrashrocker]

Will putting the 240 head on the 390 raise compression?

 

[Kartorbust]

KartFab may know.

 

[Poboy kartman]

KartFab may know.

No...Grant may not know...but a warm flat beer says he WILL respond!!!!

 

[Flyinhillbilly]

Will putting the 240 head on the 390 raise compression?

This was the first thing I though of as well

 

[Branderino]

This was the first thing I though of as well

Wouldn't that head also have less flow?

 

[Whitetrashrocker]

Your the one with both engines.
Tear them suckers​ down and measure. That will tell us everything.

 

[Kartorbust]

Milling the head may end up being better.

 

[Branderino]

Your the one with both engines.
Tear them suckers​ down and measure. That will tell us everything.

**** your right... Time to pull a Frankenstein

 

[Whitetrashrocker]

You'll probally find the same size piston and different strokes or the opposite, same stroke different piston.
That's usually how they get the different HP ratings.
The heads will probally be the same with different deck height. Not sure on the valve sizes.

I'd try to use the big piston with the stroked crank, the bigger valves and deck the head till the clearance is just right.

 

[Kartorbust]

Well old engines had different bore/stroke for listed displacement. New ones are just different carbs...like the GX270 and 240, same 270cc displacement just different carb and head. Think the change over was 2008.

 

[Whitetrashrocker]

Well old engines had different bore/stroke for listed displacement. New ones are just different carbs...like the GX270 and 240, same 270cc displacement just different carb and head. Think the change over was 2008.

So you mean it's the same cc just choked down with a small carb?
That means the exponentially larger price between the small and large HP engines is in the carb?
What a joke.

 

[Kartorbust]

Pretty much. I mean you can get the same options on a "smaller" engine and pay like $60 for the "larger" carb and still be ahead.