duramax 16hp

donetheconversion

hey thinking about a clone swap. i am looking at the duramax 16hp 420cc motor, and am trying to find performance parts for it. i was reading some posts and ended up at agk, but they dont have 420cc parts are 390cc parts interchangable? specifically camshafts?

BGW

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danman

From what I understand, the 420 is just a bored and stroked version of the 390. So most 390 parts work on them. I am not 100%, but honda carbs and other parts should bolt right on.

Sho should chime in here soon, he's the guy to talk to about clones

geoffw

390 parts are interchangeable for the most part. The 420 is a 90mm bore x 66mm stroke.

I will have the 18HP 440cc Clones mid-February, much better alternative to the 420cc since they are setup for performance out of the box.

donetheconversion

what's the price gonna be on one of those 440s?

geoffw

Around $350, however, it will make a REAL 18hp, have a much beefier valvetrain setup rated to 6500rpm, more timing, a carb designed for performance use (instead of a lawnmower carb), a 32mm intake manifold which allows for the use of any carb you want, and much more.

Out of the box 420s only make 14hp, even though they are advertised at 15 and 16hp.

-Geoff

sho305

Far as I know the crank is different and the piston is, due to more stroke and bore. All other parts including the cam and rod are the same I'm told. Most parts interchange with hondas also. There are a few differences but minor, such as the port shape inside the head. Check out NR racing, precision cams, parsons racing, there are others. Just search for gx390 performance parts.

Geoff, maybe I can put my ported head on your 18hp lol. What cam is going to come in them? That would be a screaming deal for sure at 350 or so.

geoffw

Yep, Piston, Block and Crank are different.

Your head will fit the 440, no problem.. Its basically a bored 420.

sho305

I have to get a clutch and maybe change the carb, though its been running great in the cold weather for some reason. After that I plan to look for another cart and certain it will need some things! I might put a cam in this one if I don't find another cart soon enough.

geoffw

sho,

Time is on your side buddy, March i will have cams in for $49.99.

You really will not believe what a cam does to these things...The entire rpm range is boosted dramatically, especially on the top end.

There is absolutely nothing wrong with the stock carb....UNTIL you put a cam in, then its garbage. Likewise, we did gain noticable power with a 32mm slide carb with stock cam and some head porting/milling.

bradsterlouman

I have one can't get it to idle low enough think I need to totally remove governor? Any suggestions.