Author Topic: 21 hp racing engine suggestions  (Read 783 times)

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Offline Tylertyco

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21 hp racing engine suggestions
« on: December 08, 2019, 06:54:26 PM »
Hi , Iím new to this awesome site !!!
Just have a few questions I want to ask you experts ,
So I bought a 21 hp Intek v twin.  Model is 406677   0403 E1  050526YG
It came with a single barrel carburetor and want to change it out for a newer 2 barrel carb ,
Is there one that you guys can suggest ?
Also Iíd like to put new connecting rods in it but the ones from arc are pretty expensive!
Just wondering if Briggs made a better connecting rod out of there bigger cubic inch engines that I could use , Iíve herd of 1 guy that had a 40 Cubic inch and put 49 cubic inch rods in , is that a folk tale ?
I also would like to shave the heads down a bit , do you guys a have a suggestion on how much ?

Thanks for yours guys help
I probably have a lot more questions lol
Thanks !! 




Offline cycloneracer

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Re: 21 hp racing engine suggestions
« Reply #1 on: December 09, 2019, 01:09:44 PM »
If you are going to run this without a governor spend the money on the good parts.

Billet Flywheel is a must if your running ungoverned.   Billet rods will make it last.   Some have used the 49 rods, but in the end they are still cast rods designed to be in a lawnmower running 3500 RPM.


What class are you racing this in?    If in FXT I'd go with twin Mikkuni carbs.   The 2 barrel carbs are better than the single, but not by much.    Even modified the 2 barrel carbs suck and are at a huge disadvantage to "real" carbs.

I had a 44 that I took .125 off of the heads and installed briggs single intake valves.   I'm sure there are better valves out there now, but this was a long time ago and was a easy mod for the machine shop to do.

Your also going to need to upgrade your valve springs and retainers.

I'd recommend a cam as well.
Paul Krueger

****2017 USLMRA FXT points Champion****

#150 Worlds First "sidewinder" FX (now dismantled)

#150 FXT  Sponsored by Zach Kerber Machine. http://zkbrmachine.com/

Easy Parcheesy Racing


Offline Tylertyco

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Re: 21 hp racing engine suggestions
« Reply #2 on: December 09, 2019, 04:05:53 PM »
Thanks for the reply !!!!!
I'm not in a racing class, were just racing for fun on my buddy's dirt bike track for cash lol
I just want to build a reliable strong engine! there wont be a governor on it,
yes i was thinking on doing a billet flywheel , valve springs , and decking the head,with copper head gaskets,
could I use the stock retainers, or will they blow apart?  and for the push rods I was going to change out the aluminum ones for the steel , or because i'm going to be decking the heads will I need the chrome molly cut to fit ones?
and for a cam what one would you suggest, and from where?
also what do you mean about you putting in briggs single intake valves ? I don't know what that is?

Also i'm having a hard time trying to find a 90 degree gear box do you know where I could look for one, because i'm at a loss lol

Thanks for your help!!!!!!!

Offline cycloneracer

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Re: 21 hp racing engine suggestions
« Reply #3 on: December 09, 2019, 05:05:53 PM »

I'm not in a racing class, were just racing for fun on my buddy's dirt bike track for cash lol

This is a horrible idea.    Someone will get hurt.   Find a group to race with they are everywhere.    Especially if your going to sink a couple of grand into an engine. 

Steel stock push rods will work until they bend.

Can run stock rocker arms.

Will need different retainers if your upgrading springs.

The briggs single OHV intake valve is much larger than the one in the twin.   It is the same length and same stem so all you need to do is machine in a new valve seat.

As for a cam, find a builder you like and go from there.

90 degree box can be found on ebay, junk yard.   Can buy a new one from just about any mower shop. 
Paul Krueger

****2017 USLMRA FXT points Champion****

#150 Worlds First "sidewinder" FX (now dismantled)

#150 FXT  Sponsored by Zach Kerber Machine. http://zkbrmachine.com/

Easy Parcheesy Racing

Offline Tylertyco

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Re: 21 hp racing engine suggestions
« Reply #4 on: December 09, 2019, 05:43:42 PM »
As for the dirt bike track, we knocked down the jumps so there just small hills, nothing to bad lol

Thank you for your help!!!!!!!!! 



Offline Tylertyco

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Re: 21 hp racing engine suggestions
« Reply #5 on: December 12, 2019, 10:40:22 AM »
Just another quick question,
i'm definitely going to do the duel carbs!  just wondering how big to go?  the heads are 28mm
so should i find 28mm carbs or should I go smaller like 26mm
I just think that a 28mm carb is to big, the engine wont have enough suction to draw the fuel in ?
or am i wrong ?
I want a fast rev up when I stab the throttle,


Thanks


 

anything