Author Topic: Opposed Magnum  (Read 8009 times)

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Wheelhorseracer

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Opposed Magnum
« on: August 18, 2008, 09:01:21 am »
Would the opposed benefit from two spark plugs per cylinder like the pullers use?

Or would milling the heads help more for power.. the compression is really low on these engines.. so I'm thinking it might need a boost in compression to wake it up.. and maybe extra spark...

Offline mightymowe

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Re: Opposed Magnum
« Reply #1 on: August 18, 2008, 09:07:45 am »
The extra plug would probably not be legal.
David Peters

Wheelhorseracer

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Re: Opposed Magnum
« Reply #2 on: August 18, 2008, 09:09:05 am »
In my class flatheads can have any modification... it's kinda to even up the flatties and the OHV in the class..

Offline iused2mow

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Re: Opposed Magnum
« Reply #3 on: August 18, 2008, 10:26:15 am »
The extra plug would benefit it is so if you are runnin more fuel in  the cylinder it WILL burn more efficently and more complete.

And almost all flatheads have pour compression.
wide open into the corner, pray to god i make it out

Offline 300xdeere

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Re: Opposed Magnum
« Reply #4 on: August 18, 2008, 11:21:34 am »
Unless you get one killer valve job done to that motor, milling your heads with actualy hurt your power. The gain you will get in compression will kill your flow. And your getting way more power from the flow the you will from the compression. I hurd this whole talk from ryan already when he did my valves for me.

Offline outlawmower

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Re: Opposed Magnum
« Reply #5 on: August 18, 2008, 12:25:39 pm »
OK here it goes-

Kohler in general is bad FOR NOT FLOWING from the factory...This presents an issue with trying to build up compression.... It will KILL EVEN MORE FLOW!!!

So you really need to open up the ports.... Not to big but slightly large.... When you do this you are going to need more CARB so maybe get a #30 Bored out from Brian Miller or even a #26 Bored will flow just as well as a stock #30 (kohler Carb)

Now the heads............. Well shave them... Use the old clay trick put some on the valve with your head and head gasket on... See how much valve clearance you have....

ALOT of people are taking the Kohler and when they build a high-pro engine they will eliminate all the flow above the valve so it all goes under.... In this case you might want to change your valve angle from either 60 or 45 (cant remember stock? Help me out) and you want to change it so that when the valve opens Fuel can get in ALOT faster and sooner.

As 300xdeere mentioned above if you don’t have a good valve job it just is not going to run!

So really you want to have a good valve job period…. What I did is I found a DIRT-cheap valve machine and played and played around with different angles until I found the best power. Kind of like they use to do with the Ford Flatheads back in the day!

Now on your dual plugs yeah go for it! I run them and can’t be happier! I use a system called Dual Point Saver from http://www.kirkengines.com/ …



I’m not sure if your Magnum has these type of points that are on the K-Series but this would work great for your dual plug setup! Also you could try a Crank Trigger Ignition (CTI).

Last thing- when you shave your heads make sure you take a little off the block for some extra TQ….

If you have any more questions you can email me or send me a PM here.

-Outlaw
PUT YOUR GAME FACE ON!!!

Wheelhorseracer

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Re: Opposed Magnum
« Reply #6 on: August 18, 2008, 12:49:45 pm »
The Magnum doesn't use points...

I was looking into that kit for my K-series puller with a Kohler..

My little K is ported, three angle valve job , decked and the head is milled.. haven't got it back together to see the difference.

This opposed magnum has the magnetic pickup found on most lawn tractor engines.. I kinda wished it ran points as it creates more options..

Mine is running stronger all the time.. I made an intake and that evened out the fuel between the two cylinders ( front used to be lean and the rear used to be fat ), the timing has been advanced..I'm running stepped headers.

I'm always looking to make more power and the way the rules are in my club for flatties. the sky is the limit.. but I really don't want to tear it down..



Offline fordman21

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Re: Opposed Magnum
« Reply #7 on: August 18, 2008, 01:23:52 pm »
A bit more compression wouldn't hurt, just make sure the valves are not shrouded too much. You may have to do some work in there....I'm not familiar with the Kohler flatty.
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Wheelhorseracer

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Re: Opposed Magnum
« Reply #8 on: August 18, 2008, 01:37:38 pm »
I thought about pulling the heads to check them for flatness and unshrouding the valves.. it seemed to make a big difference on my K-181 in my puller before I torn it down for a rebuild..

I also polished the combustion chamber on the little Kohler.. but I'm not sure that helped much as the valves being unshrouded...

I was assuming the same could be transferred to the bigger magnum

Offline Big daddy

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Re: Opposed Magnum
« Reply #9 on: August 19, 2008, 06:35:16 am »
You definately have to unshroud the valves. Air must flow over the valves or you kill a good portion of your cam lift flow. You do not need an excessive amount of clearance above the valves, about 0.060 should be fine. You simply leave a good side clearance to the valves and leave a 1/8"-3/16" blend radius between the vertical and horizontal sections of the head. As the valve opens if the air does not flow over the valves it will kill your torque. Remember, the valve will spend more time at low to mid lift than it will at the top of the cam lobe. You cannot compress air that does not get into the cylinder!
Bruce Litton

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Re: Opposed Magnum
« Reply #10 on: August 19, 2008, 08:32:15 am »
Good points... I think I will pick up some head gaskets and head bolts and pull off the heads next week...

It would be good to see how everything looks in there and clean the tops of the valves and the deck surface anyways..

But I will check to see how shrouded the valves are and polish the combustion chambers...

Offline Big daddy

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Re: Opposed Magnum
« Reply #11 on: August 19, 2008, 09:44:25 am »
A trick you can do if you are running race gas in the motor is to look at the head and look for places where the carbon has scoured off, these are the places you need to remove material. But remove a little at a time. This will help the air flow in the cylinder head, but don't rely soley on air flow in the head to make power, you have to get the air into the head first. In my opinion the importance of the ports over the head is about 60/40 in favor of the ports. The trick is to flow the air through the head without creating a swamp head.
Bruce Litton

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Re: Opposed Magnum
« Reply #12 on: August 19, 2008, 12:06:16 pm »
Good points.... The ports are very large in the magnum .. but do have casting marks too..

Should the short side radius need the most attention more than smoothing the areas around the valve guide?

Offline Big daddy

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Re: Opposed Magnum
« Reply #13 on: August 19, 2008, 12:24:15 pm »
The short side radius is where most of the flow will be in a Kohler motor, the valve guides just blend slightly to the port floor, leave the complete diameter of the guide hole intact. If you are not changing to larger valves then don't make it any larger. To properly port this area you will need to weld up the top of the port flange to the deck of the motor, build this up and out to the port flange itself. If you don't then you will have breakage problems as well as sealing problems with the flange. Again, if you are not putting larger valves in it then I would not make it much larger, just blend and smooth out the rough spots.
Bruce Litton