nothing fancy--lolol


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Posted by clueless [201.202.22.114] on Monday, April 15, 2013 at 23:41:31 :

In Reply to: 6000 rpm flathead mopars in tractor pulls posted by clueless [201.202.22.114] on Monday, April 15, 2013 at 23:05:13 :

Hudson,
Sounds like you have a heavily modified flathead. Would you care to share some of the details and performance with us?
Jim R
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Hudson
Active Inliner posted 08-21-2001 05:11 PM
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First, don't anybody jump out and bore your B&B carbs out to those dimentions. The step up jet is wayyyyy too big. Even though the tractor would run up and down the road like top fuel dragster, its too much fuel under the type of load a tractor pull inflicts on an engine. I buzzed down the track until the load popped up the step up jet - then billowing black soot rolled out, and the rpms stopped going up. I backed out to let the step up seat and hopefully gain my vacuum back, this may work on a drag strip - it won't on a pulling track. The main jet wasn't enough and the step up jet was too much. Ideally, the step up jet would pick up the load and additional fuel needed to sustain the engine. Mine is simply too rich.
Luckily, a new step up jet for these carbs comes with an overhaul kit from The Carburetor Shop in Eldon Missouri.
Now, as for modifications, nothing real outlandish has been done to the engine. It was noticed that is full potential should be gained at 5000 rpm, but the crank didn't seem to want to stand that.

The crank was fully cross drilled from the mains to each adjacent rod and from rod to rod between mains. An oil groove was cut in the main & rod bearings to allow continuous oil flow to the crank at all points. We are running stock stroke and had the entire rotating assembly balanced out to run 6000 rpm.

Another important modification to get this rpm is to plug all the oil bleeds from the rods. Depending on what type of chrysler engine it is, some have holes in the yoke to spray the cam, others have in addition ports drilled through the rod beams to lubricate the wrist pins and spray the piston head. Be sure and plug these up to conserve all the oil and associated cooling in the rod bearing. Almost all the engines we tore down had some degree of damage to #2 and #5 rods, attributed to poor oil distribution and the excessive bleeding of oil from the adjacent rod nearest the source oil port.

The rest is pretty vanilla in terms of hardware. '58 head cut .090, stock valve diameters, homemade split exhaust, and a custom grind on the cam 270 duration seat to seat with a .425 lift and 110 separation angle and centerline.

The valves were left stock because of the shrouding that would occur if they got nearer to the head relief at full lift. We could have ground this shrouding away for better flow, but that costs CC's in a situation that doesn't allow many compression boosts. Perhaps if we stroke it, these CC's can be made up with cylinder displacement. We run 9.5 compression and can burn 93 octane pump gas.

That's about it, nothing very elaborate - but we can turn some wicked sustained rpm's. Two years of some very hard, winding service without a hitch. We needed some more induction, just need to get it harnessed!

Hudson

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