46 JD A cylinder head modification

Rottenground · Dec 16, 2017

Wonder how much one can cut the head down? it has been cut once before. Does anyone have the original head thickness?
Also I'm going to Port match the head and manifold smooth up the exhaust ports. Just going to barley hit the intake ports. What is the best thing to do with the eyebrow? Engine is going to get some later model higher compression pistons. Has a gas manifold,51 carb pretty much stock. Any other ideas for a little more power thanks for the info.

matt fleisher · Dec 16, 2017

camshaft reground

Mike N Mo · Dec 16, 2017

Instead of cutting a bunch off of the A2325R head, buy a late A head to start with, casting # A3367R or A4226R. It starts off with around 6
CU.In. less volume that the early head. A set of higher ratio roller rockers from Murphy's usually adds about 4 HP to a mostly stock engine.
Grind back the eyebrow some away from the intake valve. As Matt said, a better cam will help some, stock is .300" lift, going to .360-.400
will help combined with the roller rockers. For a stock sized engine don't go crazy with the intake duration, or you'll go backwards! no more
that 210 [email protected], and 206-208 would probably be better. Stock duration on the exhaust, just more lift.

I'm assuming that this will be a limited use/puller tractor. Once you get above around 8:1 compression, 93 octane gas won't be enough.

MSD · Dec 16, 2017

Porting the intake and exhaust ports on the head and matching them to the manifold will make a big difference. If you have never done it or don't have access to a flow bench don't bother. Cam
grind and correct degree timing of it helps also. Distributor will need reworked to add some cheap hp also, they are all shot as far as timing advance goes. Brian can help you out on all that. He's
at 605 359-20 four three.

Brooks E. · Dec 16, 2017

I have the head off my '51 A now, just doing a VJ and mill. It's at my shop now, but if i remember on Monday, I'll measure the height and let you know. I have a hard time believing that porting can actually help these low RPM engines. I'm new to the old tractors, but have a cyl head shop. How fast can these engines turn?

Rottenground · Dec 16, 2017

(reply to post at 17:39:13 12/16/17)

I don't think u want to go crazy on smoothing up the intake ports just lightly hitting it, but I plan on working the exhaust over good as well as matching the gasket to the head and manifold. I am going to take a grinder to the eyebrow also and feather it back They won't turn many rpm's 1075 is what book says mines right around 1125 or so.

buickanddeere · Dec 17, 2017

Hand held grinder to relieve the eyebrows...............say what ? Why not have the machine shop just use an oversize cutter and remove the eyebrows?
Needs pistons for compression. Definitely a reground cam. port matching. The machine shop can perform a three angle valve job on the seats.

Brooks E. · Dec 17, 2017

I wouldn't completely remove it, that'll increase chamber volume and lower comp ratio. Just remove enough to unshroud the valve. It helps with creating a swirl in the chamber, which is something Ford has used on their 4.6 and 5.4 2 valve heads for a long time. I think it helps low end power.

Rottenground · Dec 17, 2017

Already had it milled once and done had valve job done just didn't do enough to it the first go around so I am tearing it down again for the Pistons. Guess I could have them cut the eyebrows machine shop didn't seem too keen on doing that. A flap disc works pretty good. Should look into a cam kit it is all original specs. Put new cam bearings in the first go around also should have done all this the first time. Thanks for the info

JLG · Dec 18, 2017

I had 1600 rpm out of my G just by adjusting
the throttle linkage. Didn't sound like it
was screaming. I was surprised it was that
fast when I checked it. 2000 is doable, not
advisable with that big cast flywheel
spinning out there though, ha! Not much
compared to multicylinder engines, but it is
about twice stock for these.

Rottenground · Dec 18, 2017

(quoted from post at 13:56:52 12/16/17) Instead of cutting a bunch off of the A2325R head, buy a late A head to start with, casting # A3367R or A4226R. It starts off with around 6
CU.In. less volume that the early head. A set of higher ratio roller rockers from Murphy's usually adds about 4 HP to a mostly stock engine.
Grind back the eyebrow some away from the intake valve. As Matt said, a better cam will help some, stock is .300" lift, going to .360-.400
will help combined with the roller rockers. For a stock sized engine don't go crazy with the intake duration, or you'll go backwards! no more
that 210 [email protected], and 206-208 would probably be better. Stock duration on the exhaust, just more lift.

I'm assuming that this will be a limited use/puller tractor. Once you get above around 8:1 compression, 93 octane gas won't be enough.

Going to stick with the 2325r head can it be milled down to match the later head volume wise it has been milled once before I am thinking 30 thousands but I can't remember for sure

Brooks E. · Dec 18, 2017

(quoted from post at 11:58:59 12/16/17) Wonder how much one can cut the head down? it has been cut once before. Does anyone have the original head thickness?
Also I'm going to Port match the head and manifold smooth up the exhaust ports. Just going to barley hit the intake ports. What is the best thing to do with the eyebrow? Engine is going to get some later model higher compression pistons. Has a gas manifold,51 carb pretty much stock. Any other ideas for a little more power thanks for the info.

Rotten,

I just measured my cylinder head, A4226R, and it measures right at 5.300".

46 JD A cylinder head modification

Rottenground

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matt fleisher

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Mike N Mo

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MSD

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Brooks E.

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Rottenground

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buickanddeere

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Brooks E.

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Rottenground

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JLG

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Rottenground

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Brooks E.

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