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Old 03-12-2007, 09:22 AM
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Welding combustion chambers

Raising compression ratio is a top priority here because of the 6.600 feet of altitude, since obtaining aftermarket heads or even domed piston is quiet dificult from here, I was thinking of weld filling the cc's of the sbc engines, I have some experience welding cast iron but have some doubts here, what kind of welding rod should I use? I always use pure nickel rods for welding cast iron, will brass rods used for brazing would work? they join cast iron pretty well also and is very easy to machine not so with nickel.
I have filled rice burner aluminum heads with good results but have never tried with good old american iron.
Please comment.
Augusto.

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Old 03-12-2007, 09:54 AM
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Can you not just mill the heads?

From what I know, only use nickel on cast iron. You also need to peen the weld as you go.
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Old 03-12-2007, 11:13 AM
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milling the head upsets the intake manifold alignment and I don't want to deal with that extra complicated machining operation. besides not much is gained, I need to raise like 2 points.
Augusto.
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Old 03-12-2007, 04:58 PM
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When I rechambered my heads, I completely disassembled them, heated them until red hot in an oven and filled them in with nickel while hot.

This is the only way I would weld the combustion chamber of a head. I've only done this once, but they haven't come apart yet...(knock on wood).
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Old 03-12-2007, 08:09 PM
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What cylinder head are you working on?
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Old 03-13-2007, 07:03 AM
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Quote:
will brass rods used for brazing would work? they join cast iron pretty well
The Problem there is,........
The Filler Metal Softens at 600*,+ Melts at 1200*.........

And that's a tad Low for a Combustion Chamber.......
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Old 03-13-2007, 08:21 AM
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F-BIRD'88:
chevy 350 smog heads

bondo:
yes, I agree, but I think aluminum melting point is lower and heads are made of it, besides the heads never reach that temperatures, only the burnt gases do, they transfer part of that heat to the head but not all, most goes down the exaust pipe, in my karting racing motors wich have aluminum air cooled heads, the temp probe under the spark plugs reads around 350 deg and that is with a 45+ hp motor turning 19.000 rpm, the exaust temp probe reads 1.200 deg at full power.

I see no problem with brass, but that is only my opinion, I would like to hear from others since I've never done it and don't want to screw up, listening others opinions is great and improves knowledge.

Augusto.
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Old 03-13-2007, 09:28 AM
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Seems to me here's a case where swapping to 53 cc chamber 305 cid heads would be the easiest and most econmical way to go. And yes, I know he's out of the states and is at high altitude. It just seems to make the most sense to me. Anyone else? BUTCH.
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Old 03-13-2007, 09:58 AM
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Surely you can find a suitable 305 to work with.
Some have 58cc/60cc chambers (416) some have tiny 53cc/55cc chambers (801 , some 601's)

Once you put a 1.94" valve in these heads they flow as good as the old 76cc 350 heads. Head porting will get you well down the road to what ever power level you need up to about
400hp. I find the 416's work great.
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Old 03-13-2007, 02:11 PM
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I do have a set of 305 heads, I tougth 1.94 valves did not fit in this heads (I don't know where did I get this idea from) I'm gonna cc them to see what I got, thanks for the tip.
Any reccomendations for porting the 305's?
I bet some intake valve unshrouding must be done.
Augusto.
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Old 03-13-2007, 04:48 PM
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Porting a 305 head is no different than porting any other SBC head. generally open up the bowls under the valves seats. Radius the sharp edges and short side to port floor transistion. Widen the bowl on either side of the guide boss.
Slim, trim and streamline the guide boss. Square up the intake port opening. Do not make it huge. widen the push rod pinch a bit. Raise the roof of the port all the way from the intake flange to the bowl. Do the same to the exhaust side carve two flow paths around either side of the exhaust guide boss. Widen the port walls and raise the roof but do not get carried away with the exhaust port exit size at the flange. All that serves is to ensure the manifolds or headers will leak. Needs to be no bigger than your headers.
Opening up and raising the intake to a 1205 gasket is plenty. match the intake manifold to that gasket too.

To deshroud for larger 1.94" valves find a drill bit or allen key that will just fit between the partially open stock valve in the stock 305 head. Now using a 1.94" valve and that same drill bit, grind the chamber wall to just allow the drill bit to clear around the partially open valve. The 1.94" vale is .100" bigger than a 1.84" 305 valve. So to maintain the same space between the valve edge and chamber wall you need to grind away .050" from the chamber wall at and near the closest point. Then to increase the breathing around the larger valve while it is at low lift in the chamber where most of the flow is concentrated, (near the sparkplug) rework the areas shown. only a small amount of material needs to be ground away. Don't get carried away.
The third pic is a corvette L98 chamber but the job is the same. Be sure to protect the valve seat from the die grinder while working on the chamber. Stick some old valves in.
Do not grind out the protruding spark plug boss ring. All that will achieve is to expose sparkplug treads to combustion and create detonation and preignition points.
After they are all ported and deshrouded you'll need a new valve job for the new larger valves. For a 350ci motor use 1.94x 1.60" valves. For a 305 use 1.94x 1.50" valves.
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Last edited by F-BIRD'88; 03-13-2007 at 05:07 PM.
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Old 03-14-2007, 08:08 AM
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very informative, thanks a lot.
Augusto.
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