This is the head after welding and before machining. I wanted small chambers (without milling) and quench. It's a 170 so the pistons will be at zero deck. $200 for the welding, more for the machine work and hours with my carbide cutters in store. Doc says the peanut plug heads are heavier and hold a head gasket better on high compression engines. Since I'm shooting for 13:1 I hope it's true.

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Joshua

Thats really cool! I'm building a 318 with '920 casting heads right now and I'm psyched to have closed chambers. I'm getting 9.4:1 CR with mine .030 in the hole, with 0 deck and those tiny combustion chambers you should have no problem getting some squeeze!

So did you have to preheat the heck out of the head, then weld with nickel rods? I would be scared to try welding on a cast iron head. Are you going to have a hard time getting equal volume between the chambers? Home made 'porting' templates and carbide bits? Fancy cnc porting program? Worried about shrouding or planning for a heart shape?

Can't wait to see how it runs. I don't know much about race gas combos but Im guessing quench is still very important for gas prices and efficiency?

Lots of questions, but mostly wow and congrats for taking that radical step. That thing is going to sound sweet.

rdr

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madam im adam

I'm not familiar with '920 casting 318 heads. I built a zero-deck 318 with '302 heads and it was about 9.7:1 with the big valve reliefs KB machines into their pistons. Your pistons being .030" in the hole are going to kill the quench effect. The KB web site states: "A running quench height in excess of .060" will forfeit most of the benefits of the quench head design and can push the engine into severe detonation." With pistons .030" in the hole and a .039" thick head gasket your quench distance is .069".

I did not do the welding. I don't have the furnace/oven needed to preheat the head. Rick's Cylinder Head in Milwaukie, Oregon did the welding. I've had this done before and I think the last head they did looked better.

I will make templates to make the chambers as alike as possible. I do have access to a mill, but a lot of this will be hand work. I'll be able to equalize the chamber volumes as I go. The way the welder filled the chambers I don't see the finished product looking very heart shaped.

Quench is very desirable from a power and efficiency standpoint. There are several good articles on quench on the KB-Silvolite web site. Engine Building with KB pistons is a good one. http://www.kb-silvolite.com/article.php

This is the other head I had welded, but never finished.

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Joshua

Josh

I am familiar with quench but only as applied to a street motor. I built a 408 last year with zero deck pistons and closed chambers. No problems yet with 10.5:1 compression and pump gas. 16*initial timing 35*total. The aluminum heads are probably also helping bleed off some heat.

I guess what I was getting at was whether the benefits had diminishing returns as you get into much higher compression ratios. Of course any improvement in efficiency is a good thing.

The '920 heads are 1967-68 only closed chamber heads the factory put on 273s and 318s. Mine have a little over 64cc chambers. They are supposed to have better ports than the 302 swirl heads.

My rebuild of this '67 318 with these rare heads is the super duper budget kind. My only concessions to performance are the hard to find thin steel head gasket I got for it (.028 mr gasket also sold by MP no longer in production) and a mild cam. I would deck the block .025 or so to get some quench but money is tight. With the thin gaskets I should be coming in at less than 9.4:1 -that figure doesn't account for the stock piston's 4 small reliefs. The 'quench' is going to be right around .058. Decks are straight all cyls have even compression height. I don't expect any miracles but I'm hoping it won't cause any problems either. I am hoping it mostly affects CR and should let me run 36*+vacuume advance on the street. The engine is going in a lightened 73 swinger, so it won't be pulling too much of a brick. I'm putting in a 115* @ .050 cam with .454 lift- mild but should match the CR to get the most out of a mild combo and still use the stock converter and my 3.73 gears.

My plan only includes breaking the glaze, re-ring, valve springs and seals, bearings, and general clean up. No machine shop this time but there is no ridge in the bores and the guides are not too sloppy. Basically a spraypaint rebuild with a little freshening up, oh yeah can't forget the 650 dp, melling oil pump, ld4b intake, and small tube headers. I'm going to run all the stuff I have laying around! I'm on a $1500 budget and the motor was $400, 904 trans was $125, comp valvetrain kit $300 and you know all the little stuff adds up FAST...

Anyway, your heads look really different from the average build. It looks more like 'bathtub' chambers than the heart shape, unless you are also relocating the spark plugs! Should run pretty well for you.

Thanks for posting the cool pictures and nice work!

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madam im adam

Nice job there, some of the best running slants incorporated a similar modificaton. It is very necessary with a 170 to get high compression without sinking the valve notches through the top of the piston.

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If you didn't drive it there, it's not a street car.

.058" quench height is no good. Gotta keep it below .050" at least and preferably <.045". You'd have less detonation with better quench even with the higher compression ratio. My current machinist says .036" quench distance for 6000 RPM with stock rods and crank as .035" isn't enough. Funny guy. I'm planning on 8000 RPM so I'm going about .043" and all the deck heights will be equal!

I guess I am familiar with '920 heads as I have them on my HP 273 and I ported them too. I didn't think they were any better than the '302 heads, but I didn't directly compare the two. The '302 does have crap exhaust ports.

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Joshua