Any machine shop guys out there, or anyone that has done this, chime in here. I have found a very good deal on some Dart iron eagle heads, and was thinking about picking them up. The problem is, they are the 49cc chamber heads. Has anyone ever opened the chambers on a head, so as to reduce compression? How much would a shop charge, on average to do this? I was thinking it wouldnt be hard, but I dont want to tackle it myself, because I am afraid I wouldnt get it right (take out too little or much, or not have them consistant). Any ideas? Anyone done this?

 

Anyone? Ever done it, know what kind of cost to expect??

 

Yes people do it all the time to put 305 heads on a 350 or 383. Just grind a little around the valves to unshroud them. You going to have to grind quite abit though, or run blower dished pistons to use them.

 

Thats the thing, they already have 2.02 1.60 valves installed, they are just small 49cc chamber heads. I have flattops, and the 49cc just isnt going to work. I am runnign 305 heads now, but these are gonna need some real metal taken out. I was just hoping to find a machine shop guy that could give me a guess on the cost of doing the work.

 

Are these used heads? 49cc is really small, like something you'd find on a hardcore racing head. Did the owner mill off enough metal to make the chamber 49cc ? If so, I'd pass on that deal.

From personal experience, I took 1985 LG4 heads and did a 3 angle valve job and a chamber polish, and when I cc'd the chambers I got from 61.2 to 62.8 cc. Doing the valve seat cutting increases the chamber size a little bit.

But jeez, if you're looking to take out like 10 cc, that seems like a lot of metal that has to be removed.

 

Thats what i'm saying unshroud them, grind around the chamber where the valves open into. Grind the sparkplug boss down, cleanup the chamber alittle. I know some people have got 8cc out of 305 heads not really trying. You might also be able to get the chambers CNC machined, but i don't know if their program will work for machined heads like that.

 

Of course, these are ONLY the specification numbers for a SBC, and virtually all are subject to variance; assume your piston has a perfect 9"height at the top of the bore, 6cc for valve reliefs, a 9.025" deck height, .051" gasket and exactly 49cc chambers. Your 350 would have 11.14:1.

Assuming all the above except you open the heads to 54 cc, your static compression would be 10.47:1. Still a bit high for iron IMO.

I don't think you could expect to open them up 5cc with just 'unshrouding the valves'. You would have to do quite a bit more grinding, and still you have a high compression ratio for iron heads. You would have to open the heads up to 58cc to get the compression ratio down to 10:1 (with EFI, that is doable, but might require a bigger cam and 94+ octane with a carb).

The only way you going to make that combo work, is with dished pistons. But you probably already knew that.

 

No, these are brand new dart heads



I'm running a carb, not FI. Never really could get into TPI. As far as compression ratio, I am looking to have a final ratio of around 10.5-10.75:1. I am running a standard deck height block. I think if they were cut out to 58cc that would be perfect. I know quite a few guys that run 11:1 on iron heads, on 93 octane.

 

Here's a link where they open up some Al L98 chamber like you are looking to do. Note Fig16-21.

http://www.crossfire.homeip.net:81/c...ID=18&CAT_ID=1