Hey guys, I've been shopping for new heads recently, and have come up with a few questions. Looking for a smaller aluminum head, I see chamber sizes available anywhere from 56cc to 67cc. The AFR 180 eliminator for example is only offered with a 64cc (or larger) chamber. These heads may very well be what I need, but that chamber is too large! I'm thinking around 10:1 compression is "about" where I'm shooting for. I know you can have them milled, but are any of you guys really dropping $1500 on brand new AFR heads, then sending them off to the machine shop!!???!?!? The Brodix IK180 is another example. ...I guess milling is part of the game then? No way around it?

 

Generally so, yes.

Although, the REALLY correct way to approach it, is to know in advance that those are the sizes that heads are available in, and design the short block accordingly. Since, also in general, the reason the mfrs offer the heads in those chamber sizes, is that those are the sizes that are usually the most appropriate to the short block setups that the heads are tailored for.

How are you ending up so far off that you have to do that?

 

I agree that the correct way to do this would be to start with building the correct shortblock/pistons. ....I'm planning on using the the L31 shortblock. Cost, warranty, durability (given my goals), all leads this direction. ...and off the top of my head I think it's got 4 valve relief pistons at -13cc. ...which is about right for vortec iron heads with 64cc chambers. ...but for aluminum, I think I'd want closer to 58cc chambers. LOTs of generalizations here, I know. I'm still making decisions. LOL.

 

Mill them down. Its not a big deal, just an extra cost on top of new heads. Most 64-65cc heads as cast can be shaved down to 58-60cc without an issue.

I just bought a set of 2800 buck heads that I had to have milled from 68 to 64 cc Really wouldnt have been an issue to leave it at 68 but I wanted 64. I had the manufacturer/head creator do it before shipping them out so I didnt have to take them anywhere.

 

I suggest calling AFR and asking them about this, because sometimes they can make miracles happen, depending on who you talk to.
By that I mean that they can sometimes get you the head with the ports you want combined with the chamber size you want without losing some of your deck thickness.
They do take special requests, and are sometimes able to deliver on them.
Dart or Brodix may also be able to do this. You just have to ask or you'll never know.

 

http://www.carcraft.com/techarticles...t/viewall.html

Definitely not accepted hot rodder concensus, but it's really interesting and weird to read. I'd probably leave the AFR's alone unless you're just running a cam so large that your resultant compression ratio makes it ineffective.

 

I'm not actually leaning towards the AFRs, I was merely using them as an example. And for the record, they DO offer 55cc chambered versions, but they're a bit pricier and have L98 angled plugs. Musta missed that on my first search. I was just thinking that a smaller chamber woulda been more the norm, and was a little surprised that it wasn't.

...oh, and interesting article on the Iron vs. Aluminum.

 

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Interesting article that I had read before however how they tested really leaves a lot to be desired. 185 psi cranking pressure is on the short side at best and certainly FAR below what you would want to run with aluminum heads. 200 psi minimum for a healthy street engine on pump gas. With a full point extra in the SCR the aluminum heads should be good for another 4% give or take.
As far as combustion chamber volume goes, EQ makes a 50 cc IRON head that's proving to be very popular in the racing crowd. Note that with a conventional .039 gasket, stock piston below deck height of .025" (quench of .064") and flat top pistons (with your specified 13cc reliefs) you're into the 10:35:1 SCR range. Paired with the right camshaft, you can see how it would work.