I bought some freshly ported heads here that the seller was going to use on a N/A 383, I'm wanting to use them on an stock bottom end 350. I didn't get any cards/specs on them from the seller yet, so I decided to have them CC'd and flowed myself. Here's what I found:

Chamber: 63cc
Runner: 180.5 cc

63 .100 53
96 .150 87
131 .200 112
162 .250 135
189 .300 155
210 .350 174
230 .400 187
244 .450 200
256 .500 206
263 .550 210
267 .600 215

Bret advised me that this was really large, and now that I've been forced to do some research - he seems to be right and I'm worried! Should I be???

My rough calculations put me around 9.7:1... (using a .036 gasket and -.010 from the heads) So, my question is... Is it that bad? Am I stuck with a low compression with a crappy low-end power if I use these? Anything else (short of $3k+ for blower to make use, rebuild bottom end to bring it up, etc) that I could reasonably do?

PS - If you want to see a chamber for yourself and comment, be my guest. Are they really abnormally large???
http://beeph.no-ip.com/heads/Valves.JPG

Thoughts? I'm in desperate need of direction...

 

Also, it's my unprofessional opinion looking at these that because of the good exhaust numbers, average intake numbers, and big chambers that these babies are crying for forced induction.

Is that True?

 

I just got a supercharger and I'm looking for a way to lower my compression! These heads are perfect for what I want to do. Maybe we can work some kind of deal. Would you be interested in selling them so you can buy some other heads? How much do you have in them and what have they had done? Please get back to me, I was just about to order some of the trick flow heads next week and we may be able to work a deal that will benefit both of us.

 

You can find thinner Head gaskets, the Mr gaskets are .026 compressed, that and maybe just a liitle more off the heads shold get you what you are looking for. Breakmyfootoff sounds like maybe a better deal for all involved.

 

Well, that's kind of what I was afraid of... These heads appear VERY VERY nice, are stage-III, and were built with all top-notch stuff, and I really hate to let go of them so I'm not ready to make that call yet.

I'm not sure if I'm up for a complete plans change to forced induction though, so I want to hear a few more opinions on the subject and I guess we'll cross that bridge when we get there.

Craig

 

Craig.....

You could have them milled.... Angle Milling would be the most aggressive way to go, but you should be able to get them down there with flat milling.

Them being for a 383 makes sense that the chambers are that big... I'm suprised they can even GET that big.

Bret

 

I was worried about valve clearance problems milling too much... any idea the max I can mill and where that would put my ratio? Any downsides to this approach?

Also, did they actually LOOK like 63cc to you, or do you just think the shop is drunk?

 

Make sure they didn't CC the heads without spark plugs, most people agree that the heads should be CCd with the spark plugs in place. If they measured the combustion chambers without spark plugs that would make them larger.

 

Well, after giving them a good once over in paint shop (zoom in and out dontch know..) and comapring them to pics of my heads (no chamber enlargement over stock sized, it would seem plausible to me that they have been opened up to 63cc. They have been opened a considerable amount; Around the exhaust valve, some on the intake, and the back of the chamber has been laid back quite a bit. You don't have to find 10cc all in one spot. A little here and a little there adds up...

I have often wanted to take a set of LT1's and lay back that portion of the chamber to get a smoother transition, but I was always afraid getting the casting too thin. I don't have a sonic tester, or I would have already done it. The low lift numbers on those heads is impressive to say the least. 200 on the exhaust side @ .450 lift is unreal. You might wanna contact the head work guy and see if he can tell you what head gasket he used to match that with too to make sure you get the most out of 'em. I have to go with Bret and say mill 'em down a little for the compression and go with em. They look very nice..

Dave C.

 

How do you cc a head without a spark plug?

 

Some places have been known to cc heads with the spark plug hole simply blocked off allowing for some extra volume to be measured in the threaded area of the spark plug hole.

 

Blocked off how? You gotta have something liquid tight. Heck, it'd be easier to just use a spark plug.

 

True...

The chambers look big to me too.

If the valves are 2.02 or 2.00 (I can't remember at this point... it's late and I can't sleep) and you do mill them and they end up hanging over the deck surface it's not a issue really. We can design a cam around P to V problems.

Remember that the block has the piston really far in the hole to start with and even with a thin .026" gasket that piston never gets close to the valve in static conditions.

You are probably looking at a .035 to .040 cut on the heads here to get you to a decent 55-56cc range and you will be back to normal.

BTW I've seen GTP heads as small as 52cc

Bret

 

I dont remember how they blocked them off, but it's been done. Do a search if you want to know, I read it on here. something about the debate on what size chambers the stock heads came with.

 

The heads I run are 69 cc...so I see your pain.

What bore are you going to run? I would be curious to as to how big that combustion chamber is across vs your bore?

IMO...pull the motor and put a set of pistons with a 5 cc dome with run a .041 head gasket and be done with it.

You could also run a .015 head gasket as mentioned...your stock pistons should be in the hole .030...it would give you around 10.4:1.