6 replies to this topic

[kit352]

So my CAM 4810 head is in need of a rebuild so its time to get a new head i think.  Problem is i am in the states and there isnt a lot of options out here. I can get a 12g1316 head fairly easily though.  This is supposed to be a good upgrade for a 998 since its a cousin of the 940.  On a stock 998 i shouldnt need to pocket the block or anything according to most here while i researched.  It seems the biggest hurdle for me in compression. I have stock flat tops in mine and with the 21.4cc chambers on the 1316 i am pushing close to 11 to 1 which i dont think my car and driving style can deal with. So the question is how to lower compression enough to be streetable?  Thicker head gasket maybe but those are crazy money compared to regular ones.  Are some regular ones better to use for this or are the semi custom thicker ones the way to go?  Sinking the valves is also a partial solution as well but maybe not such a great one.  How about taking material out of the combustion chamber? I can do some by hand but it doesnt look very suitable for removing enough to get the compression down lower.  Anything else i can do to drop compression a half point or so?

[nicklouse]

It is basically the same as a 12G940 so you will have shrouded valves. You will need to do a dry build to check for enough clearance between the exhaust valves and the block surface. 1275 head gasket to be used.

[DeadSquare]

Don't sink the valves, please.  If you are only going to use the head while working on the original, a good fuel additive and retarded ignition ought to cope with 11:1 compression.

 

If there is any chance of the valves nearly touching the block, abandon using that head because by the time you have messed about, the time, effort and money would be better spent on work for your existing head.

[Spider]

There is several other heads you can use instead of the CAM4810, that are quite similar to that head. I feel replacing it with something similar could save a heap of headaches, unless you are looking to modify the engine ?  In which case, to make the fitting of a 12G1316 head worthwhile, you'd also want to change the cam.

 

Alternative heads that are similar are;- 2A262, 2A269, 12A1456 and CAM4004

 

[kit352]

If i can get more power out of a head swap i am all for it.  At this point in time i'm hoarding parts that are becoming harder to get over here.  Ideally i would get a better head and rebuild the CAM head at my leisure and keep it as a spare for down the road.  There are not a ton of heads available to me here that are going to be a direct fit anyway or just needing a ton of work to get fit for purpose.

[Spider]

the 1275 heads compared to the 998 heads have bigger ports and bigger valves. They do also have a smaller combustion chamber, but we'll put that to one side for the moment.

 

The Bigger Ports and Valves will give very slow gas flow through them at low engine revs, around the range of revs where you'd be doing probably 80 - 90% of your driving. You'll find you'll loose power in that rev range due to the lower gas flow speed, it won't 'come alive' until you're up around 4000 RPM+, however, the stock cam will start to peter out about 5000 - 5500 RPM. It will work and be drivable, but it won't be as 'nice' as it is with a stock head.

[bpirie1000]

Maybe best sourcing a full 1275 cc engine from somewhere..