Milling the head for higher compression?

[RevDave]

I'll probably have the head off of my '82 Spider 2000 FI this winter. My understanding is that it's current (stock) compression ratio is around 8:1 - which seems awfully low for a naturally aspirated engine.

I was wondering about having the head milled to bump the compression ratio up a bit. Any thoughts about this modification and perhaps how much to mill off the head? What is the highest practical CR for a street engine running pump high test fuel?

Thanks - Dave

[So Cal Mark]

how are you planning on handling the cam timing issues after substantial milling?

[pope]

and make sure your valves clear your pistons.

[htchevyii]

Croft says you can mill alot off of t/c heads, but may need adj. cam pulleys to get iming marks to align. He also recomends a dry build to check clearances.

[Curly]

Tensioning the cam belt can be another problem if you take a substantial chunk off the head face. The tensioner can only move so far to take up the extra belt slack before it jambs up against the stud running through its centre. You may have to find a larger diameter tensioner bearing or make up a sleeve to go over it, thus increasing its diameter.

[manoa matt]

Instead paying a machinist to mill the head, buying adjustable cam pulleys, and buying a larger diameter tensioner, you could just buy an 1800 head and drop it on and go, or just get high compression pistons. All three options will probably cost about the same.

[Jim DeShon]

I've been wondering about this too. I read a lot of negitive comments about doing this. I wonder if anyone has any real experience in doing this job? You would not have to take much more than about .040" max. I do not see where that is going to be that much of a problem. Yes, you may have to re- machine the relief in the pistons for clearence but, if you are serious enough to go this far, I would assume you know what you are doing. Note : I have NOT done this yet ! Yes dry fitting everything is not recommended, IT IS REQUIRED ! ...J.D.

[bradartigue]

It is not worth the trouble.

I have a lot of respect for Guy Croft but the majority of his efforts are for high performance. You can mill it, and the result is as described above - lots of custom parts to compensate for the milling. Then you end up with a custom motor that requires some special attention to tune. For most folks that's not all that enjoyable.

I see three options for HP boosts without getting all crazy:

1800 head. Works every time and bolts right on. Carb or FI it just works.

HC pistons. Also works every time and they bolt right in, so to speak. 9.1:1 is a lot of fun without pushing the envelope.

HC pistons and an 1800 head. I ran 9.1:1 pistons and the 1800 head on an FI Spider for a long time and enjoyed every minute. The "feel" of the car was fantastic, the first Spider I had that felt like a modern car in terms of acceleration and throttle response.

I wouldn't even bother with a camshaft swap (with FI you'll have more trouble than it is worth IMHO).

[Jim DeShon]

The milling the head approach is not for the guy that just wants to "kick it up a notch". It all depends on what you want to use the car for. Mine, when I get it back together, is going to be just a weekend toy. I don't care about having to "tweak" with it some or if I have to run special fuel. If these things bother you or, are not in line with what you want to use the car for then go with the 1800 head or high comp. pistons. It IS a lot easier. ...J.D.