To surface the head, or not?

I've got a used aftermarket aluminum head I will be putting on my B soon and am trying to decide whether to surface it or not. The head is almost new and in stock form. I will be doing a little bit of porting/smoothing and having a valve job done on it to help increase flow.

Would taking 0.010" of the head be beneficial other then providing a perfectly smooth surface? What I mean is, would the compression ratio increase improve performance any? It doesn't need to be surfaced, so if it isn't going to improve performance, I don't wan tot bother with it.

Running 92 octane fuel isn't a problem and my machine shop only charges $40 to do it. Would there be any downsides?

Aluminum heads warp more ready than cast iron when they get overheated, so if it were me I'd not touch it. because who knows..you may need that extra ten some day...

Cutting the head .010 won't effect the compression much at all. Decking the block will raise the compression faster. But then you get into valve train geometry, valve clearence ect.

i would at least have the head checked for flatness so to get a proper seal when installed......dont wanna put a warped head on that just asks for problems

Hap does a .020" shave to bump compression. You should compare the chamber CCs to your old head before you make the decision though. I think the aluminum heads are "high compression" already!

If you cut the head or the block the end result is the rocker shaft is moved closer to the cam. Consequently, cutting either should cause some valve train geometry change.

Clifton

Andrew,
0.101 off the head will make little difference.

I would have the head checked for flatness and go from there.
If it is where it is meant to be then leave it and fit it as is.

If it needs machining then have it done at the same time as the rest of the work.

Cheers , Pete.

I am with Jeff on the volume thing.

Before you go whacking on the head try to do three things.

Find out who made the head and try to get a measurement from them from the block face to the top of the rocker side machining. In other words you want to know if the thing has been machined already. Sometimes a milling shop will not stamp their work and you could be going too thin.

Then teach yourself all about CCing the chambers. Do this to see if there is any appreciable volume differences and clear that you before you machine it if you end up doing so.

Third, read up on head work in the Vizard and Burgess books.

You might want to contact Sean Brown at http://www.flowspeed.com/. I am certain that he would be happy to advise you.

Jack

I'll throw this in too, it's always good to straight edge check a head that hasn't been decked, generally a good head gasket will handle anything up to .002" and under. I can't agree more with what Jeff and Jack said about checking volume in a head, this MG stuff passes thru so many hands alot of the time before we get it, the only way to know where you're at for sure is to CC the combustion chambers and do the the math. One of the most popular questions I get asked by DIYers is how much should I cut off the head, and my answer is always the same, where are you now. You have to do alot more than people think to get the compression up on a MGB, a .020" cut on a virgin deck MGB cast iron head, and stock deck height is less than a 1/2 point, putting you around 9 to 1. with the newer pistons we get now. Here's a good example, to get Fred McConnell's new MGB race engine to it begining compression ratio of 12 to 1 with flat top JE race pistons we had to deck aprox .030' off the block, and cut the head .060", and there's still room to grow.