just started work on polishing the heads . (see pics ) . -66 toro B heads As a result there may be some variation in cubic capacity . --how much difference is allowable ?? How much variation is there in the factory product ? cheers
mike

 

I don't understand why you are polishing the chambers. Are you trying to lower your compression ratio?
As far as differences, I suppose they are what they are.

As long as they are within a cc or 2 I wouldn't worry too much. Your block isn't perfectly cast, and neither are the pistons. Match them up as best as you can.

 

If your taking metal out of the chambers that's not good. It's ok to clean them.

 

I disagree with Both of those responses. I polished the chambers in my EFI'd 350 and I truly believe that's one of the reasons I get by with using 89 octane with 9.7:1 compression and 45 degrees of timing at cruise and 38 under full throttle. By poilishing them you take away a bit of surface area because of no more nooks and crannies. That's a good thing. Make sure you smooth all sharp edges as well, everywhere. Plus if you smooth the area around the valves seats and eliminate the lip there, that can help low lift flow. And whatever you lose in cc's, just mill the heads and you're back to square one. Unless you've spent a bunch of time and money making sure everything else is spot on then 1 or 2 cc's is fine.

Time well spent.

 

What you explained is fine and works, but you have to carefull not to take to much metal in the chamber. Head work is where power is made or lost. Big thing would be to open things up lit more air in and bigger valves is always an improvement. Plus you make more power with a smaller chamber. With a stock rebuild I would just have the heads leveled cleaned, and a valve job.

 

Smaller chambers normally are more efficient. However they can inhibit breathing and the Olds heads are big and not real efficient to begin with. I don't think taking a little bit of metal out is going to make it less efficient. If anything you may be able to up the compression a bit because of a lower tendency for detonation, therefore making it more efficient.

I still say time well spent.

 

What he said. I would add that a proper polish job should match the chambers to within a CC or so. Once you do this, you may need to surface the heads to restore the chamber volume to the desired size.

 

Yes I agree 100% no I wouldn't run a 68cc on a 455 that would stuiped I think were trying to make the same point, but just have a different way of looking at it.

 

thanks guys . cutlass efi--will take your advice and remove the lip around the valves .I have started one chamber and a bit of care and the right tool selection ,it seems fine.
I will cc them later .Am having hardened seats inserted at some stage and some head milling .Amount ,yet to be determined as I have new pistons arriving etc etc .
J chicago --the initial reason for starting this ,truly, was to avoid mowing lawns --initially I was happy with the exhaust ports polished !!
mike
Thanks all

 

ok a question to be answered please.

I have cc`ed the heads and have between 80.5 and 83 . one @ 81.5 and the rest 82 ml. If I can get the 80.5 up to 81.5 I reckon I will be happy.If the chamber still looks good I may go on to 82.
That I guess is just an update.
My problem is that one p[lug thread has obviously been stripped in the past and rebushed .The issue here is that the bush hasn`t gone fully in and the plug consequently only pokes into the chamber by 1/16 " whereas the others are maybe protruding 3/8 ".
Can I get a longer plug with similar characteristics to the other 7 ??
My plugs are NGK BP5S
THANKS MIKE

 

I believe the 85-88 olds 307 plugs are longer. You could try one of those, if you match the heat range of your other 7.

 

lol what's wrong wit ha 68cc chamber? mine is 65cc :P, 'course i'm running 12:1 comp too..