Who's using "over skimmed" YB head
06-08-2012, 12:16 PM
#1
Who's using "over skimmed" YB head
Just curious who is running YB head that is thinner than 138.5mm ?
Would i be mad to consider using a 137.8mm
head with:
pocketed pistons (valve cut outs)
standard cams
grp A head gasket
what are the potential consequences?
slightly higher compression (det ?)
valve seat integrity
thanks
Would i be mad to consider using a 137.8mm
head with:pocketed pistons (valve cut outs)
standard cams
grp A head gasket
what are the potential consequences?
slightly higher compression (det ?)
valve seat integrity
thanks
Last edited by Ridgey; 06-08-2012 at 06:45 PM.
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06-08-2012, 03:41 PM
#8
Is'nt there issue with squish and if you start porting a over skimmed head.
Sure theres a very long thread on here about squish and the effects.
Why would ford/cosworth give the 138.68mm measurement for some Fred in the shed to say thats ok bud u can go to 138 and more.
Ridgey get some correct advice before you make your descision
Sure theres a very long thread on here about squish and the effects.
Why would ford/cosworth give the 138.68mm measurement for some Fred in the shed to say thats ok bud u can go to 138 and more.
Ridgey get some correct advice before you make your descision
06-08-2012, 04:11 PM
#12
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The cr will change so obviously the map would need a tweak depending on how close your map is in the first instance..
As for porting that wont have any effect on the heads depth..
Its not ideal to run a head thats skimmed to depth but on an engine of your spec it will be fine..
Back in the day when works teams starting raising cr the actually started to skim the heads lower than yours just to get the cr up!!!
Ive seen a few perfectly good heads skimmed to 137,7 just to get the disered 9.1 cr they needed!!
cheers danny
As for porting that wont have any effect on the heads depth..
Its not ideal to run a head thats skimmed to depth but on an engine of your spec it will be fine..
Back in the day when works teams starting raising cr the actually started to skim the heads lower than yours just to get the cr up!!!
Ive seen a few perfectly good heads skimmed to 137,7 just to get the disered 9.1 cr they needed!!
cheers danny
06-08-2012, 04:31 PM
#13
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Interesting thread that can at least shy people away from spending good money on maybe not such a good head..
If you have an engine that has been fine and you need to do a gead gasket or similar and find your heads under the 138.6 then there really isnt any worry..just re fit,its very unlightly to go wrong seeing as it hasnt already..
If your doing and big power engine build then find the best you can but these days id say anything over 138.5 is a result..
Niel roper and others im sure can drop valve seats and the like also so can save another life there
cheers danny
06-08-2012, 06:59 PM
#15
joffy: I ment to put Higher comp in my first post.
The original engine with this head showed that the valves had touched and marked the pistons. So it would seem reasonable that head depths were physically dicated by a mechanical interferance issue which on a standard engine with standard pistons would be valve clearance.
As well as the impact of higher CR which will be some what offset by the material removed from the valve cut outs and my current setup has valve cut outs.
I have seen the thread about valve seats, however, is this big power engines running high lift CAMS? double valve springs etc, as that would put far more material stress on the seat.
Graham: Head gasket looked OK mate, but i don't want to put that head back on (always leaked water around the exhaust ports), so i'd like to use this other one.
The original engine with this head showed that the valves had touched and marked the pistons. So it would seem reasonable that head depths were physically dicated by a mechanical interferance issue which on a standard engine with standard pistons would be valve clearance.
As well as the impact of higher CR which will be some what offset by the material removed from the valve cut outs and my current setup has valve cut outs.
I have seen the thread about valve seats, however, is this big power engines running high lift CAMS? double valve springs etc, as that would put far more material stress on the seat.
Graham: Head gasket looked OK mate, but i don't want to put that head back on (always leaked water around the exhaust ports), so i'd like to use this other one.
07-08-2012, 11:46 PM
#19
Too many posts.. I need a life!!
My head is skimmed right into the valve seats , I've not recessed them or anything, it's running 460 bhp dyno'd with nitrous (400 nitro jet and can't remember the fuel jet) I kick its head in everywhere and done 3 track days one of which it was borrowed for the lancs rs show at Anglesey and was driven hard by 3 people giving passenger rides all day non stop never let me down once!
10-08-2012, 10:22 AM
#21
joffy: I ment to put Higher comp in my first post.
The original engine with this head showed that the valves had touched and marked the pistons. So it would seem reasonable that head depths were physically dicated by a mechanical interferance issue which on a standard engine with standard pistons would be valve clearance.
As well as the impact of higher CR which will be some what offset by the material removed from the valve cut outs and my current setup has valve cut outs.
I have seen the thread about valve seats, however, is this big power engines running high lift CAMS? double valve springs etc, as that would put far more material stress on the seat.
Graham: Head gasket looked OK mate, but i don't want to put that head back on (always leaked water around the exhaust ports), so i'd like to use this other one.
The original engine with this head showed that the valves had touched and marked the pistons. So it would seem reasonable that head depths were physically dicated by a mechanical interferance issue which on a standard engine with standard pistons would be valve clearance.
As well as the impact of higher CR which will be some what offset by the material removed from the valve cut outs and my current setup has valve cut outs.
I have seen the thread about valve seats, however, is this big power engines running high lift CAMS? double valve springs etc, as that would put far more material stress on the seat.
Graham: Head gasket looked OK mate, but i don't want to put that head back on (always leaked water around the exhaust ports), so i'd like to use this other one.
As said above is the best advice as all tuners have there way of doing things.
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