GTE head skimming?

[phil_sorensen]

I am currently rebuilding a 1.6GTE lump, which I am converting to carbs, with twin carbs. I am looking to rebuild it with as much possible go as I can. Therefore I'm looking into getting the head skimmed, which I know can be dodgy. Does anyone know how much I could get away with taking off without changing pistons etc. And also whether the head gasket would have to be different? Cheers.

[mowgli]

I would imagine that any reputable recon shop will do a good job and ensure that it won't raise the comp too much..... remember that these modern advanced unleaded (cheap cr*p and low octane) fuels don't go well in cars with a cr of much more than 10:1, that is why efi systems have anti knock sensors etc.

[mowgli]

I would imagine that any reputable recon shop will do a good job and ensure that it won't raise the comp too much..... remember that these modern advanced unleaded (cheap cr*p and low octane) fuels don't go well in cars with a cr of much more than 10:1, that is why efi systems have anti knock sensors etc.

[Gunzi]

if u doin a full rebuild u could skim the piston heads, as well as the cylinder head, to increase the capacity (cc) of the engine. I read this in TV a couple of months back, seems like a good idea to me! (Wish I'd thought of it when I was in your position!)

[Stuart]

skimming the pistons will leave the capacity the same, but it will reduce the compression ratio!

[Gunzi]

Would it?
If you remove some of the metal from the top of the pistons then surely the area in which the combustion takes place would be greater, hence an increase in capacity?
What is the difference between this and increasing the bore of the cylinders? Both increase the size of combustion chamber?

I could see that it would reduce the cr tho'

I'm not sure with this one!

[Stuart]

the capacity of an engine isnt the total capacity including the combuation volume. Its the volume of air that the pistons can draw in, eg vol of one stroke of one cyliners, times No. Cyliners = capacity.


so skimming the piston top will increase the combustion volume, but it wont do anything for swept volume.

which means the CR will drop.

decreasing the combustion volume, or increasing the swept volume (eg over bore) WILL increase the Cr

[phil_sorensen]

I have found a place that will skim the head, and also balance the pistions crank, conrodsand flywheel. I am also thinking along the lines of kent cams. Any other ideas for more power?

[Gunzi]

the capacity of an engine isnt the total capacity including the combuation volume. Its the volume of air that the pistons can draw in,


I'm still not sure about this! Surely by removing some of the metal from the top of the pistons will increase the amount of air / fuel mix that is drawn into the cylinders therefore increasing the cc? As the metal is replaced by more air/fuel mix?

Just trying to get this clear in my head!!!

Oh and more mods, get the head ported & polished, Bill Blydenstein is the man for this

gunzi

[Stuart]

but the swept volume will still be the same!

the only way to change the swept volume is to over bore and or offset grind the crank to change the stroke (or slap a turbo on to increase the ammount of air oushed in)

skimming the piston will only increase the combustion voulme, which means reducing the CR

[DrivingSpanner]

i've only ever heard of the pistons being skimmed because they are either too close to the valves and they are then pocketed (more localised than just skimming) or to get them level with the top o0f the block when at TDC this is oftern called decking.

As camb siad the volume or size of the engine is the amount that the piston moves up and down (stroke) x the diston diameter (bore) whatever is above the piston at TDC does not count as it isnt moved, just compressed hense it is the Compression Ratio (CR). does that make it any clearer, exactly what camb said only in slightly different sentancing to try to make it clearier, probably no different i know!

[Gunzi]

Right got the hang of it now!!
Cheers for the explainations camb & spanner!


This helped!

volume or size of the engine is the amount that the piston moves up and down (stroke) x the piston diameter (bore)


gunzi

[DrivingSpanner]

yeap got it in one boyo