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| phongus |
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hey everyone. im a noob at all of this head shaving jazz. now so far i have read that by shaving the head ur increasing compression ratio...meaning higher revs? and what exactly do u do? do u literally shave the head evenly like ur planing a plank of wood? does this mean that something needs to be shorten because the head is a tad lower then usual? BTW does increasing compression ratio give a worse or a better fuel eco?
yes im a noob at this =D......oh yeah im guessing its not a good idea to do this on my own if i was to ever change my Head gasket when it blows. cheers phong =P~
_________________ phongus = Post whore 2006 |
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| Gaz |
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saving the head, is just that, shave some material off the bottom of the head.
it will increase compression, and should give you better fuel economy. wont let it rev any higher. things wont need to be shortened, theres limit, think its about .. no idea? 40thou? off the head before your valves will hit your pistons?
_________________ 2007 Steel BF Ghia MKII V8 - 19" GTP's + Superlows |
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| phongus |
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Gaz wrote: saving the head, is just that, shave some material off the bottom of the head.
it will increase compression, and should give you better fuel economy. wont let it rev any higher. things wont need to be shortened, theres limit, think its about .. no idea? 40thou? off the head before your valves will hit your pistons? so what happens if u go further then 40thou? would u need new valves/pistons to compensate? when u shave the head does that mean the cylinder chamber is smaller too? if someone could draw me a diagram that would be awesome =D
_________________ phongus = Post whore 2006 |
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| stockstandard |
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yep, shaving the head increases compression by reducing the chamber size. If you keep going eventually the pistons and valves will hit, how soon depends on what cam you have. In a stock engine you could take heaps off and not have any problems but as you put bigger cams in the valves open further for longer and if you head has had lots taken off it will hit. To get around this you would have to fly cut the pistons (cut little slots out below the valves to give more room), but if you are shaving your head that much to increase compression your better off just swapping to pistons with a smaller dish.
_________________ Stoke me a clipper, I'll be back for Christmas |
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| smiley235 |
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stockstandard wrote: yep, shaving the head increases compression by reducing the chamber size. If you keep going eventually the pistons and valves will hit, how soon depends on what cam you have. In a stock engine you could take heaps off and not have any problems but as you put bigger cams in the valves open further for longer and if you head has had lots taken off it will hit. To get around this you would have to fly cut the pistons (cut little slots out below the valves to give more room), but if you are shaving your head that much to increase compression your better off just swapping to pistons with a smaller dish.
seriously man, your like a fountain of motoring knowledge, don't ever leave this site. 
_________________ 178.3 rwkw
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| phongus |
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smiley235 wrote: stockstandard wrote: yep, shaving the head increases compression by reducing the chamber size. If you keep going eventually the pistons and valves will hit, how soon depends on what cam you have. In a stock engine you could take heaps off and not have any problems but as you put bigger cams in the valves open further for longer and if you head has had lots taken off it will hit. To get around this you would have to fly cut the pistons (cut little slots out below the valves to give more room), but if you are shaving your head that much to increase compression your better off just swapping to pistons with a smaller dish. seriously man, your like a fountain of motoring knowledge, don't ever leave this site. i agree with smiley =D okay so all that was great information.....now does that mean that the 4L engine will be more like a 3.9L if u go too far? or is the 4L I6 engine stand for something else. If i do it on a stock standard engine without a cam.....my effiency would increase but i won't get as much power if i had a cam... but there would still be a slight power increase? i have extractors, hi-flow cat and 2.5" exhaust coming up...if that makes any difference. phong =P~
_________________ phongus = Post whore 2006 |
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| Gaz |
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just picture your cars head phongus.
now the bottom surface where it meets the block, a tiny bit gets shaved off the bottom area, making the head height shorter. bringing the valves closer to the pistons. by shaving the head, the volume in the top of the head gets smaller, thus when a full stroke of air/fuel is compressed, it is done into a smaller area than normal, increasing the compression.
_________________ 2007 Steel BF Ghia MKII V8 - 19" GTP's + Superlows |
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| phongus |
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Gaz wrote: just picture your cars head phongus.
now the bottom surface where it meets the block, a tiny bit gets shaved off the bottom area, making the head height shorter. bringing the valves closer to the pistons. by shaving the head, the volume in the top of the head gets smaller, thus when a full stroke of air/fuel is compressed, it is done into a smaller area than normal, increasing the compression. yup...i actually had the motion of the piston image in my head.
_________________ phongus = Post whore 2006 |
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| stockstandard |
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phongus wrote: okay so all that was great information.....now does that mean that the 4L engine will be more like a 3.9L if u go too far? or is the 4L I6 engine stand for something else. nope, it will still be a 4L engine. The capacity (4L) is worked by how much air the pistions are moving, so unless you change the bore or stroke that will stay the same. phongus wrote: If i do it on a stock standard engine without a cam.....my effiency would increase but i won't get as much power if i had a cam... but there would still be a slight power increase?
Yes you would see a power increase, but only to a point. As you increase compression you get more power and economy but you also run a finer line with engine tuning. For example, you will probably have to run premium fuel or risk pinging/knocking which can damage your engine. This is because as the piston moves up and compresses the air and fuel you are generating heat. Too much heat and the air and fuel will explode before the spark plug ignites it and this puts massive stress on the engine. Increasing compression ratio is really beneficial when your putting a big cam in. It gets a little complicated here because what we are talking about in this thread is static compression, which is only a part of the more complex dynamic compression ratio that also depends on the cam your running. Basically when you put a performance cam in you lose compression. This is when you can safely shave the head or change pistons and get more power and economy. i hope that makes some sense....
_________________ Stoke me a clipper, I'll be back for Christmas |
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| phongus |
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stockstandard wrote: phongus wrote: okay so all that was great information.....now does that mean that the 4L engine will be more like a 3.9L if u go too far? or is the 4L I6 engine stand for something else. nope, it will still be a 4L engine. The capacity (4L) is worked by how much air the pistions are moving, so unless you change the bore or stroke that will stay the same. phongus wrote: If i do it on a stock standard engine without a cam.....my effiency would increase but i won't get as much power if i had a cam... but there would still be a slight power increase? Yes you would see a power increase, but only to a point. As you increase compression you get more power and economy but you also run a finer line with engine tuning. For example, you will probably have to run premium fuel or risk pinging/knocking which can damage your engine. This is because as the piston moves up and compresses the air and fuel you are generating heat. Too much heat and the air and fuel will explode before the spark plug ignites it and this puts massive stress on the engine. Increasing compression ratio is really beneficial when your putting a big cam in. It gets a little complicated here because what we are talking about in this thread is static compression, which is only a part of the more complex dynamic compression ratio that also depends on the cam your running. Basically when you put a performance cam in you lose compression. This is when you can safely shave the head or change pistons and get more power and economy. i hope that makes some sense.... well that all makes sense now...nanotechnology...physics and chem put together did come in handy after all lol thanks mate =D looks like shaving my head with new cam would be nice...but not tooo much. thanks a lot stockstandard. now to sleep over it.
_________________ phongus = Post whore 2006 |
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| Gaz |
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just outta interest, how high compression would people go on a NA engine safely?
would 11:1 be unreasonable if you ran 98RON on the standard competeR?
_________________ 2007 Steel BF Ghia MKII V8 - 19" GTP's + Superlows |
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| phongus |
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Gaz wrote: just outta interest, how high compression would people go on a NA engine safely?
would 11:1 be unreasonable if you ran 98RON on the standard competeR? ....and another question on that.....what compression for standard fuel...91RON.
_________________ phongus = Post whore 2006 |
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| twr7cx |
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if you shave too far then you'll have to use double headgasket or shim or whatever to build it back up.
also plan when you've removed the head to ensure it's nice and flat for refitting. |
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| eb_guy888 |
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phongus wrote: do u literally shave the head evenly like ur planing a plank of wood?
sorta mate  But its un-noticable to naked eye I think
I had my old head shaved about 25thou I think, Im pretty sure thats about 25thousands of a mil or somethin? Not completely sure but u wouldnt be able 2 do it by hand with a planer lol |
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| phongus |
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eb_guy888 wrote: phongus wrote: do u literally shave the head evenly like ur planing a plank of wood? sorta mate But its un-noticable to naked eye I thinkI had my old head shaved about 25thou I think, Im pretty sure thats about 25thousands of a mil or somethin? Not completely sure but u wouldnt be able 2 do it by hand with a planer lol lol i figured that I guess ill give my mate a call and see what he can do once my head gasket blows. =D cheers everyone
_________________ phongus = Post whore 2006 |
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