Just finished watching a video on porting heads and it got me thinking a bit. I'm using double gaskets on my 3.6 to drop compression for turbocharging. I'm wondering how much material can be safely removed from the heads to achieve the same goal? Cant be much worse than milling pistons for the same purpose... Just thinking out loud.
Increasing combustion chamber volume to drop compression?
a4kquattro
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Just finished watching a video on porting heads and it got me thinking a bit. I'm using double gaskets on my 3.6 to drop compression for turbocharging. I'm wondering how much material can be safely removed from the heads to achieve the same goal? Cant be much worse than milling pistons for the same purpose... Just thinking out loud.
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If anybody wants to experiment and find out, I have a pair of brandy new bare 3.6L V8 head castings I'll let go inexpensively. Unfortunately, they're not a right-and-left pair and I forget which side they're for, but if you're experimenting, this probably doesn't matter, right?a4kquattro said:
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quite a lot I bet. the issue is maintaining the basic shape of the combustion chamber to avoid hot spots etc.a_CQ said:
Figure that the average thickness of a compressed gasket is around 1 mm, so simple math on the area of the bore times the gasket thickness (in this case 84.6mm for the ABH). Keeping everything in cm so we wind up with cc's thats = pi * (8.46/2)^2 * .1 = 5.6cc (meaning if I wanted to run just one gasket and still wind up with about a point lower CR I could do it by removing that much from the combustion chamber)
i'd imagine just leveling out all the curved surfaces between the valves and to the edges of the cylinder, and the walls would do the trick nicely. i'd just say to CC them to make sure you have a consistency. it won't take that much time to CC and grind 
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i did something similar to my 12v v6 heads... you do want to see pics? its very very slight though, i did it more to remove casting sharp edges to reduce knock, but it gained about 2-5 cc's i forget exactly what
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jes please.the_natrix said:
ics:
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ok here it is... you can see an untouched chamber and the scribe lines from the cyl head gasket... along with the trimmed chamber in a pre polished state....
ideally after i get it matched to the gasket and all the sharp edges gone from the squish band, i hit it with 3m scotchbrite pads mounted to the dremel or the grinder.. depending on the accuracy i need.
once its polished its all nice n smooth n purdy...
im also planning on clearning the sparkplug pockets a bit more, help the ignition kernal propogate out easier and leave less unburned fuel.
please ignore the green paint, used for porting purposes on the intake port.
ideally after i get it matched to the gasket and all the sharp edges gone from the squish band, i hit it with 3m scotchbrite pads mounted to the dremel or the grinder.. depending on the accuracy i need.
once its polished its all nice n smooth n purdy...
im also planning on clearning the sparkplug pockets a bit more, help the ignition kernal propogate out easier and leave less unburned fuel.
please ignore the green paint, used for porting purposes on the intake port.
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that sure does look like ~5ccs. Hmmmm
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yea it doesnt take much, even clearing the sharp edges dropped a bit....
all you really need is a syringe and oil oh yea a level surface.
all you really need is a syringe and oil
oh yea a level surface.
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ONe thing to remember is that the shape of the combustion chamber is very precisely designed to create swirls and stuff, so keeping things the same shape or improving it would be nice.
I have thought the same thing about doing this..... Its gotta be wort a shot on some scrap heads to see what 5-10cc looks like.
H
I have thought the same thing about doing this..... Its gotta be wort a shot on some scrap heads to see what 5-10cc looks like.
H
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5-10 cc's is easy without affecting much, its going beyond that, to 10's of cc's that will become hard to deal with... cleaning up a casting here, smoothing out there, thats easy 5 cc's
i remember now that the stock cc of the chamber was 28cc's and i bumped it up to 32cc's with just that minor stuff alone... that went from 8.8 to 8.5 on the combustion chamber calculation i used...
the higher the compression ratio the more a few cc's make a difference in raising or lowering the compression ratio.. so if you need a nice program check this out.
http://www.csgnetwork.com/compcalc.html
i remember now that the stock cc of the chamber was 28cc's and i bumped it up to 32cc's with just that minor stuff alone... that went from 8.8 to 8.5 on the combustion chamber calculation i used...
the higher the compression ratio the more a few cc's make a difference in raising or lowering the compression ratio.. so if you need a nice program check this out.
http://www.csgnetwork.com/compcalc.html
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