removing my head on B3, machine it to higher compression?

[sasquatch]

i heard they give more power cause the direct the spark in to the F/A mixture and has a faster ignition

[festivaWES]

I heard that that block the whole spark area and cause premature fowling of the plug...

[festivaWES]

and there is now way decking the head will gain you a 1.3 bump in CR ratio...For every full compression ratio point you go up you might see 4whp

[twisted]

hmm im also planning on getting my head milled. people here who have tried it, is safe to mill up to 0.020, is there enough clearance for the pistons to valves or the sparkpulgs?

[festivaWES]

There is definately enough clearance for .020 probably enough for .040, but what I'm saying is...don't have it decked beyond the service limitations. I'm getting my block decked right now at .030. That way later if i want to raise the compression more i can take the rebuilt head i have off and have it decked too.

[twisted]

ok. so up to howmuch can you mill off the head of a bone stock BP engine? i think im getting excited, i just might drop my head at the machine shop tomorrow :lol:

[festivaWES]

I personally wouldn't do more than .040, if you have some time on your hands you can figure out the before and after CR ratios of your decked head.




Cylinder Volume

First, calculate the cylinder volume in ccs by using the adjoining formula. For those who are intimidated by pi, another way to get the cylinder volume in ccs is to multiply the bore times itself (bore squared) x 0.785 x the stoke (in inches) x 16.387. Our Buick's bore diameter was 4.352 inches or 18.94 when squared and our stroke was 3.90 inches. So, its cylinder volume is 950.19 ccs: 18.94 x 0.785 x 3.90 x 16.387. Next, we did the same computation for the ylinder head gasket, which had a little larger bore and a 0.040-inch stroke (compress gasket thickness). It worked out to 12.2 ccs.

Compression Ratio |

Now we had all of the needed volumes to calculate the compression ratio. Our Buick turned out to be 8.97:1, which we got by adding 950.19, 12.2, 35 and 72 to get 1069.37, then dividing by 119.18. We were shooting for a 9.5:1 compression ratio. Our solution was to install thinner (0.020-inch-thick) head gaskets that had a volume of 4.92ccs compared to the composition gasket's 12.2ccs. That was enough to get us to 9.5:1. If we hadn't physically measured the compression ratio, we could have given up about 50hp. No self-respecting hot rodder could live with that.

[festivaWES]

That's for the BP

New Head Thick.: 5.268-5.276" (133.807-134.01 mm)
Min. Head Thick.: 5.2677" (133.8 mm)

[ejp2fast]

OR, if you are lazy, here is a link:

http://www.csgnetwork.com/compcalc.html

[festivaWES]

in a festiva if you deck the head .020 you get a bump from 9.7 to 10.25 CR

[twisted]

found this formula in http://andrews-products.com. they sell motorcycle stuff. its simpler though i dont if its the right one.



T=stroke length X (1/original CR - 1/new CR)

T is the amount of material to mill off
so BP has 3.35 stroke
orig cr is 9.0
so if i want to raise cr to say 11.0 the it should go like this



T= 3.35 X (1/9.0 - 1/11.0)
T= 3.35 X ( 0.11 - 0.09)
T= 0.067

so amount to mill off is 0.067 is that right????

[funky technician]

I decked my head 10 thou. on my b6, I didn't need to switch gas or anything, but if I run supreme in it I swear it runs faster, but that's that probably just a placebo

[ejp2fast]

Just dropped my head off at the shop for clean up and 0.020" will be off by Friday... all new valves and new springs plus new hydraulic lash adjusters... so she shall hopefully run a bit better.

[sasquatch]

that is what i had done to my bp and now it runs so good

[twisted]

Just dropped my head off at the shop for clean up and 0.020" will be off by Friday... all new valves and new springs plus new hydraulic lash adjusters... so she shall hopefully run a bit better.

nice, let us know what happens