LithiumX

for a thicker head gasket is it every .25 inches (~6.4 mm) extra is roughly a drop of 1 compression???

where can you get thicker metal gaskets ne1 try running dbl (stacked) gaskets ?(i know diavolo was talkin abouts metal and some other ref but any other suggestions?)

while we are on the subject of decompression how do you achieve a dynamic drop using camshafts as apposed to static drop w/ piston/gasket??


edit: should be .025" ,~.64mm ...

LithiumX

nvm post contains huge errors figured it out neways will post calculations after i sleep on it and recheck it .... still dont know anything about dynamic compression but will figure it out i guess

chowetime

iTrader: (16)

check the rpw website I was reading some info on it about this please don't ask me to explain too hard right now but when you read it it does make sense

GearDownSon

iTrader: (11)

I may be just talkin out my *** but are you getting at raising the head to decompress with bigger head gaskets?
And if you are will this make a boosted care run a lit safer?

DangerousDan

iTrader: (8)

the lower compression rate will allow greater boost. less stresses and the like on the internals. safer if you don't up the boost after decompression

LithiumX

in theory it woudl allow; higher safer boost but dont wanan go too thick or you lose strength, would be a good idea to get studs at that time. you will most likely lose a bit of low end response i think but with our 2.4 and 16g i think its a non issue but if you had a bigger turbo and/or higher boost it may effect spoolup (many other factors). conversly milling the head would raise compression but you would have to lower the boost and the stock internals prob wouldnt like the high comp+boost nto to mention that the risk of detonation would quadrouple.


gimme like a couple of hours i was studying for stat exam but will post up the calculations i did, if i have em somewhere here.

LithiumX

before i start one other thing that would happen with lowering your static compression woudl be that you would lose some hp (especially lower end i think) but gain a much cooler engine (a problem for us i think) .

basic

Stroke 100mm
Bore 87mm

gasket thickness ... i dint know but worked around


comp ratio = (cylinder volume + combustion chamber volume)/ combiustion chamber volume = 9.5

combustion chamber volume = some complicated stuff + head gasket volume
- head gasket volume = (.5bore ^2) * pi * height(thickness) = 69937.3965 (using algebra and solving for this in above formula w/ the 2 knowns)

cylinder volume = (.5bore ^2) * pi * stroke = 594467.87

to achieve about ~ 8.9:1

assuming

X = desired compression ratio
TCV = CCV + G = total combustion chamber volume
CCV = combustion chamber
G = gasket volume = (.5bore ^2) * pi * height(thickness)
using some algebra that would be tedious to type we get:

Cylinder volume = (X - 1) TCV .. some more algebra etc

i was trying to find a thickness to get me around 8.9

594467.87 = 7.9 * (69937.3965 + G) more algebra solve for g or shouldve done it earlier..

G = 5311.70095 (volume of addditional gasket) now solve for thickness

assuming the new gasket has the same bore as the cylinder (87mm)

additional gasket thinckness would be ~.89 mm or ~.035 inches to achieve static 8.9:1 compression

feel free to correct just from my understanding and research plus i could have messed up the numbers somewhere but atleast gives a good idea

edit: assumes flat piston
- source: http://www.everything2.com/index.pl?node_id=766464

LithiumX

so to answer my original question an additional .025 inches or .635 mm should bring down the compression ration to about 9.0647:1

assumong the same bore as the cylinder

now does anyone know the stock head gasket thickness ?? i think it was .2" but i cant confirm it

edit: bah once again should be .02"

DangerousDan

iTrader: (8)

much smaller than .2, maybe .025 or .030.

our piston tops rise a little at the edge IIRC, and the combustion chambers are not perfectly shaped. have you tried using your equations to confirm some of these values? If your values are right you should be able to calculate the stock compression ratio, and if you can than you're on the right track.

I read quite a bit on compression ratio when I was looking into the head and cam, lot's of interesting stuff to say the least.

LithiumX

yea very interesting, still learning here though. meant to say .02" (but rpw claims .3mm on all post 96 mitsu 4 bangers) ..
i actually used the stock compression ratio and main cylinder volume to figure out the combustion chamber volume so i wouldnt have to deal w/ shape deck height and all the other crap the numbers all work out and give u 9.5 so the lil bit of variance in the piston is negligible (only because i was going for ball park figure -- and volume change by piston will carry over to the combustion chamber for the most part but -- cylinder volume would be less but so would combustion chamber)

looks like our gasket is actually .3mm (still unconfirmed)... but the stuff i am learning definitely will come in handy someday(soon hopefully)

the rough numbers on rpws site roughly correspond to my rough numbers leaving me with a rough sense of satisfaction.... roughly speakin