Does anyone have an Idea how much Compression a 105mm should make with a 12:5:1 piston? I am curious because I used thicker base gaskets this time and I am not sure how much of my Ratio I may have lost. They had to shave .005 of the head and they had already shaved about .013 off the cylinder. The stock base gasket is .020 I ran 2 of these last time which after being torqued down makes it .036 roughly. Well when i over revved it the piston slapped the head again, but just by about .002 thousanths I figured. so after shaving off that .005 off the head I figured I could run a .050 base gasket and I would be perfect! But coming across that gasket isn't very easy. So I ran an .040 aluminum with a stock .020 paper and after being torqued it should come out to .057 to .058. I thought I would rather be safe than sorry if you know what i mean! So I probably have lost about .010 to.015 thosandths of compression. Which from what i figure comes out to be roughly 12:2:1or 12:1. I don't know though![img]i/expressions/face-icon-small-mad.gif[/img] Does anyone have any Ideas on this? Please throw in you opinions on this will ya.?[img]i/expressions/face-icon-small-confused.gif[/img][img]i/expressions/face-icon-small-smile.gif[/img] There has to be some chart or some rule for how many thousandths gained or lost is equal to compression points wouldn't you think? Thanks.

 

Is that a rhetorical question? What'd ya think we are, a bunch of wrench-heads???[img]i/expressions/face-icon-small-confused.gif[/img]

 

Angry!!!!!! if you did the true math calculations to compensate for the .040 aluminum gasket you also need to compensate for the high heat expansion of your piston and head which caused your piston to slap probably from revving tooo high...from my calculations after you crank down your .040 base gasket at 50lbs this should bring the compression down to about .020 NOT .010 or.015 therefore your compression would be substancially decrease do to your miss- calculation!!!!without getting into any tecknical details, your compression would be somewhere near 11:5:1 ???....i would recomend getting a true compression reading and correct piston just to be safe. then call me up with your math and i will be more than happy to walk you through this simple procedure..and by the way with the new JE piston for this kit should clear the head and and even out the compression problem without having only one side of your piston to make contact with head. this shape of piston, as you should know would squeeze the compression out of the radiator jacket side of head which would result in your overflow problem......right ??your ds is very fast ,but you could get a few more ponys out of it.. the overheating issue troubles me .I hope you can get to the bottom of this ........dont get angry im only trying to help you ... the right piston cut will make for more efficiency when it comes to true compression readings and will allow a hot piston and cylinder to expand creating more compression at higher temps

 

Angry, I was wondering if this would help i was just brain storming. Lets talk about compression ratio, in general. The Change in horse power due to the change in compression ratio is relative but not directly porportional. That is to say that a change from 8:1 to 9:1 will give you a larger increase than would the change from 13;1 to 14;1. I seem to recall from every point change around 7:1, that is the change from 7:1 to 8:1 would be slghtly more than a 3% power increase. Once you get up to 13:1, that same one point change in only good for about 1.5% power increase. The rule of thumb for the compression ratio's run in most street engines is; for every point change in the compression ratio your power out-put will change by 2%. Using this rule of thumb on an engine that produces 400hp, every 1 point change in compression ratio will result in aprox. 8hp change in output. One thing that you have to remember with this perticular model, the only variable changing is the compression ratio. Most of the time when compression ratio change is made, significant other factors are changed which can significantly effect power out-put on available pump gas, it probably could be argued that your power might actually increase. This would be true if your compression ratio were high enough to force the use of a retarded timeing curve. (Due to pre-egnition) so with this in mind it is vital to really get your compression accuratly checked so at least you can burn fuel the will fire correctly , just trying to help dude!!!

 

[img]i/expressions/face-icon-small-confused.gif[/img][img]i/expressions/face-icon-small-blush.gif[/img]

 

[img]i/expressions/face-icon-small-shocked.gif[/img][img]i/expressions/face-icon-small-confused.gif[/img] I agree with you AZ.