I was looking over the parts of my 331 engine kit from coast high performance and the catalog says my engine would fall at 10.1:1 compression . . . was wondering if someone could point me in the right direction for calculating the compression.
if you have all the numbers, punch them in here: http://www.fordmuscle.com/calculators/compression.php
oh oh, problem. . . seems a little high for running boost. What can I do about this? I'm at 9.77. But I didn't know what my deck height and gasket thickness is so I guesstimated 0.06.
so in that last part of the equation they needed deck height and gasket thickness, supposed to add them up. I don't know what my deck height is but I guessed 0.02 and added another 0.04 for the gasket thickness to a total of 0.06 but I need to figure it out for sure.
so how can I lower engine compression, I wouldn't think a lot of people would be interested in that but it seems to be my dilemma now.
New pistons or a really thick head gasket. To make enough difference to actually make boost worth doing you should get dished pistons. You can get a kit from most performance suppliers (or chemistry glassware supply houses) to check the compression ratio with oil. Pull the plug withe piston at BDC and then check the amount of oil it takes to fill the cylinder and chamber completely. Rotate the crank to TDC on that cylinder and see how much oil that displaces. You use a bit of math to compare the amount you started with to the oil left and that gives you the actual compression ratio. (this must be done with the rockers off the valves so they both stay closed for the entire event)
Have you bought heads already ? Bigger combustion chambers would be what you might need to lower the ratio. And one other thing........what block are you using ? 331 + aftermarket heads + big cam + a supercharger + too many rpms = split block.
Add all of the above together and you WILL have the recipe for a split block. And who told you that a hydraulic cam wouldn't go over 6500 rpms before floating the valves ?
Try this calaulactor, Watch your dynamic, Try to keep it in the mid 8s. And you really need to know if the piston is "in the hole" or not. http://www.jeepstrokers.com/calculator/ If you haven't built it yet a piston swap would be the simplest way to drop compression, Although 9.9 is a little high. With the rite tune, I wouldn't be scared to run it. Your cam will have to be chosen wisely.
So it looks like my dynamic compression is less than 8. But yea, maybe I can get different pistons because I'm kinda worried about that much compression and boost. It says my dynamic is around 7:1
Here's how my 331 spec'd out: SRP forged flat tops.....006 down the hole at TDC, 57 cc chambers (Canfield's 64 cc's milled .060) Cam is a Ford Racing Z303 roller, W/1.7 ratio rockers. When I first ran it in the Ranger, the fuel tank was full of 87 octane gas. First time out the driveway, 1 block down the street, it sounded like it was crushing gravel in the cylinders. Went straight back home, syphoned 15 gals out of the tank and replaced it with the same amount of Chevron 93. Never had anything else thru it since.
