I want to know EXACTLY what my compression ratio is before I fully assemble my engine. Whats the best way to do this? Have the machine shop do this for me? Buy the equipment from Summit and do it myself? If I buy the tools from Summit, what all do I need? I know I need the buret, what else? I spec'd the Auto Tech pistons 11 to 1, but I want to check what EXACTLY it is in the engine, it may be less, or more. Im curious, and like to know stuff
Buy the complete kit with a plastic burette if you can as the glass ones are hard to keep safe when your working, ask me how I know! Not included in the kits which are needed is clay and a good single edge rasor blade. The kits tell you have to do every check you need to know how to do , everything but how to level the darn head itself which can take up the most time in some cases!
Respectfully this is a bit out of order. You ought to know what it is before you order parts, not on assembly! The cc burette is your best bet with a dial indicator or piston stop to find tdc...
All the required specs were sent to Auto Tech before the pistons were made, I requested 11 to 1 comp. ratio. Im just wanting to know what it actually is before heads are bolted on
All you need is how much the pistons are in the hole, the head gasket thickness, the chamber size, and how many cc’s are in the piston dish/valve reliefs. (Didn’t Autotec furnish this?). Have the heads been milled? Chambers should be around 58cc. Head gasket , .040. Were the Autotecs ordered with the right CD to make them 0 deck?
Yep there damn close to zero deck, I just wanna measure for the hell of it Auto Tech did furnish all piston specs.
You can get the buret, stand, and clamp cheaper from Amazon than from Summit. The difference is the graduations are marked in ML’s and not CC’s. One ML equals one CC. Here’s a four pack from Grainger for $37 https://m.grainger.com/mobile/product/LAB-SAFETY-SUPPLY-Burette-6CDP3?breadcrumbCatId=23967
Put a straight edge over cylinder and use a feeler gauge get a guesstimate if piston depth. If your at zero deck , I got about 10.98 with 58 cc head. If block is not milled, I’m guessing you are at .038 below deck at 1.855 ch. That’s using summit racing compression calculator.
The most accurate way to determine compression ratio, with the least amount of "formulas" involved, with an assembled shortblock, is to use a dial indicator to get the piston to tdc. Then use grease to seal between the cylinder wall and piston.. do it neatly, so there is a solid seal there, but no extra.. then you need a 4" square piece of 1/8" plexi-glass.. Drill a hole in it to feed the burret thru, and a bunch of small holes to allow air to escape... Position the block about 1- 2* off of level, and fill that cylinder. Fill cylinder and obtain CC number.. Use this number as your Piston CC, and that along with head cc and head gasket thickness and head gasket cylinder diameter, will give you exact static compression ratio. Look for a compression calculator online that asks for both head gasket thickness, and the actual diameter of the opening of the gasket over the pistons. For instance, the 8494 PT 455 head gasket that we typically use on the 4.350 455 based motors, actually has a diameter of 4.385. Now .035 over the bore size, in that application is not a big deal, but consider this is the same gasket that goes on a 4.040 Bore 400 ci motor, then you can see the importance of considering that number, if your wanting exact static compression. If you really want to know what the gasket is without knowing the exact bore size, then seal it up with some light grease on a flat surface, and CC it with your burrett.. then just add that number to the number you generated above. Put zero's in the formula's for everything but piston CC and head CC when you do this. JW
Yep, you can get an exact head cc using same plexiglass method with valves closed and spark plug installed.
Or you can make your high school math teacher proud and do the simple math. Add the numbers up do some dividing...
I’m with ya Jim remove as many variables and possible and get the real compression ratio with less math and more fact.