![]() INSTRUCTIONS: Choose units (default is cubic inches), and enter the following: 3 weeks may seem like a long time now, but once the car is together you're not going to want to tear it apart to swap the cam, so 3 weeks in the grand scheme of things isn't that long.The Engine Compression Ratio calculator computes Single Engine Cylinder the compression ratio (CR) of a combustion engine cylinder. If it's going to be a daily driver you may want to stick with the grinder's recommendation. It really comes down to how you use the car, if this is just a fun weekend car I don't see how it's going to be a problem. I wouldn't have any hesitation running the Comp cam your dad has. It would have been easier for me to downgrade my cam than install a T56 and 4.30's, but I kept my cam and did all that other work anyway. The Comp cam that your Dad has is definitely hotter than what is being recommended to you, but it's still within what your engine can support and it's less than the 704 I run. The 702 and 703 are pretty well regarded as good street cams. It's a little rowdy when you get stuck in bumper to bumper traffic but it does work! And it's a lot easier to deal with now that I have 4.30's instead of 3.55's, 4.10's would be fine. And although the 704 is a little wild for commuting, I've put over 30k miles on my car as a daily driver with that cam. But honestly, your engine compression can support a 704 and so can your gearing. I run the 704, which I already said is a bit hot for what I do. ![]() It's not a massive difference but it is a difference. Biggest thing is the lobe separation, the 112 that your grinder is recommending will give you a little more vacuum and a little more lower end compared to the 110 that all the lunati's and that comp have. And it's closer to the 703 than it is the 704 IMO. Your Dad's cam has a bit more duration than a Lunati 703, but less lift. Duration wise it's about halfway between a Lunati 702 and 703. The recommended cam is light on lift compared to all the Lunati cams, it has much slower ramps. I'm going to compare with what I know, which is the Lunati Voodoo series. So you won't turn the engine into a dog with the bigger cam. And with 4.10's you'll have the gearing too. Even if you're at the lower end of that compression number you'll have enough compression to run a hotter cam. The engine itself can support more cam that what was recommended by a decent amount. Remember that what the cam grinder is recommending is going off of what you told him you wanted. Then we know how close to 6cc or 7.3 cc KB was on their estimate. Subtract measured half inch down volume from a calculated perfect half inch tall cylinder with your 4.08" in bore and that will give you the true cc of that piston. You would "travel" the piston down half and inch from true TDC, not just measure the piston to the top of the deck directly. Is this engine already assembled? If not, maybe you can test the half inch down fill volume and that will give you exact numbers. With those numbers in the calculator on the website, it comes out to 9.99 to 1, and that is including. 018" above the deck, assuming 9.6" deck height, and the numbers measured from 72bluNblu confirm this on his engine. But, the numbers say that "flat top" would sit about. If we treat that as a flat top piston, which typically has around 5 or 6 cc valve pockets, you would add the volume of that little step around the piston to the valve notch volume, and that is how they get 7.3 cc. Do you know for sure if yours was previously decked?Īs for the numbers, I think I agree with KB on this one, or at least they are pretty close. In the picture of post number 7, the deck surface appears to show markings from previous decking. You may need to adjust that clearance with a thicker head gasket. 018" over the deck like they're supposed to be you'll need to check your piston to head clearance if you run closed chamber heads. ![]() I ended up running a different head gasket than the one I gave the Tech and my head chambers ended up 1cc larger, so it calculated a little differently when I updated the gasket View attachment 1715876343Īlso, with the KB 243's if you do end up with the tops of the pistons. Instead, he told me to use a deck height of 0 and a 7.3cc volume, with that volume accounting for the protrusion and the valve reliefs. I'm not entirely sure where the 6cc volume comes from that they advertise, but the tech I spoke to at KB straight up told me not to use it. 030" protrusion, so the shoulder of the piston sits. The compression calculators I was using, including the Wallace calculator, had some issue dealing with the deck height and the piston volumes because of the way that piston is shaped. 018" over the deck (which is the spec with the stock deck height). I have KB 243's in my 340, they measured.
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