Dynamic compression simplified

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hey welcome to gold scratch so uh based on the feedback i've been getting by the way we're not in gold scratch today we're in the office so uh it's convenient to make this video um based on feedback i'm getting from subscribers there's a need for more information or practical explanation and some concepts that are not widely understood in a way that they can be understood they don't have to be a math genius in order to deal with some of these issues and if you're planning a build the build is really a combination of parts cam shafts compression pistons all that stuff and those parts have to go together in order to get a desirable result so you need to understand this up before you start even buying parts so this fault this discussion is about dynamic compression and i did talk about it in a previous video and i did describe it and i described how you could calculate your own static compression ratio and then i said dynamic is pretty complicated go online find the formula fill in the numbers and you'll get an answer so and you will but it's always better if you understand it so i've come up with kind of an example that i hope will help people understand it without doing a lot of complicated math so once again let's take an example of an engine that has a 10 to 1 compression ratio and a 4 inch stroke just to make all the math nice and easy so right off first of all just cover this off tend to want the pressure ratio the volume of the cylinder the chamber when the pistons at the bottom of the chamber before the stroke starts to go up is 10 times more than the volume when the pistons at top dead center and i already described how you can calculate that dynamic compression on the other hand is a little more complicated so you can fill in the formula but here's a way to understand it let's take an assumption view back to our four inch stroke and let's assume that the intake valve closes when the piston is one inch from the bottom of the bottom dead center so out of the four inches uh the mixture is only being compressed three of the four inches instead of four so if you have a ten to one statical pressure ratio and you're only compressing the mixture three out of the four inches then you have a 7.5 to one dynamic compressor ratio it's really that simple and if you're degreeing a camshaft and you've located the intake center line this camshaft example i used here uh it's the comp cams 276 that i used in the 427 that i built last summer the intake valve closes 64 degrees after bottom is center and you could actually find your center line of your intake 160 degrees rotate around to 64 degrees after bottom dead center and actually measure from the top of the block down to the top of the piston and you will have your dynamic compression uh the amount of stroke that's left in your damaging compression so you take that first let's say it's three out of the four inches once you get 75 so that's a quick way to understand dynamic depression and it's really important and i will cover off uh in future videos hopefully in a simplified way uh why that's important and what you need to understand and how what you can do to change it and you can change it by retarding and advancing your camp and what conditions you do that so hope you found that interesting i will actually leave my email address in the description and if anyone has any questions feel free to contact me look forward to your comments uh and questions and likes of course and uh always looking for new subscribers so if you want to hear more information like this please click the subscribe button and thank you for watching gold scratch
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Channel: Gold's Garage
Views: 1,548
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Id: sH4lUbzGLvY
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Length: 4min 22sec (262 seconds)
Published: Wed Dec 01 2021
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