Malyc Posted January 3, 2015 Share Posted January 3, 2015 Don't know if this has been asked, but I've been trying to figure out the compression ratio of the vortec small block I'm currently building (mainly so I can figure out if I want to go with different pistons). So far, the major hangup I'm running into is the effective dome volume for the stock flat tops with the 4 valve reliefs. Does +9.92 cc sound right? Supposedly the motor came with a 9.1:1 compression ratio from the factory, and it adds up if the deck clearance on it is .02"... And, if that does all sound like it adds up... Is it worth going to a piston with a lower dome volume to get somewhere around 10-10.5:1 compression ratio? Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted January 3, 2015 Share Posted January 3, 2015 if you are using iron heads, you won't want a compression ration over 9.5:1 unless you plan on having to use some race fuel or a mixture of pump gas and race fuel now that can be fudged some depending on the duration of your camshaft (this is where you need to start looking at your dynamic compression ratio) the last thing you want is to build an engine that will be detonation prone, and being stuck having to use race fuel at 7-8.00 a gallon, esp if you plan on driving it a lot my recommendation would be to stick with the stock compression of 9.0:1 so you can enjoy it and not have to worry about it Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted January 3, 2015 Share Posted January 3, 2015 but to answer your question, you would add dome volume to increase compression but when doing the math, it's backwards, increased dome volume is a negative when doing the math Quote Link to comment Share on other sites More sharing options...
Malyc Posted January 3, 2015 Author Share Posted January 3, 2015 Ok, I was using Summit's compression calculator, and they wanted dish Pistons as a positive. What about converting to run an ethanol blend if I go to more compression? Up here in mn, it's pretty easy to find. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted January 3, 2015 Share Posted January 3, 2015 almost all pump gas is 10% ethanol anymore "they wanted dish Pistons as a positive" yes.... when doing the math.... because it increases the combustion chamber size adding dome volume decreases the combustion chamber size, so it's a negative Quote Link to comment Share on other sites More sharing options...
Malyc Posted January 3, 2015 Author Share Posted January 3, 2015 Sorry, lack of caffeine made me confused. Thanks for clearing it up Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted January 3, 2015 Share Posted January 3, 2015 there are always trade-offs when making power, make sure you are willing to make them Quote Link to comment Share on other sites More sharing options...
Murphy Posted January 4, 2015 Share Posted January 4, 2015 In your statement Sam about the iron heads, is that because they retain more heat than aluminum heads? If using aluminum heads, can compression be increased and still use pump gas?? Thanks............. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted January 5, 2015 Share Posted January 5, 2015 yes, alum heads are slightly more tolerable to more compression, you can't use your static compression as gospel, there are many other factors that come into play, cam duration, valve timing, valve overlap, it's more about cylinder pressure and dynamic compression ratio Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.