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| Increasing compression ratio. https://www.slantsix.org/forum/viewtopic.php?t=65217 |
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| Author: | Smokeyfl [ Fri Aug 14, 2020 7:11 pm ] |
| Post subject: | Increasing compression ratio. |
I am rebuilding my first slant 6. I would like to have a compression ratio between 9 and 9.5 but can only find stock type pistons at 8.2 or wiseco pistons with a ratio of 10.3, nothing in between. Can I achieve my goal by using the stock pistons and shaving the block? I am going 30 over. My block is a 225 from a 1965 dart. How much can I take off safely and achieve my goal? |
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| Author: | DadTruck [ Fri Aug 14, 2020 9:30 pm ] |
| Post subject: | Re: Increasing compression ratio. |
Stock style pistons have been used to achieve the compression ratio that you have targeted. If you have not done so, start by cc’ing the cylinder head and measuring the piston recession on the engine as it is currently. Then use one of the online compression calculators to determine how much to cut the block to get to your target compression ratio. Or you can use the formula of each .0069 cut from the head removes one cc from the head combustion chambers. here is one of the on line compression calculators https://www.rbracing-rsr.com/compstaticcalc.html I normally do a clean up cut on the block have the cylinders bored to the correct size and temporary install the #1 and #6 pistons that I will use to get the new piston recession then calculate what to cut on the head to get to the target ratio. Aftermarket stock style pistons do not necessarily have the exact same compression height as the pistons currently in your motor. One more item, there is nothing wrong with just going .030 over, but going .060 over will start to deshroud the valves for better breathing. |
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| Author: | Doctor Dodge [ Sun Aug 16, 2020 8:39 am ] |
| Post subject: | Re: Increasing compression ratio. |
The "next level" step is to calculate the engine's effective compression ratio. You need to find the intake valve closing point for the cam you want to use and plug-in the info on a different calculator. https://uempistons.com/p-27-compression ... lator.html Setting the effective compression in the 7.8 to 8.2 range will get you the best performance when running common "pump" fuel. (87 - 91 octane) |
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| Author: | Smokeyfl [ Sun Aug 16, 2020 6:27 pm ] |
| Post subject: | Re: Increasing compression ratio. |
Thank you both. There is a lot to learn. |
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