Vette engines and Piston Types
My Vette has a more modern v8 in it as its an 89 it was born with a roller cam and better shaped heads than normal v8s of the same time period. But in my case I am building one up from scratch.
Now a lot of engine from the 80’s had low compression pistons. Many of these are freaking terrible. The one shown below is best for knocking and pre-ignition. I personally call these rattle cans. If you rebuild an engine and see these pistons your going to have some problems. First off if you replace them with the pistons shown below. You will raise the compression ratio. Not really a bad thing but once you go up on compression the cam and heads may need to be changed. Along with valve springs and other support equipment.
Now with the proper pistons heads and cam you will make lot more power. But it may be beyond your budget. Some engine combos factory and other wise can just have the pistons replaced with the ones below. But without a larger cam and at least good flowing stock heads it will still be a dog.
Here we have a standard sizes stock flat top piston from a 70’s Camaro. This engine made almost 300 hp from the factory and was no more prone to detonation than engine with dished pistons. The reason for this is shape the dished relieved piston are so poorly designed they are more likely to knock than ones that are higher compression. Sounds backwards but its true now there is a butter zone of compression where no types of piston matter and detonation is not an issue. But if you wish to make over 300 hp compression is going to be needed to make the engine snap off like you want for heavy street driven engine. With 9:1 compression an engine with a 300 duration race style heavy loping cam will only have about 6:1 actual compression or Dynamic compression ratio as it commonly known. So just putting this cam into an engine with 7:1 compression its going to be a turd. But with 10:1 and flat top piston like the std sized one just above will run just fine on pump gas and the large cam. Of course this changes drastically if the stock cam is used the smaller the cam the higher the Dynamic Compression Ratio is going to be. If you ever built an engine with big cam and big valves and big carb thinking it was going to be fast only to drive the car and find out its flat. Runs slow and has a little hit in the high rpm band but no real power. You may be amazed to find out that some people drive cars on the street with pump gas that have 12:1 static compression. Now usually cars that extreme have other issues like the cam is so big it doesn’t smooth out until 3000 rpm and needs a 5000 rpm stall. Of course the trade off is 800 plus hp. So not really that bad.
With pistons one thing to remember is always get the one that work with your cam and heads. If you have a low power setup or high rpm screamer you will want the DCR to be the same for a street engine. This is the major difference to a proper build and one that is just all over the place. For road, circle, and drag racing a correct dcr is a major factor to winning the race. Missing this calculation by a few points will either leave you standing still at the starting line or broken down half way down the track.
My next post will talk about DCR in detail. Just wanted to touch on the pistons a little before moving on.
Summary if your pistons are stock and look like the one at the top of the page. Replace them with much better one either the oem flat tops from a performance model engine or with aftermarket pistons. Factory pistons will take over 400 hp as long as its N/A and no NOS. With NOS or blown you will need forged pistons. But stock ones can easily support a weekend drag racer. Don’t break the bank on pistons if you don’t have heads and everything else to use the best top of the line after market pistons. Stock ones will do just fine as long as they are the correct shape and being used with the correct compression ratios.