Thread: Domed Pistons

Tweet

What is the current thought on domed pistons (21cc dome @ .181 high) and quench? Is the 35 to 45 thousands still apply, or is it not as important on a domed piston. Compression will be under 10:1.

Keith

If there is a dome on the piston or not is not related directly to the need for quench clearance. It is needed for at least several reasons, (1) To keep your pistons from hitting the heads as R.P.M., load and heat change the clearance inside a running engine, (2) To help control detonation using a fuel of lower octane, such as the gasoline available at the corner gas station. This is very critical with a high compression ratio, or in applications using forced induction or spraying with NOX. There are other areas of engine operation that are affected by quench clearance and quench volume, such as exhaust emissions, octane sensitivity of the fuel being used, ignition timing required and fuel efficiency. Some things that need to be known to calculate a safe quench clearance are, (1) Type and octane of the fuel to be used, (2) Intended R.P.M. range of engine operation, (3) Rod selection, as aluminum and steel have different rates of expansion, (4) Piston to bore clearance, as greater bore clearances can allow for greater piston rock at T.D.C., (5) Is a power adder being used, or high compressions ratios being employed, (6) Are the cylinder heads aluminum or iron. There are probably more issues to take into account, but that is a start. I do believe that a well thought out quench clearance will enable your engine to make good and reliable power. If you are building a big block chevy with open chamber heads of the 454 or smaller size you will have some dome on your pistons to arrive at a 10:1 compression ratio. Good luck on your build!

i just got 1973 454 block,2main,have steel crank i want to built hiperf street engine,any ideas thanksguys

Blwn31, You have to take into account how close the valve follows the piston during the cycle and how well designed and how the contour of the dome was built to the head.
Then, there is a Quench or Squish question to address.
As you spec'd the parts on your post, you'll be fine and things will fall into place for flame propagation and hidden "fuel traps" are handled in your engine.
Understand that we have to assume stock, iron heads of 113 to 116 cc combustion chamber and standard valve sizing. Things will change if any of your combo peices are different from those assumptions.

YOu need to decide on head chambers and volume to then determine what type of piston. the most common heads today utilized are 119cc chamber which are common on Gm 781's and many after market companies. To use those size heads you will need a dome in your piston to achieve decent compression like in the 10:1 range. If you go to Summit' wen site many of thier pistoms available have charts indicating what compression will be using various sized head combustion chambers. for example aTRW 2465 domed piston which is a older design will yield 10:1 approx with a 119 cc head but but often times bdepending on the cam lift and duration requires reliefs to be cut into the piston because the vavle hits! I personally am not fond of this piston but is an example. Decide on heads first then you can always find a piston to mee your needs
is my opinion.

Originally Posted by blwn31

What is the current thought on domed pistons (21cc dome @ .181 high) and quench? Is the 35 to 45 thousands still apply, or is it not as important on a domed piston. Compression will be under 10:1.

Keith

i will make this short the closer you can get to the heads with out hitting it with the pistons the more power you will make . thats not to big of a dome .not a big fan of TRW but they will hold rings .i have made them work