Reducing CR and quench/squish
Discussion
I'm looking to lengthen the stroke of a current engine using a crank with a larger rotational diameter with the appropriate rods. Providing the block can accomodate this of course, does anyone have any thoughts at this point?
As this is a turbo application the compression ratio is the primary problem. Custom pistons or a bit of OE luckery may allow me to lower it, ultimately by leaving a larger space at tdc than before e.g 1mm longer.
Mathematically this is all straighforward, but what l am worried about is the effect this will have on the squish band, affecting the mixing and combustion efficiency of the mixture. Does anyone know if this is a problem l should be worrying about?
I will be using a heron (flat) head with the combustion chamber formed in the piston crown.
As this is a turbo application the compression ratio is the primary problem. Custom pistons or a bit of OE luckery may allow me to lower it, ultimately by leaving a larger space at tdc than before e.g 1mm longer.
Mathematically this is all straighforward, but what l am worried about is the effect this will have on the squish band, affecting the mixing and combustion efficiency of the mixture. Does anyone know if this is a problem l should be worrying about?
I will be using a heron (flat) head with the combustion chamber formed in the piston crown.
Well its a heron (flat) head so they would definitely be 'in the hole' at tdc. So the squish measurement is simply the tdc top of piston to head face gap?
0.03" is a very small gap. Can l assume that if the head is flat as it is with the engine l'm looking at this gap would be bigger. e.g. 90mm stoke 10:1 CR would leave a 10mm squish clearance assuming that pistons were also flat topped. (they are actually dished but for the sake of the example..)
How is this measured on dished pistons, from the edge?
0.03" is a very small gap. Can l assume that if the head is flat as it is with the engine l'm looking at this gap would be bigger. e.g. 90mm stoke 10:1 CR would leave a 10mm squish clearance assuming that pistons were also flat topped. (they are actually dished but for the sake of the example..)
How is this measured on dished pistons, from the edge?
That's what confused me.
If the head was flat and the pistonhead was flat, then you would leave a 10mm gap under a 90mm stroke 10:1 CR.
Correct?
I guess the piston bowl, alters this and allows the piston edge to come much closer and create the squish whilst retaining the CR. Cheers guys!
Dan
If the head was flat and the pistonhead was flat, then you would leave a 10mm gap under a 90mm stroke 10:1 CR.
Correct?
I guess the piston bowl, alters this and allows the piston edge to come much closer and create the squish whilst retaining the CR. Cheers guys!
Dan
Hmm yes i see why you'd say that: but its the ratio of the cylinder volume at bdc to the volume at tdc. Given a simplistic flat suface on the cylinder crown and head, this would be 100mm * Cylinder bore area : 10mm * Cylinder bore area (if the stroke was 90mm). CR is therefore 10:1
Nahnah!
Nahnah!
A proper turbo conversion would use custom or lucky OE selected pistons. Thicker gaskets are a kludge. You would lose squish, NA engines of any quality probably have some squish, but how would it effect cooling? If anything inefficiently burnt fuel may serve to cool the cylinder chambers!
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff