Lower stroke more volume? ..... Nuther stroking question.

[PQ]

Ok so I'm curious.

My engine is almost done. We lowered the stroke with shorter pistons and slightly longer (fixed) rods. For the supercharger of course.

Went from 11:1 to 10.2:1 which is 7% less static CR. (same crank)

Does this mean more volume as well? And if so how is it figured?

Is it 7% more volume or is it the same?

Nevermind the very slight bore we did to get a nice hone. It was insignificant.

[GONIF]

Each cylinder would hold more volume for sure ,if that's what you mean .As to how much % wise I have no clue.

[dlluinstra]

http://en.wikipedia.org/wiki/Engine_displacement

[62nalide]

Nice, I've always wanted to destroke a 6.2L using a 4.8L crank but keep us posted on what you do.

[Ucantctchme]

Your piston is still moving the same amount so displacement is still the same. With what you are doing you will need to make sure the piston is not moving to low in bore. If it goes to low it will not be supported and rock in the bore.

[Bo White]

If you shortened the stroke you need longer rods and/or piston. Maybe that was a typo.

[Irnwkrkev]

Yeah, OP seems to have something off or not explaining the whole story.

Normally lowering stroke = reducing stroke = taller piston and shorter rod

Increasing stroke = shorter piston & longer rod so when piston is at bottom of crank stroke the rings are still well inside the bore.

You mention same crank which means 3.622" stoke? Maybe you went with a 6.0" rod with factory pin and piston type vs. aftermarket 6.125" rod with aftermarket piston?

[trw427ss]

Originally Posted by PQ

Ok so I'm curious.

My engine is almost done. We lowered the stroke with shorter pistons and slightly shorter rods. For the supercharger of course.

Went from 11:1 to 10.2:1 which is 7% less static CR. (same crank)

Does this mean more volume as well? And if so how is it figured?

Is it 7% more volume or is it the same?

Nevermind the very slight bore we did to get a nice hone. It was insignificant.

You added about 6.5 cc more to the volume to lower the CR so about 8% more volume.

[PQ]

Hmmmmm............

Perhaps I am not explaining it well.

I did learn that to only shorten the piston or rod or lengthen it the volume moved is the same. It's just lower in the cylinder thus lowering the CR.

I was thinking that it was total cylinder volume from bottom of stroke including the compression area. But it is only bottom of stroke to top of stroke.

So in my case the piston pin placement is deeper under the piston thus shortening it a bit. Lowering the CR.

Still a safe amount to work just fine. The rods will be a tad longer but very tad. So not much increase in displacement.

So essentially I merely lowered the stroke in the cylinder and added a small bit of travel maybe adding a few cubes.

I just had the displacement and the total volume of the combustion chamber as the same thing and it is not.

[PQ]

Originally Posted by Irnwkrkev

Yeah, OP seems to have something off or not explaining the whole story.

Normally lowering stroke = reducing stroke = taller piston and shorter rod

Increasing stroke = shorter piston & longer rod so when piston is at bottom of crank stroke the rings are still well inside the bore.

You mention same crank which means 3.622" stoke? Maybe you went with a 6.0" rod with factory pin and piston type vs. aftermarket 6.125" rod with aftermarket piston?

Originally Posted by Bo White

If you shortened the stroke you need longer rods and/or piston. Maybe that was a typo.

Yup. It was a typo. Slightly longer rods but just barely.

Originally Posted by dlluinstra

http://en.wikipedia.org/wiki/Engine_displacement

Form that link. I had found it out but this agrees.

Engine displacement is the volume swept by all the pistons inside the cylinders of a reciprocating engine in a single movement from top dead centre (TDC) to bottom dead centre (BDC). It is commonly specified in cubic centimetres (cc or cm3), litres (l), or (mainly in North America) cubic inches (CID). Engine displacement does not include the total volume of the combustion chamber.

Originally Posted by 62nalide

Nice, I've always wanted to destroke a 6.2L using a 4.8L crank but keep us posted on what you do.

10-4, I'll let you guys know how it comes together. Specs are above.

Originally Posted by Ucantctchme

Your piston is still moving the same amount so displacement is still the same. With what you are doing you will need to make sure the piston is not moving to low in bore. If it goes to low it will not be supported and rock in the bore.

I think it will be fine. The guys who are doing it have done the a thousand times. hahaha, I will certainly mention it though.

[Irnwkrkev]

You're using aftermarket pistons which hopefully have a slight dish to give you the lower compression which you are seeking.

You don't want to lower compression by increasing quench (the space between the top of the piston and the bottom face of the cylinder head ((flat part around the combustion chamber)). Proper quench will promote better combustion (normally around .040" or so) and can be adjusted with custom head gasket thicknesses.

The rods are pretty long by ls standards as most aftermarket ls rods are 6.125", stock are 6.098" but with a .943" piin diameter.

[PQ]

Originally Posted by Irnwkrkev

You're using aftermarket pistons which hopefully have a slight dish to give you the lower compression which you are seeking.

You don't want to lower compression by increasing quench (the space between the top of the piston and the bottom face of the cylinder head ((flat part around the combustion chamber)). Proper quench will promote better combustion (normally around .040" or so) and can be adjusted with custom head gasket thicknesses.

The rods are pretty long by ls standards as most aftermarket ls rods are 6.125", stock are 6.098" but with a .943" piin diameter.

Says flat top but I have not seen them. They are at the machine shop.

Not sure exactly why the pin placement and adjusted rod length. I'll have to ask. He told me at the machine shop but I can't remember exactly what he said. Smaller pin diameter is interesting.