Calculating Displacement

[MassMustang]

I've been trying to figure this one out. Displacement is based on bore and stroke (and of course the number of cylinders) but if using the Boss 5.0 block, why is JDM measured at 323, MMR at 324 and Brenspeed at 326? What's the difference?

 

[JeremyH]

Final measurement varies based on the final bore of the piston used on the block. Stock to .010-.030 over is common.

 

[05stroker]

And the different crank strokes.

 

[MechE]

Isn't that Brenspeed 326 a stroked (and possibly bored) 3v? Maybe the same with the others?

 

[MassMustang]

What if the pistons are all 3.700" bore and the crank is a 3.750" stroke? The shortblocks all seem to be the same M-6010/6015-BOSS 5.0 block with a 3.750" crank with the 3.700" pistons and 5.850" rods.

I'm trying to figure out where the extra 1-3 cid comes from.

 

[MechE]

3CID is about a .020" bore difference. They are probably finishing the block to different bore sizes, what Jeremy said.

 

[tjm73]

Bore x Bore x Stroke x 6.283 for an 8 cylinder engine.

Brenspeed uses a big bore block and adding more stroke. Probably a 3.72" bore and 3.75" stroke. That makes 326 cubic inch

 

[MassMustang]

Ah! Makes sense now. The 0.010" overbore would be a 324. The 0.020" overbore would be a 326.

Now do you account for flattop or dished pistons? If they're -18cc that's 1 cubic inch, no? Pistons seem to range from flat to -11cc to -28cc.

 

[MassMustang]

Strike my question around dished pistons. I wrapped my head around the logic that a dished piston increases chamber capacity but not displacement.

Thanks for all the info guys! Very helpful!

 

[MechE]

Ah! Makes sense now. The 0.010" overbore would be a 324. The 0.020" overbore would be a 326.

Now do you account for flattop or dished pistons? If they're -18cc that's 1 cubic inch, no? Pistons seem to range from flat to -11cc to -28cc.

Displacement describes swept volume. So that same piston top geometry makes the top and bottom of the (otherwise perfect) cylinder. It can therefore be taken out of the calculation for simplicity sake.

I does however, come into play when considering compression ratio.

 

[BruceH]

A 326 comes from a 3.7 bore and 3.800" stroke. A 322 comes from a 3.700 bore and 3.750 stroke.

A big bore with a stock crank measures 304 inches.

The Big Bore block isn't made for a large overbore. There isn't too much room left in the cylinder walls, they are already siamesed as is.

 

[BruceH]

Ah! Makes sense now. The 0.010" overbore would be a 324. The 0.020" overbore would be a 326.

Now do you account for flattop or dished pistons? If they're -18cc that's 1 cubic inch, no? Pistons seem to range from flat to -11cc to -28cc.

Try http://www.wallaceracing.com/Calculators.htm for automotive calculators. Lots of good info there.

 

[drive_55_not]

Bore x Bore x Stroke x 6.283 for an 8 cylinder engine.

Brenspeed uses a big bore block and adding more stroke. Probably a 3.72" bore and 3.75" stroke. That makes 326 cubic inch

It looks like the Brenspeed "B326" moniker is carryover from their earlier B326 engines that used a 3.800" stroke, 3,700" bore that netted 326ci. The current advertised version uses a 3.75" stroke so that'll net 322ci.
I don't think anybody makes a 3.800 stroker crank anymore.

I hope they aren't doing a .020 overbore as Bruce pointed out the big bore sleeves are thin enough to begin with and that would leave you with no room to install a bigger piston later if needed.



,

 

[BruceH]

It looks like the Brenspeed "B326" moniker is carryover from their earlier B326 engines that used a 3.800" stroke, 3,700" bore that netted 326ci. The current advertised version uses a 3.75" stroke so that'll net 322ci.
I don't think anybody makes a 3.800 stroker crank anymore.

I hope they aren't doing a .020 overbore as Bruce pointed out the big bore sleeves are thin enough to begin with and that would leave you with no room to install a bigger piston later if needed.



,

There's a pic of my big bore when I got it. I'm fairly certain there weren't sleeves. Can't see them in the pic. Believe it or not I can't say for 100% because there are just too many other things in my head that are competing with memory space, lol.

How much can it be bored? I really don't know. I do know that it's not something you want to do unless you really have to.

IIRC final bore on my motor was 3.7005". I know that I speced the bore at .003" over piston size at the skirt. The pistons are uncoated 2618 alloy, a smaller ptb would of been used with skirt coated pistons.

 

[MassMustang]

Thanks for all the info guys! Very educational for me!

I have someone working on a Boss 5.0 stroker for me. It's supposed to be a 324 with Manley rods and ceramic coated pistons as well as a Kellogg double-keyed 3.750" crank.

I was confused about the various displacements.

 

[01yellerCobra]

There's a pic of my big bore when I got it. I'm fairly certain there weren't sleeves. Can't see them in the pic. Believe it or not I can't say for 100% because there are just too many other things in my head that are competing with memory space, lol.

How much can it be bored? I really don't know. I do know that it's not something you want to do unless you really have to.

IIRC final bore on my motor was 3.7005". I know that I speced the bore at .003" over piston size at the skirt. The pistons are uncoated 2618 alloy, a smaller ptb would of been used with skirt coated pistons.

None of the iron blocks have sleeves. Just the aluminum. I dint remember the max bore. I never intended to take it that far.