Calculating engine size....

[1974dodgecharger]

I got schooled today......on engine size.


Some guy with new challenger with a supercharger said he has a hemi 426 in his car.  I'm thinking 2nd gen hemi with supercharger and pops the hood shows me his 392 and I ask him I thought it was a 426.  He said it is because you add in how much extra volume the blower gives in size and add it to engine and he said its 426. 


I never heard this how your suppose to quote your engine size?

[cudaken]

Blowers don't count. 

Cuda Ken

[1974dodgecharger]

its new to me....Seems I asked on facebook and that's how guys now are calculating their engine size. 

[Bob T]

Umm, nope, I think the fb guys are using the automotive equivalent of putting socks in their undies to impress the Ladies
  Stroke length and swept volume area from the top of the slug to the cylinder head  seems to ring a bell with me.....

[c00nhunterjoe]

((Bore x bore)/4) x pi x stroke x number of cylinders= cubic inches. Always has, always will.

[A383Wing]

Bore & stroke calculates engine size....adding a blower does not increase cubic inches

[Windsor]

[XH29N0G]

I think we all understand the point he is making which relates to the amount of air used, but this doesn't change the size.  The size also doesn't change if I run my car at sea level or 5000 ft, but the amount of air does.

[Tilar]

 c00nhunterjoe is right,   Bore squared (bore X bore), times Stroke, times Pi (3.14), times # of cylinders, divided by 4.... Or use one of these web sites that have a handy dandy calculator. http://www.wallaceracing.com/cid.php

[tan top]

its new to me....Seems I asked on facebook and that's how guys now are calculating their engine size. 

news to me also !!  , still  these guys know their stuff ,   

[TUFCAT]

Man there's a lot of Bullshit out there. 

[tan top]

Man there's a lot of Bullshit out there. 

yep !!  wonder if this was the same guy in this thread   

http://www.dodgecharger.com/forum/index.php/topic,112479.0.html

[Ghoste]

Does nossssss add size too or just horsepowers (yes plural )?

[hatersaurusrex]

Or, you know, just use Algebra

[Nacho-RT74]

blower injects more mix, pressed into the "same volume"... thats all

Note and doubt I have thought since ever and the reason of the " " on my last statement: when we make the volume math about engines, we are calculating the volume of the piston stroke, however we still have volume to add into combustion chamber, deck to piston height and headgasket thickness. If we change the pistons ( more or less CH ) or change heads from closed to open or backwards, the volume ACTUALLY CHANGES, just like when we recalculate the new displacement based on pistons oversize. However we still use to make the math just on the stroke.

So at the end, the displacement is calculated just on the stroke of the crank allways. If you add correct pistons to blowers engines what as far I know piston CH must be lower, we actually GET more volume, just less CR

[Mytur Binsdirti]

Blowers don't count. 

Every guy needs at least a couple of blowers

[bakerhillpins]

Sounds like that guy is the epitome of that old 6" joke...

Q: Why can't blondes parallel park?

A: Because guys keep telling them that 1 inch is really 6 inches.

[hemigeno]

Under this "new math"     , you would also have to take into account the elevation at which the engine operates.  Thin air = less "displacement", according to that method.   

Posers.

Engine displacement is a term whose definition should remain what it was originally intended to convey... swept volume (of the pistons).  Any attempt to correlate an engine to it's "effective displacement" via superchargers, turbochargers, platinum spark plugs, oil additives, ground effects, neon lighting, racing gloves, fuzzy dice, bumper stickers, and/or dash-mounted hula girls is laughable.

[Tilar]

Blowers don't count. 

Every guy needs at least a couple of blowers

I'd be happy with just one, as long as I don't have to pay for it or keep up the maintenance. 

[six-tee-nine]

The guy is mixing up stuff i think.

I do know howerver that back in the group B rally days, a turbo charged engine was quoted with a factor of 1.4 IIRC. beacuse these cars ran in classes where engine size determened the class.
That means that say a 3 litre turbocharged engine was calculated as a 4.2 litre naturally aspirated....

[HPP]

The formulas for calculating engine displacement have not changed and once an engine is built, its displacement is a constant. I think we all know forced induce will increase the specific output of a given displacement. By saying forced induction changes their displacement, the  are "factoring" their output. Albeit they are saying it incorrectly, but I think we all understand that their specific output of a smaller engine with forced induction can be the equivilent of a larger normally aspirated engine. What the are doing is no different than what NHRA does by factoring certain combinations in their stock or super stock classes to put similarly powered vehicles in similar classes together.

[TUFCAT]

The formulas for calculating engine displacement have not changed and once an engine is built, its displacement is a constant.

Hemigeno and HPP are correct.     Displacement is a constant. It NEVER changes.... no matter if the air is thin, compressed, blue, green, dry, humid, or smelly.

As a piston travels from BDC to TDC it sweeps through, or displaces an area of volume known as "swept volume" or "displaced volume" (most of us know this as good old fashioned "displacement").  

On any given engine, the area (displaced inside each cylinder by the piston moving from BDC to TDC) won't change...unless a large hole is introduced into side of the block.  This is also known as "infinite displacement".  

 

[Nacho-RT74]

agreed on the therm SWEPT VOLUME is the DISPLACEMENT of the engine. That would be the correct therm and never changes as far you keep same stroke crankshaft. Bore of pistons affects this, due is related with the swept volume on same stroke. What it changes with a blower is the DENSITY of the same volume Vs an aspirated engine

but actuall TOTAL volume can change when you get diff heads, headgaskets and CH pistons. Thats a diff discussion

[TUFCAT]

agreed on the therm SWEPT VOLUME is the DISPLACEMENT of the engine. That would be the correct therm and never changes as far you keep same stroke crankshaft. Bore of pistons affects this, due is related with the swept volume on same stroke. What it changes with a blower is the DENSITY of the same volume Vs an aspirated engine

but actuall TOTAL volume can change when you get diff heads, headgaskets and CH pistons. Thats a diff discussion

Correct!!  

To follow-up to what Nacho is saying, A turbo or supercharger artificially increases cylinder pressure by compressing (or forcing) more air into the cylinders.  This increases the density of air in the cylinder for the compression stroke.

When you compress air, you also get more oxygen. More oxygen allows you to introduce more fuel. More fuel, more oxygen, and more pressure makes a bigger "Boom"!

Compression ratio is a set static factor that never changes. Cylinder pressure can be varied on any given engine, just by changing the induction.  If you want to test that theory, just add a supercharger to a 440 (without modifying the engine) and see how much cylinder pressure you get.  

Dense air increases the volumetric efficiency of the engine and produces extra horsepower and torque. Dense, cool air is the best type of air to compress which is why engine performance decreases in higher altitudes with thin air.  It has no effect on compression ratio, or even displacement for that matter!