A hypothetical question.

[AZ3.8Camaro]

Re: A hypothetical question.

the phrase "there's no replacement for displacement" is just a cute saying that V8 drivers use to sling at the import crowd and nitrous users. It's origins aren't really rooted in design theory

No it is real, the power comes from the amount of air (displacement) you have.
Why do all the F1 guys run the max allowable displacement?
All things held equal, the higher displacement will produce more power. Period.

[Smoke Panther]

Re: A hypothetical question.

All things held equal, the higher displacement will produce more power. Period.

Yea, but in practice, all things aren't held equal. In every context I've heard that saying used, it was always in a derogatory fashion towards someone with a FI 4- or 6-cylinder or someone who uses nitrous. There's more than one way to go fast, so there are replacements for displacement.

[99BlackW68]

Re: A hypothetical question.

well the gas mileage would be terrible since you would have larger pistons and a larger chamber... also... I do think the top end would see an increase, but your torque would be greatly depreciated causing even more mpg falls. I'm thinking out loud just like you, but I keep thinking about having 6 body builders push a car... and then what about 8 average guys pushing a car. The average guys could spread out better and therefore put just as much power into it. I don't know.... are the pistons the same size on our cars as compared to the ls1? If so then maybe its a production issue and this way they cut back on product cost not having to produce two types of cylinders.

no, our cylinder chambers are smaller. do the math 3.8/6 < 5.7/8

[camaroman1181]

Re: A hypothetical question.

an increase in displacement allows for the burning of more fuel. Fuel has a certain amount of energy per volume. So hypothetically, increasing the displacement allows for an increase in power output purely from a chemical view of things..

now, it gets tricky when comparing two engines with the same displacement, but different amounts of cylinders (or engine configurations for that matter)

for a 6 cylinder to match an 8 cylinder in displacement, it needs either an excessively long stroke, or excessively large bore. Or, the 8 cylinder needs to have a short stroke, small bore.

with either the longer stroke, or the larger bore, you are adding rotating mass to the engine. This will put a lower practical limit on the amount of RPM's the engine is capable of. With this in mind, a smaller stroke/small bore will tend to lower rotating mass, thus increasing maximum RPM's.

remember... Horsepower = Torque X RPM / 5252

so if you are able to increase your maximum RPM range, you are able to directly affect the maximum horsepower of your engine, until you max out your intake, exhaust, cam, etc.

you also run into a whole slew of issues when trying to make engines with too much bore/stroke, or not enough bore/stroke...

with too big of a bore, you have issues with properly filling the cylinder, and obtaining a proper quench in the combustion chamber... With too small of a cylinder, you run into issues where the cylinder walls shroud the valves, not allowing htem to work to there peak (as is the case with the aforementioned, chevy 305 v8). with too long/ too short of stroke, you end up with a lot of problems involving side loading of the pistons, and excess piston speeds... there are certain rod length to stroke length ratios that have been found to optimize some of these factors (more on that stuff here -> http://www.rustpuppy.org/rodstudy.htm)

and lets not even get into what you would have to do to make a 6 cylinder cylinder head comparible to the 8 cylinder engine of the same displacement, but with 2 less intake and exhaust runners...

[SpeedingFirebird]

Re: A hypothetical question.

with either the longer stroke, or the larger bore, you are adding rotating mass to the engine.

Why is that? Sure you have to make the 6 cylinders bigger, but you lose two. Is the assumption the increase in beyond linear to give it strength?

Assuming a metal strong enough, would the rotating mass be about the same? If not, then I am missing something.

[Den69RS96]

Re: A hypothetical question.

3rd gen v8's stunk because of smog rules. In the 80's the technology wasn't there and the only way to meet the smog rules was to design lo po engines. Not to mention the cats on those cars were extremely restrictive. Don't forgot most small cars like hondas were making around 100hp. As time went on computers, fuel injection, better cats, and cylinder head design etc advanced greatly and allowed them to jack up the hp while still meeting emissions standards. Computers allow the manufacturers to design/ build better parts and the computer in your car allows those parts to work and still meet emissions. Pick up a summit racing catalog and check out how many cylinder heads are available now for a smallblock chevy. Every single one of them is 100 times better than the best head to come out in the 80's.

[turbohead2332]

Re: A hypothetical question.

Yea, but in practice, all things aren't held equal. In every context I've heard that saying used, it was always in a derogatory fashion towards someone with a FI 4- or 6-cylinder or someone who uses nitrous. There's more than one way to go fast, so there are replacements for displacement.

This is true, however I think you might miss the point of what he was saying. Run FI and juice on a 4 or 6 cyl engine, you'll go fast. But with more displacement, say, a 350, you'll wield more results with the exact same setup. There's more potential with a larger amount of displacement.

[3.4 slow to go]

Re: A hypothetical question.

Ford had an interesting take on this, w/their 289 & 302 v-8's, and their 300 strait 6

also, it's seems very rare that putting a turbo on a sbc gives the same/ as good as result of the turbo buick design.

[camaroman1181]

Re: A hypothetical question.

Why is that? Sure you have to make the 6 cylinders bigger, but you lose two. Is the assumption the increase in beyond linear to give it strength?

Assuming a metal strong enough, would the rotating mass be about the same? If not, then I am missing something.

well, you do have a point there, with the fact that overall, you are only moving 6 pistons and rods, rather than 8. however, each individual cylinder assembly is getting heavier when you increase bore or stroke, simply due to the additional material normally needed to make these happen.

when you look at each individual cylinder, a heavier piston has more kenetic energy moving to TDC and BDC, simply due to its increase in mass. This energy exerts more force into the crank for that particular cylinder, thus reducing the amount of RPM's (piston velocity) that the engine can handle

same thing occurs with increasing the rod length. to obtain the same RPM's as before the increase in stroke, the piston must now move further than before, up and down. This increases piston velocity, thus the energy that is going into the crank.

make any sense?

now, you can fix this by going with different design pistons, different materials, etc, but these routes add cost..

[WishIHad$$$]

Re: A hypothetical question.

No it is real, the power comes from the amount of air (displacement) you have.
Why do all the F1 guys run the max allowable displacement?
All things held equal, the higher displacement will produce more power. Period.

Correct.

There is a reason FI Vipers are kings of the streets.

Ford had an interesting take on this, w/their 289 & 302 v-8's, and their 300 strait 6

Yeah, the 300 I6 had a much larger stroke and produced more low end torque. A 300 V8 would rev much higher and produce more horsepower. To the OP, a 5.7L V6 engine would produce the same tq numbers as a 5.7L V8 if both engines were equally efficient, the V6 would produce the tq numbers sooner resulting in less hp.