Originally posted by: RGN
Originally posted by: chris7b
There is no replacement for displacement =).
Yeah there is, its called boost. Look at the Mustang Cobra for a fine example. SRT4, WRX, EVO for others.
Nope, no replacement for displacement. So what you can match a NA V8 with 40 lbs of boost in a smaller engine, look what happens when you run 40 lbs of boost on a V8 you get 8000 HP top fuel engines that run 4 second 1/4s
Holding the fuel type constant, there is going to be a maximum heat and pressure threshold that you can hit safely without detonation. With 93 octane pump gas that is about 18-20 lbs of boost. Once you are done adding boost and you can't add any more what else can you do? You can increase displacement without passing that threshold, and that added displacement? Guess what, it is also boosted to that limit.
What do you think makes more power, a 2.0L boosted to 20 lbs, or a 4.0L boosted to 20 lbs? Given the same fuel and same cylinder pressure limits, the fuel mixture density is going to be constant, so even under boost, the engine with more displacement is going to be burning more of that boosted increased density mixture, thus making more power than the smaller engine.
What contains more fuel (thus more power): a 2L jar compressed with 34.7 psi of air fuel mixture or a 4L jar compressed with 34.7 psi of fuel mixture?
Understand that, and you'll understand the true meaning behind the saying "there is no replacement for displacement"
PS: most of the high horsepower import cars running high horsepower numbers are doing so at 35lbs of boost on 116+ octane leaded race gas without cats. Ie: they aren't street legal without the cats and not practical daily street cars where you cant pull into any corner mart when the needle is on E and gas up with 116.
1000 HP 3.0L Supra's only make a still awesome 600 HP at 20 lbs on 93 octane, but 4.0+ liter engines also running 20 lbs on 93 octane can make over 800 on the street on standard pump gas People looking for more power bore and stroke the 2JZ to 3.4L and the 3SGTE to 2.2L. Why? No replacement for displacement.
This is the reason I will be upgrading my 281 Cobra engine to a 324 in the future. All else held constant, including boost, it will make more power. Blown engines like 4v DOHC and they love being stroked since the benefit of boost occurs most between the halfway point to BDC where a non boosted mixture has already stopped expanding violently at the critical 90 deg rod angle where the work advantage of the piston is highest. Stroke and boost work hand and hand to make crazy power, and increased stroke is increased displacement.
Repeat after me: There is no replacement for displacement.