How Much More Power Will A 3-Inch Exhaust Give Compared To 2.5-Inch?
We all know a wider, less restrictive exhaust should give more power, but how much difference does the jump from 2.5 to three inches give? The Engine Masters guys from Motor Trend performed some tests to find out
Growing up on a diet of World Rally Championship highlights and lengthy Gran Turismo 2 sessions, a life in cars was as good as inevitable for Matt.
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Lets be fair, we’d be happy with 600hp…
Clarkson doesn’t think the same… LONG LIVE THE POWAAAAAAAAAAAAAAA
agreed, especially if you live in australia where they have noise restrictions on cars, which can get them defected if they are too loud. so in the long run having the full exhaust is more beneficial not only to save money on “repairs” to pay for the removal of the sticker, but also saves your hearing a little which is good, means you get to enjoy the sound of hairy engines for longer
Watched this last night. Love the stuff over at motor trend (mainly Roadkill, Hot Rod Garage and Engine Masters) and it was interesting to see that the differences your talking are only a few %…..
Euro people be like a carb , what is that?
Not necessarily. Old Euro stuff have carburettors too.
One of many reasons why Europe is f##cked with all those restrictions
Murica be like 21st century, what’s that?
Does Dellorto say anything to you?
HAHA, you’re funny. Oh wait, the carburetor was invented in Europe. We use fuel injection for decades… It’s called progression. ;)
Nice and very informative video! Do you guys think this makes a difference on a 200BHP 2litre 4 cilinder N/A engine? It will obviously will be less of a difference or would it be no difference at all when you’re under a certain amount of horsepower?
That depends on the exhaust gas flow of the engine. The more cylinders and the higher the displacement, the more exhaust gas flow. On a 2.0l 4-cylinder engine, using a 3 inch exhaust would probably give you less power as the system has no back pressure anymore.
Its all about gas flow though.
A really simple and easy way to compare restrictions in the exhaust is to compare cross-sectional areas. Remember (and they said this in the video) that the relationship is squared, so a small change can make quite a large difference.
A 3” exhaust has an area of 4560mm^2
A 2.5” exhaust has an area of 3167mm^2
That 0.5” just caused a 30% restriction in the airflow.
Also remember the engine in the video has two exhaust systems (one for each bank of 4) so would need to approximately half their figures before comparing to a 4 cylinder engine before making any decisions.
Interesting for V8, but we can’t use this test to say that on any engine there are on earth, the 2.5 will be worst than the 3. Back pressure is really important, for some engines it provides more power at low-mid rpm than 3” exhausts. The 3” will always perform better at high rpm, it’s a fact, but depending on the way you use your car the 2.5 will be better. For me, i stayed in 2.5 to have quick boost, because i usually use my car on tiny curvy road and gravel/dirty ways. 3” would be very bad in my case.
As far as I know you don’t need it for turbo fitted cars because the turbo provides enough resistance. I also went 2.5 inch because it’s less noisy and I already make enough noise as it is when I drive trough the neigbourhood.
Back pressure is not something you want and they mentioned it in the video. What you want is the exhaust to flow fast enough for the scavenging effect to work properly, smaller exhaust=higher speed and bigger exhaust=lower speed. The optimal exhaust would have zero backpressure and high exhaust speed but that is impossible. An exhaust that is smaller will give better power down low but it’s not because of the backpressure but because of the exhaust gasses traveling fast at low rpm which you wont have with a big exhaust. A car with a turbo will always work better with a bigger exhaust and less resistance because the scavenging (if there even is any, depends on manifold) happens before the turbo and it is a big resistance.
I want that on my Honda😎
Also remember, this a 600 hp motor, not a 4 cyl making 200. 3 inch might not always be the better option.
thesmokingtire podcast had a really good talk about it when the magnaflow engineer was on. The explanation is exhaust velocity drops. There is a fine point between “too small” and “too big.” Too small and you’re not getting the throughput you need at higher RPMs. With too big you aren’t getting the exhaust velocity you need and its actually losing power at lower RPM.
Yeah, cuz we skipped from steam engines and went straigth to electronic fuel injection, bypassing carburators… :-|
you need to mach the exhaust to your engine,a massive 3 inch exhaust won’t do anything ona 1.1L 4 cylinder Peugeot like mine, however i think it wouldn’t be as bad on my 3.0L V6 Ford Capri
I think even for an Essex engine 3” is probably overkill… When I had my scimitar it had twin 2” pipes and those were ¼” bigger than standard and it ran sweet. It’s not like the Essex makes huge power or revs that high and it’s a bit of an anchor by today’s standards but good fun in an old scimitar or Capri :-D
That laugh when he walks away after making car sounds in the muffler