Quote:
Originally Posted by mcrews
jtbo,
You cant dispel a 'myth' with a non-documented article by someone with no last name.
niky.
I am sure there are a lot of 500 hp engines running 2". The dameter size is rcommended of an optimal size given the max hp being run.
just like you can run 2" with a 90hp motor. you just wont be optimal.
The point here is that posters keep providing their 'personal' experiences saying larger is better. It's not. period.
If a poster disagrees with this chart, then find a chart(or study) to disprove it.
It really is that simple.
And all the talk about the exhust manifold is all well and good, except noone is going to go uot and buy a tuned manifold. they are just going to fix the pipe and muffler.
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Let's do a little search, you can pick any number of sources from this search:
https://duckduckgo.com/?q=backpressure+myth+stroke
Understanding how engine and exhaust system works is crucial when planning exhaust modifications or changes, so much is done because it is always done and because there are beliefs.
Also it is important to understand why backpressure is a myth and why smaller exhaust is good only for noise reduction side, same goes for bigger exhaust pipe, it often is just increasing the noise and as we know, noise = power, at least if you go to any parking lot and listen to teenagers and their cars.
There is difference with carburetor and fuel injection, with carburetor you can go too well flowing exhaust if carb is not tuned right, it is much more sensitive system.
People often can't separate different needs of fuel injection and carbs, there are really lot of such myths living partly because of that, even race car suspension building has lot of myths that are taken as a truth as everyone always has done so and has won.
I have not found anything that says that backpressure would be needed, other than opinions of individuals. When building 2 stroke engine, there backpressure plays important role, but that is about it, even with carb car engines don't really need it, but if those are tuned for restricting exhaust, then it would be needed to adjust carb to match new condition if exhaust is made larger, but often even that is not needed as exhaust often are not very restrictive.
Exhaust manifolds are there around 150 I guess? Custom made bit more?
I would put my money on that, not the rest of exhaust system if rest is still ok condition.
But that backpressure being myth is common knowledge, imo.