punto_matt said:

Jack you need back pressure on an NA. If you have no back pressure then the gasses arent forced away from the engine which in turn looses you power. Believe what redline say all you want but their are plenty of articles about from people with better pedigree in exhaust/engine design than a journalist so i know who im going to believe. There is an article knocking around on mk2 about it.

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I believe that its not to do with back pressure & with the velocity. Back pressure makes it harder for the gases to get out by making it go through loads of bends in the mid/backbox.

GP MATT said:

Well doesn't that make matt right? He has said I would lose power and back pressure like your article said just didn't mention exhaust velocity.

So the outcome would still be the same, get a cat back exhaust with a larger bore than standard but not as big as I said "2.5" as this would lose exhaust velocity so a smaller bore is needed, with a backbox. But all I asked was how to make an exhaust pop and bang lol

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How does it? It says back pressure isnt anything to do with losing power.

Punto.Jack said:

I believe that its not to do with back pressure & with the velocity. Back pressure makes it harder for the gases to get out by making it go through loads of bends in the mid/backbox.

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No it doesnt. Back pressure when calculated properly forces the gases out faster than just having a big **** off bore pipe.

punto_matt said:

Backpressure and velocity come hand in hand. If you dont have back pressure then you wont have any velocity because on an NA car the gases come out the engine and sit in the exhaust. The backpressure in the system then pushes the gases away from the engine which in turn gives velocity to the gases. Back pressure is not imporant on a Turbo car because the turbo pushes the gases out so you want as little restrictions as possible so that the gases can escape as quickly as possible.

Or at least that is my understanding of it.

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I understand what you mean it cant create velocity without back pressure, but there is a way around this don't fit massive exhausts on N/A cars

But according to everything you have just been saying back pressure isnt important so you should be fine to fit a massive exhaust. Stop contradicting yourself.

But as we have established to get exhaust velocity you need back pressure so Redlines "myth busting" section is crap isnt it. Because you cant have one without the other. This is why you take what performance magazines say with a pinch of salt.

punto_matt said:

No it doesnt. Back pressure when calculated properly forces the gases out faster than just having a big **** off bore pipe.

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Well its going to seem that its coming out faster because of the pressure been build up in the backbox.

punto_matt said:

But according to everything you have just been saying backpressure isnt important so you should be fine to fit a massive exhaust. Stop contradicting yourself.

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lol no basically a massive exhaust cant create the right velocity.

This is all very good and well, settle your differences and can you both tell me what would be advisable for my 1.4 8v please? Thanks

Im not wasting my time anymore. Believe redline all you want but they are talking sh*t. Argue the point all you want but i know im right.

No i cant tell you as i dont own a 1.4 8v so hold no interest in what is best for them as i will never need to know sorry.

Basically

N/A cars don't get a massive exhaust.

Turbo Cars get as big as you can.

Lol OML ok no worries, funny though how you both know so much about exhaust but cant point me in the right direction, funny old world. Thanks for your help though

I know nothing about exhaust apart from what i have read which is what i have typed. As i say i cant advise you because i know nothing about what is best for your car. Exhaust design isnt simple or easy and all a place like longlife does is bend the pipe to the right shape.

GP MATT said:

Lol OML ok no worries, funny though how you both know so much about exhaust but cant point me in the right direction, funny old world. Thanks for your help though

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mate, just go to a local recomended custom exhaust place and talk your needs threw with them just tell them what engine you have and what sound your looking for itll be roughly 250-300 for it

punto_matt said:

Im not wasting my time anymore. Believe redline all you want but they are talking sh*t. Argue the point all you want but i know im right.

No i cant tell you as i dont own a 1.4 8v so hold no interest in what is best for them as i will never need to know sorry.

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Okay, what you were saying was right to them not to not get no midbox but i was saying that its not to do with backpressure. Because im sure if a n/a car has a really short exhaust just from the cat no back box or whatever it wouldnt lose power.

James1989 said:

mate, just go to a local recomended custom exhaust place and talk your needs threw with them just tell them what engine you have and what sound your looking for itll be roughly 250-300 for it

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Yeah i was beginning to think this lol ta

It is though :bang:

You dont need lots you just need enough to give you the correct velocity to flow the gas away as quickly as possible. Exhaust should be tuned to give the best flow at whatever revs your car makes its highest power.

GP MATT said:

Yeah i was beginning to think this lol ta

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if it helps the abarth has a bore size of 2 and 1/4 which is what i asked for on my tjet, so just go smaller than 2inch as advised, although id assume aslong as it wasnt large large then back pressure wouldnt be an issue, have you tried searching the internet for what other 1.4 8valvers have done exhaust wise?

tbh none of us are experts but if you go to a decent place and talk it threw with them they should be able to help you can always go to 3places and get an average of what would be best for your needs from their combined opinions.

1.75" maximum.

punto_matt said:

It is though :bang:

You dont need lots you just need enough to give you the correct velocity to flow the gas away as quickly as possible. Exhaust should be tuned to give the best flow at whatever revs your car makes its highest power.

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You just said it there you need the correct velocity, im sure you have ****e design of exhaust that can have back pressure but if it cant create the velocity it wont be effective.

punto_matt said:

But as we have established to get exhaust velocity you need back pressure so Redlines "myth busting" section is crap isnt it. Because you cant have one without the other. .

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Ive just realised what youve said here, you cant have velocity without backpressure. but thats not right because turbo cars dont need backpressure because it restricts it from getting away the exhaust gases.

Thanks for the replies, yes I think I will visit a few exhaust places for the best recommendations as what to have, just wanted to go with a little more knowledge about exhausts, which I now have.

Im thinking 1.5" to 1.75" bore with a sporty sounding backbox with 3" twin tip. All good

Thanks