What Size Pipe?

[SIKE30 0]

Hi i got a 318i with a m10 engine. does anyone know if i changing tha size of the exhaust pipe will giv me any power gains? if so what size pipe wud u recommend? thanx

[bmwsparkle 3]

2 to possibly 2 and a quarter would be plenty on a m10. Much more and you'll probably loose power.

[Surge 1]

Tubular headers would do that engine a world of good, infact any engine that comes with nasty cast iron pieces factory. Seems almost pointless fixing a problem further down the line when the block is at the top. 4 Cyl headers would be cheap to make aswell.

[petone 0]

Yeah but by the time you've spent the money on the exhaust you could be half way to putting a 2.5 in

I have a 2.25, didn't do sh*t for power, just sounds better.

BTW: This has been covered heaps, search.

[Gus 5]

bmw manifolds are surprisingly good....i gained power (bum dyno,maybe not power but it feels better/faster) moving from headers/2.5" to stock manifold (facelift 2.5) /2.25"

too big piping reduces the heat in the exhaust and therefore gas velocity...

advice....leave most of piping, maybe change rear muffler for look/sound and if needed rear half....leave the front half alone

[bumpstop325 0]

Thats why header are more effective when they are wrapped in heat wrap.

The natural exhaust heat is to help do two things.

Maintain exhaust temperature inside the pipes for maximum reat retention.

Aside affect of this is reduced engine bay temp. This will have other positive effect.

The thing to remember is that with normal unwrapped exractors. Airflow around the pipes is increased. Therefore, faster cooling of the pipes and warmer engine bay? Sound like you Gus? That reminds me are those the non-HPC coated ones?

Make some extractors out of steam pipe. These are designed to keep heat in. But bear in mind they will be heavy, FUh Raze!!!!

[bmwsparkle 3]

More likely, as we could see from the pics of that manifold, they were a sh*t designed non equal length free flow, sh*t designed free flow or extractors will often give a power decrease, but believe me, the stock manifold is a peice of crap. Theres big gains to be had with a decent researched free flow or equal length extractor.

Also, stock bmw mufflers from the 80s are shockingly restrictive, god knows how much I gained when I chucked my exhaust on, and its not even the best I could have went for!

[Guest Andrew]

More likely, as we could see from the pics of that manifold, they were a sh*t designed non equal length free flow, sh*t designed free flow or extractors will often give a power decrease, but believe me, the stock manifold is a peice of crap. Theres big gains to be had with a decent researched free flow or equal length extractor.

Also, stock bmw mufflers from the 80s are shockingly restrictive, god knows how much I gained when I chucked my exhaust on, and its not even the best I could have went for!

By big I assume you mean around 20 hp - which i what I gained with properly made headers.

Its hardly bang for your buck.

[bmwsparkle 3]

More likely, as we could see from the pics of that manifold, they were a sh*t designed non equal length free flow, sh*t designed free flow or extractors will often give a power decrease, but believe me, the stock manifold is a peice of crap. Theres big gains to be had with a decent researched free flow or equal length extractor.

Also, stock bmw mufflers from the 80s are shockingly restrictive, god knows how much I gained when I chucked my exhaust on, and its not even the best I could have went for!

By big I assume you mean around 20 hp - which i what I gained with properly made headers.

Its hardly bang for your buck.

Yup thats what I meant. Isnt that the same sort of hp that you got out of a link? Or did you get more.

Are yours free flow or an equal length extractor andy?