Gasflowed vs pressure

[berjohansen]

Hi.
My head is in the pressure/flow area theese days and im a bit stuck :) Many people are building integrales, Fiat coupes etc in the 300-400 hp region, many of theese projects are going for all out head prep. Question is, on a turbocharged engine where you can up the pressure and get the same power, what are the benefits of gasflowing/porting?
Im using a twinscroll turbo and manifold from a Lancer evo 6 (wich really convinced me that Mitsubishi took a long hard look at the Lampredi before they came up with the "new" rally engine!)
This turbo has the same efficiency in the 300-370 hp area regardles of boost between 1,2 and 1,7 bar.
You can probbably have 350-375 hp with around 1,2 bar with headwork and 1,6-1,7 without.
Given everything is the same (cams etc) what is the benefit?

Thank you

[Guy Croft]

IT IS BEYOND DOUBT - among those who know - THAT a turbo head effectively gasflowed (inlet and exhaust) with a great valve & seat job will:

1. develop same power for less boost
2. give more power for equal boost
3. suffer lower thermal load on whole engine, intercooler, exhaust and turbo
4. have better specific fuel consumption
5. exhibit far superior throttle response and spool-up

GC

[berjohansen]

Thank you!
Confirming my thougts, my head can move on now :)

[Guy Croft]

the critical minimum pipe length on the exhaust manifold for the record is 17" - but you can just get away with 15".

Less than that and you'll have real combustion problems and the more ex valve lift around TDC the worse it will be.

GC

[berjohansen]

Well the runners seem to be 12-13 maybe a bit more, ill meassure them later, seems a good tubular one is a good idea.
lift atdc acording to spec is 1,12mm.