Exhaust Design - Backpressure question

Moderator: Other Ford Moderators

User avatar
Posts: 258
Joined: Thu Jun 02, 2011 3:18 pm
Location: Somerset West, Western Cape
Make: Ford
Model: Bantam
Type: ST90+
Year: 2009

Exhaust Design - Backpressure question

Postby Eon » Wed Feb 24, 2016 4:49 pm

I've come to notice that the exhaust shop that originally installed my exhaust had no clue about how backpressure (or the lack thereof) influences power delivery on an NA engine.

I have a 50mm 2-box free flow Cowley stainless steel system with a Steve Wyndham Racing 4-2-1 branch and no cat.

Now while the system sounds great, I'm suspecting that it might be a bit too large for my 1300cc engine. I have also found out that the branch was designed to go with the standard 43mm exhaust, and that I am actually sacrificing precious torque by going thicker. After doing some research it appeared that a 50mm diameter exhaust is better suited to engines with a capacity from 1600cc.

Now I'm contemplating to replace only the section between the branch and the first box with 45mm tubing.

Would this be an improvement, or should I replace all of it? Opinion on the effect of a 'step-up' at or just before the first silencer box would be appreciated!
'09 Ford Bantam 1.3i

K&N Apollo Induction Kit + CAI
266' Cam
SWR Branch
Ported Cylinder Head
Unichip Q
Cowley 50mm Free Flow

EX - '00 BMW E39 M5

Tubi Rumore Exhaust
TNT Branches
Xcede Software
Bilstein B14 PSS Coilovers

User avatar
Posts: 489
Joined: Sun Oct 04, 2009 12:42 am
Make: Ford
Model: Fiesta
Type: ST210+
Year: 2005

Re: Exhaust Design - Backpressure question

Postby moe676 » Wed Feb 24, 2016 9:16 pm

My personal opinion I think 50mm is fine considering what mods you have and you being at the coast
Current : 05 FIESTA ST 210+

FR&R Dyno 21/03/14 : 145whp 171nm
K.A.R Dyno 07/06/14 : 107.4wkw 175 nm
FR&R Dyno 18/06/15 : 160whp 161nm


Return to Ford Performance Mods

Who is online

Users browsing this forum: No registered users and 3 guests