Running a twinscroll on a GC8,I was on an OEM manifold&uppipe,just fitted an RCM,will I need to make map adjustments?
What affect will a different manifold&uppipe have on AFR&boost?

 

Difference in diameter and difference in gas flow will affect it, so ideally a tweak

 

Cheers,I wasn't sure if the pipes were bigger,forgot to measure before I fitted,i did notice the extension bar wouldn't pass the manifold to get to one of the mani to head nuts so must be bigger.
I'll dig the laptop out and do some runs tomorrow if I get chance.

 

I'd say so just for the fact the turbo will spool better and should make a little more boost. Or at the least a different boost graph that will need adjusting. May even be able to wind in a little more timing.

 

Ooh I like the sound of more timing
Sat waiting for bleeding rain to stop,car almost back together.
I'll get a run logged on way to work tomorrow,not sure I'll have time today.

 

Surely if the stock manifold has not become a restriction,

Then switching to a larger diameter type would result in worse spool,

 

Some of the piping on the aftermarket twin scroll manifolds is actually smaller than stock, unless they have made a copy of the updated Tomei big power version. When I was looking most of them on Ebay were based on the older design so I went for the OEM manifold.

Old https://www.rallysportdirect.com/par...-sti-2003-2007

Newer https://www.rallysportdirect.com/par...-sti-2003-2014

 

Yes looks identical to the Tomei one,pipes are defiantly bigger the oem I just didn't measure to see how much bigger,pic below are my RCM,looking at the Tomei possibly exact same with a different badge welded on?

 

https://www.tomeiusa.com/_2003web-catalogue/000_expreme/each-product/gdb-cde_exhaust-manifold_en.html

Old ​​​​version with 38mm diameter compared to stock 42.7mm

 

Thanks for the info there Turbovin
Broke down after quarter mile,luckily had my tablet with me so quick ECU reset and I was away again.
I've been out for a quick drive,took it easy but took it into boost 4th gear upto around 5.5k RPM,bum dyno said a nice increase in torque

 

Tomei, rcm, gt spec are out of the same factory, so all the same with different price tags.
They are also proven better spool and power from stock albeit the big chunky upipes compared to the as performance ones for better spool.
Maybe they have redisigned the later ones for more outright power gains if they are actually fatter or it's just the twinscroll ones due to more gas being flowed through