I am looking to go to a bigger turbo and am thinking about making a tubular header that uses the twinscoll method.
So the cummins firing order is 1-5-3-6-2-4
the idea is to divide the cylinders into two groups so you don't have one clyinder opening while another is just finishing it's exhaust stroke and having hot air forced back in.
so if this makes any sense which cylinders go well together? thanks



EXAMPLE
The concept is to DIVIDE or separate the cylinders whose cycles interfere with one another to best utilize the engine's exhaust pulse energy.

For example, on a four-cylinder engine with firing order 1-3-4-2, cylinder #1 is ending its expansion stroke and opening its exhaust valve while cylinder #2 still has its exhaust valve open (cylinder #2 is in its overlap period). In an undivided exhaust manifold, this pressure pulse from cylinder #1's exhaust blowdown event is much more likely to contaminate cylinder #2 with high pressure exhaust gas. Not only does this hurt cylinder #2's ability to breathe properly, but this pulse energy would have been better utilized in the turbine.

The proper grouping for this engine is to keep complementary cylinders grouped together-- #1 and #4 are complementary; as are cylinders #2 and #3.

 

The stock manifold has the split in the middle for that reason. Grouping the rear 3 and front 3 do that for you as you are essentially having 3 cylinder engines the valve opening events should not overlap on the 3 grouped together.

With the firing order you have 120° between firing events. Grouping only 3 cylinders on every second firing event gives 240° between pulses. Valve profiles on the cam might be around 240° give or take a few. So essentially the stock manifold does the job of splitting but just doesn't take the time to make equal length header tubes to make the pulses arrive at the turbo at equal intervals.

Hope that helps.

 

yeah thats moreless what i was looking for thanks