4-1 change to 4-2-1

[PG Tips]

Hi guys. Maybe a stupid question but will ask anyhow!

Currently I have a 4-1 system fitted on my 1800 K series with 200bhp+ DVA goodness. 

Looking to change to 4-2-1 for better midrange performance as been advised by the man it's self Dave ( DVA ) 

My question is, is it as simple as changing the cat bypass collector from 4-1 to 4-2-1 or is it new manifold too? 

 

Many thanks

[SLR No.77]

It will depend on the system you have, but in my experience and having had both, the 4-1 collector is a much shorter pipe than the 4-2-1 version which is the length of the cat pipe. If though your 4-1 collector is the longer length it should be a straight swap.

Stu.

[PG Tips]

Thanks Stu. 

Looking at Caterhams parts store the 4-2-1 collector looks almost the length of an 4-1 collector due to extra pipes to reduce it from 2-1. Out of stock though and seems like hens teeth!

https://caterhamparts.co.uk/collectors-catalysts/1066-exhaust-collector-4-2-1-rover-vhpd-fitment.html

[oilyhands]

The R300/R400 and R500 exhaust primaries are in the wrong configuration to be converted to a 4-2-1; the primaries for 2/3 and 1/4 are diagonally opposite one another in the cluster so they cannot be siamesed into a 4-2 section. Check the primaries to ensure that 1 and 4 and 2 and 3 are alongside one another either horizontally or vertically, if they are and your exhaust can is far enough back then a 4-2-1 collector can be fabricated and fitted.

Oily

[SLR No.77]

Good point!

[David_Long]

There will be an 'ideal' specification for lengths and bores of primary and secondary and it is important to keep the primaries the same length. So It depends how much you want to spend and whether you want to get the best possible performance you can, or just an improvement on what you have.  Dave may have the figures and I would suggest handing the job over to an exhaust specialist such BTB exhausts if it is the former.  Typically the exhaust is grouped 1/4 and 2/3 as the firing order  is 1342. I believe the other configuration still works, but is seldom used, and probably not the best option for a performance exhaust. 

[PG Tips]

Oily thanks very helpful and you might saved me from an expensive mistake. 

I will be chacking my primaries some time today.

 

Many thanks

[PG Tips]

Thanks David all great explanation and more I have learned. Fascinating reading mate thank you.

I be checking my primaries and then making decision. The cars performance is great as it is and not sure how much of a difference a 4-2-1 will make. If it's a full sytem is not something I want to stomach right now though. 

Many thanks.