K series 4-2-1 exhaust manifold gains

[jody391]

What power increase do the 4-2-1 manifolds give?

on my Elise (std apart from 135 cams) the smaller bore 4-2-1 manifold gave a great increase of mid high end power torque, no dyno figures to show this but my butt dyno showed great improvements.

I also tried a large bore manifold and this was a huge down grade on my engine spec.

I’ve just fitted a 52mm throttle and 135 cams to my 1.6 K caterham and this was my next upgrade choice.

interested in the results people have found.

[p.mole1]

I fitted a 4-2-1 manifold to my 1.4 ss and it made it worse due to the primaries having a too large bore size, so stay away from anything made for a large powered 1.8. 

Try the Supersport cams they seem to give a good increase in power combined with a Emerald K6  or you may be able to get your MEMs Rover ecu reprogrammed if it is the later model 

[p.mole1]

Have a look at the DVA web page, it tells you everything you need to know about the K series

[jody391]

Hi mate, as mentioned I’ve been there and done most on my Elise 1.8 so understand the primary bore size issue.

I fancy making my own, so I might have a play.

[SM25T]

Fitting 4-2-1 to our 1.8 VVC k-series gave better mid range performance for sure. 

[p.mole1]

You might get lucky with Caterham spares? I tried looking everywhere but couldn't find any 

[john milner]

On 26/10/2023 at 11:45, p.mole1 said:

I fitted a 4-2-1 manifold to my 1.4 ss and it made it worse due to the primaries having a too large bore size, so stay away from anything made for a large powered 1.8. 

Try the Supersport cams they seem to give a good increase in power combined with a Emerald K6  or you may be able to get your MEMs Rover ecu reprogrammed if it is the later model 

How does a large bore exhaust degrade performance?

[p.mole1]

Hi John,

If the primary bores are too large for the engine size, it slows down the gas speed and the exhaust scavenging is reduced and reduces the horse power.

That is probably an over simplification, but there is generally an ideal size of exhaust for a given engine capacity/ power output to obtain best results.