New exhaust on old primaries

[Andy Lef]

Hi I have an old (25 years) 4-1 exhaust with the primaries sitting outside the side skin.  I am looking for some lower down grunt (1.8 k series with some Dave Andrews pixie dust liberally applied) by adding a 4-2-1 exhaust.  

Question for the great and the good;

1. Can i keep my existing primaries and add the 2 from 4 collector and the 1 from 2 collector plus a new can.
2. or do i need the whole system?  
3. If the old primaries can be left on will the low down grunt still be seen or..............?
   
    Yes I am trying to save money - I've seen the prices that are being asked for a 4-2-1 system!  
   
   Thanks Andy

[Nick Chan]

I suppose its possible to have a new collector made up but really its option 2 and replacing the whole system with a 4-2-1 one I'd say

Nick

[TomB]

Yep, I concur.   You can't swop and change bits around unless you want to start cutting and welding, the systems are designed a whole.  I looked at fitting a larger SLR silencer to this system and the inlet was too short.  If you fit the 4-2-1 collector to your manifolds it will be too long and you'd need a bespoke silencer.  It not a bad system, much better than than the standard exhaust, so your not in bad position for engine mods.          

[Nick Bassett]

Agreeing with TomB - you've already got a pretty efficient system fitted, I'm not sure a change to a 4-2-1 system would make that much of a difference TBH.

A decent polish of the exhaust and removal of the tax disc holder (adding lightness!) would make a world of a difference though! 

[Andy Lef]

Thanks for the comments

Suspect then that to get any low/mid torque gains i will need to replace the original MEMs and put a programmable ECU in (plus RR for mapping)?

Dave Andrews has already provided me with the 1.4 to 1.8 conversion plus a ported head good for 175.  Think i am probably at around 150 no idea what lbs/ft i have.  All i know is that it feels a bit flat until i get in to 3rd and get to about 5000rpm.

Was looking for something more before then so i don't have to hammer it - yes it's a little lazy but the people round here scare easily.

Happy with the old 5 spd box (yes it could be more refined and 1st could be used occasionally so could go BGH but not before i get the lower grunt) money is always an issue.

Also recognise that it might be sensible to go for some sort of TB at the same time as ECU and RR - but £££ as I don't really have the time or nowse to do it myself.

Andy

[Toby S]

A bit of harpic bog cleaner on those primaries and collector with wet and dry and elbow grease will get them back to colour.

I have - the same 4 into 1 primaries although with a VHPD collector (wider bore exit than standard) and VHPD box - again with wider bore inlet and tail pipe - bought it a few years ago off here -  can't tell from pictures whether that's what you got - made a bit of difference on my 1400 Supersport  when I fitted it, but not that much so would agree with #4

Trick with all the k series (especially the smaller capacity ones)  is to keep them spinning at 5,000 rpm plus for any real grunt

 

[TomB]

Your engine project is something I did many moon ago - a 1.4-1.8k conversion.  DVA made me up a new bottom end, then I transferred everything across, inc the Supersport head, to the new short motor, running it on MEMS with new injectors for the first year.  Then I fitted a set of the KV6/ SLR throttle bodies and an Emerald with a mapping session, all with the 5 speed box.  Have you a set of Vernier pulleys on the cams?  Incorrectly timed cams would make it feel flat, and can make a noticeable difference when dialled in properly.  The 1.8k with 5 speed is a good set up on the road IMO - the torque of the bigger engine suits the gearbox much better than the 1.4 did.