Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) 4/4 Sigma 1600 Sports manifold and cat.

I have a 300 cells metal cat which works like a ceramic one regarding the efficacy but with a better flow. I never have smell in the car. To your question the longer the pipes the more are the lower revs enhanced you can read in the net. My manifold maker says the opposite, I don‘t know who is right. My manifold works good in the middle rev band.
On the other hand, I have a 4-1 manifold which is more suited to push the upper revs. Your both versions are 4-2-1 obviously amplifies the lower an mid section...al that is readed stuff and I cannot proof it.

I also have read a lot of contradictions in the net. I am not sure what is for which intention the best way. Better you dig in the net yourself.

The design of the Librands 4.2.1 manifold makes the most of the low dynamic pressure from the preceding exhaust stroke evacuate the gasses from the current exhaust stroke as efficiently as possible. Having long primaries negates this 'advantage' at lower RPM...

I also preferred the smother 'turn' into the '1' collector pipe of the Librands manifold compared to the tight turn of the Aero Racing version. My previous experiences with manifolds on the 1.8L 'K' series engines in the Lotus Elise, drew me to the similar looking manifold from the same manufacture (Janspeed) that Lotus had used the 4.2.1 manifold on the higher power Elise/Exige S1 versions.

My 'seat of pants' detector felt a noticeable difference in power and mid range torque, once I had the Librands fitted. I would have thought that the 'Aero Racing' version would give a better advantage with power at the higher RPM's...

Anyway! I am a happy camper with the result!

Either way, either version is worth some Torque/BHP increases :>) MUCH better than the OEM 'bagpipe' that is a free flow 'disaster'!

Interesting information pete757. Agree about the OEM being a free-flow disaster and like your description of it as a "bagpipe".

There is so much science around exhaust headers - I had no idea but as Heinz suggested diving into the web does give hours of reading.....

In many ways driving it is all the evidence needed. I too am a happy camper.

Pete757 - you have come to a 4/4 from a plus 4 haven't you? I'd love to know the differences as you see them and how they compare - have you had the ECU remapped by the way?

Nothing beats research on the internet for stuff like this!

There are so many thoughts on 'header' design... it's really specific to the application. For our cars, something for most people has to 'work' all the time... without any 'how to drive a car changes'! The Honda Civic 'Type R' was a great example of this... bugger any torque below about 4,000 RPM, and all the power above 6,000 RPM! But if you were minded to drive it as it was designed (for a 'petrolhead'!), it was great fun! Revving the nuts off it with WOT up to 8,500 RMP... and the Honda S 2000 was even better... up to 9,000 RPM!

I noticed a HUGE difference after fitting the LIbrands manifold. Today I had the 'Williams' re-map done... I have now driven about 200 miles with it and have found it hard to tell any real difference, aside from a willingness to rev cleaner up to 6,500 RPM and also generally a smoother power delivery. Which is nice, so it has been worthwhile doing.

Re the comparison to the 'Plus 4' that yes, I did indeed own before 'upgrading' to my 80th Anniversary 4/4! The GDI version which I had, yes it has more power of course, but then it's also quite a bit heavier. So overall, I would struggle to actually feel that difference. But the 4/4 is so much lighter, it's much more fun (IMHO) to drive! Smaller, more responsive, and the Sigma revs very freely... it's such a nice experience!

I would love more power... I think about 160BHP would be perfect. Not too much to then maybe need the 'anti-tramp' bars or leaf springs, but enough to sing and breath more. Caterham have done some great stuff with their Sigma offerings...

Watch this space... I have some irons in some fires! I don't want to go for TB's... a bit to extreme for me as I will not be 'tracking' my car, even though the noise is addictive!

Hope this has been useful!

Cheers, Pete >)

Great choice of car & I enjoyed your observations. Here are some thoughts for what they are worth:

1) If you think your Sigma revs freely now, wait until there are a few more miles on the engine. They are quite tight from new and do get even better...

2) I'm not sure that Throttle Bodies are extreme on this engine. Noise wise, I don't find the induction sound intrusive. Maybe if you had individual foam socks on the trumpets, but with a backing plate and a large foam cover, it's there in the background but only at higher revs. (In any case, it's on the passenger side... )

3) Driveability wise, the TBs do impart their own personality, but probably not for the reasons you expect. There are two aspects to be aware of. Firstly, the (OMEX) ECU mapping of the cold start is a bit crude, so the car is a bit grumpy and needs a slightly firmer touch of throttle for the first few minutes/miles, but thereafter it's as smooth as you'd want. Secondly, TBs require the replacement of the standard fly-by-wire throttle position potentiometer with a good old fashioned throttle cable (with the ECU TPS signal taken from the butterfly linkage rails, not the pedal). The kinked routing of the throttle cable and the strong spring on the butterfly linkage does give some 'stiction' feel at the pedal. It's not a bad thing, just a more mechanical feel with a distinct increase in pedal resistance as you go from a tiny throttle opening (ie parking, crawling in traffic) to a proper prod at the pedal. Actually, I like that mechanical sensation as it helps prevent over-eager inputs, but it's not as light on/off throttle as the standard pedal set up.

4) Overall, I'd say the TBs exaggerate the existing characteristics of the Sigma (rev-happy, more power than torque, very vocal in the last 1,000 rpm) rather than changing its nature. Miles per tankful unchanged, which was an unexpected bonus.

Downside is the cost - though you can throw a lot of money at the Sigma engine (fancy cone filters, cold air induction pipes etc) and still be left with a restrictive and heat-soak prone plastic inlet manifold. Tbh, if 160bhp is your goal and you can afford the outlay in one go, it may ultimately be more cost effective to start by junking the whole plastic inlet system.

Thats great info, thanks!

I also got Williams to fit their ITG induction kit which seems good value for money and has certainly removed a lot of the restrictive plastic/heat prone OEM induction set-up. However it's still sucking in warm air from being adjacent to the top of the radiator... I am going to have a look at mitigating that!

Yes... TB's would be great... but it's an expensive upgrade! I think I would then also want some more 'aggressive' cams and port the head as well... the usual 'slippery slope'!

BTW, how are the TB's without the 'pushed out' side cowl air intake as per the ARP4 and the P4 SS?

Cheers.

Regarding placing of air-intake this very informative link - with Utube video - shows just where the air flow goes around a morgan and may help with positioning the air intake.

https://www.wolfperformance.co.uk/faq-s.html

A recent long drive with masses of dead bugs on the car has confirmed the findings in the video - this helped me locate a decent position to place the intake to obtain max air-flow.


I went for a flexi aluminum pipe from the standard air box ( with K and N filter fitted) down to a long slim air scoop mounted at the base of the radiator. I guessed it would maximise air flow - ram effect and also be sucking colder air. Seems to work really well.

I had the re-map done first ( Wolf version) that made a huge difference to the power delivery - smoother and more responsive. The manifold and cat came later - again a noticeable hike in pull from 2000rpm and even keener to rev. More noise however - that's down to personal taste but I think a quieter tail pipe trim may be needed!

Good point about miles and the Sigma - they do get better with miles on. A gradual sweetening of the engine.

I would be very tempted to use STBs. But in the end they were the main reason why I sold my P4SS because they are very cutting in the ear at low medium rpm when you have an LHD especially on long trips which we like to do. As a passenger in my car it was much smoother because the hood and engine are a barrier. So soundwise it‘s OK for a RHD.
Does VCT still work equally well with the other ECU and STBs on the Sigma?

I love the sound of my throttle bodies on my rhd P4SS Heinz..
and if any thing I would welcome more induction roar !!!

Would individual foam trumpet filters sound different to the full size foam filter I wonder ?

I think so! But it would be hard to sense the VCT in operation because the Sigma isn't designed to give a noticeably 'cammy' delivery - though on TBs you do get a more urgent rush in the last 1,000 rpm of operation. (By 'cammy' I mean that there is not a discernable powerband or jump in delivery at the point in the rev range at which the cam timing/profile changes, such as you can feel with a Honda N/A VTEC engine for example).