...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!
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...
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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.
