Post
by PeterCrespin » Tue May 07, 2013 12:56 pm
This is a complex issue and there are no hard and fast answers except to say that what the factory fitted is a very good compromise, with scope for modest power gains without changing carb or exhaust types.
It is perfectly possible, however, to fit both Webers and multibranched exhausts and not have dire consequences. The devil is in the detail. Yes, slapping on 'bigger is better' carbs or pipes straight out of the box can certainly ruin a power band, especially for street use. Nevertheless, by doing some calculations beforehand and exhaustive ('scuse pun) setting up afterwards, the best setup for the intended use can be arrived at, depending on the desired outright performance, power band, driveability and economy.
It is inherently better to have one choke per cylinder and one exhaust pipe per cylinder for a certain distance, before 'tuning' the diameters and lengths of each to get whatever performance characteristics one requires. That's why modern engines almost invariably have separate inlet runners, whether they be little commuter vehicles or full-on performance cars.
There's no magic recipe either for or against Utz's suggestions and whereas someone with a standard engine would be very well advised to keep it that way, with the mods Utz has already done I'd say a set of narrowish bore long primary headers into decent collectors and absorption silencers would give him a strong engine with plenty of tractability in excess of standard if he keeps the Weber choke sizes at the lower end. Wider headers with bigger chokes will make it fussy around town but fly on the track. Both conditions assume ignition and fuelling are optimised on a rolling road or by extensive development testing. a standard engine in good condition is an excellent compromise but he's past that point already.
Pete
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas
The site is available in German as well.
