Following on in our series of parts tests so you know what does and what doesn't work, we come onto the subject of TS1 manifolds. There are only three different systems available - the standard TS1 manifold which comes supplied with TS1 200 and 225 kits; the MRB cast replacement manifold; and the MRB 6-petal reed block conversiaon manifold.
There are several reasons why MB Developments decided to manufacture the alternative manifolds. The replacement MRB manifold is machined with a chamfer and countersunk fixing screwholes so that frame clearance of the manifold is improved. The manifold entrance has been re-angled slightly so the carb doesn't touch on the toolbox and less of the panel requires cutting away. The final alteration to the design has been to add internal gasflow "fingers" to smooth the passageway of gas through the manifold into the reed block. All the modifications are improvements that can be tested in practice except the alterations to aid gasflow which must be checked in a back-to-back dyno test or not at all.
The spec of the scooter we used was a mildly roadported TS1 225 with opened and matched engine casings. The exhaust was an early PM Tuning type (loud!). Reedblock is Yamaha YPVS 350 with single piece high power reeds. Once we were happy with the way the engine was running on the first manifold we took a power reading in third gear only then dropped the motor to change the manifold leaving everything else as before in terms of carb jetting etc.
The results of the test are in Graph 1. The blue line is the standard manifold and the MB manifold is the black line. As you can see, with this engine set-up there is little or no performance change with either manifold and despite minor fluctuations, to all intents and purposes the results were identical.
The second test was on the MB 6-petal reedblock manifold conversion. The aim of this conversion is to allow the use of a larger 6-petal rather than 4-petal reedblock on a standard TS1 barrel without any modifications. The Japanese have moved in favour of 6 and 8 petal reedblocks in recent years because the theory is that a lot of smaller, lighter petals are easier for crankcase pressure to lift than fewer, larger, stiffer ones and hence you get better crankcase filling. The MB reedblock conversion was designed to have several advantages over the original set-up; firstly various proper carb rubber sizes are available to allow use of a good range of different carb sizes and secondly the absence of a reedblock sat close to the piston allows the free flow of gas to pass to the rear boost port.
The actual results gave a bit of a different story though (see Graph 2) with the 6-petal manifold giving over 1 hp less over much of the rev change, which was a bit disappointing. We think the cause of this reduction in power is that despite the theoretical advantages, moving the reedblock away from the barrel creates a large area behind the reeds that effectively increases the volume of the crankcase, reducing crankcase compression and pumping efficiency. These results were borne out by an earlier independant test on Mike the Bike's racing scooter. However, several other machines are being raced on these reedblock manifold conversions with some success, so it appears to be horses for courses!
The whole reedvalve inlet system is a complete minefield where there are so many different options; types of reedblock, number of petals, types of petals, thickness of petals, position of reedblock etc. etc. but there is very little reliable information on what is actually best for what, leaving all the individual motorcycle and scooter tuners to make up their own minds as to which set-ups are best.
There appears to be a strong case for putting packing plates (usually 6mm) under TS1 reedblocks particularly on 225's, because on the standard set-up the reed petal can actually touch the piston and the reed stops mask the transfer boost port. Spacing the reedblock away by 6mm should allow the boost port to breathe properly but unfortunately we didn't have the time or parts to allow us to test the motor with a pack plate fitted. Maybe next time.
STICKY
An MRB replacement TS1 manifold costs £22.14 inc. VAT; a 6-petal conversiion costs £117.52 inc. VAT; with a choice of different rubbers from MB Developments, 01709-869756.
Standard TS1 manifolds are available from AF Rayspeed (01944-70693) priced £16.81.