ST2  Hi Compression, Cams And Stuff - Written Nov ‘04, updated 04/08

In a moment of stupidity I offered a customer a rather silly (or so I thought) price for his ST2 that was in being quoted for quite a bit of work.  He apparently accepted the offer (presented by someone else) without hesitation.  Which was not really what I was expecting and certainly not what I needed.

But, you get that.  As in shit you don’t need.  Well, I certainly do.  So I now owned a 95,000 km old ST2 that needed something of a chassis and engine resto.  The usual sort of high km stuff – steering head bearings, brake discs, chain and sprockets, oil leaks from the cylinder/head join.  When I pulled the cylinders the good old big end oil gallery plug problem was obvious too – in fact, it had wound out as far as it was going to, and was just sitting there.

Once the engine was out and apart and the rods removed the reason for the oil pressure light coming on at idle was apparent, as was the effect – the big end shells were through to the copper.  But, that’s their job, and the crank was fine.  So I rebuilt the thing with all new bearings and quite a few new gears (the one thing that may wear out on these engines) and had the head and cylinder mating faces machined.

Plus I had some basic (ie, cheap) porting done on the heads (2 hours by a professional equates to many hours by Brad and a much nicer job).  This engine had been fitted with some Vee Two 10.5:1 high comp pistons, std size valves and 212 cams about 20,000 km before I bought it by someone else.  And it had the same Staintune carbon mufflers we’d fitted when we sold it new back in ’98.  I’m pretty sure Duane mapped it when the Vee Two stuff went in – he told me about one that fitted this description he had that was a ‘dog’ in his opinion.  Riding this one before I pulled it apart (to the dyno and back for some before runs) gave me the same impression.

One reason for this I would expect was the three base gaskets that had been fitted.  I’m not really sure why you’d fit 3 base gaskets, but I calculated the compression would have been back down to the std level or less.  Needless to say, it went back together with only one base gasket.  I actually had to machine the piston crowns a little to give some more piston to head clearance – I’d say the cylinder head face machining was the reason for this, as both cylinders were pretty much the same.  So it now has a little more than 10.5:1 (about 10.9:1 if it was 10.5 to start with, I was too lazy to check it), some nicely cleaned up heads and the Vee Two cams reset to their recommended 112 degree inlet centreline.

The cams fitted – Vee Two p.n. V2-03-212 - are higher lift and shorter duration than the original ST2 cams.  The specs are below.

 

VALVE EVENTS

DURATION

CENTRELINE

MAX LIFT

I O

I C

E O

E C

IN

EXH

INLET

EXH

INLET

EXH

ST2

29

73

71

30

282

281

112

110.5

11.8

11.4

V2-212

20

65

61

27

265

268

112.5

107

13.1

11.4

Whether or not the cams make any more power I’m not sure.  I don’t think I’d expect a peak power increase from fitting them over the std cams, but I would expect the same top end at least with more midrange and better response.

When I got it all back together (it took several months with a big holiday in between) I rode it around for a few hundred km then went back to the dyno.  Even though they’ve been around since ’97, this was the first time I’d ridden an ST series bike for much more than an after job test ride.  And I was quite impressed.  It goes well, steers rather nicely and stops well.  Apart from the seat it’s a very cool thing.  I’d always seen then as something akin to a taxi previously, but I take that back now – I could very much get used to this one.  Although it’s too fast for my licence in every day use and it wheelies way too easily.

It has also had suspension work done previously too, although I had to get the shock pulled down due to a seized rebound adjuster.  And the general chassis and big service work done means it’s all pretty much new.

For the dyno testing I fitted an adjustable Ultimap eprom I had laying around and just added fuel till I found the max power, the usual procedure.  The fact it need the same fuel before as after is clouded a little by the fact the old fuel filter was so blocked I could hardly blow through it.  Plus I had the injectors cleaned too.

In the end it made the most power with the same fuel added across the whole range for all 3 combos – before rebuild, after rebuild and after rebuild with air filter kit.  Although it would ideally have like a little more around 8,000 RPM with the air filter kit.  This was ultimately remedied by taking the bike down to Duane’s one Saturday and remapping it – both for std air filter and DP air filter kit.  The graph shows before the rebuild in green, after the rebuild in pink and after the rebuild with air filter kit in blue.  Very cool, and my most powerful 2V thus far. 

The big increase with the air filter kit really surprises me.   Sitting on the bike while on the dyno between runs I initially thought it had lost a little and needed more fuel, then I was just disappointed when it didn’t really respond to that.  Only when I got off the bike and had a close look at the monitor did I realise it had picked up about 6 hp.  I’ve never seen an increase that big with an open lid before – certainly not on any of the other ST models.  The minor difference in fuel requirement is fairly surprising for such a power increase too.  The next graph shows torque and air/fuel.

Given this bike now has higher comp than before, I tried provoking it by running it on std unleaded fuel, which is 91 octane in our system.  When I first ran it on the dyno I tried varying max spark (ignition) advance from the std 36 all the way down to 18 degrees BTDC.  I’d show you, but it’s the same line 7 times.  I did the same thing after the rebuild, with the compression notably higher, with the same result.  So there you go – no spark advance issues for this one.  I think the short manifolds and gradual spark advance curve under 5,000 RPM of the injected bikes helps kill the pinging problems the long manifold carb bikes have with their greater low RPM cylinder pressure and single step ignition advance.

The next step was a Ducati Performance 45mm exhaust I’d bought cheap.  It runs 45mm tube as opposed to the std system’s 40mm and has a fabricated cross over instead of the std stamped piece.  In real terms it looks very much like the ST4 system I fitted to the 888, just a bit smaller.  It came with alloy mufflers, but I used the Staintunes already fitted.  The graph below shows the result. 

Again, max power came with the same fuelling with a little extra required around 8,000 RPM.  Green is std headers, pink is DP 45mm.

The speed versus time graph below shows the bigger exhaust was a bit quicker through the mid range - in reality, I think you’d be hard pressed to pick the difference on the road.  Which is a pity, because you wouldn’t buy it just for its looks.  That said, one of the things I noticed when I went to 45mm headers from the std 40mm on the 851 was the increase in response – much easier to wheelie.  I didn’t ride this bike around with the 45mm system so can’t comment on that, but it could certainly be one of those impossible to measure ‘feel’ things.  And, on the up side, I have now sampled the ‘big pipe on a 2V’ thing for myself. 

Compared to a couple of std ST2 the final result does look pretty good.  The final combination is high comp pistons, V2-03-212 cams, minor porting, air filter kit and slip on mufflers.  Not that hard to replicate, and certainly not much harder than the fairly poor result the person who owned it paid for when the Vee Two stuff initially went in.  Which goes to show good components can get a bad name pretty easily when fitted like these ones originally were.

The green is an ST2 with Arrow mufflers and chip, pink is a std ST2 and blue is mine with its remapped eprom.  Looks like a different engine really.

Another thing I tried with this bike was losing some flywheel weight.  The early ST2 came with a flywheel that’s about 1kg heavier than the flywheel on a 900 carb or 748/916.  I replaced the original bolt on weight (it has no trigger on a single pick up injected bike) with one from a 748.  I did this because I didn’t want to go too light – I had also thought of machining the 748 one down – so it still has 1.8kg of flywheel as opposed to 2.75kg std.  Given the results we’ve had recently with 916 and no flywheel weight (not really noticeable at all in low speed riding) I could have gone lighter, but it wheelies easily enough as it is (and it is meant to be a touring bike).

Finally I’ll compare this ST2 to some others models.  Green is this bike after the rebuild with the air filter kit and remapped eprom.  Pink is the demo ST3 with the air filter kit, mufflers and more fuel.  Blue is a high comp 900SS with some porting, air filter kit, mufflers and mapped to suit.  Red is the last 1000SS demo I dyno’d – mufflers and air filter kit.  This ST2 is certainly strong through the middle and the top end loss to the ST3 is not too bad at all for what it is.

So, the only question remaining is - anyone want an ST2?

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