Hey peeps.What are the merits of this?Is it worth it on a race bike or just a waste of time.Also tyga state just to raise the exhast port to 28mm or there abouts.Has anyone done this what were the gains?.(its for my race bike next season,more SV's about)

Single rings pistons have less friction, but the trade-off is ring life. The top ring always wears the fastest. and if there are two, you get alot more life.

The NSR exhaust port can be effectively changed. The top of the exhaust ports are angled down on the sides. If you make them straight across, matching the sides to the height of the middle, it puts the porting much closer to where it should be (more blow-down timing). Dont raise the existing port height more than about .5mm, you may be disappointed in the results.

Also, dont bother polishing the exhaust port. It really does nothing for power. And dont bother with the port where it transfers to the pipe. Alot of guys hog this out to match the pipe diameter, but in my experience it does nothing but hurt low-end / midrange power with no gains on top. It makes the bike feel more peaky, an illusion of more power, but nothing is actually gained.
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Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS

Just an idea..
You could go further on the exhaust provided you change the blow-down value and alter the transfer height.

I run around 76-78degrees on a 350 twin, 4 / 5 mm on the exhaust from stock and a lift on the 2 forward transfers of 1.5mm but extensive cutting of the liner lower is needed to optimise the transfer volumes. Works a treat - masses of low down grunt, huge midrange and top end. The motor effectively has no real powerband as such. The concensus from the 'in the know' community was that it wouldn't run.... however, the reality is something quite different. Dead right about the polishing - waste of time. Matching the port end to the pipe works well on older, crude strokers bus can't say on the H-Honda !

Mind you, there's bound to be useful gains from matching the barrel to each crank case and working the transfer lowers etc..

There's my 10p's worth

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These aren't the droids you're looking for.

Thanks wrench.So what gains could i expect with that port mod?.I need to keep up with the SV's as its getting harder to draft them these days.The NSR does seem to be a bit down on the top end ponies especially at Pukekohe with its long back straight.Thinking about the VHM/JHA kit heads might help a little.Just a bit cooler and easier to set up the squish.

What pipes are you using? Out of all the mods I have done, the pipes made the second most dramatic difference (the overbore being the biggest). And that was just a switch from the early JHA versions to a set of Tyga GP's.

Just cleaning up the ports and modding the exhaust as I described doesnt make a huge noticeable difference. But here's why: the biggest difference felt starts at 6k, and that difference will go all the way to 12k. Because the midrange is beefed up, the peak doesnt feel much higher even though it is.

Also, what are you setting your squish at? Going less than 1.1mm with the stock SE/SP combustion chambers puts the compression ratio and squish velocity less favorable for peak power and more prone to detonation. If you want to stick with .8mm like the GP bikes, you really need to reshape the combustion chambers. I had a 2000 HRC RS250 that had stock combustion chambers almost identical to ours, but the modified spares I had with lower CR and narrower squishband were much better on the track (and much more reliable).

Also, the stock airbox is a peak power hindrance. Not just the airbox itself, but the rubbers between the carbs and the box. Open carbs and a pair of those cool bolt-on venturies for the NSR are probably the best way to go for power, but you risk engine damage from unfiltered air. I have my airbox heavily modified, and it works just as well as open carbs now, while still using a filter.

And finally, jet kits. I am no fan of the jet kits for the NSR. I have tried them (using the stock oil injection system) with nothing but poor results. Major spooge out the pipe (too rich at low RPM) and degraded midrange power. The best way to go is to get adjustable needles and tune all the circuits as you normally would, retaining the powerjet system.

Almost forgot: reeds. I have found nothing that works as well as the Tyga (or equivalent) Carbon fiber reeds on the stock cage. And I have tried all kinds of combos. The carbon fiber reeds are the only ones that kept my engine from falling on its face at 11,500 without hurting midrange, regardless of my engine/pipe/intake combo. If you can get a set of V-force cages that will fit, or a larger reed cage assembly like the HRC RS250 uses, that may be the only better alternative. I myself am searching for a set of V-force cages that will fit our bikes.
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Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS

Not sure what the pipes are they look like early ethos pipes they made a huge difference.Will be ordering some Tygas in a couple of weeks time.This is my first race season on the NSR just got out there and raced to start with have done some work on the forks and replaced the rear suspension .But the bike was going well but one of the guys here has a super trick Aprilia rs 250 it is way quick and he leaves me for dead on the straights.So i need some more ponies.I have not set the squish on this bike yet but what you say is spot on I just need to go out and set it up.The VHM heads are i belive set for .8 set up.They are very similar to the rs heads and come in two parts they look like they will do the job and have center plug placement.
As we speak i have just piked up some large blocks of polystyrene.These are to make a large volume air box.Just get the shape i want then wrap with fiber glass and dissolve the inner.The carbs wll sit inside this airbox.
At the moment am using the tyga blocks with spacers and stuffers this NSR has bags of over rev also using a lightened flywheel hrc head conversion and jet kit with premix bike goes well just not as well as the guys in front of me and its not the corners they just power away and me on full throttle just left for dead.But i am working on it.

G'day
That super trick 'priller would be Andy Graham.

An Idea for you. Put race pipes and 36mm keihin carbs off earlier RS125GP bikes on. I've got 38mm ones on my Aprilia, and I'm going to buy 36's.
I had a look at the angle that the carbs go in at on the NSR, and with the right hand carb rubber off an RGV250 the angle is about right. You would need a block of probably 12 or 16mm aluminium or petrol resistant plastic to bolt onto the NSR intake, that you could bolt the RGV rubber to. One side would have to be milled to angle the carb outward.
You would also have to cut the rubber lugs that stick into the reed block off the carb rubber.
Untill you've tried it, you wouldn't believe the difference in power
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The Chopster

G'day
If you're going to use the lost foam process, make sure that you've got enough clearence so that when the FG is put on, it actually fits.
Also, use epoxy resin. Polyester resin will eat your polystyrene

The last airbox I built: First, I taped the backs of the reed blocks. Then I got some fine alloy mesh from Mitre Ten, shaped that in the bike to the shape I wanted, and taped the inside with duct tape (the proper cloth stuff-think the brand I used was bear), and capscrewed on the two plates I had prepared over the reed blocks.
Then I fibreglassed the inside till I was happy, and when it set,
I used a dremel to get at the capscrews-put a little circle of tape on the back of them so you can unscrew them, and took them out, so I could remove the box.
I discovered that the Duct tape has an oily layer-the one that stops it sticking to itself- and it all peeled off in one hit
Then I fibreglassed the flanges on at the top, cleaned it all up, and bolted it in.
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The Chopster

Thanks kieran,i was going to make a large divided air box as big as i could like an rs.The box would enclose the carbs and mount onto the reed block rubber bolts on the carb side.First a polystyrene box would be made to get all in the right place then fiber the mold then disolve the mold out.Big box!.How did yours go did it make a difference?.