Tyga NSR300

TYGA NSR 300

May 2003

Well, it's taken a couple of years, and a few headaches here and there, but the 300's finally done, and is now being used in anger!

Of course, it's not really finished as these sort of projects never really are, but here's the run down so far.

Engine

 

The base for the 300 is a '92 MC21 SP motor. The stock cylinders and pistons were junked and I got an old (seized) NSR150 cylinder to test the plan of fitting this bigger cylinder to the 250 bottom end. As luck would have it, the bolts pattern of the 150 and 250 cylinders is the same, but the 150 cylinder is somewhat taller, and also the skirt support on the bottom of the cylinder doesn't fit into the 250 cases. Not to worry, threw it in the lathe and set about chopping chunks off until it was a nice snug fit in the cases.

The next problem to resolve was the choice of piston. The NSR150 piston has a 16mm wrist pin (the 250 is 15mm), so I thought about going the route of a special Wiseco piston, but after much hunting I came up with a 59mm piston (non Honda) that would do the job. This required that the bottom of the cylinder was skimmed to get the port timing where I wanted. Back to the lathe....sorted!

The cases were a bit of a mismatch to the transfer port entry and needed a bit of cutting. It was a toss up whether to cut the cases (for top end power) or to epoxy the cylinder (midrange). I went for the former. While I was in the cases, I smoothed out all the lumps and bumps for a smoother flow.

The heads are obviously NSR150 too, and just needed a little skimming to get the compression where I wanted. The 150 heads have a central spark plug position, so this in itself is a good thing. Although the water exit of the head is in the wrong position for the front head, so this was cut off and rewelded to give bodywork clearance.

The carburation was to be taken care of by a set of RS250 PJ38 carbs. These went on without too much fuss, but I was then lucky to get hold of a set of HRC factory carbs, so these of course took the place of the RS carbs without further discussion! The oil injector has been removed so it's running 30:1 premixed 95 unleaded with Shell advance racing 2T.

The transmission is stock MC21. Primary drive and dry clutch are also stock MC21. Stronger clutch springs are fitted.

 

Electrics

 An MC21 PGMIII is running the show. Spliced of course. The flywheel is lightened, and that's about it. I chopped all the unused wires out of the harness just to try and tidy things up a bit. The HRC carbs don't use a TPS, so I just pulled the TPS off the stock carbs, wired it at WOT position and plugged it into the harness.

The RC valve servo motor has been moved to the front right engine mount frame spar, basically as it was the only place I could fit it without making new cables!

 Oh yeah, it's running the tacho and temperature gauge off a '91 RS250, and yesterday I wired up some warning light LEDs for the side stand, neutral and indicators. Paul pointed out that I don't have any indicators. Good call, but maybe I'll fit them if I can find something sexy enough

Chassis

The bare bones of the bike are MC21. I don't like the look of the 28 proarm. It looks way too spindly. The MC21 swinger looks great and works well.

The engine is held in the frame using HRC SP kit solid rubber bushes. A touch more vibes, but less engine movement in the frame.

The suspension has been changed front and rear. Up the sharp end is a set of Kawasaki ZXR250 USD forks. Not my first choice, but seeing as my RS forks look very comfortable on the NRS, it seemed a shame to steal them! On top of that, the ZXR forks work very well and cope with a lot of abuse. The rear SP shock was dumped in favour of an NSR250 Formula 3 shock. Aluminium body and excellent damping control. Perfect. I rebuilt it with fresh oil just to be on the safe side. Glad I did, the goo that came out of the 13 year old shock wouldn't have been up to much!

TYGA step kit (obviously) keeps the feet off the ground, with precise gear changing and braking.

The wheels are TZ250 Marvics. The same that were running on the NRS. The NRS now has a set of RS250 wheels fitted, so the TZ wheels went the full circle and are now back on the 300. Sizes are 3.5" front and 5.25" rear, wearing 120 and 160 section Dunlops GPr70SP's.

Slowing things down are stock MC21 calipers at the front, biting on fully floating 300mm FZR400 disks, and a tiny billet Brembo at the rear, tickling a modded TZR250 disk.

An HRC steering damper is fitted to control those high speed wobbles.

 

Bodywork

Full TYGA GP250 bodywork is fitted, painted in our colours. When I can be bothered I'll get the wheels painted pearl white to match the rest of the bodywork, but for now they'll stay black

 

Riding impression

This bike is crazy...........absolutely mad!!!!

The gearing is 15/42, so it's good for about 125mph @ 12,500 in top, but it gets there in an instant. This is how I like it. Who needs ridiculous top speeds anyway? I would suspect that with a change of sprockets it'd go well over 140mph, but there's no where in town to hit those sort of speeds.

Wheelies are something you have to become used to. First gear....no choice, as it tries to throw you off the back. Second.......up it comes again, excellent!

I was considering fitting an F3 close ratio transmission, but with all this midrange it would be a waste. The wider spacing of the MC21 'box is not a problem as the low rpm oomph pulls you out of any trouble.

The carburation is almost there. It's a little rich down low, but I've got some more needles on their way so that should sort that out.

The suspension's a little firm on the rear end for Thailand's bumpy roads, but is easy to dial in thanks to the adjustability. Front end is great. The tyres seem up to the job, but I have had it spinning up on roads with less than perfect grip (4th gear wheels spin anyone?). The NRS has just had a set of Michelin race H2's fitted (not tested yet), so if they're the ones for the job then I'll have to do a switch-a-roo.

Town use and traffic is a bit of a pain, but at least the F3 rad keeps temperatures down in the 60's, but the NSR doesn't like it, and neither do my wrists. This bike likes to fly, and I like to fly with it.

My girlfriend now hates me, and she definitely hates the 300 :-)

Oh yeah, latest addition is a very noisy alarm. I had my Dash125 nicked a couple of weeks ago, so I'm taking no chances with the 300.

Future Plans

 It's hard to find much wrong with this bike. I initially thought that I may have teething troubles, but it's been 100% reliable this far. It hasn't been on the dyno yet, but only yesterday I put it up against Paul who was riding his 63hp Aprilia and it was a joke. The Prilla was screaming it's heart out, but the 300 just romped away laughing at the Italian pretender!

One thing that does need attention though is the front brakes. It might be a mismatch between pads and disks, but they need a fair squeeze to slow things down. Not a patch on the Aprilia brake, and certainly nothing like the VTR disk set-up that both Paul and Luke are running on their NSR's. Maybe a re-think's in order here.

I'm also looking at making an airbox for it. It'll need a fully enclosed ram air system. Easier said than done, but it needs it.

 TYGA NSR300 Kit

Now that I'm happy that this thing's not about to self destruct, the production version is under way.

The plan is to make it a simple bolt on to the stock bottom end, keeping as many of the OEM parts as possible. This will make it a breeze to fit, no different to changing a set of pistons, and it will also be possible to revert back to 250 spec if anyone wants to sell the bike, but keep the 300 kit.

Stock carbs and 2T injector will be used, so street use doesn't become a headache. I've already got a set of bored MC21 carbs to try, which will help performance, but the original set-up will be with the stock stuff.

Luke's down to be the first recipient of a 300 motor. He'll be a good test pilot 'cos he manages to destroy pretty much anything he sits on, so if he can't break it nobody can!

(added Feb 2004: This production version of the 300 big bore kit is now available for sale)

The dyno graphs show the NSR300 vs the stock MC21 vs a power up kitted MC21.

As you can see, the 300 has almost 10hp on the power up kit almost everywhere.

The lower top speed reached by the 300 in the acceleration tests is due to the different final ratio gearing fitted. I like short gearing for whipping around the town. With different gearing 140+mph would be easily possible in the right conditions.

Peak Horsepower - 72.8hp @ 11,200rpm

Peak Torque - 34.6 ft-lbs @ 10,600rpm

Peak Horsepower - TBA

Peak Torque - TBA

Spec Rundown

Base machine - 1992 NSR250 MC21

Engine Type - 90 degree V twin 2 stroke. Crankcase reed valve induction

Bore x Stroke - 59mm x 54.5mm

Displacement - 298cc

Carburetor - 38mm HRC Special

Fuel - ULG95, Shell Advance Racing 2 Stroke Oil (30:1).

Primary Drive - 25/59 (2.360)

Transmission - MC21

Gear ratio - 1st: 2.846

2nd: 2.000

3rd: 1.578

4th: 1.333

5th: 1.190

6th: 1.083

Final Ratio - 15/42 (2.800)

Peak Horsepower - TBA

Peak Torque - TBA

Top Speed - 125mph @ 12,500rpm

Chassis - '92 MC21

Suspension Fr. - Kawasaki ZXR250 USD (preload, comp, reb adjustable)

Suspension Rr. - NSR250 Formula Three (preload, comp, reb, ride height adjustable)

Wheels - Yamaha TZ250 Marvic. 3'50" x 17" front. 5.25" x 17" rear.

Tyres - Dunlop GPR70sp 120/60-17, 160/70/17

Brakes - Front, MC21 system. FZR400 disks. Rr, Billet Brembo. TZR250 disk.

Parts used below