New to this site, soon to be proud owner of a 1988 MC18, for track days and vintage club racing. It has been derestricted but I want to do any other readily available performance upgrades (not planning to open up the engine this year) and wondering which are specific to the different models. The tuning guide on this site indicates there is no benefit to installing a central plug head on the MC18. Why is that? Also, Tyga lists carbon reeds and HRC stuffers for the MC21 but not the MC18. Again, is there a reason these won't work on the MC18? How about the total loss ignition they list for the MC28?

Also, what is the experience with squish clearance on the stock engine? is it normally under 1 mm, and if not, is there a problem skimming the head to optimize squish clearance? I don't mind running race gas (although it would be nice to mix with pump gas to control cost).

Thanks for any input.

Hello "tleighbell", and welcome to NSR-WORLD.

The 1988 is pretty good to begin with, once delimited, and to get any substantial gains will require getting inside the motor.

It's not that there is no benefit to fitting the HRC heads to an MC18, it's just that the difference is virtually immeasurable. The heads are part of an extremely extensive HRC kit, and fitting one part alone is hardly worth the effort. An HRC MC18 makes over 70hp, but has different crank, cases, barrels, heads, ignition, carbs, inlets, exhausts, electronics, etc.

I'd advise refreshing the motor and chassis, and then taking it to a track day to see how you get on with it, before diving in. An MC18 needs work on the chassis more than it does on the motor! The best mod, pound for pound, is to open up the airbox a little, or fit foam pod filters, if you can find some adjustable needles and you're adept at setup. (Otherwise, just stick to the airbox mod.)

The TYGA pipes will save you weight, and look great, but you'll lose a huge chunk of mid-range on the MC18. If you can keep the motor at peak 95% of the time, then great, but if you can live with the weight of the stock pipes, then I would keep them. The MC18 has a different inlet manifold setup to the MC21 and MC28, The stock setup works well, and the HRC parts for the MC28 were to try and restore the performance lost from changing from the MC18 type of inlet. Again, throwing good money after bad.

The total loss flywheel is no good for anything but the 28. Basically, the static timing is wrong for any other model. More trouble than it's worth.
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Andy.
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Andy, thanks for a full and informative answer.

Just to add to Andy's post. The more it's tuned, the more often it will need servicing and special fuel. It depends on how much you want to spend. I would suggest a dyno run to confirm you are getting around 56bhp at the rear wheel. Then make sure the brakes and suspension is in good order. I've read of people going straight on track then discovering they had treacle, not brake fluid, etc
Parts are getting rarer, so you should look out for good spares if you're planning on keeping it for a while.
A translated workshop manual and parts guide will be useful
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Why do things simply when you can complicate them

Thanks RobH. I agree and understand about servicing. My RS125 has a piston life of 300 miles. I don't want to be replacing two pistons that often! Race fuel is not so much of an issue. Looking for the point of diminishing returns. for sure suspension, brakes and tires come first. Which brings up another question but I'll start a new thread on forks.

A good fresh delimited R2/4J should be closer to 60hp, Rob. Yours was just a tad under 58rwhp last time it was run.

The R5/6K tends to give the best results of any NSR250 as stock [delimited]. I would say the '88 PGM and big flywheel are what really hinders it, compared to the later PGM-II and smaller flywheel. The 1988 motor has great potential though.

I'd like to swap '88 and '89 pipes one day, to see what difference they make back-to-back on the MC18s.
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Andy.
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AS it turns out my 88 MC18 has '89 pipes. If I ever get it on a dyno I'll let you know the results but won't likely have the 88 pipes for comparison.