has enybody tried vhm heads . i will mostly use my mc28 on the road.
with odd track day . are there power gains to be had ? plus reliability ?

I don't think reliabilty will be any issue. As always, that's always down to setup and the condition of all the other components as a package.

As for being worth it, well I haven't tried them myself, but there are only two main areas the NSR motor can benefit from a redesign compared to the RS250 motor, and one of those is the head design.

I personally think that VHM (or similar) heads will bring a full spec MC21 motor to within just a gnat's whisker of the output of an RS250. A full F3 motor is close, but it will never quite be there because HRC made sure it can never be quite as good as the GP motor!

As for whether it's worth it on a road bike? Well that all depends on if you are going to submit it to Posers World really!
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!

Bolted them on last night but wont be back out to the track for another 2 to 3 weeks after this weekend. I'll let u know.
_________________
1995 A kit TZ 250
1994 Rothmans NSR 300sp SOLD
1998 RM 250 freestyle/motorcross
1998 Meathanol burning CR 500 AF super retard/motorcross/sand dunes/play bike

As Andy says, it's all down to design.

The stock NSR heads are ok for basic shape, but they suffer in two areas. First being the squish clearance too big, and the second is the plug position.

The VHM NSR250 headsets reposition the plug to the centre of the head. This helps for complete combustion. However, in my opinion the squish is still a little loose at a shade over 1mm. They're 12.6cc volume which is good for pump fuel. If you reset the squish for 0.7mm (0.3mm thinner base gaskets) this would give you a volume of around 11.9cc, meaning that you'd have to run minimum 98 octane, or there abouts.

The VHM heads also offer better cooling (very slightly) and are more efficient, so I've found I could run leaner jetting. Be sure to check though before shuffling the brass.

Jeremy's got NSR300 heads, with inserts for both pump fuel and rocket fuel, so it'll be good to see how he gets on. Tread carefully brother Jeremy!

The other nice part about the VHM heads are you can get a blank insert and get it machined to your specs. So basically you can get the shape and squish you want.
_________________
Charles Gallant