what would running 350 pipes on a 250 work like?

[JonW]

Im tempted to build a 250 RZ engine in my latest project. Ive never ridden one and those that do tell me they are a lot of run as the motor is revvy and long lasting (a factor of the piston weight and the crank/crankcase was designed for it of course). I believe they put out 48bhp vs the 350s 59-63, so none too shabby as standard.

I would probably fit PWK28s, dynatek coil and a programmable ignition for extra fun.

I have a set of hydroformed Gibsons that Ive never used but the seller told me they are race oriented with power up high and would probably use them on this build and wondered if Im being foolish or smart partnering high revving small ccs with a revvy pipe on a road bike, or is is that the larger 350 pipe would have some other effect on the power, and provide torque lower down?

Of course I also have a 350 top end as well, but I already have a 350 and a 421, I was just thinking I might do something different... happy to hear people's views...

[L.B.]

Come and take mine for a ride first Jon....

[JonW]

Cool, Id love to mate.

Pete G also offered me a ride on his which is totally standard Japanese spec, I should also try to cadge a ride on James' modded one I guess.

Anyway Jase, on another topic did ya get my emails re forks, postage and other bike related stuff the past few weeks? Ive not seen any replies as yet... you still ill or just working double shifts? what is this, 20 questions?

Ok back on topic... LOL

[jools58]

I once ran some 250LC pipes on my Terry Becket tuned RD400............
Age has got to me as I can't really remember what it went like LOL

[JonW]

Er, the other way Jools... RZ350 pipes on a RZ250... While RZ pipes might improve an AC (unlikely I reckon) I know that going the other way would be a mistake for me, the 250 pipes are restricted LOL.

[hybrid]

I can't see the 350 pipes being too much of an issue on the 250. Length should be OK as I bet the port timings are similar on both. The only issue might be overall volume, but again I think it would still run fine.

Do you know what the stinger size is? You could always change it for a slightly smaller one to bring the belly pressure up a bit, but I doubt it will matter.

[JonW]

I agree with you on the port timings as I believe the RZ350 is pretty similar, and the YPVS engines were quite different to the old LC and ACs, In fact I did some port maps for Ed Erlenbach a while back when he was researching that stuff.

Its the volume I was a bit worried about really. I didnt know if it was like the old Roy Chubby Brown Joke (...the girl said "You've only got a small organ" I said "It's not used to playing in cathedrals").

Stingers are 20mm ID...

[OzzyElsie]

Where's Lozza when you need him .

My understanding of chambers is that the stroke is the critical factor in chamber design. Volume, header length, porting and stinger all come into it but the stoke is the dominant factor.

Given that the 250 and 350 have the same stroke the pipes should interchange without too many issues.

(RG250 pipes work great on RD because they have the same stroke )


Ciao.

[hybrid]

I don't see how the stroke is relevant. You need to know the port timing so you can time the return wave. I don't see how the distance that the piston travels makes any difference?

I think you'll find that RG250 pipes work is because the timing is right.

[Jeram]

The larger volume should be ok. Measure the volume of the pipe and compare it to each cylinders capacity...it will be between 20 and 30x the volume.
with 20x being more like motox/road and 30x being gp spec

and post a pic of the pipes, lozza will be able to tell you what it will behave like

[JonW]

Thanks guys.

Jeram, Silly thought... to measure the capacity I just fill one of them with water? And of course the the capacity of the engine is already known.

Can find a pic, or take more, they are just hanging in my garage...

[JonW]

Actually found a (not so great) pic on my website, right at the top of this page:

http://2smoked.com/Yamaha_RZ350_RD350_Y ... 3_31k.html

Obviously they are the shiny hydroformed ones, not the mild steel welded sectional pipesin the pic, those are Wicked pipes and on my LC421 now. The other pipes are MT250 boat anchors that hold my garage roof on in storms LOL

[Jeram]

Thanks guys.

Jeram, Silly thought... to measure the capacity I just fill one of them with water? And of course the the capacity of the engine is already known.

Can find a pic, or take more, they are just hanging in my garage...

yep!

[jools58]

I thought it was a case that fatter larger volume pipes would give a better midrange ?

[JonW]

Ok finally got a chance to pour water in one of my Gibson 350 pipes. These are Hydroformed so no strangers to H2O LOL.

I made the volume 'about 4liters', it wasnt an exact science filling a jug and holding the pipe at an angle it would fill at the same time LOL

So given that 175cc is 1 cylinder of a 350 and this is 4000cc, thats 22.8 times the volume. Fitting them on a 250 (150 into the 4000) gives 26.666666.

The seller of the pipes told me he didnt like the pipes as they were all top end and he didnt ride much where he could use that so fitted some that made power lower down.

So, what do we think lads?