Exhaust Pipe Tuned Length

[fastharry]

Has anyone got any tips on exhaust header pipe lengths for morini 350/400 mildly tuned engines. Some people say its a must to have equal lengths and they go much better, One thing that puzzles me, certain people go on about how much thought went in to the complete package on these bikes, So why do's my 81 350s now a 400 have unequal header pipes? Anyone out there that has one that works better than an original italian made system, can you please share as im running out of time till the next race. regards, Harry.

[George 350]

Hi Harry,
Regarding 1980 and earlier,(Don't know about later K1 and on models) on the Sport model the rear pot/left hand pipe was close to equal length to the front pot/right hand pipe as it extended into the silencer by about 200 -250mm, while the RHS pipe stops just after the clamp. The only difference was the location of the balance pipe.
My '78 Sport has this extension. However my '78 Strada does not have this extension to the pipe and the downpipe stops where it enters the silencer. Could be because of the milder cam in the Strada means it is unnecessary?
Both are on genuine and original pipes. Bizarrely, the parts listing for the 350 shows only one pipe!

Have a look at http://www.seismo.com/personal/morini/e ... haust2.gif for a diagram for a racing exhaust for the Morini 350. Alleges peak torque at 7700rpm and peak power at 9000rpm. This particular design has been around for years, but I have no knowledge of its effectiveness. Could be a good starting point for you though.
All the best,
George.

[MickeyMoto]

Look at the Excalibur. Or the NLM racer.... think Valentino did a left pipe that went forward over the engine.....

Does the balance pipe exist to assist with this?

[smotorboy]

Hi Harry,,,,

I pulled my note book and looked at the calculations I did when I started the Supercharged Morini project...

I also looked at the drawing supplied by George 350 and it goes along nicely with my numbers,,... I would suggest the following for racing:

Discard the stinger and endcap and go with the megaphone full open.... also shorten the megaphone by half for a stronger effect (at the expense of band width of course) you can always weld it back on
if it doesn't work to your liking...

My calculation show that changing the primary pipe length changes the resonation by 350 rpm/inch up or down....

Don't expect too much gain,,, the 350 exhaust valve size and the crooked exhaust port in the head prevent the full potential of the motor to a great degree...

Good Luck Harry,,,, I'm off to Denver Colorado in 3 weeks to run a standing mile event there with the Baron...

Robert in California

[smotorboy]

Oh Yes Harry,, on the uneven length pipes sometimes it is just an OEM packaging issue, however it can be a performance trick to widen the powerband on an engine that needs lots of torque across a maximum rpm spread..

The cylinder with the longest pipe will resonate through it range then the shorter pipe will start resonating through its range ... Half the hit of both cylinders resonating at the same time , but the solter hit last for twice as long... Ah Ha,, there is method to the madness...

Good luck and ride safe,
Robert in California

[fastharry]

Thanks guys. Yes i do have the drawing George, The header is quite short at 570mm but easily made so i will give it a try, i did cut my silencer down to roughly the same dimensions as the drawing but left i bit in the middle, as Chris at Nlm had mentioned they like a bit of back pressure? Must admit most of my road race engines megas where open. A test i remember well was done by a great tuner Leon Moss ( who sadly died when a tarmac roller went through his windscreen on the way to work) He did all the testing for Superbike magazine on a proper water brake dyno. They spent 2 days on Mark Forsyths Rotax 500 single that has twin exhaust ports, they found that 22" was the best for a good spread of power or multiples of 11" But for best mid range and only a bit less top end they found 18 and 22 where a good combo. So maybe thats what Morini were up to. If anyone has an old set of 350 header pipes going cheap i would be very interested to hear from you.

[mad muller]

cant comment on the science , but I have tried all sorts of different combinations of exhaust pipes and silencers mostly backyard type knock ups , the length of downpipe doesn't seem to make any difference as long as they extend further than the balance pipe, iam running a two into one open mega at moment great on full throttle but not as smooth getting up there , but well worth it, best results I found was keep the balance pipe and use two straight thru pipes , I work on the old school principles it performs or it doesn't, stick with it. muller.

[fastharry]

Thats very interesting. i will test it with and without a balance pipe, see if old seat of the pants can feel a difference.

[MarkB]

Here's a photo of my 1977 project 350 Sport, imported from Italy and with what seems to be the original downpipe still in place, with an enooooormous tuned length of pipe (maybe a later tuning mod, but it looks original). Propped up beneath it is the original exhaust downpipe from my '76 350 Sport, without any internal extension. Harry, you're welcome to have the pair of headers from the '76 Sport (one's lost the collar that goes into the inlet manifold) and to borrow the one from the project bike if you can pick up from Stevenage...

[Daddy Dom]

Hmmm, that length of tuned pipe looks very, very familiar from last time I de-mufflered a few years ago .... I'm going to investigate this further.
DD

[texaskitty]

'75 Sport: on the left header pipe, the inner pipe extends 21.5 cm past the end of the outer pipe. The Strada did not have the inner pipe extension. I think the 500 (1980/81) has the left inner pipe extended. MarkB's picture appears to show a Sport header and a Strada header.

[smotorboy]

It looks very much like the and I came out with the same length for the pipes....I'd bet we used the same reference book ....

http://www.goodreads.com/book/show/1460 ... ke_Systems

Left Megaphone.jpg (128.98 KiB) Viewed 19628 times

[corsaro chris]

My first Strada, purchased new at the end of 1977 (wire wheel, disc brake) had the extended pipe on one side; I'd guess than some inadvisedly 'tune' the exhaust on the machine to extract more performance. Mine pulled well after proper running in, even two up with luggage around the south of France, and was more fun than the 500 which followed it (although not as comfortable on long journeys).

I also guess that the equalised gas flow lengths is something to do with torque, as Lambertini tells us that he designed the really convoluted plumbing of the New York 501 to enhance the power of the motor. Something to do with balancing the exhaust pulses?

Good riding,

CC

[fastharry]

Thanks for the offer Markb. I may well take you up on it if nothing is found closer to home, I have a mate with a transport firm who might pick them up if he gets down that way, Looks like a bit of dyno work is going to be called for. That must sound good smotorboy.

[smotorboy]

Sure does Fast Harry,,,, I think it will be some of the best value money and time spent you will do....

I know it is hard to burn thru limited resources just to get a few concrete numbers,,, we "guess" too much without those hard and true references....

Robert

PS: I'm over due to put the Baron back on the dyno myself.....I've changed so very many things that new baseline runs will help get the last little bit that is there...