Exhaust Anti-Reversion Cones - Tried Them?

[geodoc]

header pipe ID: 38mm
Cam: Megacyc;e 620X10
Displacement: 917cc

I'd suggest heading back to the dyno with a different exhaust. You may be surprised. That and the cam will significantly affect your midrange. 2 into 1's on Guzzis are difficult to get right the first time you fab one up. Anti reversion cones are a last ditch effort to solve a very specific problem and will probably not be helpful here.

If you want some help, George, please post the exhaust pipe primary ID, cam, and displacement of the motor. Good luck.

Ed

 

[ed]

Hi George- 917cc? Not 949cc?

Check this out- https://www.guzzitech.com/Strokerdyno.html

Note the difference in the midrange response. The two pipes were 1. a long 2 into 2, 38mm Conti replica system with a crossover in front of the engine, and 2. a 42mm bub big dog system with crossover under sump - for a Sport 1100. The larger the displacement, the more you will need a larger diameter header.

If I were you, I'd throw on another system and re-dyno. Possibly go up in ID. Probably more important in filling the midrange hole is reducing the primary header length through one or more crossovers. You may want to weld in a crossover at the front of the engine, above the alternator to possibly break up the strong low frequency fundamental that may be killing your midrange. Mayeb add two crossovers. 2 into 1's are tricky. The ones I see on many guzzis might look good, but they can cost you torque and power. You can just throw a system on, dont worry about brackets or looks, and re-dyno it to check the theory.

An x10 cammed bike should have a HUGE bottom end and midrange. I think that pipe is killing your torque. My 850 LM racer with an X10 (and conti system described above) was simply bitchen with 68hp and huge, flat torque...https://www.guzzitech.com/850LMdyno2-ed.html

Ed

 

[ed]

PS- post any dyno results, too, if you can.

ed

 

[geodoc]

Heh ed,

One of the winter projects was to install a cross-over which is now done.
Like I mentioned before, the seat o' the pants result seems to be that there is a feel-able improvement in lower RPM
throttle response and what feels like a flatter torque curve. Sometime in the next few weeks I plan to go back to the dyno
to verify this and in any case, also try the anti-reversion cones just to see what effect they have.
Building another exhaust for this unit is a last resort if it's to be avoided.

As soon as I get the dyno results, I will surly post them.

Oh yes, The 917cc displacement is not a typo. When I built up the engine, there was no Gilardoni option, one of the perioric droughts
(not that I'm a fan or their pistons anyway).Wanting Nikasil rather than iron liners, I got a pair of used 850T barrels w/ bad chrome and
had them bored to the maximum diameter that was possible and still keep a cylinder spigot thickness. This was done through Mike Rich
who at the time had other customers who were up against the same problem so he ordered up a few pairs of 86mm pistons w/ LM head
appropriate domes from JE and had Millenium bore and plate to suit.

GD

PS- post any dyno results, too, if you can.

ed

 

[Offcamber1]

Here is a good picture of an anti-reversion exhaust on a Formula Ford race car. FWIW, these have been all the rage for the last 15 years or so in FF. Since the rules dictate a stock camshaft and compression ratio in this class, head flow is a big issue. But there is only so much flow work that can result in HP/torque, as augering out the intake/exhaust ports too much has a detrimental effect. In this case the upgraded exhaust has a minor positive effect on top power, but a bit more on torque.

A friend of mine just spent $1200 on an exhaust for his FF car. The car is worth maybe $7500.00. That's a healthy percentage for half a second a lap or so.

If dyno sheets with/without would help in anyway, I can snag some, but I'm not sure it crosses over to highly tuned race bikes.

 

[magi111]

This is really interesting very good article, if this is your new post then really you working is appreciative keep it continue hard working...Thank you

Car Exhausts

 

[contractor20]

should get rid of the link or the whole post :evil: above, and this post when you do