The Zephyr Zone

Has anyone tried fitting one of these? Would it take much effort to have it run well?

bubba_zanetti wrote:Has anyone tried fitting one of these? Would it take much effort to have it run well?

Is the bike a 750 or 1100? I personally wouldn't fit any 4:1 on a 750. While you may end up with more top end grunt, there is a high likelihood you could end up with a mid range 'bog'. That's the reason few race bikes run 4:1 these days, vitally all 4:2:1 to reduce the mid range problem. So for a 750, top end is fine, if it could do with more grunt its lower in the rev range, and a 4:1 is like to hurt not improve that area.

If your bike is an 1100 disregard the above, no idea how it would go on an 1100.

750.

mostly looking to shave weight and titanium is also nice.

So according to the manual, with the rough google translate the exhaust is engineered for the stock set up so doesn't need any major tuning to run correctly. Also, according to these roughly translated webike reviews no one is saying anything about a loss of power or torque on the low end and most people seem to enjoy it for the corrosion resistance and weight savings (over 20 pounds)

So I think it might be gtg. I'm going to give it a shot if I pick up the zeph 750.

The reason a 4:1 can create a hole in the mid range has nothing to do with tuning (well not tuning as most people think of it e.g carby jets). Anywhere there is a change in diameter or connection in an exhaust (even the end of the pipe) creates a reflective wave that travels back up the exhaust. At a certain point in each rotation of the engine both the exhaust and inlet valves are open at the same time. If one of the many reflective exhaust waves arrives back at the exhaust valves at this point of valve overlap it inhibits air/fuel mixture flowing into the engine, and so a loss of power.

In a 4:1 exhaust that massive common connection where the 4 pipes join creates an VERY big back pressure wave. And that is the reason they fell out of favor a very long time ago on race bikes, and cars for that matter. You may see only one pipe sticking out the back of a modern 4 cylinder race bike, but you can just about bet your house on it the exhaust is a 4:2:1 design. It's done to eliminate that problematic big common connection point where the 4 pipes join.

By all means go for it if its the look your after. I'm just pointing the above out so you are aware of the possible technical issues as you did ask about performance. The biggest performance improvement in my experience is just work on getting the main jetting correct for the stock intake and stock exhaust system. The 750, well certainly the D1 model was jetted way lean to obviously meet the tightening emissions standards of the time.

P.S. wouldn't take much notice of 'review' on the Jap web page. Actually your don't better than me if you can even understand most of em. If I wanted to save some weight I'd replace the lead/acid battery with one of the modern high-tech batteries. Going to be a LOT less expensive than that exhaust. You'd still have a stack of money left over to fix the suspension (in my opinion the weakest point of the bike).

I read your post Freddy and agree but pipe design probably gets around this
I have run a 4:1 on my 750 and have done so on track days as well as weekend warrior rides. It is a race pipe - so no baffle - and have had not trouble with bog down.

clone5 wrote:I read your post Freddy and agree but pipe design probably gets around this
I have run a 4:1 on my 750 and have done so on track days as well as weekend warrior rides. It is a race pipe - so no baffle - and have had not trouble with bog down.

Does any modern race bike run a 4:1 exhaust? Even Eddie Lawson would eventually abandoned a 4:1 for a 4:2:1 some 40 years ago on his Kawasaki muscle bike. The last thing you want is a bloody great pipe diameter change where the 4 pipes go into a single collector. Just creates massive return pressure waves.

I don't know about modern race bikes but our engine designs are prob 40 years old or more. If backpressure were affecting this I can't feel it. It pulls clean through the rev range and doesn't bog down.

The pipes were Australian made from a company called Formula 1. Not sure if they're still around. Manifold pipes are roughly 35mm outside diameter gather into 1 and size steps up to 45mm

When I say race pipe I'm only referring to an aftermarket free flowing with little or no baffling. Perhaps too liberal for the term "race pipe" as not titanium etc. Race maybe not but not technically street legal here. Rejetted jets and needles to suit

Freddy wrote:Does any modern race bike run a 4:1 exhaust? Even Eddie Lawson would eventually abandoned a 4:1 for a 4:2:1 some 40 years ago on his Kawasaki muscle bike. The last thing you want is a bloody great pipe diameter change where the 4 pipes go into a single collector. Just creates massive return pressure waves.

If I recall correctly, MotoGP bikes try to run individual pipes - no collectors where possible. This enables them to run all the same length pipes

clone5 wrote:

Freddy wrote:Does any modern race bike run a 4:1 exhaust? Even Eddie Lawson would eventually abandoned a 4:1 for a 4:2:1 some 40 years ago on his Kawasaki muscle bike. The last thing you want is a bloody great pipe diameter change where the 4 pipes go into a single collector. Just creates massive return pressure waves.

If I recall correctly, MotoGP bikes try to run individual pipes - no collectors where possible. This enables them to run all the same length pipes

Modern I4 cylinder race bikes virtually exclusively run 4:2:1 configuration exhausts. V4's run 2 2:1 systems.

You must have a vastly different 750 to me, as I find mine gutless under 6000 rpm. The LAST thing I want is to make any changes that would push the power band up higher in the rev range.