650 central's exhaust port optimizers and torque peak optimizers

So has anyone installed these on their bike? From what I've read on the web site they are like magic for your bike. I plan to do some more research and talk with MMM to get a better understanding of what these magic parts do exactly. Probably going to order them up when I get my bike running and report my results on this thread. Please anyone who has used these parts please share your experience good and bad so that we all can have a better idea of the potential performance expected from these "EPO's" "TPO's".

Here' s a thread that talks abit about them, hope it helps.

http://www.xs650.com/forum/showthread.php?t=21665&highlight=exhaust+port+optimizers

Cool thanks man I am going with after market pipes so... going to talk with Mike at 650 central for a bit and try to come up with the best carb/ exhaust options and hopefully get the best results for torque and power for my $....

knuckle draggin monkey said:

Cool thanks man I am going with after market pipes so... going to talk with Mike at 650 central for a bit and try to come up with the best carb/ exhaust options and hopefully get the best results for torque and power for my $....

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Mike is the real deal he'll help you out. I have the stainless steel headers with the inserts on both ends per his recommendation.
Head side
http://www.mikesxs.net/product/07-0769.html

Muffler side
650central Torque Peak Optimizers

I use MMM's inserts on full-on 750 XS race engines ... just the exhaust insert to manage the reversion effect. The pipes are 1 3/4" and the inserts are very effective in overcoming the engine's tendency to have a bit of a hole or dip in the torque curve in the 5 - 6,000 rpm range. With them installed the curve is very linear and smooth and peaks at 51 lbs. at the rear wheel. As noted by others, 1 3/4" pipes are too big for all 650s and almost all 700s.

I use both EPO and TPO inserts in 1-3/4" pipes on a cammed and ported 700. I'd be running 1-1/5" pipes if any were offered in stainless.

Pipe diameter influences where peak torque occurs in the rpm range--the fatter the pipe, the higher the rpm it's tuned for. By sleeving down the pipe in front of the exit, the TPO inserts accomplish two things: they tune the pipe for a torque peak occurring at a usable rpm, and they boost the velocity of the exhaust gas.

One thing to bear in mind is that MMM didn't just knock these things off. He has a background in loudspeaker design, and when you're designing exhaust components, controlling pressure waves is one of the main considerations.

The general consensus on exhaust port optimizers is they are a band-aid for too large of a pipe. 1 3/4" is a very large primary for a cylinder that displaces 300cc-350cc.

If you want to optimize your exhaust, I suggest either paying someone like Burns Stainless to design it or pick up a copy of PipeMax. I modeled the OU72 motor in PipeMax the best I could - figuring a 8500rpm redline and 85 flywheel hp, it's calling for a primary of 1.3-1.45" off the head for 26.5-28.5", before a collector that is 2.5" dia. and is 14" long. This is for a 2-1 system. You can use a Burns merge collector base, which goes from 1.5 primary to a 2.125 outlet and expand to 2.5" off that to make a proper merge collector.

Granted, that's a very modified XS motor, it will have to be custom sized to your application.

PipeMax designed one for my SR500 with a 1.625" head tube before stepping up and I built it around Christmas time. This went against every performance header out there using 1 3/4". Since then, it has surfaced that a top speed SR effort is using a 1.625" pipe and making great power, and a very fast flat track bike out west showed up with a stepped header starting at 1.625". Not saying I started a trend, but it shows development didn't end in 1980.

Applying calculators and asserting (undocumented) consensus is one thing. Putting up some test numbers to show what kind of performance gain expensive one-off custom pipes have provided versus off-the-shelf pipes with inserts (all other things being equal) would be more convincing. I wasn't aware that Yamaha had gotten the OU72 race motor to hold together with 80 hp at the crank, let alone 85.

grizld1 said:

Applying calculators and asserting (undocumented) consensus is one thing. Putting up some test numbers to show what kind of performance gain expensive one-off custom pipes have provided versus off-the-shelf pipes with inserts (all other things being equal) would be more convincing. I wasn't aware that Yamaha had gotten the OU72 race motor to hold together with 80 hp at the crank, let alone 85.

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I crew on friends road racing cars. I've personally seen the calculators work. This on a 4cyl engine that has been raced since 1963 and is now making at the rear wheels what most of our competitors are making at the flywheel. Obviously, it's more than just exhaust design, but it's part of the total package. I've spent a lot of time in race car paddocks and I know what other high end engines of various designs are running ($30k+ engine builds). The calculators are pretty spot on.

I have the old White Brothers exhaust that came with my bike. I will be doing back to back dyno tests this summer.

This quote taken directly from the OU72 literature:

On May 6th the engines were run on an engine dyno (not a chassis dyno) and
recorded numbers that translate to approximately 90 horsepower.

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Keep in mind the primary length I quoted is from the valve seat.

The factors influencing pipe design are so plentiful (e.g. how much built in reversion is contained in the exhaust port's casting, etc., etc.) that the easiest - and only - real means to determine the "best" pipe for a cylinder/engine is to simply put together a bunch of alternatives and run them on a dyno.
It might be different with SBC or Ford engines ... there is a huge body of data available for them that has no doubt found its way into various software dyno simulations, but such is not the case for the XS650.
Even then, I read an interview with someone from Hendrick's shop (they build top flight NASCAR engines) who said that before all is said and done they empirically test the exhaust sizing and lengths on a chassis dyno.
Here's a link to a write up of what XS650 pipes were used by various tuners and racers in the '70s.

http://downloads.650performance.com/XS650_750_engine_modiffication_guide_sample.pdf

We'll have to agree to disagree then. The 4cyl example I gave above is a non-crossflow cylinder head with poor exhaust ports. The calculators work off a few items specific to your engine, and a poppet valve internal combustion engine is a poppet valve internal combustion engine. Wave speed is a known (and is a function of EGT, those calculators take that into account), and is determined by the opening and closing events of the valve. Volumen (diameter) is a function displacement, rpm, and volumetric efficiency (roughly how much gasoline is burned - alcohol motors will need larger diameter pipes). NASCAR is concerned with every last .5hp so that's true with what he said, but the calculators will get you 99% of the way there and that's the point.

Some points that have been posted by Calvin Elston (http://www.elstonheaders.com/index.html) who builds and designs NASCAR, top level NHRA (cars and bikes) headers and exhausts has made elsewhere:

f you reduce tube diameter you need to step it at least every 8-10 inches or so and it can be shorter if you work with final choke diameters. The megaphone and reverse cone help to keep power going past power peak for what would normally be a too small header. Stepping quicker helps everywhere. Last point I would make and I have made it on several other posts, just because the factory/engine designers designed a exh port that is say 3.2" long to the header interface does not mean that that is the best or proper place to have the exhaust experience its first "sudden" step. The PS bikes I have worked on (Suzuki's and Kawasaki), I have to do a lot of work to do what I would call properly exit the head. Most stuff I have seen has a very large pipe coming off a very small port. A serious loss of exhaust energy given up early in the event. IMO.

My current PS header matches port shape and area exactly and will step 3 to 4 times in 18-21". Good luck.

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The header I built includes a spigot that is port matched exactly to the head and tapers up to the id. of a 1.625"od pipe (so there is no step). It then steps up before entering the megaphone (which matches the criteria that Blair authored about megaphones / reverse cones on single cylinders). It's out right now at H.M. Elliott getting coated. I saved money by having a race/motorcycle shop assemble a kit for me that I fitted and tacked up and sent back to be welded.

Not trying to troll this thread, I read this forum and have some XS items I don't need laying around that I'll post to sell when I get the time. Just surprised to see discussion on these here as I thought it was pretty well known that AR cones are band-aids and that the racing engine business/technology/knowledge has moved past the '70s and early '80s.

No one has to do what I said - just sharing what I know, friends have experienced, and what I've observed at the track. If someone was seriously trying to develop these motors again, they would call up Burns or use other models, and they would leave everyone in the dust. My 2 cents.

Cheers,
Bob

A picture of your bike would be nice. Your pipes just saw the pictures look good. I run 1 1/2 pipes on mine. Most people buy the 1 3/4 pipe for the look not performance. The inserts help peformance lost by the look. Racers look for whatever gives them the edge. Whatever floats your boat works best for most.

I don't think we are disagreeing. Either something works or it doesn't. Using software to create an initial pipe design might save hours of fabbing up "let's see if it works" tubing.

Ducati superbikes have used step up pipes, and I have no doubt the factory didn't do it without obtaining a gain in part or all of the power band. I don't know if current MotoGP bikes have step ups or not, although their power bands are much higher.

650performance said:

I don't think we are disagreeing. Either something works or it doesn't. Using software to create an initial pipe design might save hours of fabbing up "let's see if it works" tubing.

Ducati superbikes have used step up pipes, and I have no doubt the factory didn't do it without obtaining a gain in part or all of the power band. I don't know if current MotoGP bikes have step ups or not, although their power bands are much higher.

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I re-read your post. I agree we're not disagreeing - not sure why I took it that way. Rough week...

I looked at some of the last years Moto GP bikes - megaphones are still popular and some look to have steps. Your F1, NASCAR, NHRA (excluding nitro fueled cars) all do. I don't think steps within themselves are the end all be all as some Moto GP teams were/are using a constant taper. Usually steps are designed to be at certain harmonic lengths. A nice thing about them is they're a lot easier to fabricate and the step does help to impede reversion.

I think the part I bolded in the quote I posted is a really key principle in exhaust design. As is getting the proper angle off the head - which Calvin emphasizes often. Here is an illustration showing that on an Alfa Romeo engine. This guy paid a lot of money, had Burns design and sell the parts (they don't actually do the fabrication, just design and sell components), and his fabricator did what you see in red, not green.


Another one I've seen Calvin mention is that a pipe on a 6" radius can be a smaller diameter and can flow more than the same size pipe on a 3" radius. Something to keep in mind.

Ideally the pipe I built would have had three steps, but the diameter of the port makes it so the smallest od pipe I can run is 1.625". Ideally, I would use a 1.5" od pipe and the exhaust port would be welded up some. This is made obvious when doing more engine math and seeing the port csa is larger than it should be for the operating range / displacement of the TT/SR motor.

As for the exhaust kit, the same shop has a OU72 motor that they're about to start doing work on.

As for my bike, I've attached photos of my bike when I bought it and how it is now (left photo). I bought it as a 'SR500 with White Brother's engine: not running. Box of extra parts included'. A new coil and it started up. I built it over my college winter break - it's almost done. Including the bike, I have about $2000 in it - but I have a pile of parts to sell of which should recoup some of the cost. I'm looking at purchasing a 'framer' asap to race with. The old swing arm and rear wheel are off a XS650. I'll make a thread in the tracker section as to not spam this thread.

By the way hoffman900 welcome to the site nice bikes. Back to exhaust very interesting.

Re the OU engine you reference, Hoff, perhaps you already know that there were only about 25 of the primo OU heads ported in Axtell's shop. The other 40 or so were supplied as castings by Yamaha with only a pencil-size "port" in each of the IN and EX ports. The purchaser was required to complete the process. Needless to say, many of these heads turned out to be truly crap ("Let's open 'er way up and she'll really fly!"). A head that was actually prepared in Ax's shop is uniquely marked (not that that couldn't be copied) and if anyone wants to be sure they should flow it on a Super Flow 600 or similar state of the art bench and then compare it to the OU flow numbers Yamaha published. While the numbers wouldn't be the same (different bench, different head), it should be easy to spot a winner or loser. I hope the OU you reference is a "keeper."

AR inserts a band-aid fix ?? That'll depend on who you talk to, the intended performance goal and for all particle purposes,AR inserts can be a viable asset in tuning an exhaust system for dirt or asphalt,reviving a lazy exhaust port or alter the exhaust flow ratio,etc. Band-aid fix,on the contrary.

Stepped headers for the XS isn't a new concept as a former racer of the Garage, member Diesel,built a very complex stepped header system for his Yammer Hammer about a decade ago and if my memory is correct,Diesel was very pleased how his racer excelled and pulled away from the competition,but for everyday usage,just not practical IMO where engine RPM spends most of time around 3000 to 4000 for the average rider.

Hi Jack,

All of Richard Pollock's XS powered bikes have stepped headers. It's not a ground breaking technology - car racers were using them by the late 70s. Jerry Stahl was one of the pioneers.

By your own admission, it is a band-aid. It's a band-aid to too large of a pipe for the application (1.75" header on the street or a smaller motor that wants a smaller pipe or a port too big for the application). I have one of those cones that came in a box of parts with my bike; it measures 1.18" (30mm) id at it's smallest. Read the quote below and think about it.

A 1.5" header would be good for a street bike, anyway.

Here is another quote from Calvin Elston of Elston headers:

It helps to not think in terms of "port" verses "tubing". The tube becomes the port. You do not introduce tight radius for the same reason you do not do it in the ports. The only way to overcome the loss, especially in the transition area and the first 6-8" of the header, is by using larger tubing diameters. And the problem keeps going down the toilet. "Well, if we made a bigger header, it would make a little more power",(because we overcome the flow loss up front). But the larger tube now needs an even tighter radius to clear the obstruction... And you are now so far away from what the engine wants for a header, it really does not matter what you do from there, the engine won't respond to changes.

The smallest diameter tube allows for the largest radius. It can even be smaller in area than the port, especially if it allows a larger radius. (the application can trump this though)

The first 6-8" of the header is just as important as the first 3 or 4" in the cylinder head. The same rules and thinking that a head porter uses apply to the header. Most headers I see break all the rules.

The last thought is this, the reason the first 10" of the exhaust track is so important as opposed to just the port in the casting? The gas particles, the mass...only gets that far before the ex valve closes behind it, and it no longer is connected to its pressure differential, if you will. At that point in the exhaust track, everything changes. But anything you do to the "particulate-mass" flow in the port while the valve is open that violates flow, will cost you power and you can not get it back. You want to get the "mass-flow" as far away from the ex valve and the cylinder as you can. Larger "anything" in this area does not usually help.

I do understand that many applications force the header to break all these rules and larger is the only answer if you need maximum power.

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I think this is a good topic and hopefully it gets people thinking and talking.

Cheers,
Bob

PS: 650, hopefully! I'm sure he'll start a build thread here when he gets working on it. An old timer friend raced Harley XR's in the '70s, he had the package - Lawwill engine kit, Axtell cam, and Branch heads.

AR inserts a band-aid fix ?? That'll depend on who you talk to, the intended performance goal and for all particle purposes,AR inserts can be a viable asset in tuning an exhaust system for dirt or asphalt,reviving a lazy exhaust port or alter the exhaust flow ratio,etc. Band-aid fix,on the contrary.

Stepped headers for the XS isn't a new concept as a former racer of the Garage, member Diesel,built a very complex stepped header system for his Yammer Hammer about a decade ago and if my memory is correct,Diesel was very pleased how his racer excelled and pulled away from the competition,but for everyday usage,just not practical IMO where engine RPM spends most of time around 3000 to 4000 for the average rider.

The first step leading from from the exhaust port IMO to the first radius should be as along as you can get it to provide the least amount of resistance as possible to maximize the pulling effect on the port and to enhance the exhaust pulse speed momentum before entering the first radius thus helping in shooting the E/P through the radius quicker.