Let down by Motad

[MAXIMAN]

Well boyz I'm utterly BUMMED!

I'll get all this info up and posted in a thread later to let you all know what the heck is going on with Zilla.

We've had pretty good results with hop up so far. But the Motad header ...I hate to say and hope it doesn't piss any of UK friends off...the Motad is a dawg.

With the Motad installed and the bike tuned the most we could get was 80 hp. With the OEM exhaust and bike tuned we're seeing 87-88 hp. I am certain when I can find a good Kerker or Supertrapp...or V&H header for the Eleven will see an Additional 10 - 12% on top of that 88. This would put us around 96 to 98 hp at the rear wheel.

Also I haven't explained the dyno we are using is very conservative for bikes. It was designed for legend racecars. Generally you can add 4-5 horsepower onto any of these numbers and that would be what you'd see on a Dynojet 250. As a matter of fact as soon as I get this baby dialed in best we can I'll take it to another dealer to run it on a Dynjet 200 series dyno just to get an A-B comparo.

As it is I'm stuck with the OEM exhaust and about 10% shy of where we should be. I've ridden the bike and there is a huge difference. Bone stock Zilla was dyno'd back a few weeks ago at 72 hp. Now it's at 87 hp which is a 21% increase in peak power with the OEM exhaust.

Here's a pic of the Motad. Pay close attention to the collector diameter versus the primary pipe diameters.


If you look at other 4 into one headers the primary pipes flow into a collector that is significantly larger than primaries. However the Motad maintains the same diameter pipe through out the flow path! This must creatre a restriction. You're trying to flow the gas from four (4) w35 mm down pipes into one (1) 35 mm collector! What type of idiocy is that?

Look at any other 4 into 1 and you'll see the collector is much larger than the down pipes.

Seriously...my OEM pipes flow quite a bit better than this piece of British Sterling (read BS).

I'm looking for a bedderhedder. I've come this far and spent this much so I'll have to sit tight until a slick Supertrapp or Kerker pops up.

[xschop]

your problem

the exit of the one side of the collector is stopping the flow of the other because of its exiting angle...

[MAXIMAN]

Actually the angle should be about right to facilitate "jetting" or scavenging.

The point is 4...that's four... 35mm primary headers are feeding into 1..that's ONE 35mm collector. There is the restriction. This a fundamental gas flow design. I am surprised Motad screwed this up. Of course I had no really good photos of the collector system prior to buying the BS (British Sterling)

This is so basic it makes my head hurt If I have four 2 inch pipelines from four wells in the field and they are all feeding equal volumes of gas into ONE 2 inch pipeline I will have an INCREASE in pressure at the point of convergence. You would need a 4 or 6 inch line to feed these into. (the function of gas flow volume in any pipe is directly proportional to the area of the diameter of the pipe - pi*r*r)

If you look at any other 4-1 header you'll see four 35mm or 38mm or whatever they are feeding into a collector that is about 2 - 2.5 inches!!! (50 to 60 mm).

It's a gas flow principal well defined in engineering. Using the Panhandle equation of gas flow in piping we can readily predict a huge restriction in the Motad 4-2-1 "Y" collector.

But ya don't even need to be an engin-idiot (please no flames..I too am an engineer/geology double major)...to see this. Common sense tells you there would be a restriction.

Simply put the 4-2-1 design needs to be upsized at every stage of convergence (collection).

[Pat Kelly]

The exhaust I just got off Ebay (I'm assuming it's a MAC) is 4 into 1. The head pipes (35mm I guess) go into one collector at the center of the bike, 2 1/4" diameter. This 2 1/4" curves to the left and is welded to the megaphone with a 4" outlet.
I got a 4" baffle at the local boneyard so the bike is slightly not as loud.
Looking on the web I discovered the Supertrapp and Kerker are the same company. I have a set of diffuser discs and endcap on the way.
A later project will be to make a 'Y' from the collector and run 2 mufflers. Probably go from the 2 1/4" to two 2" exits. Supertrapp makes a 10" long muffler. Using the dics I can dial-in the back-pressure to get back to stock. Currently the motor is tired (60,000 miles) and a K&N in the airbox. I was hoping to do the big-bore kit this winter but that may have to wait.

[MAXIMAN]

Originally posted by Pat Kelly
Looking on the web I discovered the Supertrapp and Kerker are the same company. I have a set of diffuser discs and endcap on the way.

On the way for what? Your MAC? Or is it going into a Kerker/Supertrapp you have?

And secondly...CAN you still get diffuser discs and endcaps for these old Kerker headers? I thought they had completely discontinued them.

[trbig]

Those pipes are about like a woman I guess Cody.... just because they're pretty... doesn't necessarily mean they are worth a sh&%. Sorry to hear about the problems with them. They are beautiful and I know you gave alot of money to get them to you. It sure cost you alot to teach us a lesson. I do appreciate it though! If you remember, I had contacted you about them because I liked them so much.

I never really understood that about these bikes. On a car, the less resistance on the exhaust, the more horsepower. (EX. Open headers versus full exhaust) On a bike though, 4-1 makes better power than a 4-4 or a 4-2. I guess as we learned here though, at some point it becomes too much.

Tod

[xschop]

more power

From what I have heard, even here on the forum, the 4-1 makes more top end power, but the 4-2 makes more low end power. Please correct me if i"m wrong....

[79XS11F]

I actually contacted Supertrap about the possibility of getting a Kerker pipe. I'm sure they got a laugh out of my request and the answer was NO. So I did a Internet search on Exhaust design and found a few VERY interesting articles about this "black" science. There are a lot of things about an exhaust system that will affect where the added power will be seen. The collector DIA, method of connection and LENGTH are KEY issues for these systems. I have pictures of my old bike with a Kerker on it and I think I will make my own based on the pics. I will use parts of the bike in the pic to determine the scale. Use the headers of my MAC pipe and build the rest from the collector back with the help of any local muffler shop. they have PIPE BENDERS eh.
Rob

[John]

Bummer Cody

I know you dished out some big green for that system. Any chance of getting a refund?

[pggg]

Yeah Max that ain't a performance system, you can tell pretty much in one glance. It's a 'shiny showroom' exhaust For 4-2-1 you want 1 & 3 connected and 2 & 4 connected to 2 long wide diameter collecters before running to a large diameter funnel shaped exit to a well designed end can. 4-2-1 won't have the full kick of a good 4-1, but should be less peaky than the 4-1. There's an outfit down here(NZ) that make really good performance 4-1's (street legal) with S.S. muffler and a great sound, and they have the XS11 pattern. Might be a bit prohibitive shipping to the States, but then again the NZ dollar is only 63 US cents...

[MAXIMAN]

Well I don't wann be down too hard on them. The pipe made a lot of torque. 64 ft-lbs. The bike ran very good with the Motad. I could even get the front wheel up in first.

I think for a stock XS with no other mods you'd actually see more grunt and a little top end gain. But with this highly modified motor they don't flow enough and neither does the OEM exhaust.

I'll be putting them on Ebay soon. I won;t get the $500 I have in them but probably half that. Beats a stab in the eye with a sharp stick...huh?

I think they would work great for someone that needed a "replacement exhaust". They do sound very good.

But for a engine wiht as many mods as mine I need a honkin' 4-1. I just bought a Kerker from Bob Jones earlier today. Should be here in a few. next week we'll get it dialed in then we'll see if that helps. If that does no better then you 'ol XSive pal Cody maybe suckin' on a pistol...

[John]

Don't do that

That sudden, instant lead poisoning sux.

[MAXIMAN]

Well John it's either that or drop the Eleven and ride a Harley.

Now I ask you ...what would be your choice.

[MAXIMAN]

Re: more power

Originally posted by xschop
From what I have heard, even here on the forum, the 4-1 makes more top end power, but the 4-2 makes more low end power. Please correct me if i"m wrong....

It's not really even the configuration but backpressure. 4-1...4-2...4-4 ...6/8...220 or 221 whatever it takes... (thank you michael keaton)

Seriously though a little backpressure help build torque and low end. But it also restricts flow when the engine really gets winding on the top end because it can't get rid of the exhaust fast enough.

On the other hand if the exhaust flows so freely there is no restriction on top in then at high rpm it will really generate the juice. But you have to keep it revved up to get anything and you loose a lot of bottom.

However the reason I lost "bottom" initially on Zilla was the idle jets were way rich. Once I got them leaned up and tweeked the cam timing the bottom came back. My bottom loss had little to do wiht exhaust flow.

However my top end DID. The Motad simply couldn't keep up with the hot cam and the 1200cc engine and FJ1200 carbs. The OEM is doing a little better job. But as soon as I get this Kerker on it should really help across the range.

The Motad would be an excellent header for as a replacement and re-jet just pick up a few points. But for a serious overhaul as in my case it just won't flow enough on top to get rid of the exhaust gases.

Also ... I've learned tuning a bike can be a tedious process at best. Just ask Larry (GNEPIG). He had his red rocket on the dyno so long it wore out the rear tire! There are so many variables in an engine that have to be addressed in order to get the system on the money and running right. When you do a complete rebuild it just complicates the entire process.

(...mumble mumble...shoulda listened to Dan!)

[xschop]

we'll have to talk later

I have an extra engine that I want to put the 1200 kit in next summer. I know that others here have done it with varying outcomes....I want to learn as much as i can before jumping into it....thanks for the info.....chop