[phoenixt]

I "may be wrong" (I will use this qualifier more now that the forum seems to have turned into the high school debate club) but I believe the pipe cross section is a cut piece. It also appears to have more than 2 layers of steel and one layer of some heat resistant fiber. 

Steve

I am surely checking my spelling and grammar too.  My old english II teacher is roaming about. 

[Guaire]

Do me a favor. Since your stock head pipe is now off your bike, can you take a scotch brite (or the like) and clean the pipe up at the head?

Then possibly shoot a couple pics?

My curiosity is pretty strong that you may have an anomaly on your hands as an oddball single wall pipe. You may indeed, have the ONLY "thick wall pipe" GT in the world!

Could you do that, just to see?

Thanx.

  I'll be replacing my stocker with a Carpy. I will get some pics on it.
Cheers,
Bill

[Farmer_John]

I "may be wrong" (I will use this qualifier more now that the forum seems to have turned into the high school debate club) but I believe the pipe cross section is a cut piece. It also appears to have more than 2 layers of steel and one layer of some heat resistant fiber. 

Steve

I am surely checking my spelling and grammar too.  My old english II teacher is roaming about. 

I'm often wrong and There's nothing at all wrong with being wrong.  It's how well you reference what's right that makes the difference between success and failure or being professional or an expert.

This is a quality many humans lack. It's real easy on the Internet to sit at a keyboard and pound out your expertise and quite another to have the humility to say "oops, I screwed up" when found in error.

It's how we learn.

I now present this photo of a cute puppy in a swing as a token of my sincerity.

[ace.cafe]

I just had a conversation with a guy who is one of the leading exhaust system designers for NASCAR.
He says that the step position needs to be tested, but the usual lengths involved will be between 8"-15", depending on the rpm range intended.
So, the step in this pipe is probably aimed a bit on the lower end of the rpm range scale, which probably is not so bad for our intended street use.
We will have to see how it tests out. At least it has a step in it, which is more than can be said for the other pipes.I think it is likely that the tail end of it will need to be cut shorter. Depending on where the bracket mount is near the tail, we may be able to get it as short as we use it on the Fireball.
The OAL of the whole system with the megaphone on it wants to be around 42"-45" to the back.

[former_rider]

The OAL of the whole system with the megaphone on it wants to be around 42"-45" to the back.

If the step turns out to be in the right place, or perfect place, or whatever - that would be great.

As far as the OAL here is what I'm thinking.

1) Carpy's pipe (like most, I suspect) is designed to terminate at roughly the same position as the stock pipe. This allows folks to use his pipe with a factory megaphone, or a hitchcock megaphone, or any other megaphone that is designed specifically for the stock header and using "factory" mounting points.
2) If the OAL needs to be shortened there is the option to cut Carpy's pipe - as long as you understand it might require more fiddling to get a given megaphone to fit.

For example, I've got Carpy's pipe and megaphone. Carpy's pipe termination is straight (no upsweep). Carpy's megaphone starts with an upsweep and attaches at the passenger peg mount just like stock. I can cut Carpy's pipe maybe an inch or two before the angle of the megaphone causes clearance issues with the peg/brake pedal - due to the upsweep. If I did cut it I would need to fabricate an attachment.

And if I wanted to reduce the OAL even more I could cut the pipe and use a custom/generic silencer - to get the length I was after - and have to fab the mounting bracket.

I imagine that since Carpy's pipe is SS - not chromed - cutting it should be no problem. Depending what it's cut with I guess it might introduce the possibility of rust at the cut. But that could be dealt with as well.

So all we need now are the magic dimensions. Length to step and overall.

=)

[Guaire]

Stock header, angle adapter, HD Sportster silencer = 59 1/2". Outside length.

[Farmer_John]

Hey Ace, before everyone starts hacking up their exhausts, how large a variance COULD there be in balancing exhaust length:absolute power?

What sort of loss (expressed in percentage) could you possibly be looking at?

I really do appreciate your ridiculously hard work on this project.

I realize that at the moment it's all a poker game and you can't be 100% on that figure, but it's that way even with the head at the moment (I'm really looking forward to a real world report on a 535).

[ace.cafe]

Hey Ace, before everyone starts hacking up their exhausts, how large a variance COULD there be in balancing exhaust length:absolute power?

What sort of loss (expressed in percentage) could you possibly be looking at?

I really do appreciate your ridiculously hard work on this project.

I realize that at the moment it's all a poker game and you can't be 100% on that figure, but it's that way even with the head at the moment (I'm really looking forward to a real world report on a 535).

Okay, let's back up a bit here, and start at the beginning.

First, I'm not recommending that everyone start hacking up their exhaust pipes. This is in the context of a performance build, not a stock GT.The stock GT cannot support a 6000 rpm hp peak, so there is no point in tuning the exhaust for an rpm range that the engine cannot possibly reach. I'm talking primarily to people using Ace heads here, which we are tuning for higher rpm range and different power curve entirely than stock.

Second, regarding the tuned length, every pipe has a tuned length. It just depends on what it is tuned to. So, it comes down to where you want to bolster the power curve with the reflected waves that the pipe is producing. Any random pipe will give you some wave results, but the idea of tuning it is to get the wave doing what you want it to do. So, your stock pipe, or your regular Carpy pipe, or your Hitchcock pipe, all are going to have some wave activity based on the length and diameter, and they are probably going to be similar, because they all bolt up about the same, and they all have similar length. It's designed around the stock bike. Cutting the header shorter on a stock engine may end up with just a loss of lower end torque, and no increase in higher rpm power because the engine can't reach up there, due to lack of breathing potential in the head and cams. So, we don't want to jump the shark. Don't cut anything until we know what to start doing for the engine set-up that we are working with, and we may not all be working with the same engines, especially when talking about stock head vs Ace head which will be very different. As a general "rule of thumb", the shorter you make the pipe, the higher the rpm that it is tuned to, and the longer the pipe, the lower the rpm that it is tuned to. But every pipe length has the tuning that is associated with its length, sort of like organ pipes with the big long bass pipes, and the short treble pipes.

Regarding silencers, the ones that tune best are open silencers without baffles, such as megaphones. Any baffle stacks in the silencer breaks up the wave action, and make it less useful, which might be a good thing, or a bad thing, depending on what you are aiming at. In a stock bike, it is probably not a bad thing to break up the waves to some degree, because the stock bike is aimed at a very broad powerband that doesn't have much peak to it. Tuning the exhaust wave tends to make a peak higher, but narrower. This is sort of shifting power from one part of the power curve to another, in order to get it where you want it.

So, let's start with the caveat that I'm giving information here based on potential users of the Ace Billet GT Head, and estimated tuning characteristics based on that. Stock GT bikes have different parameters, and different needs. Tuning them needs to be addressed based on the state of the mods on the given bike, and the rpm range that it will be accessing, and the aims of the user.

Regarding your question about "how much difference does it make", it's probably just a couple hp, but it matters where that couple hp happens, If we are hitting 98 mph at top speed, and that's all we can do, having that exhaust pipe tuned to the right spot to give us a couple extra ponies right at that rpm where we are hitting top speed can push us over The Ton, and we have seen exactly that in some previous Fireball applications. So, it's a matter of "how much" AND "where in the rpm range" we put it.

[Farmer_John]

Perfect Tom.

But I have to admit, it makes me wonder if the billet head is really what I'm after, if it is aimed mainly at top end power, when most my riding is on twisty 2 lane, where I'm working the midrange.

I personally am not fond of freeways even on large displacement bikes (I mean, they're boring as hell to ride 90% of the time), so busting the ton isn't all that important to me, where low end with a big midrange hit may be it.

Time will tell. But again, I enjoy reading your stuff. I walked away from Motos in the late 90s from burnout and this bike is just sucking me back in. You're providing knowledge that is pretty priceless.

[ace.cafe]

Perfect Tom.

But I have to admit, it makes me wonder if the billet head is really what I'm after, if it is aimed mainly at top end power, when most my riding is on twisty 2 lane, where I'm working the midrange.

I personally am not fond of freeways even on large displacement bikes (I mean, they're boring as hell to ride 90% of the time), so busting the ton isn't all that important to me, where low end with a big midrange hit may be it.

Time will tell. But again, I enjoy reading your stuff. I walked away from Motos in the late 90s from burnout and this bike is just sucking me back in. You're providing knowledge that is pretty priceless.

A couple of points.
First, I have addressed the expected estimations of the shape of the power curve for the Ace GT head previously, but in the event that anyone missed that, I will go over it again.

Second, while I used the exhaust tuning example in a scenario where the aim was increasing the hp peak at the top end of the scale, that is not by any means the only result that can be tuned. It can be tuned for any rpm in the range, based on what the need is. In fact, as I previously stated, the header length commonly tunes for peak hp, and the OAL length of the exhaust system is commonly tuned for torque peak which is usually smack in the middle of the midrange. This ends up being a "dual tuning" system, which is advantageous when we can do it.  However, it is common to set the hp peak to occur near the top speed of the bike, with the intended gearing, because top speed is typically one aspect that people associate with a performance machine.

Now, back to the power curve with the Ace GT Head.
We are anticipating using the stock cams with this head, for the reasons of hoping to protect the sprag system with the auto-decompressor, and also saving some money because we can add breathing with the high ratio rockers.
So, this works out as mostly a valve lift increase over the entire lift cycle, with the added result of a slight increase in overall effective duration, and increasing duration of all the lift points along the entire lift curve. This brings a big breathing increase, but not much duration increase at the opening and closing ends of the lift cycle.
Effectively, this helps keep the cylinder pressure high such as is characteristic of a short cam, which helps torque. The added breathing of the rocker ratio lift and the port and valve flow give more air into the cylinder at ALL rpms. The effective result of this is MUCH more torque thru the entire range, AND the benefit of increased breathing which can extend the rpm range some amount, without extending duration, simply because we can get more air into the cylinder in the same amount of time as before. So, rpm can be extended some, but probably not a whole lot. We expect 6000 rpm or so will be where it will peak out, but that's as far as the Power Commander will allow with its rev limiter increase, and as high as most users would even want to rev it anyway.
However, the big impact of this high lift and bigger flow will be seen in the "meat" of the powerband, such as the all-important midrange.
I mentioned before that as a general rule, "Lift = Torque" and "Duration = rpms". We are not doing hardly any duration increase at the very ends of the cycle where it counts, but are increasing lift by 43% over the entire lift cycle. This will raise the torque output at all rpms. The hp increase will come due to the inherent rpm multiplier of torque that is part of the hp equation(hp = tq x rpm/5252). So, as you can see by this equation, hp will automatically increase at every rpm over the range that sees a tq increase, by definition.
And if that isn't enough, we are making a smaller and more efficient combustion chamber, which will raise the compression ratio by about a full point, increasing the torque  output even further, while fighting detonation with improved squish and more compact chamber for faster burn time.

If I were to make a general statement about what we planned for this Ace GT Head, the torque output over the whole range will see more increase, than rpm increase of the top rpm. It is primarily a torque building approach with this head, and the hp will automatically follow by definition of the equation.

I hope that clears it up.
We designed this to give more power EVERYWHERE from bottom to top, with just that 500-1000 rpm increase at the top of the rpm scale for increased top speed along with it. All of the techniques employed in this design follow this goal. Just because we are getting more at the top, doesn't mean we aren't getting more in the midrange too.
 

[phoenixt]

Ace, I have read that Bultaco Matadors had a tunable exhaust system that let the rider change the amount of power and where the peak power fell in the RPM range. I have been trying to find how they worked but can't.

Have you ever heard of something like that?

Thanks,
Steve

[ace.cafe]

Ace, I have read that Bultaco Matadors had a tunable exhaust system that let the rider change the amount of power and where the peak power fell in the RPM range. I have been trying to find how they worked but can't.

Have you ever heard of something like that?

Thanks,
Steve

It was a 2-stroke engine, and those types of engines are particularly sensitive to exhaust tuning.
The basic idea of rider adjusted intake and exhaust lengths  is too much to expect the rider to do during actual competition. For street use, it isn't practical.
However, due to the advent of computer control over engine management, it is quite common to see high-zoot sport bikes with computer adjusted intake stack lengths which change length at various rpms for increasing power over the range. Not so much with exhaust systems, though.

[phoenixt]

I was thinking it was to make the bike easier to use for different types of use. They were an enduro. 

Back then (I am sure you know this already) it was more common for people to use their bike during the week and compete with it on the weekends. No need for a trailer, truck or van either. Just ride it there.

Steve

[mevocgt]

After reading a few of these posts today, I feel like this story may be entertaining and related:

I had a freind, who just passed last month, that raced a formula 3 Ducati single back in the sixties.  He had just had some work done on the bike and had it out for it's first race weekend after.  He went out on his first practice lap.  When he came back in the pits, he began to complain about how the bike just wasn't running right, there wasn't any power in the turns, WTF?  His mentor walked over to his paddack with some plyers, bent down and crimped the end of his exhaust.  Told him to shut up and take it out again.  He did as told, and the bike ran great.  He won his race, and all was good.  How's that for tuning?

[ace.cafe]

After reading a few of these posts today, I feel like this story may be entertaining and related:

I had a freind, who just passed last month, that raced a formula 3 Ducati single back in the sixties.  He had just had some work done on the bike and had it out for it's first race weekend after.  He went out on his first practice lap.  When he came back in the pits, he began to complain about how the bike just wasn't running right, there wasn't any power in the turns, WTF?  His mentor walked over to his paddack with some plyers, bent down and crimped the end of his exhaust.  Told him to shut up and take it out again.  He did as told, and the bike ran great.  He won his race, and all was good.  How's that for tuning?

This is the old "back pressure" discussion. It comes up frequently during exhaust discussions.
 

Basically, pinching off the end of the pipe may have helped a condition mostly in the lower rpms, but it did nothing good for the higher rpms. If that helped the engine performance, it was in a pretty horrible state of tune for a race bike. If a bike like that won a race, it doesn't say much for the other bikes in the race.
I am not saying that this type of thing could not make an improvement, but if it did make an improvement, the engine was very poorly tuned to begin with. If the engine was built and tuned right, doing something like that to the exhaust would kill the performance.