HarleyTechTalk

 >What is interesting is that some like to say CV self compensate on the low end but it's obvious here that they don't...<

AFR data might show why......

Take the 110 exhaust port for example. Huge, 1.625 exhaust valve and 88% throat. 220cfm on a good day out of the box with very slow velocity.

Quote from: hardyheadscom on May 26, 2009, 08:56:42 AM

Quote from: mscoolone on May 25, 2009, 05:25:32 PM
The goal is to open and close the valves throughout the crank rotations and keep the torque and cylinder pressure maximized. Increased flow and/or increased cylinder volume gives increased power. In short, the intake/exhaust moved less volume as the rpm is increased.

Restrictive exhaust - close early - the cylinder volume is not completely emptied of exhaust gases, has residual pressure and the inlet charge is compromised by exhaust pressure and spent gases still in the cylinder.

Exhaust is effectively designed and timed correctly; it will not have residual pressure at the closing point. It is possible to help draw clean intake charge into the cylinder referred to as scavenging.

Over exhaust - close later - the cylinder volume will be contaminated with residual exhaust gases coming back toward the cylinder, lessen the total cylinder filling, in turn reduces the cylinder pressure due to the exhaust system seeing atmospheric pressure.

If this were the case the bigger the exhaust the better the engine will perform.............but it`s not the case.

During overlap, there is charge exchange possible between the inlet and exhaust ports. If the intake and exhaust timing events have been optimized to produce maximum cylinder filling and pressure, the TDC overlap activity has to be a balance of intake opening and exhaust outflow. The inlet port effectiveness and valve timing events control cylinder-filling capability.

What controls exhaust effectiveness at a given RPM range with a fixed size inlet port & valve?  Lag, Inertia?  A balance of exhaust valve timing events, the emptying of the cylinder volume and exhaust outflow?

All true which is why one size that flows well does not fit all.
People use different cams, pipes, compression. Many heads work OK but to leverage the advantages of the overlap cylinder filling and emptying the relationship and exhaust flow and velocity come into play during this period. Remember Mayor this topic comes up again.

Quote from: Deweysheads on May 26, 2009, 11:03:58 AM
All true which is why one size that flows well does not fit all.
People use different cams, pipes, compression. Many heads work OK but to leverage the advantages of the overlap cylinder filling and emptying the relationship and exhaust flow and velocity come into play during this period. Remember Mayor this topic comes up again.

yep, I think this is definitely a good topic for discusion.  I think there may actually be enough grounds for two sepperate conversations.....one based on exhaust port flow in the heads, the other being the actual exhaust system.....I guess that's the tough part for you pro's to make sure both work together. 

to kinda hi-jack Bruce's over exhaust question, I'd like some comments on the results of the autotune (T-Max) results that I got using my tunable Supertrapp internal disc mufflers (currently 18 discs in each).  I used the base map for Rinstone TD's and stock 88" ('01-'04).  Here's the front:

and the rear offset:


the blue was baseline, and the green was what the autotune changed from the base map settings.  if I'm reading this correct, the front cylinder needed fuel to be trimmed out and the back cylinder needed fuel to be added?  if that's the case, couldn't I add discs to the front muffler and subtract discs from the back cyclinder to tune the mufflers more to the bike?

the other being the actual exhaust system

Well many assume their system actually scavenges, some do, so do not very evenly, so do overly well.

QuoteIf this were the case the bigger the exhaust the better the engine will perform.............but it`s not the case.

I would say not always the case..

I had a 95 ci TC FXDX 10.8 to 1 CR, a 122 cfm intake and 115 CFM exhaust home ported heads(didn't knoe how bad the intakes were until I got the flow bench and at that time the motor no longer existed), G carb, CS slipons, TW50 cam.. Bike ran great, tried a TH and power dropped.. If I'd known about baffle bending I would have tried it. When to arIIIs and the motor picked up 6 hp..

Flip side,

113 SnS evo 11 to 1, 640 cam mild clen up on the stock heads pick up 10 hp (114 to 124) going from pretty much any high perforamce muffler to a 2 1/4 stepped exhaust system with straight through glass pack exhaust. All it wanted was flow...

Max




 

Mayor,

I would have used the VnH true duals as the pipe diameter is probably closer to you pipes.

Sonny,

Caught me on that one.. 

Max

the only V&H I saw a map for was staggered duals for Softails...

map 428 was the base map I used.

Mayor.... maybe you are under exhausting   

Quote from: Sonny S. on May 26, 2009, 02:00:39 PM
Mayor.... maybe you are under exhausting   

that's what I was thinking with the front pipe, yet seems like the rear pipe probably flows a little more than needed (but probably ok).  I may look for 4 3" discs to through on the front pipe muffler. 

How bout valve timing events?
Was the lift and the duration checked at the valve to insure the cam is installed per specific requirements, Do both cylinders have equal amounts of cylinder compression?
Could there be a manufactures error in one of the cams/hydraulic lifters?
Could one cam be lagging behind due to lash adjustment, sprocket wear, chain stretch?
Could retarding or advancing the camshafts improve on the desired performance?

Over exhausting? There is no 'one size fits all' answer, although exhaust manufacturers may want you to believe that. One thing that must be kept in mind, and most people overlook, is the state of the air/fuel mixture. On one side of the equation you basically have atmospheric pressure, on the other you have a heated compressed gas. An exhaust system must not only pass this compressed gas, but it must also control the expansion rate. The expansion rate, I feel, plays a more important role in velocity, than simply the size and shape of the exhaust, to put it simply.

With this being the case, over exhausting would then be defined as uncontrolled expansion of a gas.

Quote from: mayor on May 26, 2009, 01:31:08 PM
the only V&H I saw a map for was staggered duals for Softails...

map 428 was the base map I used.

I'll look at home but I bet you are right and I'm in error..

BTW based on what the thing leaned out on the front The swing on the rear makes sense since it is referenced to the front.

QuoteThere is no 'one size fits all' answer, although exhaust manufacturers may want you to believe that.

absolutely,,,


Max

In fact the only exhaust rule of thumb I know of is:
A well designed exhaust system will work better than a poorly designed one no matter what the application.
IE: Thunderheader, Fatcat, Supermeg, etc work well for most all builds, whereas straightpipes, bagger tru-duals with open muffs, and other systems produced for looks rather than performance, do not work well no matter what they are bolted onto.
Just my $.02,
Bob

The V&H true duals & Hooker adjustable slip ons played fairly well on my bagger with the HQ split duration cams, but not so much with the Tman cams I'm running now...just food for thought Bob not trying to start an argument 

Quote from: 05FLHTC on May 26, 2009, 05:02:50 PM
The V&H true duals & Hooker adjustable slip ons played fairly well on my bagger with the HQ split duration cams, but not so much with the Tman cams I'm running now...

Can you elaborate? You must admit your comment isn't very technical addressing the differences in cams and how they worked with the V&H w/Hooker slipons.
Did you dyno tune the different cams with the same exhaust? What was the finding?

Yep the Propipe busted the rear nipple off for the 2nd time & I had the duals & Hookers from prior. Took it in had it dynoed, the setup duals actually made more on the bottom end & left about 6 HP off the top from what I recall. This was on the same 250I at Valley racing & with the same dyno operator Brian. When I decided to swap out the 33G's for the Tman 625's over the winter, they did not fair well with the duals but did well with the Propipe.

By the way at that time the pipe then & continues to shine now was the new Bub 7 (2 in 1), the only way we could get anything to compare close was to close off a couple of rows on the Propipe stock baffle. That Bub has performed well on everything that it has been tried on...I'm just tired of forking out 500 bucs for another exhaust system & my Propipe sounds good & only lack like maybe a couple numbers behind.

Hope that was technical enough

Edit addition so I guess if I had to draw a conclusion based on my own experience, the split duration cams do not seem to be as sensitive to exhaust needs scavenging ... or maybe it was just a fluke coincidence?

Quote from: 05FLHTC on May 26, 2009, 05:52:34 PM
When I decided to swap out the 33G's for the Tman 625's over the winter, they did not fair well with the duals but did well with the Propipe.

Guess what I'm asking is for a more specific comparison such as where the power moved from and/or to with the change. Did the power increase in an area where the other pipe lost? etc.
Where did the duals look desireable over the 2into1, if at all?
IMO cam timing can make even the best of pipes look bad.

QuoteEdit addition so I guess if I had to draw a conclusion based on my own experience, the split duration cams do not seem to be as sensitive to exhaust needs scavenging ...

Totally agree with this statement.
Bob

Quote from: FLTRI on May 26, 2009, 06:22:37 PM
Guess what I'm asking is for a more specific comparison such as where the power moved from and/or to with the change. Did the power increase in an area where the other pipe lost? etc.
Where did the duals look desireable over the 2into1, if at all?
IMO cam timing can make even the best of pipes look bad.

Yep moved the Tq & Hp like said about 6 numbers from 6K rpm & transferred it right into the 3K rpm range. I was shocked based on all the readings & bad rap the duals receive, never would have believed it & would not be saying it without seeing it on the dyno. Oh and buy the way, nothing & I mean nothing sounded as good as them true duals & hookers did though they were a tad loud at 80 mph on the slap IMHO.

Edit sorry Max didn't mean to side track the thread

Quotefrom 6K rpm & transferred it right into the 3K rpm

So the Duals made 6 less hp/tq @6k but made 6 more hp/tq in the 3k range as compared to a Propipe?
Sorry just trying to garner some knowledge from the comparison as I have not done back to back tests with these 2 exhaust systems, but definitely interested.
Thanks,
Bob

O.K...............it seems some have a good grasp to what`s going on... so when is a good time for the intake to close and the ex to open.

Quote from: hardyheadscom on May 26, 2009, 09:36:38 PM
O.K...............it seems some have a good grasp to what`s going on... so when is a good time for the intake to close and the ex to open.

When I finished eating and gotta take a .... 

QuoteEdit sorry Max didn't mean to side track the thread

Actually you are right on the money.. See below

QuoteBy the way at that time the pipe then & continues to shine now was the new Bub 7 (2 in 1), the only way we could get anything to compare close was to close off a couple of rows on the Propipe stock baffle.

So wouldn't you say that the pro-pipe was over exhausting? By blocking it off you picked up power.

IMO Hookers make good low end TQ because they are not a "flow through"  exhaust and have a good reflection point.. Cycle shacks are another.. Give a nice power band but not maximum power..

QuoteEdit addition so I guess if I had to draw a conclusion based on my own experience, the split duration cams do not seem to be as sensitive to exhaust needs scavenging ...

If you mean longer exhaust duration than intake, I would disagree here. I assume the split duration cam did better than the non split one with the propipe when the holes were covered. over exhausting..

BTW
Larry not sure the answer to your question but I'd bet the exhaust system will have an effect as to where the best timing is and vise versa..

Bob, I though you didn't think that an exhaust would have any effect on pushing the TQ curve around..

Max

Quote from: MaxHeadflow on May 26, 2009, 10:07:35 PM
Bob, I though you didn't think that an exhaust would have any effect on pushing the TQ curve around..

Max

What I meant to convey was the cam's profile sets the peronality and the exhaust can either help or hurt that personality show through.
Peak power rpm should be dictated by the cam profile not the exhaust.

QuoteWhat I meant to convey was the cam's profile sets the peronality and the exhaust can either help or hurt that personality show through.
Peak power rpm should be dictated by the cam profile not the exhaust.

Gotcha,
We're saying the same thing only, I like to add that you can used the exhaust to change the personality.. I like to think of all the major systems/components of a motor as a simple tuned circuits .. In electronics the simplest is an LCR (LC is the ideal but there is always R).

http://www.electronics.dit.ie/staff/ptobin/lab007.pdf

Now if you take all these circuits and stack them together right you cam make very good power.. Miss-tune a bunch and you get them fighting each other and a sucko output.

The dreaded torque dip is a prime example.. But you can also use the "miss tuning" of the exhaust to spread a torque peak of narrow LSA cam.. 2 into 1s? They have 2 tuned circuits, one in the head pipe, the other in the muffler.

Max