Over Exhausting.

[Admiral Akbar]

This seems to be a buz word... What does it mean?

I'd figure rhinestones with too much exhaust cam to the rest of the build may be "over exhausting" but that that'd be about it..

Max

[wfolarry]

Too much exhaust duration or a high intake/exhaust flow ratio. You don't want to know what I think about that because it's the opposite of what everybody else does.

[mayor]

good question Max, I'm curious to the answer as well (maybe I even helped inspire the question?).  My little pea brain kinda thinks that as longs as the fuel supply keeps up with the air flow, why would the torque suffer?  ....although I would think that would be contingent on the exhaust creating enough back pressure.  so, how much is enough back pressure?   

Too much exhaust duration or a high intake/exhaust flow ratio. You don't want to know what I think about that because it's the opposite of what everybody else does.

actually, I would like to know...I'm all ears:

[mscoolone]

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.

[Admiral Akbar]

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.

Good stuff now what's the best way to control this problem..

BTW Larry I'd bet that you are not alone.. Max

[Admiral Akbar]

I'm all ears

Why?
I been listing to my computer and all I hear is the fans..  Max

[Showdog75]

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.

Good stuff now what's the best way to control this problem..

BTW Larry I'd bet that you are not alone.. Max

WildThings TW-26g cams

[mscoolone]

Variable Valve Timing

[mayor]

I'm all ears

Why?
I been listing to my computer and all I hear is the fans..  Max

you mean your computer don't have the "word to talk" software?  well, mine must be a newer version.   

[Admiral Akbar]

you mean your computer don't have the "word to talk" software?  well, mine must be a newer version.

Oh,, I sorry mayor,,, Didn't know you couldn't read..    Max

[joelp34252]

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.

Good stuff now what's the best way to control this problem..

BTW Larry I'd bet that you are not alone.. Max

On a two stroke make sure your expansion chamber is matched to your port timing
Joel 2001 FLHT

[barny7655]

Barny here Max , perhaps do a dyno run ,with what you have, then one with a washer in the exaust port head, drilled out to restrict the out let ,eg if you have1, 3/4 inche put it at1,1/2, this im sure will flow back to the port more so than one  down further, like the old two stroke motors,see how the dyno excepts this towards your inlet over lap , be nice to try ,if it was variable it im sure it  would flow different numbers,but as it was said before variable cam timming will be on the agenda for HD in the future easy to do  ,cheers Barny

[mayor]

Oh,, I sorry mayor,,, Didn't know you couldn't read..   Max

that's ok, happens all the time.     that's why I prefer when people post pictures of how they did something.     a picture says a thousand words...

[PanHeadRed]

>What does it mean<

Drag pipes on a street bike.

You might find these next three interesting.

95" @ 9.7:1 CV40 V&H Straight Shots

[attachment removed after 60 days by system]

[PanHeadRed]

95" @ 9.7:1 CV44 Borzilla

[attachment removed after 60 days by system]

[PanHeadRed]

Borzilla CV44 vs. V&H CV40

[attachment removed after 60 days by system]

[hollywood63]

Too much exhaust duration or a high intake/exhaust flow ratio. You don't want to know what I think about that because it's the opposite of what everybody else does.

Larry we do want to hear what you think.  The following is a qoute I saw on Speed Talk

"If the results don't agree with the Theory,
believe the results, and get a new Theory"

[Admiral Akbar]

Red,

I assume the better curve shows what a the 44 can do over the 40 with a set of good flowing heads.. 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...

"If the results don't agree with the Theory,
believe the results, and get a new Theory"

I would change this a little.. "If the results consistently don't agree with the Theory"  One of the biggest problems is that bad data leads to bad theories. Max

[Don D]

This logic may hold water if the builds were identical time after time. Unfortunately they are not.

[PanHeadRed]

Max, what I found interesting is it has been reported on a few occasions that a Borzilla is to much exhaust for a 95", TQ dips and all that.

What I find to be true is the better the heads breath on BOTH ends, the better the potential of the entire rpm range the cam is designed to work in, including the low end. A wise man once told me "if you choke your exhaust in an attempt to improve your low end, you should rethink you system".

I also have heard a lot about "over exhausting" and like you I am waiting for the explanation.

IMO exhausting an engine in and of it's self is a system. Not just an arbitrary thing, defined by the size of a valve.

[Don D]

I might believe that if a cam such as a TW37 with these heads could reach 107+ tq rather consistently with 9.2/1 corrected compression in an older model at 95". I don't see that happening with many heads. I have a set of competitor heads here now that if I was looking for problems would not be able to find them they are high flow from the bottom up and exhaust is right there at 80+ % all the way up. Problem is this only makes a little over 90hp and 95tq with a good pipe (roadrage) and tune (Latus), TW6h cams.
Red your heads are just working well with the cams you chose and of course the pipe just enhances that. I think that heads that don't have flow problems such as vortexing and hot spots work better across the board but still not sold on 90+ exhaust ratio with most cams, or for that matter 70% range with some cams. Matched parts work well together, simple as that. VE is picked up when the exhaust is working properly during overlap and assuming the cam choice is not too long that is where the desired torque band occurs. I am inclined to like the idea of a little more head flow and throttle that back with a shorter cam rather than a longer cam and an inadequate head

[PanHeadRed]

>assuming the cam choice is not too long<

Long cams = higher rpm range, and as you know RPMs have a big effect on exhausting.

[Admiral Akbar]

I think that heads that don't have flow problems such as vortexing and hot spots work better across the board but still not sold on 90+ exhaust ratio with most cams,

If you were designing a set of heads from scratch, it would be advantageous to pick a more appropriate intake to exhaust valve ratio. Since head porters here are dealing with heads that HD has already designed, shrinking the exhaust valve to get more intake might be more than what the average guy wants to pay.. (I guarantee mayor ain't buyin' it..  )  Might as well buy a new head. With that in mind it seems to me that you get the best flow out of what you got and find a set of cams intake and exhaust that giver you a power band you want. I think on of the issues here is that many find a set of heads with good power numbers, a cam on another build that gave good numbers, and an exhaust system that give nice torque where wanted (and sound).  They throw the combo together and it don't run.. The problem is that they don't look at the motor as a complete system that needs to function with all the components together..  They complain that the head, cam, or exhaust is a piece of poop..

Now me? I don't mind trying different combos and striking out (well I do but I expect to strike out occasionally  ) .. Eventually you get a hit or two but there is still that swing and miss.. Those wanting to get on base need to go with proven combos.. Even then it doesn't guarantee that here is some obscure problem that needs sorting out..

Max.

[mayor]

If you were designing a set of heads from scratch, it would be advantageous to pick a more appropriate intake to exhaust valve ratio. Since head porters here are dealing with heads that HD has already designed, shrinking the exhaust valve to get more intake might be more than what the average guy wants to pay.. (I guarantee mayor ain't buyin' it..  ) 

Max.

well, I wouldn't be the least bit surprised if my level of cheapness may be far more advanced than the average person.     although, I do agree that most enthusiasts have a price point that they are unwilling to cross in pursuit of being faster than their buddies.  Lucky for me, I'm satisfied with just being cooler

[hardyheadscom]

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.