Popping Exhaust

[Guest Alan_builder]

Well gents,

 

That is it, I have had enough, I am throwing all my toys out of the pram!

 

I don't mind the jokes, I feel sorry for those with insufficient education to follow the Science - not their fault, but those who state black is white have p****d me off for the last time.

 

The last contradiction, it's the overlap on the valves causing the low pressure in exhaust to suck air in and cause the Poppoing - as likely a cause as seeing a blue moon.

We all (some of us) that between 30 degrees BTDC and ATDC the piston is almost stationary on it journey up and dow acting as a pump. The Valve timing on the overlap for the standard Pinto which pops is inlet opens 24 degrees BTDC and the exhaust closes 18 degrees ATDC.

The piston movement between 30 degrees and TDC is stroke 77

is 77/2*(1-.866)

which is about 5mm up and then 5mm down

So if you think that will decrease the pressure in the exhaust to less than atmospheric please go and look for blue moons.

 

The concept of air being sucked in through a hole. Well so many people have holes in their exhausts I for one don't believe that. Its easy to test, press a rag ball over the end of your and you should hear a leak from your hole which lets air in. Block it up as Nigel says and you will still find it pops. Well mine for one has no leak and pops, so BANG goes the theory!

 

What you know it all know nothing experts have missed is there is horse power to be gained by enriching the fuel!

 

By

 

PS instead of a Zero web get a Technical Section?

[fry61]

Yup -- gases.

[Guest zoomzoom]

Is it me or is this post getting shorter?

[agent_zed]

Its a shame you feel that way as i thought it was actually an interesting debate mixed with a little bit of humour just to ease the science along. A proper scientific debate should not really come down to 'i'am right and everyone else is wrong cus i said so' i have no problem with you explaining why you think you are correct with examples and even proving why someone else is incorrect.

 

for example i find it interesting that you are adamant that gasses will not go in through a hole in the exhaust when Mikuni state on their website

 

 

'Other possible causes:

 

Air Leaks:

 

Any source of fresh air into the exhaust system can create or worsen the conditions that bring about exhaust backfiring. The most common entry point is the junction of the header pipes and mufflers. Even a small air leak can dramatically increase the intensity or likelihood of exhaust system backfiring.

 

A high temperature silicone sealant, as can be found in many auto parts stores, may be used to seal the pipe/muffler junction. '

 

http://www.mikuni.com/tg_backfires_in_exhaust.html

 

unless ive miss-read what they have said. Maybe they are wrong but iam hoping a major carb manufacturer knows something about gas flow.

Maybe it is due to something else, resonance maybe?, but my car definitely doesn't sound like its pops as much on the overrun as it did before i fixed the leak at the manifold flange.

[Guest mower man]

Well gents,

 

That is it, I have had enough, I am throwing all my toys out of the pram!

 

I don't mind the jokes, I feel sorry for those with insufficient education to follow the Science - not their fault, but those who state black is white have p****d me off for the last time.

 

The last contradiction, it's the overlap on the valves causing the low pressure in exhaust to suck air in and cause the Poppoing - as likely a cause as seeing a blue moon.

We all (some of us) that between 30 degrees BTDC and ATDC the piston is almost stationary on it journey up and dow acting as a pump. The Valve timing on the overlap for the standard Pinto which pops is inlet opens 24 degrees BTDC and the exhaust closes 18 degrees ATDC.

The piston movement between 30 degrees and TDC is stroke 77

is 77/2*(1-.866)

which is about 5mm up and then 5mm down

So if you think that will decrease the pressure in the exhaust to less than atmospheric please go and look for blue moons.

 

The concept of air being sucked in through a hole. Well so many people have holes in their exhausts I for one don't believe that. Its easy to test, press a rag ball over the end of your and you should hear a leak from your hole which lets air in. Block it up as Nigel says and you will still find it pops. Well mine for one has no leak and pops, so BANG goes the theory!

 

What you know it all know nothing experts have missed is there is horse power to be gained by enriching the fuel!

 

By

 

PS instead of a Zero web get a Technical Section?

It is not theory ,after 40 years both playing for fun and working as a tech in varied dealer ships on various vehicles I can CATERGORICALY state that exhaust leaks cause overrun popping perhaps not the only cause but DEFINITLY the major one ,mixture ,timing ,cam profile can all play a part, but usualy get the exhaust right and the problem will disapear I know nothing about the theory that has been bandied about but offer alife times experience ,if Ihave upset any one tough!

you stick to your theory and I'll carry on curing it in practice mowerman

[Guest smartfazer]

I don't care too much about the theories. I like the popping sound on over-run.

[Guest Alan_builder]

Its a shame you feel that way as i thought it was actually an interesting debate mixed with a little bit of humour just to ease the science along. A proper scientific debate should not really come down to 'i'am right and everyone else is wrong cus i said so' i have no problem with you explaining why you think you are correct with examples and even proving why someone else is incorrect.

 

for example i find it interesting that you are adamant that gasses will not go in through a hole in the exhaust when Mikuni state on their website

 

 

 

 

http://www.mikuni.co...in_exhaust.html

 

unless ive miss-read what they have said. Maybe they are wrong but iam hoping a major carb manufacturer knows something about gas flow.

Maybe it is due to something else, resonance maybe?, but my car definitely doesn't sound like its pops as much on the overrun as it did before i fixed the leak at the manifold flange.

 

Its a shame the above link was made a reference when I initially asked for one as all the holes I have ever experienced with NORNAL cars is blows not sucks in the last 50 years.

The Mikuni article is about tuned bike engines revving much higher than Mr Pinto, so that may make some difference. The first section explains well what happens, the section which follows Lean Carburetion is exactly what I was on about..

 

So I apologize for not being given what I asked for and having never seen a suck.

The problem is who to take any account of without independent verification.

 

Yes its got shorter, removing myself from the board.

The final straw was being called silly or was it stupid by a MODERATOR for a serious debate

[Guest Botbuilder]

 

Here's another bit of theory for you from the BG Tuning Manual:

 

Exhaust pipe length and size.

 

As the exhaust valve opens, a positive or pressure wave front is created which travels down the exhaust pipe at the speed of sound.

As this pressure wave reaches the end of the pipe, it expands and a negative or suction pulse travels back up the pipe towards the engine. As the negative wave front in turn reaches the cylinder, it reverses again and moves back towards the end of the pipe. This fluctuating pressure pulse effect can be used to great advantage in tuning the engine. If the system is designed in such a way that the negative or suction pulses return to the cylinder at overlap T.D.C., then they will assist in clearing the combustion chamber of exhaust gases. In turn, this will cause a depression at the inlet valve, which will help draw in the inlet charge. Coupling the pipes of multi-cylinder engines will also mean that the pulse effects from one cylinder can be used to assist

the breathing of another. The following formula can be used to calculate the ideal length for a given application:

 

 

L = 129540 x E.T./R.P.M. x 6

 

 

Where:

L = Primary pipe length in mms measured from the exhaust valve head.

E.T. = Exhaust valve duration in degrees from point of valve opening before B.D.C plus the full

180 degree stroke up to T.D.C.

R.P.M. = The estimated revs, at which max. power will be achieved minus five hundred.

Example:

Exhaust timing = 80 B.B.D.C. to 50 A.T.D.C. Estimated maximum power R.P.M. = 7200

E.T. = 80 + 180 = 260

R.P.M. will be 7200 - 500 = 6700

Therefore :

 

Primary pipe length = 129540 x 260/6700 x 6 = 837 mms. or 32 ins.

 

 

 

If it were not for these negative pressure waves two stokes would barely work and there would certainly be no power band. The Yamaha FZR and EXUP wouldn't be much good either.

 

As some people seem to be getting a bit tetchy on this subject, I never said sucking air into the exhaust was the only reason for popping and banging on the overun, just one of them, and easy to fix.

 

Having wrote all that I'm now going to put some of Mr Benoullis olive oil on my pasta and carefully analyse the glug effect as it comes out the bottle. I suppose now I'll have started a heated discussion on the effects viscosity and the temperature of pasta.

 

[Guest Alan_builder]

 

Here's another bit of theory for you from the BG Tuning Manual:

 

Exhaust pipe length and size.

 

As the exhaust valve opens, a positive or pressure wave front is created which travels down the exhaust pipe at the speed of sound.

As this pressure wave reaches the end of the pipe, it expands and a negative or suction pulse travels back up the pipe towards the engine. As the negative wave front in turn reaches the cylinder, it reverses again and moves back towards the end of the pipe. This fluctuating pressure pulse effect can be used to great advantage in tuning the engine. If the system is designed in such a way that the negative or suction pulses return to the cylinder at overlap T.D.C., then they will assist in clearing the combustion chamber of exhaust gases. In turn, this will cause a depression at the inlet valve, which will help draw in the inlet charge. Coupling the pipes of multi-cylinder engines will also mean that the pulse effects from one cylinder can be used to assist

the breathing of another. The following formula can be used to calculate the ideal length for a given application:

 

 

L = 129540 x E.T./R.P.M. x 6

 

 

Where:

L = Primary pipe length in mms measured from the exhaust valve head.

E.T. = Exhaust valve duration in degrees from point of valve opening before B.D.C plus the full

180 degree stroke up to T.D.C.

R.P.M. = The estimated revs, at which max. power will be achieved minus five hundred.

Example:

Exhaust timing = 80 B.B.D.C. to 50 A.T.D.C. Estimated maximum power R.P.M. = 7200

E.T. = 80 + 180 = 260

R.P.M. will be 7200 - 500 = 6700

Therefore :

 

Primary pipe length = 129540 x 260/6700 x 6 = 837 mms. or 32 ins.

 

 

 

If it were not for these negative pressure waves two stokes would barely work and there would certainly be no power band. The Yamaha FZR and EXUP wouldn't be much good either.

 

As some people seem to be getting a bit tetchy on this subject, I never said sucking air into the exhaust was the only reason for popping and banging on the overun, just one of them, and easy to fix.

 

Having wrote all that I'm now going to put some of Mr Benoullis olive oil on my pasta and carefully analyse the glug effect as it comes out the bottle. I suppose now I'll have started a heated discussion on the effects viscosity and the temperature of pasta.

 

Lost your opertunity

[Guest dinger]

Can you all just agree to disagree?

 

Or can we just agree that the popping is unburnt fuel exploding in the exhaust exagerated by excess oqygen from a hole in the exhaust?

[Guest gixerboy600]

Just when you thought WW3 had been avoided!!! Back to defcon 3

[fry61]

On a much lower tehnical level--- do we not all fit longer headers (than manufacturers cast iron)before the collection point in order to improve breathing; therefore in my understanding the exhaust gas is pulling more charge into the cylinders; therefore it must be sucking at some point. Me? I don't know for sure.

[speedtripledan]

On a much lower tehnical level--- do we not all fit longer headers (than manufacturers cast iron)before the collection point in order to improve breathing; therefore in my understanding the exhaust gas is pulling more charge into the cylinders; therefore it must be sucking at some point. Me? I don't know for sure.

 

In coming take cover,,,,, wait for it

[Guest zoomzoom]

Or can we just agree that the popping is unburnt fuel exploding in the exhaust exagerated by excess oqygen from a hole in the exhaust?

 

 

PMSL very funny

[fry61]

"oqygen" is that a compressible fluid?