4722 replies to this topic

[Nev]

 

 

Anyway, details aside, the outline calcs highlight the importance of > 3" pipework 

 

Well that's where the details become important. The gas expansion is the difference between the IAT and EGT, and I believe your calculations underestimate IATs and overestimate EGTs which results in a calculation overstating the volume of gas you need to flow and thus the exhaust diameter needed.

You may argue that you want to build in a safety margin but with the amount of work this safey margin involves (assuming that correct numbers allows use of a 3 inch diameter exhaust) that it would be tolerable to accept a slight loss of power on the rare occasions where these gas volume is slightly greater.

 

 

Sheesh, you always have to get stuck on trivial/unimportant details. Lets just take your numbers and say the inlet temps are 45 degrees (the max I've ever seen in 8 years) and the EGT is 900 degrees (which would be startling low indeed). Even then:

 

Inlet air temp = 45 degrees C,

EGT from engine = 900 degrees C,

Then the exhaust gas will be 3.68 times the initial volume (according to Charles law).

Based on power of 520 BHP, the engine will consume circa 22000 Litres of inlet air per minute.

So multiply 22,000 litres * 3.64 = 80,080 Litres/min coming out of the cylinders.

Push this down a 3" OD exhaust pipe with an internal X-sectional diameter of 73mm means that the gas will attempt to move at 731 MPH.

 

So, even in this best case situation the speeds of the gas in the exhaust will (attempt to) travel at 731 MPH (rather than 850 MPH I previously calculated). Either way you don't have to be Einstein to realise that at 731 MPH the gas will face a lots of resistance due to the restriction of a 3" exhaust.

 

And this is why I chose to install a 3.5" exhaust.

 

 

 

Edited by Nev, 18 November 2016 - 03:43 PM.

[The Batman]

Will be interesting to see your iat on track, although I doubt you will get on track with a 3.5" exhaust

[Nev]

Will be interesting to see your iat on track, although I doubt you will get on track with a 3.5" exhaust

 

My max IATs in Autumn about 4 years ago (around 12 degrees C ambient at a guess) on a 6 mile stretch at more or less full chat non stop only reached about 43 degrees. That more than emulated the use of the engine on a track IMO.

 

IATs are not a problem on my car, its the oil temps that I suspect to be too high.  

Edited by Nev, 18 November 2016 - 03:48 PM.

[The Batman]

Imagine constant on/off power for 20mins

[KurtVerbose]

So, even in this best case situation the speeds of the gas in the exhaust will (attempt to) travel at 731 MPH (rather than 850 MPH I previously calculated). Either way you don't have to be Einstein to realise that at 731 MPH the gas will face a lots of resistance due to the restriction of a 3" exhaust.

 

 

And this is why I chose to install a 3.5" exhaust.

 

I thought it was the speed of sound that you need to avoid, both for gas flow efficiency and noise?

 

Speed of sound at 45°C is approx 800mph, at 900°C it's +1500mph (not sure about pressures with these numbers but higher pressures raise the speed of sound). You should be no where near the speed of sound.

 

Briefly looking at other engines of similar bhp they don't need such wide diameter pipes, and most of them won't be near you on EGT or pressure. Also, looking at aftermarket pipe replacements that are wider, there's not much BHP liberated.

 

 

 

 

 

* The above might be rubbish.
 

[Nev]

Imagine constant on/off power for 20mins

 

I think you are not taking into account that on a track an engine gets to "rest" for many of the corners, whereas the test I did was 6 miles non stop at 6000 to 8000 RPM with heavy load on the engine, with a few mild bends maybe at 5000 RPM. After a brief stop of about 30 secs I repeated the test several times, probably over about 30 minutes in total before I was exhausted and told my passenger (who was collecting metrics on his laptop) that I had to stop !

 

On the other hand most UK tracks have quite a low attainable speed, so ram effect on the rads is considerably less, maybe this would mount up a lack of cooling issue. Having said that once Nipper gets up to about 70 MPH the rads do deffo seem to work well.
 

Edited by Nev, 18 November 2016 - 05:15 PM.

[CHILL Gone DUTCH]

Yourvengine should deffinayely not be resting in the corners on track nev In fact its probably under most load on corner exit as your loading up tires and chassis and trying to be on full throttle Even when slowing down your not really resting the engine as your using it to brake to I've said this before but track use is 1000 times harder on a car than any road driving

[fezzasus]

 

 

 

Anyway, details aside, the outline calcs highlight the importance of > 3" pipework 

 

Well that's where the details become important. The gas expansion is the difference between the IAT and EGT, and I believe your calculations underestimate IATs and overestimate EGTs which results in a calculation overstating the volume of gas you need to flow and thus the exhaust diameter needed.

You may argue that you want to build in a safety margin but with the amount of work this safey margin involves (assuming that correct numbers allows use of a 3 inch diameter exhaust) that it would be tolerable to accept a slight loss of power on the rare occasions where these gas volume is slightly greater.

 

 

Sheesh, you always have to get stuck on trivial/unimportant details. Lets just take your numbers and say the inlet temps are 45 degrees (the max I've ever seen in 8 years) and the EGT is 900 degrees (which would be startling low indeed). Even then:

 

Inlet air temp = 45 degrees C,

EGT from engine = 900 degrees C,

Then the exhaust gas will be 3.68 times the initial volume (according to Charles law).

Based on power of 520 BHP, the engine will consume circa 22000 Litres of inlet air per minute.

So multiply 22,000 litres * 3.64 = 80,080 Litres/min coming out of the cylinders.

Push this down a 3" OD exhaust pipe with an internal X-sectional diameter of 73mm means that the gas will attempt to move at 731 MPH.

 

So, even in this best case situation the speeds of the gas in the exhaust will (attempt to) travel at 731 MPH (rather than 850 MPH I previously calculated). Either way you don't have to be Einstein to realise that at 731 MPH the gas will face a lots of resistance due to the restriction of a 3" exhaust.

 

And this is why I chose to install a 3.5" exhaust.

 

 

 

 

 

And have you calculated an acceptable exhaust gas speed? For example, at what point does a 2 inch exhaust start to become a limiting factor? 

[Bakazan]

Wouldn't you have been better off with 304L steel with all the welds and high temperatures?

[stu8v]

Will be interesting to see your iat on track, although I doubt you will get on track with a 3.5" exhaust

  My max IATs in Autumn about 4 years ago (around 12 degrees C ambient at a guess) on a 6 mile stretch at more or less full chat non stop only reached about 43 degrees. That more than emulated the use of the engine on a track IMO.   IATs are not a problem on my car, its the oil temps that I suspect to be too high.  

Probably not even close to emulating track conditions imho. I think you massively underestimate heatsoak etc You can't access a truly fast car on the road, it's night and day different.

[The Batman]

but what do us trackdrivers know

[Nev]

Oh boy

[CocoPops]

Contrary to your belief Nev, not all of the replies above are digs so no need for rolling eyes. However, I am of the same opinion as the others, I just cannot see how a road session can generate same heat as a 20 minute track session... legally. Please do come to Pembrey next year and put the car on track, only then will you be able to prove or disprove your road vs track theories for load and heat. I'm sure there are many many people that want you to succeed with your exhaust quest, not least so they can copy the ideas for their own setup, but for you to be so dismissive of input is a little short sighted perhaps?

[vocky]

I too look forward to your finished product, not many owners 'think outside the box' when tweaking these little plastic things we call our pride and joys

 

Keep it up, a little banter and some good info makes a good read

[stu8v]

Development is quicker and easier on track as it's so extreme. Why do you think manufacturers use it so much.

[KurtVerbose]

And have you calculated an acceptable exhaust gas speed? For example, at what point does a 2 inch exhaust start to become a limiting factor? 

 

Isn't it when things start getting transonic?  

[Nev]

I started on the build this morning, a couple of hours work and logged it here: https://sites.google...gn/05-build-log

[chris_uk]

come on now nev. we all know this is bollox. lol 

 

[color=rgb(255,255,255);font-family:'Lucida Grande', 'Lucida Sans Unicode', sans-serif;font-size:13.3333px;background-color:rgb(27,27,27);]2. Reduce static noise at 4500 RPM @45 degrees @ 0.5m to below 105 dB, ideally around 100 dB. This would allow me to get on most UK tracks.[/color]

[Nev]

come on now nev. we all know this is bollox. lol 

 

[color=rgb(255,255,255);font-family:'Lucida Grande', 'Lucida Sans Unicode', sans-serif;font-size:13.3333px;background-color:rgb(27,27,27);]2. Reduce static noise at 4500 RPM @45 degrees @ 0.5m to below 105 dB, ideally around 100 dB. This would allow me to get on most UK tracks.[/color]

 

Which bit, realistically getting the noise down or taking Nipper on track?

 

I was mocking things up in the garage yesterday and packaging the butterfly flap is going to be hard in the space. It's likely to be pretty important though I think.

Edited by Nev, 20 November 2016 - 08:56 AM.

[vocky]

looking forward to see the build