Heat wrapping downpipe,yes or no

[driftin jo]

[QUOTE=QuattroFever;527730]Where are you going with this.


As for where am I going with this :

In your first post you said:
"think of it as a liquid and not a gas. oil will flow much faster when hot because of the viscosity. The same applies to air just at a different level."

I commented that this was not the case and that gaseous viscosity works the opposite way to liquid viscosity and you came back with “I'm not wrong”, when in fact you were wrong, and here we are.

[QuattroFever]

i love it really! Any excuse to have a geek rant about gas flow

[GazzaG60]

personally i think wrapping the dp will help. wrapping cast not really. cast retains heat well enough.

i go for wrapping the dp but not the manifold.

[prj]

i love it really! Any excuse to have a geek rant about gas flow

Sore loser spotted.

[QuattroFever]

you spurring me on?

EDIT: alrighty then...

density is increased with a cooler temp meaning that you get more mass in a given volume but it has more "mass" and so is heavier and requires more force to move....viscosity or "flow" is affected by the internal friction on the pipe walls as mentioned earlier, cool gas on the internal pipe wall due to a cooling outer pipe affects laminar flow.

if you have a 3" pipe wrapping it will almost certainly make it more efficient and will increase your flow rate at a given pressure.

what drifting jo is talking about is in an enclosed space the pressure goes up with expansion and so the gas actual viscosity is adversly affected. except we are not talking about an enclosed space is a pipe with a hole at the end

[5banger]

****in hell. You both right. One is refering to viscosity on a molecular level and one is using as a way to describe how the viscosity is restrained by laminar flow.
You guys could argue to the end of the earth on this.

[driftin jo]

you spurring me on?


what drifting jo is talking about is in an enclosed space the pressure goes up with expansion and so the gas actual viscosity is adversly affected. except we are not talking about an enclosed space is a pipe with a hole at the end

I said nothing of the kind , pressure goes down as the gas expands as it exits the turbo into the down pipe. And as this is a turbine the lower the pressure the better , don't confuse tuning NA engines with turbos. NA engines can gain a lot of power from proper sized pipe to utilize the scavenging effect to draw the next pulse of gas forward, I'm not debating this . Putting a massive pipe on a properly tuned NA 2.0 motor like a Honda or such will almost certainly loose power as you would loose gas speed and thus loose the scavenging effect.

On a turbocharged car there is no point trying to gain any scavenging after the turbo outlet as the gains are ALWAYS less than the gain from lower pressure after the turbine as a turbine works on pressure ratios, pre turbine and post turbine, as you lower the post turbine pressure the ratio is greater , so the greater the size of pipe the lower the post turbine pressure as the gas can expand and cool and the higher the efficiency of the turbo ,Period. As long as you put a nice taper from the back of the turbo outlet to you big down pipe there will be no turbulence to speak of . To sum up you will never loose power from a bigger down pipe on a turbo car despite what some tuners will say , they just don't understand how a turbo works , even a tiny increase in a turbos pre/post turbine ratio will completely negate any other exhaust tuning aspects.

[QuattroFever]

im not confusing turbo engine with n\a. Im talking about increasing exhaust efficiency for a given size.

The whole topic was about heat wrapping and retaining heat in the exhaust, not if he should buy a bigger exhaust. undeniably...a drag car as an example a 8" long peice of tube sticking out of the wing is the best exhaust you can have.

[driftin jo]

Just had an interesting conversation with a mate with a scooby , he wrapped his down pipe in an bid to stop heat rising in his engine bay and heating up his top mounted inter cooler .
He said that after heat rapping he could not hit full boost and the car did not like it at all . He took the rap off and the car ran fine again .

[GazzaG60]

so this has gone from physics to ********. lol

we wrapped zillions of subaru pipes, ported header, wrapped them. does it help. hell yes.

[220bhp]

Right now the dust has settled between the boys in the red corner and the boys in the blue,has anyone done this to an s2 with a 3" DP without,A,it catching fire [JAMO]
B, causing a fight,C turning the tread into a lecture at Cambridge,or D, without using the laws of confusion by answering the simple btdt question with a yes or no.

[Thuppu]

My S4 didn't catch fire, but it must be because I have a 3,5" DP.

[Evert Thomas]

so the greater the size of pipe the lower the post turbine pressure as the gas can expand and cool and the higher the efficiency of the turbo ,Period.

So what is the effect of the wrapping the downpipe on the ability to cool. I would say when you wrap the downpipe, the ability to cool down is less?

[driftin jo]

so this has gone from physics to ********. lol

we wrapped zillions of subaru pipes, ported header, wrapped them. does it help. hell yes.

If you have a look a the chart for pipe size for HP you will see that Audi + Porsche build in a bit of head room in terms of size of exhaust when they made the S2/ RS2 , this is most certainly due to the fact that the engines were turbocharged and as I have pointed out at least twice in this thread already the turbine in a turbo works on pressure differential pre / post turbine and the lower the pressure post turbine the better . Now heat wrapping a downpipe will increase the temperature and thus the pressure of the post turbine gas , this is not going to have an effect on a standard output S2 / RS2 , etc , but if you are running the turbo / downpipe close to what it is capable of in terms of flow , think most home fried S2's out there with standard downpipe making circa 280HPp on a 2.5 inch pipe, they are close to the restriction dia for the pipe size . Heat wrapping is going to cause turbine to loose efficiency in these cases , this is obviously what was going on with my friends Subaru as he was not running a big enough downpipe . So to conclude if you are running a 2.75 / 3 pipe on a sub 400 HP set-up then heat wrapping is not going to cost you any efficiency loss a the turbine and would be beneficial in keeping heat out of the engine bay .



This chart is one I made years ago and was taken from S.E.A testing on an engine dyno not theory.

Pipe bore size. inch / mm
BHP obtainable without
pipe causing restriction.

2 / 50.8 --- 185

2.25 /57.15 --- 235

2.5 / 63.5 --- 285

2.75 / 69.85 --- 350

3 / 76.2 --- 415

3.25 / 82.55 --- 490

3.5 / 88.9 --- 565

3.75 / 95.25 --- 650

The above figures are based on petrol engines running a full length exhaust system 4 metres / 13 feet in length with free flowing silencers . More HP is obviously attainable from each size of pipe but beyond these figures the exhaust is increasingly restrictive .

[AndyP]