Myth busters: Intake tube wrap ... works or not?

[Akrion]

I have been lurking around various forums since my intake "exchange" asking myself one "stupid" question ... does it make sense at all what these people are doing ... wrapping their intakes with heat resistant/reflective sleves/tapes etc?

So I thought I would bring the question here ... see what the more technicly inclined mambers would say.

Please keep it civilized ...

Few links for reference:

http://mbworld.org/forums/w211-amg/3...ictures-2.html
http://my350z.com/forum/intake-exhau...take-tube.html

And few interesting images:





Here is also an interesting product mentioned ...

http://www.summitracing.com/parts/DEI-010417/

[Gromit]

David or Greg at Eurocode have thoughts?

Personally I've always been a little skeptical about this concept of intake air getting heated significantly. Think about it: if the engine is running at any decent rpm, you have a decent velocity of the intake air. The tube is short. That means the residence time of air in the intake duct is REALLY short.

Even if the intake tube is fairly hot, you're only going to get heat transfer into air that flows across the outside of the cross-sectional area, particularly under laminar flow conditions that aftermarket tubes claim (the situation is slightly different with turbulent flow). The outer edge air that gets heated slightly is a small fraction of the mass flow through a cross-sectional area, so you'll get minimal average heat increase of the total air once it gets fully mixed in the cylinder.

So to me the key criterion is where the air comes from. Sucking in cold air versus warm air will matter much more than the minimal heat increase during flow along the tube. Maybe I'm missing something but to me, basic engineering principles say focus far more on intake location than temp of intake duct.

[aaronz]

I agree with ^ but only thing I can think of is our tubes are not that direct, Roc-Euro has two significant bends that could cause more air than the outside path to make contact and heat up...the real idea is if it raises it by say 5 degrees does it make any impact? Where is the breaks g point?

[Akrion]

David or Greg at Eurocode have thoughts?

Personally I've always been a little skeptical about this concept of intake air getting heated significantly. Think about it: if the engine is running at any decent rpm, you have a decent velocity of the intake air. The tube is short. That means the residence time of air in the intake duct is REALLY short.

Even if the intake tube is fairly hot, you're only going to get heat transfer into air that flows across the outside of the cross-sectional area, particularly under laminar flow conditions that aftermarket tubes claim (the situation is slightly different with turbulent flow). The outer edge air that gets heated slightly is a small fraction of the mass flow through a cross-sectional area, so you'll get minimal average heat increase of the total air once it gets fully mixed in the cylinder.

So to me the key criterion is where the air comes from. Sucking in cold air versus warm air will matter much more than the minimal heat increase during flow along the tube. Maybe I'm missing something but to me, basic engineering principles say focus far more on intake location than temp of intake duct.

That was one of arguments as well in the MB forum. However it still makes me wonder if this approach does not help to some degree with the heat soaked problem where the engine bay temps are high ...
If you trust the enthusiast tests on the "internets" one of the guys on the MB forum says that based on his tests the temps shown ware 10+F lower with the wrap than without it ...

Here is the quote:

"I wrapped my intake tubes about a month ago. I finally got a change to log the temps in the tubes. Results are very positive, temp difference between the inside surface of the heat shielded and non heat shielded tubes was 13F. The test conditions were as follows - drove the car for about 15min in 93F ambient temp to get engine bay and engine up to operating temp, inserted temp probe from both ends of the tube, results very the same.

IMO worth $20. Even if this lower IAT's by a couple of F it is worth it."

[Gromit]

I agree with ^ but only thing I can think of is our tubes are not that direct, Roc-Euro has two significant bends that could cause more air than the outside path to make contact and heat up...the real idea is if it raises it by say 5 degrees does it make any impact? Where is the breaks g point?

Yeah, the bends could disrupt laminar flow and cause turbulent flow, which theoretically might cause more air to be heated (turbulent air could lower the temp profile of air along the duct length and heat transfer is a second-order function of temp differential across the duct sidewall). But I'm not sure that would cause greater temp increase given the residence time of air in the tube. More importantly, given that short residence time, I'd be surprised if you got a 5 degree difference in air temp between the duct opening and the cylinder. It'd be great to know if their are measurements out there.

[Gromit]

Here is the quote:

"I wrapped my intake tubes about a month ago. I finally got a change to log the temps in the tubes. Results are very positive, temp difference between the inside surface of the heat shielded and non heat shielded tubes was 13F. The test conditions were as follows - drove the car for about 15min in 93F ambient temp to get engine bay and engine up to operating temp, inserted temp probe from both ends of the tube, results very the same.

Hmmm. Sounds like he warmed the car, the stopped it, then inserted temp probes. That's a very different situation and I can see him getting some measurable differences. But that's nothing like what goes on when you're driving. Real measurements would have probes INSIDE the duct at beginning and end and measurements taken WHILE the car is running, particularly at rpms you drive hard at. My point is under those conditions the air is in that duct too short a time to get heated. That guy was comparing water skis to elephants.

When I get more time I'm going to crunch some numbers on this, as I think it's a really interesting question.

But in the meantime $20 is cheap, and if it only provides the fun of getting under the hood and doing some work, I'm all for it.

[dparm]

Once the car is moving, the under-hood temperatures are effectively ambient.

[aaronz]

For the drag racers...might be worth it when sitting in staging

[cspcrx]

I think what the tube is made out of is going to impact this more than radiant heat transfer. Tubes like those from eurocode are going to conduct and retain heat differently than a metal tube.

[Infra]

For the drag racers...might be worth it when sitting in staging

+1.

This is the only use of a mod like this. If the car is moving, there is no hot air entering the intake.

It would also be good for the dyno as many don't get proper air flow.