adam c

iTrader: (2)

The later posts on this subject seem to confirm my original statement. Wrapping the DP will keep the immediate area outside of the pipe cooler. Other than that it doesn't do anything. I'm not convinced that it is worth doing.

Sgtblue

iTrader: (16)

Agree to disagree Adam......ya cheap bastard.

Dudemaaanownsanrx7

iTrader: (23)

Interesting. I never thought about hotter air having more velocity also having a higher pressure. I did read somwhere that slower moving gasses from cooling could become a restriction for the gasses coming right out of the combustion chamber, but this may only apply to na engines or an exhaust thats just too small. In a turbo application the turbo itself would be the biggest restriction. Also i would think colder exhaust would have a higher density. There is probably certain gains and losses in both containing the heat, and releasing it that events out the effects.

Viking War Hammer

iTrader: (8)

I needed 100 ft of the 2 inch stuff. I sat the rolls in a bucket, then slowly wrapped the downpipe with a half overlap. Let it sit out in the sun for a few days and dry, then use DEI heat paint on it. The paint keeps the fibers from flying everywhere.

Make sure you wrap it tight, use hose clamps if you want.

thewird

iTrader: (8)

An NA is an entire different animal when comes exhaust tuning as the effects of exhaust scavenging comes into affect and a certain amount of backpressure is desirable. Bigger isn't always better and sometimes you might want a slightly bigger or smaller exhaust depending on your needs for powerband.

With a turbo its easy, you want the exhaust coming out of the turbo to have the least amount of restriction/backpressure as possible to extract as much of the setup as possible. Having no downpipe at all and burning your passenger would be the most ideal setup for a given configuration. Exhaust tuning for a turbo happens at the manifold and the hotside's A/R and size.

thewird

adam c

iTrader: (2)

Lets talk about heat. By wrapping your downpipe, you do not allow the downpipe to release its heat through normal radiation. It will become hotter than an unwrapped DP. That extra heat has to go somewhere. It does not simply vanish. While the car is running, you would expect most of the extra heat to be passed along to the cat/midpipe and catback. Some of the heat will radiate into the turbos. Maybe not significant. How about after shutting down the engine? Since heat rises, and your DP is wrapped (and hotter than normal because it is wrapped), most of the heat from your DP is going to wind up radiating directly into your turbos. Intuition tells me that this can't be good. Turbos get extremely hot, and you want them to cool as quickly as possible after shutdown.

Other opinions welcome

Speed of light

iTrader: (8)

+1

Any cooling in the exhaust gasses increases their density, hence weight. Any gain by a reduction in pressure necessary to maintain velocity is lost to an increase in density. It is much easier too "push" a less viscous hot air. Loosing energy as the exhaust exits is a loss that will have to be made up in another way, granted it is a small loss.

Note that radiant heat will continue to fry things, even though there may be the presence of cooling air. Further, on a complex casting such as a turbo, it is not the highest rate of cooling that is important so much it is desirable to have a rate of cooling that allows the casting to cool most evenly, reducing internal stresses.

Finally, the presence of a turbine does not totally negate exhaust tuning. There are still strong pulses and acoustic effects present in the exhaust, energy which can be used to tune the system for best response, especially at the low end to improve turbine spool up.... before back-pressure rises to become the dominate factor.

ArmenMAxx

iTrader: (21)

^ thewird did you notice and power differences between the Racingbeat and titanium catback?

thewird

iTrader: (8)

I had to add 6% of fuel at 7200 RPM and 1-3% around that. And yes I did notice it as I pulled the car to 8,400 RPM and I've never done that before during tuning (I really only went out for testing backpressure, wasn't expecting I would have to add fuel), usually I only pull to just under or to 8,000 RPM. The top-end definitely improved, the low-end was unchanged.

I actually made a thread about it. https://www.rx7club.com/canadian-forum-42/new-exhaust-less-backpressure-more-fuel-853587/

I did mention that exhaust tuning is still important before the turbo and the hotside sizing. But after the turbo, you just want the biggest hole possible.

thewird

money

iTrader: (2)

anyone have common on this?

where all the well know rotary head at?

Sgtblue

iTrader: (16)

No science background, but.........
If in fact a wrapped DP does make my hi-flow cat run a little hotter, wouldn't that be good? A quality cat is designed for it. And this benefit might especially be so (for me) since I'm without an airpump and it's less likely to plug with time. Further, the cat must be designed to run hotter if an airpump was in operation.
If wrapped, radiated heat from the DP to surrounding engine parts, hoses, tunnels, transmission cases etc. maybe be significantly reduced, but that doesn't mean the corresponding increase in temps to the exhaust components themselves is significant. And when the engine stops with a wrapped DP, most heat will end up being conducted away, not radiated. And doesn't conducted heat tend to travel from hot to cold? Which is hotter, the cat or the turbo hot sides? The point is, why assume that the heat would automatically travel upstream to the turbos hot sides and manifold? I'm thinking most of the heat would be conducted toward whatever end of the DP is coolest....or cooling the fastest. With less mass and more surface area exposed, why couldn't that be the cat and cat-back? And if that's so, isn't that further reducing underhood heatsoak?
Either way, I think we might be over-intellectualizing the issue. As you suggested I doubt it's significant to turbos.
Admittedly it's anecdotal, but my underhood heat issues and heat to the tunnel (and by inference to the transmission) was improved after wrapping the DP.

FD3S2005

iTrader: (11)

humm i brought up a good thread lol, maybe sticky worthy??

adam c

iTrader: (2)

Maybe the smartest thing either of us has said

Speed of light

iTrader: (8)

Over-intellectualizing? Perhaps; however, there are important gains to be realized by properly shielding and insulating components.

The foregoing is a good observation: wrapping the DP will improve the performance of the cat. This is generally true, and I know this to be factually true for my own FD.

Conducted Heat does flow from hot to cold, and will tend to resist flowing down. I don't think that the amount of heat conducted out of a stainless downpipe is very significant, especially in consideration of the amount of radiated heat which is much more severe than generally realized. It's no different than a broiler oven and that's no joke.

Just a note on materials: steel, cast iron and esp. stainless steel have a relatively low specific heat, e.g., the materials just don't hold that much heat. Nor do they conduct heat very well. (This is contrary to popular belief.) Stainless tends to radiate heat very well, and is well worth wrapping; in reality, you're just not trapping that much heat. This is followed by cast iron, and wrapping cast iron not only reduces radiation, it will tend to improve the life of the casting because it heats and cools more evenly and cools over a longer period of time--which reduces stress and improves its stability.

t-von

iTrader: (8)

On a NA vehicle, the main benefit is the reduced underhood temps when the vehicle is shut off. Reduced temps means all your engine components will last longer and you will have less heat soak. The turbo Fd is a whole different story.