BPM

Check out our feature on HPC coatings on our website. The HPC company is the most used coating in Motorsport being utilised in WRC, Nascar, and Formula 1.
In a nuthshell the greater the heat retainment of an exhaust the superior the scavenging hence a power increase. Exhaust wrappings work as well although not as a refined solution.

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Greg Nikolettos
BPM Marketing Division
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GavinP

Seeing a couple of recent postings, I have a few questions on coating / wrapping the various exhaust components:

1. If you coat/wrap the exhaust manifold, I believe the heat is retained, the gas flows quicker and lag is reduced - is this correct ?

2. If you coat/wrap the downpipe, this reduces the underbonnet temperature and bring the cat (if fitted) up to optimum temperature quicker. Are there any other benefits/disadvantages ?

3. Do coatings such as TechLine's "Black Satin" work well ? This apparently cures on the car rather than being baked in an oven. Is this similar to HPC coating ?

4. Does exhaust wrap work ? What experiences have people had with it ?

5. What are the pros and cons of insulating the turbo with wrap or blankets ?

Thanks

Gavin

JayDee

Shoot me down in flames, but

How does heat retension in the exhaust improve scavenging?

I would have thought the opposite, that greater mass flow of the gas would result from cooling, as indeed is the case for inlet gases - this what the intercooler does.

Explanation?

firefox? DYNT?

JD

Mike Tuckwood

On its way in you want the air to be as dense as possible.

On its way out (through the whole system) you want it to retain its lower (hotter) density as long as possible, otherwise you get back pressure building up further towards the back of the car.

Mike.

mike_nunan

[Please note, I started writing this reply before lunch, and by the time I got back there were already three replies here. I've left it unchanged as I think it raises some interesting issues, but BPM/Mike please don't take anything I've said here in the wrong context - I wrote it before I saw your posts...]

I think this whole area (along with the parallel discussion on downpipes and back pressure) is full of complex issues, and the psuedo-science we've heard so far doesn't stand up to close consideration.

OK, so you wrap the manifold thus keeping the gases hotter, which means they become less dense, and thus you get a higher volume of less dense gas flying through the headers more quickly, compared with unwrapped headers. But... if the gas is less dense, it will be less effective at rotating the turbo, so the benefits of the increased velocity are going to be negated to some extent.

There could still be a net gain, for example if the turning force on the turbo turns out to be proportional to the gas density and also proportional to the *square* of the velocity (I made these relationships up, BTW, they're just for illustration) then having faster, thinner exhaust gas would get the turbo moving more quickly.

It would take a lot of effort to get a proper answer to this. I don't believe anyone near here has the technical expertise to do a full analysis. Empirically, no-one is able to provide clear before-and-after experimental results that have proper control over the other variables such as ambient temperature. In the end, manufacturers invest millions in this kind of research, and you just have to accept the hit-and-miss nature of the aftermarket as the suppliers are too small to do proper research.

I could say all the same things about the effects of exhaust gas scavenging (sp?) that allegedly mean that a more restrictive exhaust system (e.g., 2.5 inch) can yield more mid-range torque than wider (3 inch or bigger) systems. Ditto for the "twin dump" downpipes. All these things may make an observable difference, or they may not, and the level of information that has been provided so far ain't enough to persuade me to part with the sums of money involved.

Bald assertions made by suppliers - and I won't name names, but I have heard and seen many examples - don't convince me. Just because someone says "our danglewidget gives more power because it reduces the eddy currents in your morning porridge" doesn't mean jacks**t unless they can prove that (a) it does indeed reduce the eddy currents and, more importantly, (b) that reducing the eddy currents by the given amount actually produces more power.

I have a certain amount of respect for those tuners who have spent time fine-tuning their approach and have a "rule of thumb" approach to the various decisions that have to be made. However, without applying some actual science it will be impossible to make informed decisions if you wish to deviate from the tuner's chosen path, especially with things like customisable ECUs adding a whole extra layer of complexity to the mix.

Anyway, returning to the subject in hand, I personally wouldn't go with the wrapping, as I suspect a side-effect would be to increase the cylinder temperature and hence the risk of lean detonation. However, I'm no expert (just a sceptic!)

It might be informative to look at competition engines and see what they do. Does anyone here have any *direct* experience that they can share?

-= mike =-

mike_nunan

Ok, now the individual points

Mike, your comment about building up back-pressure in the exhaust system, how is that going to happen more with less gas volume to move (as will be the case if the gas has already cooled and shrunk?) I'm not arguing with the outcome (i.e., more power from keeping the gases hot), just the reasoning behind it.

Greg, when it comes to scavenging, doesn't that only have a significant effect when the inlet and exhaust valves are open at the same time? Come to that, does anyone know what the cam profiles are like on the various versions of the scooby powerplant? Is there much valve overlap in any event?

-= mike =-

DYNT

GavinP - HPC ... I used this to cut friction down on the bearing and the piston. Is a very complicated process .. needs Lab. type of oven. I used ceramic for the piston crown and chamber volume ..... U will need to calculate this cos it does effect the compression values.

Less friction ... less heat.

As for the exhaust wrap ... keeps the engine bay cool and help to draw in more colder air if the hot gas velocity is increase.

Cold air is heavy ... Hot air is light.

All engine do have overlap period .... especially on the subaru. Check out the cam profile and the duration too.

In the end of the day ... all this does help to keep the engine running better... increase HP ... not really. It just help to keep the HP loss to minimum.

Is easy to build high HP engine but is hard to get rid of the heat fast enough. This is where the engine loss its power.

As for the wrap ... side effect .... U might crack the frontpipe .... that is as far as I know.

If u like to know more... look into HEAT and ENERGY ..... internal combustion engine.

Cheers.

MikeN - STI 3 cams onwards ... Centre line 114.5 Degree .. need more info for other type of cams ... Type 1 ..Type 2 ..Type 3... e-mail me..... if I can be any help.

By the way .. Type 1..2..3 will be out by this year. It should reach UK soon...maybe.

As for the Asymmetrical cams profile ... still working on it ... maybe mid of next year??

U will need to Use solid lifter for all this cams. Not to worry U can convert from Hydro. lifter to solid if U like... is easy.

[This message has been edited by DYNT (edited 09-12-1999).]

[This message has been edited by DYNT (edited 09-12-1999).]

Bob Rawle

HPC coating is ...

A bond coat ie it does not just envelope, it sticks.


Is less than 0.05 microns thick

Reduces heat loss when applied to the outside of a system

Minimises corrosion when applied to the outside of a system

Improves gas flow by heat retention and "smoothing" the surface grain structure when applied to the inside of the system

Is applied by a spray process.

Can be applied to a wide range of base materials.

Can be supplied in different colours !!

It is used extensively on race engine systems.

Just thought you all might want to know that.

It also does what it claims.

Oh, just to remember that exhaust gas velocity has to be kept within limits else performance suffers so choice of pipe diameter is very important to an individual engine design.

Bob


[This message has been edited by Bob Rawle (edited 09-12-1999).]

[This message has been edited by Bob Rawle (edited 09-12-1999).]

[This message has been edited by Bob Rawle (edited 09-12-1999).]

Mike Tuckwood

Mike, You cynic.

I referred to the density not the volume, my understanding was that the density is what slows the gasses down.

The further back you get the cooler (slower) the gas gets, potentially causing a bottleneck which at full steam can cause back pressure to build up.

Mike.

Area 52 Autosport

Mike Nunan!

You legend (although not at GT!!). I think your reasoning makes some sense particularly when referring to "before the turbo". However, unless I've missed the point, I think everybody is referring to "after the turbo" where the lesser densities are more desirable due to lower inertia and therefore higher velocities.

Ben

mike_nunan

Hello Bob and ScoobyManiacs

I've had a think and tried to come up with a meaningful analysis of all this, but I'm still having trouble. It seems against all intuition that by letting the gas cool you will do anything other than *reduce* back-pressure (simply because hot gas = high pressure, so the more heat you lose and the quicker you lose it, the better off you'll be). MikeT's comment about the "ideal" turbo exhaust being a fat pipe straight out the side of the car goes along with this.

I understand that things may be a bit different before the turbo, especially when the interplay between the different cylinders is taken into account. I think this is the area where Bob's comments about pipe diameter are really important. Header length also has an important part to play, because you want the previous cylinder's spent charge to have just blown past the collector (the junction of the header tubes) when the next cylinder's exhaust valve opens. That way the vacuum left in the wake of the previous gas pulse will help evacuate the cylinder and also help with induction if the valve timing includes some overlap. This is "inertial scavenging", as opposed to "wave scavenging" which is a totally different effect that is very important to 2-stroke NA engines (go and look at some power boat tuning sites if you're interested) but has less bearing on 4-stroke turbo motors.

Anyway, I can see some sense in keeping the heat in the headers, as it will help keep the gas flowing along, which then enables the inertial scavenging. It will also mean that the pressure difference across the turbo is higher, which should reduce the spooling-up time. I can't see a good reason why you don't want the rest of the exhaust to be as wide and cool as possible, though.

This is all hurting my head now, so I'm off for the weekend. Have a good'un everybody!

-= mike =-

PS. Ben, I'll getcha next time

Anders

As promised I have read the above!

I detest Poor Engineering!