TOPIC: A New kind of mod...on the Exhaust

Well.. I've always thought that Subaru's were Different, maybe a little Weird. I mean for instance, who else used to stick the spare tire atop the engine...?

Re: insulating the exhaust system, well again the folks who put the Pleadies on their logo, did it their own way. My '02 Outback has 3 cat. converters. But, BOTH O2 sensors are on the forward most-upstream cat...?!

Looking downstream at the other two cats, there is a big round opening in the metal heat shield over those two cats. To me that looks like an access hole where maybe some models had the electrical wiring go thru to the downstream cat(s). Why else put that big hole there, it's not like ya needed access to the Catalytic Converter Fill Plug or anything. But on my Outback at least, that hole in the heat shield has no reason to be there.

Meanwhile they stuck the upstream O2 right at the entry end of the upstream cat, then they stuck the downstream O2 at the output end OF the Same Cat. The 2 O2's are a foot apart on the same upstream cat. Then there's 2 more cat's downstream, a short resonator and on out to the muffler/tailpipe.

It's all OEM stuff in good outward appearance, like the rest of the car.

Man, I was looking forward to trying this neat trick of insulating the exhaust to bring up temp's to the downstream O2 sensor. But I just don't think there is a reasonable method of this on this car. I'm not gonna try to insulate that upstream cat... uh-uh!

And actually, I guess I need to look into just what strategy Subaru uses re: engine and emissions control management for my Outback. There doesn't appear to be any kind of sensor on/in the air inlet tract, just ducting and an air filter. IT has the usual TPS sensor and IAC valve on the TB. It has temp sensors on the engine, and what must be a MAP sensor on the intake plenum. There is a switch/valve in the fuel vapor line, then that hose integrates into the IAC setup.

I've already re-routed the PCV and crankcase breather hoses. And it has the 2 O2's on the upstream cat so close together they can pass notes in class. Far as I yet know, that's it.

So far on this car, the Groove/IAC/PCV mods along with the initial RVS engine oil treat. have yielded a big change in driveability, and hot air at the tailpipe once it's driven and all warmed up.

MPG's on the other hand- I did my usual 50 mile "Orange teat" between Fernley and Fallon one night a few weeks back, and saw no improvement at all. But I'm not completely sure on that. The first time I tried filling the tank all the way up the filler neck, the engine bucked and had issues for a short while. I think that liquid gas got into the fuel vapor management system, and causes those hiccups. In subsequent fillups, I've avoided filling it to the brim, stopping instead after a couple click-off's of the nozzle.

This car has no onboard display of MPG's. So it falls to paper/pencil, an accurate duplicate-able gas tank fill method, and a test drive route with as few variables as possible. It's the tank fill method that I question now. I'm not yet really used to the way this tank acts when I get real close to completely full. When you need to get it spot-on, to be able to fill it to within ounces of gas volume each time, then even how you park at the pump (I use the same pump, shooting for the exact same parking stance) and even the pump pressure can be important variables. The last main variable- is just exactly WHEN you decide it's full. On this 50 mile run, a 10'th of a gallon of gas really means something, see?

Despite all this- I do hope that the rest of you will try the exhaust insulation method to increase temp's for the downstream O2's. It's a simple method, and if we can get some proof's of it documented, well then it's another tool in the Gadgetman Arsenal!

Tracy G[color=][/color]

well, if you can't keep the heat in where we've been discussing, maybe making sure as much of it as you can gets to where you want it is the way to go about it? I think Ron encouraged us to be open minded in our application of this heat management, right? Every application is different, and that means there's more than one way to skin the cat.
Why not put the insulation on the y-pipe? and maybe the headers too, if there's room? This is where the ceramic blanket would shine, and if you can keep the heat in the exhaust starting there, the engine bay won't get as warm, so your incoming air might be cooler/denser when it hits the groove, your AC and Radiator might function better...

Filling the tank - yeah, Wendy's like that too. For her, she takes a full fill best when in a nose-down attitude, rolling slightly to the right; I slow down pumping when I can hear the gas going in isn't displacing as much air (the pitch of the resonance in the filler neck gets higher), and then right down to a trickle nozzle til the nozzle trips off. Then I give her a nudge or two to see if there might be a bubble lurking (reminds me of tightening the saddle down when I was taking riding lessons), and I can usually get another litre or so in til it clicks again. At that point, I squeeze in another few cents til I've got an even amount (no pennies here), and I call it full.
finding the right pump at the station generally means a walk into the store to pay, because it's usually the furthest.

Yes insulating the exhaust before the first (upstream) cat would have to be the way to go on the Outback. In fact, Ron was just interviewed by Sarah Westall on her youtube podcast/channel. I literally was just looking through my youtube feed for something to watch, and saw Sarah's youtube there, with a title saying something about the "system" stealing from us through gas- I forget the exact title of it.

So I click on it- and here is highlights of Ron's interview with Sarah! I grinned hugely and immediately watched the whole interview. Sarah, thank you for giving Ron a great interview, and getting across with Ron the spirit of what he and we are doing here! I left a comment as well. And now I See that both Ron and Sarah Westall are in the Forum as I type. What a small world... Ron mentioned the exhaust insulation trick in the interview, and that got me thinking on this again.

Back to the Outback's exhaust system. basically the pipes leave each cylinder head at the exhaust flange--there are no exhaust manifolds or headers. The pipes are fully enclosed in metal heat shielding thru the Y connection right to the upstream cat. So at least there is some air gap between pipe and shielding. That initially gives me less reason to worry about potential overheating the pipes or cat.
(I worry and think about details). I'll take another look-see under there to see what size of the Owens-Corning split tubular insulation might work. Probably also get infrared thermometer readings on those pipes/cat when it's all warmed up too. Good thing is- the Owens-Corning stuff is cheap, can't cost much to try.

Tracy G

Today I finally got back under Sheila the Outback, and measured the exhaust pipe diameter. All of the pipe upstream of the first cat, has that metal shielding over all of it. This shield has flanges, and outside diameter is 3". So I went back to Ron's post re: the Insulation vendor. That post, has the link to their site. I went there, and ordered the 3" diameter insulation in the 1/2" thickness. This stuff comes in 3 foot lengths and I only need about 30" or so- so I got just one section. It was only a little over 7 bucks. After reading further, they recommend getting some of the special tape for this insulation, so I got that too. This white tape comes in either a 25 foot or 150 foot roll, I got the 150' one. That was 20 bucks, and shipping was about 15 bucks. My order total was $42 and change.

Customer reviews on this site say that this tape is pretty good stuff and really sticky. I might use some regular woven basalt header wrap on this job as well, it'll depend. I'm really curious to see how well this stuff can hold up.

This Subaru, like Subie, my '85, has the pipe bolted direct to the exhaust ports on the heads. No manifolds. The 2.5 Liter engine has individual exhaust ports, close together- 2 ports per head, 2 heads. The ports point straight down, the exhaust pipes bolt straight up to the heads. A short Y becomes a single pipe on each side, leading to another Y where the 2 sides meet, just before the upstream cat. A "dual-Y" system, sorta like old "tri-Y" headers on American V-8 hotrods.

Looks reasonably free-flowing for stock exhaust on basically a Soccer Mom's car. After the upstream cat, it's just plain 'ol pipe, thru the downstream cat, a resonator, then the stock muffler, and out. A Long-Ass system!

anyhow, I'll post further on this when there's something to say!

Tracy G

So you're thinking the insulation OVER the wrap? That'll be interesting...

So the insulation showed up last week. I got the car on jackstands, and went to it. After about an hour, both upstream exhaust pipes leading to the first (upstream) cat. are now insulated. The insulation has this white outer covering and it's pretty tough for being as thin as it is. The insulation is slit all down one side, and is fairly stiff. So cut it to size to cover the pipe(s) in the straight sections. You just cut it, get it in place then remove the paper off the sticky band along one edge, and stick it down.

On the bends, I cut wedge-shaped pieces, stuck them into place, then I used the extra white tape the vendor sells to wrap over the joints. No tape or anything sticky touches the metal. So now there is a 1/2" thick insulation layer over the metal shielding on the pipes. IF going with this product line, DEFINITELY but the extra tape! You will need it. I reinforced the overlaps and joints along the insulation with this white tape. I wouldn't want to try this job without that tape. What I wound up with is the insulation's outer layer and the tape over all joints form a continuous layer as an outer jacket.

MY exhaust and under car area in general is quite clean. I would not want to try this on a car that's oily underneath...

I didn't use any regular header wrap on this job. I've done no testing yet, so far, I'm just driving it and keeping an eye on how the insulation holds up. So far, so good. MY main concern re: how it holds up is-- wet weather.

Anyhow, here's the pics of the job.

Tracy G

I'd do yourself a favor and tape up the open fiberglass on the ends somehow. wind and moisture might help each other to rip your work off after a while, so I'd plug the biggest holes they can get in through

that's a good idea, Dr. dude. I Think I'll stick a small piece of the tape direct on the shield and watch how it does. I also have some Nashua foil tape made for metal HVAC ducts, I'll try a piece of that too.

It looks like the front ends of the wrap would be most vulnerable to wind/water. Pass. side is more up out of the way, driver side is lower and more exposed. I was looking under there, there's a large plastic shield under the engine that ends close to the front end of the insulation. I could fashion an extension to the plastic from some aluminum sheet and attach it to the plastic to protect the insulation from wind and water. The pipe insulation outer white jacketing itself, seems that it will resist wind/water well, as long as it isn't impacted and punctured. it's about the joints and exposed ends of the material, where it is most vulnerable. The white tape seems to fix the joints pretty well. The label on the tape claims a temp. range of -20 to 280F. So on the metal pipe shield I think it can do OK.

Insulating directly over bare exhaust pipe will/would be another case for this white tape.

I'll stick some on the metal shield and report back.

IT was these considerations of resistance to wind and water, that made me originally think of using header wrap tape instead of this pipe insulation in the first place. Header wrap seems more durable, but much more expensive. But- once you add the cost of the white tape roll, and shipping, the price gap narrows some. I don't know which- header wrap, or this pipe insulation, is the better heat insulator. But the pipe insulation IS available in so many different thicknesses.

And, of course, I'm taking Ron's word, that this mod is effective to begin with, though it does make sense.

Tracy G

Wrapping the exhaust is the same as blocking off some of the radiator to some extent; in cold environments, I have no doubt it helps fairly significantly. It probably won't hurt in warmer ones either.
My Wendy's sensors are heated, so getting whatever heat to them and keeping it there will probably be helpful in the long run to shortening "time to closed loop" on a cold start; I know that I'm coming close to having the computer read/follow the o2 because once the coolant temperature approaches 60 degrees Centigrade, the computer cycles the EGR valve (audible in the cabin), and then it really starts to idle down to normal.
once we achieve gains with a groove and the PCV reroute etc, we should start to REALLY dig in to the intricacies of the computer - if we can get the warm up cycle to complete faster, we're not running in open loop/default fuel delivery for as long, and we're saving fuel and the environment.

Tracy are you trying to cool air leaving engine in pipes or cool O2 sensor ? May not be good to stop air from cooling close to engine, but may help O2 sensors increase reading by ECU to increase mpg . So with pipe wrapped close to O2 sensors would this keep temp at O2 sensors higher in pipe at O2 sensors ?
geraldc

Hey, Gerald! I missed seeing you here!

The idea behind this (start at Post #1) is to RETAIN the heat in the exhaust up to the LAST sensor in the system. This sensor serves as the Omnipotent One, and will override all other fuel delivery parameters, should the temp at the cat drop. At which point, it will force over-fueling of the engine until there is waste fuel to heat the cat.

Just think that every BTU created burning your fuel creates that is lost out the walls of the exhaust COST YOU MONEY...

Ron

OK that is what I though we wanted. I may have found material which may do this very easily and is very strong. If my truck is running I can put this material in my hand and hold truck exhaust pipe without feeling any heat.
geraldc