TrevorS

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Probably a controversial move since it isn't cheap and I'm not certain what the value will turn out to be, but I'm curious having just installed a header. I already have a 2.5" cat-back exhaust, so I wanted to replace the OE 'S'-Pipe (2-1/4" entry half and 2" exit half) with a 2.5". I did some hunting, got pretty much nowhere, and decided to order a Weapon-R. So, now I'm waiting for it to arrive -- hopefully by Tuesday.

In the meantime, I might as well prepare for it. First, I wanted to evaluate constrictions in the final exhaust setup. Relative to 2-1/2", there's a very short 2-1/4" header exit plus longer "scuba" (OE resonator/main cat combination) 2-1/4" entry and 1-3/4" exit. I don't think the collector is long enough to have much impact, and the "scuba" exit carries much cooler exhaust gases that require less pipe volume, so I'm really not that concerned about either of those. The worst IMO is the "scuba" entry including the 2-1/2" to 2-1/4" junction, though with the gases already cooling a little, the temporary loss of 1/4" before they diffuse within the "scuba" is probably not as harmful as that abrupt size change. However, that I can do something about -- port the "scuba" entry pipe to smooth the transition. So, I ported the entry out to a smidgen over 2.5" and here are before and after photos.




Not perfect, but hugely better than before and very smooth to the touch (except for a slight dip where the pipe meets the flange). The "scuba" is now back under the car and ready for the new 'S'-Pipe.

FromTheOld

You're putting way too much thought into this...lol. There's a lot of theory involved, and if that isn't vague enough, you don't have the means to measure how much your theories are effecting the results (gas getting cool, gas velocity, etc.)

Just relax and enjoy the S-Pipe when you install it.

TrevorS

iTrader: (1)

What can I say, dude? I'm just trying to figure out how to get the most bang for my buck, and the bucks aren't exactly trivial (at least, not to me). Guess my curiosity's to blame, but I find it interesting stuff. It's seeming to me that in the world of exhaust velocity Vs capacity, my best bet is probably focusing on velocity. Cutting OE back pressure may be good for F/I, but not so sure for N/A street. Currently planning to paint the 'S'-Pipe for max exhaust gas temp at the "scuba" -- I see that as a velocity assist !. However, can't do anything further 'til the pipe arrives !

ScionFred

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Nice work Trevor. I'm surprised that there was enough material thickness to allow such enlargement to the scuba entry. While FromtheOld has a good point, I'm often inclined to take the extra time to tweak the little things like this. It may not produce a significant improvement but it's still an improvement. It's an individual decision as to whether the little tweaks are worth the effort or not. The time I spent port matching my manifold and gasket to my turbine housing may have been a waste but I don't regret doing it.

Not to rain on your paint idea but if it's a thermal barrier you want, VHT, Ceramic paint or even Jet-Hot don't do much. You need a thicker ceramic coating or better yet, thermal wrap. Hi-temp paint is just for appearance.

FromTheOld

Yeah I understand. I used to be similar to you in the sense that I would tirelessly research every little thing I could to get the most out of things, but I've been way busier with life in general so I don't really have time to think about stuff like that. By the way, the whole backpressure thing is a whole myth. Backpressure is NEVER needed....exhaust gas velocity is needed. When using a smaller diameter pipe, people would notice better low-end torque and would assume it was cause of backpressure, but in reality, it was cause the exhaust velocity was increased. I used to be a hardcore N/A guy interested in getting the most out of it, but in the end, I just ended up dealing with turbo stuff cause making power on a turbo car is way easier. Anyways, I just recommended you go with the "standard" for N/A so you don't stress yourself out too much.

Yeah, like I said above, it's up to you if you want to do the little modifications for improvement.

Also, about the thermal barrier, you need high temperature Ceramic Coating to act as a good thermal barrier. Ceramic coating retains heat as long as the temperature doesn't exceed the Ceramic Coating's rating. Most people think 1300 deg sufficient enough for exhaust headers, but I prefer 2000 deg coating for exhaust headers. Having a higher temperature rating also prevents flaking, which is another common complaint. The thing is though, the parts after the exhaust get significantly cooler so coating 2000 deg isn't really needed, but underneath the car is a pretty harsh environment. As durable as ceramic coating is, it won't last underneath a car.

So all-in-all... for thermal barriers underneath your car, you'll need heat wrap.

TrevorS

iTrader: (1)

The whole back pressure thing is interesting in that given ECU AFR control, increasing it is necessarily counterproductive (reduces torque due to less charge in the cylinder), but how much leeway is there in decreasing it given the valve timing is tuned with the OE exhaust? If scavenging increases much, raw charge will begin to flow directly into the exhaust during valve overlap, and even though the engine is VVT-I, I don't see how it would recognize that situation and adjust intake valve timing to correct it. Do you just increase velocity until the mpg drops and then back up?

Seems like most people are going for more peak power and that translates into fatter pipes, less velocity at a given rpm, and hence less lower to mid range torque. By bumping the 'S'-Pipe a little, I'm actually reducing post header velocity proportionally to the increased pipe cross-section. I see ceramic and silica based paint on the header and 'S'-Pipe as a way of countering that change as well as reducing heat radiation. As additional benefits, it delivers higher exhaust temperatures sooner to the "scuba" catalyst and lessens heating of the engine and chassis underside.

Guess I'm not that concerned with achieving a heat block, just a reduction in pipe losses. Painting the header provides a tangible reduction in under hood temp compared to unpainted. That's the kind of change I have in mind. However, if it really would make a significant difference to wrap the 'S'-Pipe, I could take that route instead. Since the pipe is stainless steel, perhaps moisture trapping in the wrap wouldn't be an issue? Could wrap the entry pipe to the "scuba" as well -- though that's not SS and so is probably a bad idea.

FromTheOld

Weapon-R says the S-Pipe is 304 stainless steel, so oxidation won't be a problem. The scuba is also stainless steel, but the grade is 409 (and not 304). 409 stainless steel forms a layer of oxidation on the outside to protect it from further rust. It's ugly as hell, but it'll get the job done and it saves OEMs money by using this grade of steel. Obviously this layer is not perfect and the whole thing will rust through EVENTUALLY, but it lasts a lot longer than standard mild steel. (Estimated 5-10 years.)

I'll answer the rest of your post, but I'm off to work now.

TrevorS

iTrader: (1)

Fortunately, I only had to gain about 1/4", but the flange isn't super thick and I was afraid of weakening both it and the pipe in the vicinity of the weld. I ground it as far as felt safe and perhaps could have removed more, but the weld doesn't extend very far up the flange or down the pipe. If that flange were to break, it would be a major drag !

I switched from the Dremel to a drill with a cylindrical grinder bit and that was very effective -- it's a pretty large grind area. Finished off with 220 and then 400 grit paper. It's about a 45 degree angle at the outermost and pretty smoothly transitions to the inner pipe. Took me quite awhile, but should definitely help reduce turbulence.

TrevorS

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Decided to go with this, though it'll add a few more days to the project .

http://www.amazon.com/gp/product/B00...=ATVPDKIKX0DER

ScionFred

iTrader: (1)

If you want to trap heat in the s-pipe, that's the stuff to do it. It's a lot more effective than ceramic coatings and hi-temp paint has no value whatsoever as a thermal barrier. You should also wrap the header.

TrevorS

iTrader: (1)

Problem with wrapping the header is I don't know whether the stainless is impervious to corrosion -- hard to imagine the manufacturer reached for the best quality. From what I've read in the past, the ceramic and silica suspension paints do reduce radiated heat, though no doubt the wrap is easily more effective. I'm more concerned as to whether I'll be able to bolt the different styled Weapon-R flange to the threadless header. Considering getting Helicoils and installing them in the lower flange.

Thinking of porting -- it's value is a function of flow. Low velocity generates little turbulence whereas high velocity can generate plenty, just depends on the severity of the obstruction. It's fluid mechanics and porting makes a difference whenever flow velocity matters. Your TB port opens the bore sooner resulting in a larger than OE gap between the throttle plate edge and bore, and it also reduces turbulence on both sides of the plate allowing greater max flow. Both effects boost throttle sensitivity. I've seen comparisons in the past of ported Vs non-ported and the difference can be very tangible -- true, it's not going to make the difference between a "slow" car and a "fast" car, but it can make a difference on how fast is "fast".

PS. Decided to go for the Helicoils, they and the wrap will probably arrive around the same time.

ScionFred

iTrader: (1)

Although I believe that thermal wrap is by far the most effective means of trapping heat in the exhaust gasses and reducing unwanted radiant heat, I also believe that ceramic coating is a much better solution for street cars. Ceramic coating may not be as effective as wrap as a thermal barrier but it also protects the header or pipes and looks better. Personally I'd use wrap on a race car and ceramic coated or even just marginally effective ceramic paint for a street car. FWIW a buddy of mine wrapped the SS header on his VW and the header rusted through in under 5 years of minimal use.

I agree with what you said about porting. It's long been the little things that separate 1st and 2nd place in all forms of racing. However it's also true that unless you've already optimized the bigger things, little tweaks like porting won't make up the difference. For instance, another XB with the same exhaust as you will probably still make more power if he replaced the scuba and mid-pipe and didn't bother port matching anything.

I'm not so sure about heli-coils for that app. I might be wrong but I believe they are designed to bottom out in blind holes. Maybe you could find longer shoulder bolts with the same length shoulder instead?

TrevorS

iTrader: (1)

Depends on one's vehicle goals -- currently, mine include keeping the "scuba". I've done plenty of porting on the Eclipse, but if I was really intent on power, there are plenty of much bigger parts changes that could be made -- no thanks! Better flow behavior means the engine doesn't have to work as hard doing its air pump thing -- that translates into MPG and I'm an automatic fan of that !

Don't know how the Helicoils will work out, but I don't see an inherent problem. The 10mm length stainless coils fit entirely within the flange, I already have the appropriate tap to seat them, and I believe the existing flange holes are OK as is. It's a pretty cheap experiment (<$10) and the worst that can happen is a bolt somehow bolloxing one while threading in. If that's a problem, I'll just have to stick to nuts -- guess I'll find out!

TrevorS

iTrader: (1)

The Weapon-R 'S'-Pipe arrived today (packaging was excellent) and I'm told the wrap and Helicoils were both shipped. So, here's a photo of what I received and the other items will probably arrive by Thursday. Weapon-R included a 2.5" donut gasket, a set of bolts with washers and nuts for the "scuba" end, and a set of bolts, washers, springs, and nuts for the header end. Don't yet know exactly what I'll use for the 'S'-Pipe to header spring bolts, but it's nice to have options !

ScionFred

iTrader: (1)

I see nothing wrong with keeping the scuba other than sacrificing a few ponies up top. On the plus side you're keeping a cat and the scuba does a great job of reducing header rasp and in-cabin resonance. I forgot what you're running for a mid-pipe. Is it the 1.75" oem or something else?

I guess the heli-coils might work but since they thread in and there will be nothing to bottom out on, I'm afraid they may turn in their threads as you tighten the spring bolts. Perhaps Loc-Tite red on the heli-coils might help prevent this? Or else you could not tap the flange all the way through leaving a taper for the coil to seat against.

The W-R s-pipe looks great and I hope it fits as good as it looks.

TrevorS

iTrader: (1)

I've a Tsudo dual which is a "scuba"-back with 2.5" piping. HP isn't that big a thing to me since I don't drive fast and I don't race. I'm more interested in torque and I don't think keeping the "scuba" hurts that -- my concern is more flow velocity than flow volume.

Helicoils aren't normally installed at the bottom of a drill hole, usually they're just a little below the surface (at least, that's the manufacturer's instruction with the previous ones I purchased) and they can definitely be torqued against, so I really don't see a problem with flange install. Of course, these holes are pre-drilled and may not be sized optimally for the helicoil, so I think that's my biggest risk. Still, they're a good fit for the 10MM bolts and the Helicoil requires a 12MMx1.25 tap, so I'm hopeful !

TrevorS

iTrader: (1)

Turns out the holes are indeed too small for 12MM Helicoils, so that's good -- I had to drill them out, though I chose a drill 1/64" smaller than standard for the tap (probably 1/32" smaller would have been even better). I'd bought three Helicoils and got one installed perfectly, but had trouble with the second (the pipe bends toward that side). First try I accidentally broke off the tang while positioning it, then I was so busy concentrating on not breaking the tang on my last Helicoil, I accidentally turned it a little too far through and deliberately broke off the tang before realizing it ! So, I just ordered another set of three and will hopefully get it right this time -- to bad it puts me out to next week.

The wrap should show up tomorrow.

TrevorS

iTrader: (1)

Wrap's arrived and UPS should be delivering the Helicoils at any moment -- talk about speedy !



After the other Helicoil's finally installed, I'll do a test with the 'S'-Pipe and OE spring bolts to make sure there are no issues. If the Helicoils turn out a problem, I'll just have to use the Weapon-R provided hardware .

TrevorS

iTrader: (1)

Helicoils arrived and I made yet a different mistake, but didn't break off the tang and so could re-install and this time was successful. That leaves me with two spares ! Went to start the 'S'-Pipe wrapping and noticed the inside of the header end weld was very rough and so I cleaned it up with a Dremel stone, sanding drum, and 220 grit sandpaper. The other two weld interiors are probably much the same, but since I can't get to them, it can't be helped. Here's the cleaned up weld interior.

TrevorS

iTrader: (1)

'S'-Pipe wrapped! Used 25ft of 2" wrap, got it as tight as I could, and used two 14" ties at each end. Might not look quite professional, but I think it'll do the job.