The elusive smog device


7 replies to this topic
  • dldavis_66

Posted March 06, 2008 - 05:05 PM

#1

I have read about the uncorking/desmogging process mods people are doing for some time on TT now. There is one thing most, if not all, are leaving out. There is another smog device that seems to be eluding everyone. Quite frankly, I am surprised no one on TT has even written about it, because, IMO this elusive smog device is still in fact leaving our beloved XRL's and XRR's partially smogged and corked, not in a minor way either. Better yet, this smog device is probably the simplest to understand and simplest to remove and replace(however, probably the most costly).

"What is this elusive smog device?" I am sure some of you might be asking yourselves while reading this. This elusive smog device is nothing more than the stock exhaust system, more specifically the headers.

Here's why. When I was in the process of building my own headers I became more familiar with how the stock headers were made and began to realize how restrictive they really are. (My theory of why the stock headers are a smog device is below)

The first thing that caught my eye when I took the stock headers off for the first time was the size of the Exhaust port outlet and the inside diameter of the header tubes. The Exhaust port outlet diameter is almost exactly 1 inch (I mic'd it). The header tube(s) inlet size is just about 1 inch also. The Header tubes start out being about 1 inch tubing at the factory. They expand the beginning of the header tubes to about 1.125(1 1/8) inches to join up with the mounting flange. Inside the header tubes is a big glob of weld joining the flange and the header tube. That in itself is restrictive enough. Another thing I noticed was the small radii of the bends of the tubing. The smaller the radii the more restrictive they will be. The big "U" bend on the Left Exhaust port header tube is yet another restrictive feature of these stock headers.

If you consider everything in the above paragraph you will come to realize that the stock headers are indeed very restrictive. Now to the part as to why I think the stock headers are a smog device. You take that restricted air flow in the headers and what do you get? Exhaust Gas Recirculation. Simply put, the headers are alowing more exhaust gases to recirculate back into the combustion chamber(more back pressure equals more EGR) to mix with the fresh fuel mixture to be re-burned and that equates to quite a bit of power loss.

If you have gone through all the trouble of uncorking, carb mods and desmogging your XR and still don't think the performance gains are all that impressive, try removing the stock headers and replacing them with some high flowing exhaust headers. I did and I unleashed even more performance than I expected along with all of the other mods.

  • martinfan30

Posted March 06, 2008 - 05:31 PM

#2

Yes that makes perfect sense. Thats why I took mine off and ground the welds down... That really opened up the entrance into the first bends. I dont know how much it helped, because I installed the Hotcam at the same time. I agree, nothing could help more than a larger dia. header.

Those stupid welds were probably put there just for the reasons you explain. Less NOX emitted.

  • Bibleman

Posted March 06, 2008 - 06:02 PM

#3

I've heard mixed reports on the efficacy of grinding the welds - any definitive word on the subject? If it really works it would be cheap HP:prof:

  • jdubb75

Posted March 06, 2008 - 06:37 PM

#4

I've toyed with the idea of replacing the headers on my R, but have not because I'm not 100% sold on the gains I'd get with a basically stock engine. I was a little afraid I'd lose more on the bottom than what I wanted to. If I were installing a different cam I would for sure replace the headers, but I'd want to keep the stock can. I like the way it sounds and, quite frankly, I don't want to have to fool with re-packing aftermarket exhaust right now. I know the Staintune exhaust does not require packing, but I'm leary of the db level. I don't want to shatter windows or go deaf from the constant 4500-5000 rpm hum while I'm cruising down the highway. The jury is still out for me. I'll just lay low and read about others gains/loses while I decide.:thumbsup:

All that being said, I would like to find a used HRC tip to try if anybody has one.:eek:

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  • dldavis_66

Posted March 06, 2008 - 07:17 PM

#5

I've toyed with the idea of replacing the headers on my R, but have not because I'm not 100% sold on the gains I'd get with a basically stock engine. I was a little afraid I'd lose more on the bottom than what I wanted to. If I were installing a different cam I would for sure replace the headers, but I'd want to keep the stock can. I like the way it sounds and, quite frankly, I don't want to have to fool with re-packing aftermarket exhaust right now. I know the Staintune exhaust does not require packing, but I'm leary of the db level. I don't want to shatter windows or go deaf from the constant 4500-5000 rpm hum while I'm cruising down the highway. The jury is still out for me. I'll just lay low and read about others gains/loses while I decide.:thumbsup:

All that being said, I would like to find a used HRC tip to try if anybody has one.:eek:


Well, my engine still has the stock piston and cam. The headers that I made were very nice indeed. I have pic of my headers somewhere on this forum. My header tubes are 1.25 O.D.(16g...the only thing I had available at the time, I didn't want to wait for thinner stuff :D) which = about 1.125 I.D.= better flow. Plus I have an oversized mid pipe, 1.75 OD(I had to swage my WB E2 mid-pipe to slip on) compared to to a stock and aftermarket mid-pipe of 1.62 OD.

When I first tried out my homemade headers, the bike ran kinda lean. I felt a bit of loss at the low end. However, I have since tweaked my carb by raising the slide needle up a notch. That gave me back all of the bottom end that I once had plus quite a bit more. The rest of the powerband improved remarkably as well. It does sound a little louder with the WB E2 Silencer on it.

  • martinfan30

Posted March 06, 2008 - 07:38 PM

#6

Are you using the sparky tip, or the chrome let it all out tip?

  • dldavis_66

Posted March 06, 2008 - 07:41 PM

#7

I've heard mixed reports on the efficacy of grinding the welds - any definitive word on the subject? If it really works it would be cheap HP:prof:


That will reduce some back pressure, but IMO, not very much. There are still a few other things that make the stockers restrictive:small I.D of the tubes, smaller radii of the bends, that big U bent on the Left Exhaust outlet head-pipe, there is kind of a kinky looking bend on the Right Exhaust head-pipe just before it joins the collector, and the welds: the tubing Honda uses making those stockers is of thin gauge, probably 20g (mild steel). The welds on the stockers are quite big for that thin of material. More than likely, there is a significant amount of burn-through on the inside of the tubes which will create more restrictions for the flow.

One important thing I need to say is that many people have been conditioned to think that some restriction/back pressure is a good thing. IMO that is totally false. You want the least amount of restriction/back pressure as possible(we have noise laws:bonk: ). The more restriction/back pressure an engine has to overcome to expell it's exhaust gases the more power it loses.
Simply put, get it in then get it out as quickly as possible.

  • jdubb75

Posted March 06, 2008 - 08:12 PM

#8

Well, my engine still has the stock piston and cam. The headers that I made were very nice indeed. I have pic of my headers somewhere on this forum. My header tubes are 1.25 O.D.(16g...the only thing I had available at the time, I didn't want to wait for thinner stuff :ride:) which = about 1.125 I.D.= better flow. Plus I have an oversized mid pipe, 1.75 OD(I had to swage my WB E2 mid-pipe to slip on) compared to to a stock and aftermarket mid-pipe of 1.62 OD.

When I first tried out my homemade headers, the bike ran kinda lean. I felt a bit of loss at the low end. However, I have since tweaked my carb by raising the slide needle up a notch. That gave me back all of the bottom end that I once had plus quite a bit more. The rest of the powerband improved remarkably as well. It does sound a little louder with the WB E2 Silencer on it.


I saw the pipes you made and I must say they look nice. Like I always say, if you want it done right do it yourself. It looks like you did it right! :thumbsup:
I wasn't thinking it wouldn't help. I just didn't know if it would be the couple hundred dollars for a new set of headers without the cam...in my case???


Are you using the sparky tip, or the chrome let it all out tip?.


Not sure if you are talking to me, but if you are I am running the stock tip with the outlet drilled out to 2" with a hole saw and the standoff baffle snipped off.

This is not my pic...I stole it from another thread on here.:D
The tip on the left is the HRC that I would like to try out and the one on the right is the stock tip. I have cut the four legs off, thus removing the baffle at the end.

Look at me go...multiple quotes and a pic attachment in the same post! I have almost reached the level of a Jedi Master. :eek:

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