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Exhaustexplanation for a total idiot!

2454 Views 26 Replies 9 Participants Last post by  dfib
I have read almost every thread on exhaust, and performance gains and tuning and so on. I makes things a little more clear but theres not section for the total myself.
I've been looking at the chain reaction moto cans and header now and i really like the sound and look of things. But then I read all these things about removing SAI and Cat and so on. I really don't know what this means. Am I a moron? Yes Maybe, but if someone would be kind enough to tell me, do I have to remove anything and make my own mods to fit the CRM cans and header? Is there a place for the O2sensor? ( I have emailed bob but he seems to be on vacation) ;D
I'm not an engine trimming freak, if I could get the sound and a little more power over all I would be most satisfied.
Oh, and i forgot to mention, I have a -06 and I'm going to buy the package with the tuneboy if I go ahead with the deal.
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SAI is on top of the cylinder head. It is removed or plugged by most to eliminate the backfiring that happens when you let off the throttle. The factory cans are too restrictive and quiet to hear it well. Aftermarket exhausts exacerbate this some. When plugged, you still get a nice rumbly overrun sound, just no popping. If you have watched any videos of exhausts being revved while sitting, you have probably seen this in the form of flames coming from the exhaust.

The pre-cat is in the header pipe, just before the slip joint below the footpeg. It is commonly removed for performance reasons. The sound is improved as well. It will increase power through the whole rev range. The rumble is deeper afterwards as well.

Neither one will affect your putting on an exhaust of your choice. I do suggest that you do plug the SAI at least, the bike will sound MUCH better when you are slowing down in gear. It involves removing the tank to do it, but that is actually pretty easy. I used a 4mm bolt, two washers, a nut, and an inch long piece of vacuum hose. A washer on each end of the hose, with the bolt through it, tighten the nut, hose expands, easy...
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How do I remove the pre-cat? Is it the cable coming down from the engine that goes into the exhaust pipes?

So even if I would get the CRM cans with header and tuneboy I would get some popping?

And finally so blocking the SAI wont hurt the engine really? I kind of see how to block it. You don't happen to have some pics of the thing so I know what to block? ;D

You see, moron was the word! ;)
I have to say though, i really appreciate the help available here on the forum. I would be a straight up stock-guy without you guys!
The cable coming down to the pipes is wiring for the O2 sensor. The pre-cat is a perforated tube inside the exhaust piping. You have to remove the exhaust header, the work at the pre-cat with a drill, chisel, whatever to remove it, the weld the 4 holes left in the pipe closed. The holes are left there from the two mounting pins that hold the cat in place. If you get an aftermarket header (you mentioned the CRM), it won't have the pre-cat, so no problem.

Without plugging or removing the SAI, you will get popping with ANY aftermarket exhaust. Even with tuneboy. Just plug it and be done with the issue, it's easy to do. It won't hurt the engine at all. In fact, I think it may be better for the bike as a whole. I know the header stays cooler when the SAI is plugged.

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Haha okay so now I'm probably gonna piss u off. But If I understand correctly I don't have to drill or do anything if I get the CRM half system? About the pre-cat that is. Just plug in, tune and go?
Besides plugging the SAI that is.
Bare with me here...I probably will have to :smiley-asskiss: for all eternity after this! ;D
No worries M8! The pre-cat is in the header part of the exhaust, and the half system does not replace this. In fact, when you remove the factory half system, you bike will look just like that pic, that is the slip joint where the half system starts. And you don't HAVE to remove the pre-cat at all. It just makes for a slight gain in torque everywhere, and sounds better. Only when you replace the actual header the pre-cat goes away with the factory header.
I forgot to mention...

If your bike is '07 or later, it has a second pre-cat. This one is located immediately after the same slip joint. If you are replacing the half system, it goes with the old mid pipe. No worries there.
I see where you're getting at. I was of course talking about the half system..didn't realize it. :slap: I don't know if Bob has finished the new full system? I think he only has the half system on his website. You say that removing the pre-cat does much for the sound. Do you mean louder or deeper?

Do you think the CRM half system is worth buying? I don't find that a lot of people here have it?

Finally, removing the pre-cat seems quite easy then if you have a weld and such? Do you know if it's easy the ruin the header while doing this?
The sound is louder AND deeper. Mostly deeper.

CRM header is still in prototype stage. Coming sooner than later.

Half system is definitely worth buying.

Hard part of removing the pre-cat is removing the header. Little risk in damaging the header. I have heard it is easy to damage the radiator or oil cooler during header removal. I would tape a piece of cardboard to the backs of these during that process, and all should be well. The fins are easy to bump and bend.
Removing the pre-cat is actually very easy. To oversimplify it: you drill 4, 1/4" holes, pull the pre-cat, then have the holes welded shut. Almost any shop (auto or bike) that does exhaust work should be able to weld the holes shut cheaply.

Side note - Look at us giving tuning advice, gotta think DVS is smiling reading this. He's created a little herd of tuning monsters. :eboy:
Yep. We are all Devious Disciples.
Dfib said:
Side note - Look at us giving tuning advice, gotta think DVS is smiling reading this. He's created a little herd of tuning monsters. :eboy:
A little knowledge is dangerous eh Dfib?
Just in case anyone with an 07 is reading this and decides to act on the (VERY good advice for the older ex. system) TAKE CARE. You might have a FULL Cat in your midpipe. DO more reading here before deciding to drill and remove.
legman said:
Dfib said:
Side note - Look at us giving tuning advice, gotta think DVS is smiling reading this. He's created a little herd of tuning monsters. :eboy:
A little knowledge is dangerous eh Dfib?
But it's sooooo much fun and feels sooo good while you're doing it! ;) :eboy:
So how much power and torque does this pre-cat removal actually give? Is it worth the hassle? My uncle is a mechanic since 50 years or so and is a pretty good welder. So i guess the work itself is fixed quite easily. The question is more if it's worth it? I mean, this is something that isn't to easy to return to stock if you want to sell. (god forbid!!)
Or is it more of a sound thing?
I was going to get the CRM and tune anyway and I guess that only that mod will be noticed?
Anyway you guys get the point! ;D
I'm running the ChainReaction 1/2 system, bolted to the factory header that has been modified. i.e. pre-cat removed and the header flanges ported. In my opinion it's well worth it, as long as you have Tuneboy and the proper tune. There is a quite noticeable difference between what I'm running now and a stock system. It hasn't been on the dyno, but I'm guessing it's added 15-18 HP to the stock setup.

Still waiting on Devious with his dyno work for a proper tune and some good numbers.

(Everything I say is my own opinion. It could be an added 4-6 HP, but it sure feels like a lot more. I've also gained 1/2 second on the 1/4 mile drag strip. YMMV.)
Now I want the chain reactions even more! ;D
Shit I hope Bob has some to ship on the double! Do you know if he keeps some in stock? Or does he make them when ordered?

I don't understand what you mean by having the header flanges ported. Is it a hard thing to do? Maybe just the system is enough for me to start with! :drink:

And then maybe removing the pre-cat. All in good time.;D
I think I'll notice a difference in just the pipes.
This picture doesn't show it very well, but the top of the header is somewhat restrictive coming out of the head. If you take a dremel tool and grind it out there are some cheap/easy horsepower to be found. Just port it out until you have about a 1/16 inch lip all the way around.

Really worth it.

I'm talking about the header, NOT the actual head.

A better explanation:

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here's what crash means by having the header flanges ported...

The casting work is very rough, and cleaning them up and smoothing them out helps increase flow. :drink:

Looks like Crash beat me, but here's another pic fer ya too. ;) ;D
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Ah! Thanks! Great pics you guys!

Ha ha this shit never ends does it? ;D
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