thirty_ought_six

someone told me if you cut out the extra metal located inside the right header just before the mid pipe mounts the it help preformance. has anyone heard about this mod? if so did it work and has it helped?

motojoe

Someone was right. Every little bit does helps reduce restriction
It's all about the "flow". Try a search on this site.

mikstr

I discussed this matter with VTR guru Roger Ditchfield from Revolution Racing (who built some impressive racing VTR's) and his advice was to NOT remove the so-called obstacle. In fact, he stated quite clearly that it was there for a reason (alluding to the fact that Honda could easily have made sure there was no such protrusion if they had wanted it that way). He went on to say that in the early days of the VTR, a few well-known aftermarket pipe manufacturers designed headers that were "unrestricted" only to find out later that they needed to alter their initial designs to incorporate some form of similar device (achieved through other means) to ensure better performance.
On anohter note, I also recall some people having tried the "mod" and seeing no discernible gain on a dyno.
It's up to you but I chose to listen to Roger, his advice has been spot on every time I have called on him so far.

cheers
Mikstr

Scooberhawk

It's awfully counterintuitive to think that a restriction would be a good thing, especially like the one we're talking about. Anything's possible though. Maybe there's some harmonic resonance there, where that restriction in that exact spot smoothes out the air flow in certain parts of the rpm range.

I dunno. It just seems strange that Honda engineers would incorporate such a restricition into the design.

Just fyi, I'm not arguing. I just felt like stating my opinion/observation.

superbling

Carburators and valve ports are two good examples of how "restrictions" work. Open them up too much and flow rates drop off.

I think (WAG) the header restriction is there to help with rear cylinder scavenging since it has a less than optimal route (more bends) compared to the front.

Scooberhawk

That makes sense. I've just never heard of such a technique for the exhaust. It seems like the rear cylinder scavenging issue could be resolved by making sharper bends in the front pipe and smoother bends in the rear pipe. As space is an issue, maybe the compromise ended up being the restriction.

Hawkrider

I think they put it there to "balance" the flow between the left and right pipes, because the header to the left pipe makes that sharp right turn. But I also think Honda overdid it. Before the mod, my left pipe was significantly hotter than my right. Now they are equal. To me that says something.

superhawk22

When I was thinking of doing a single sided exhaust, just to see how it looked I plugged up the right side,(side with the overlap), and there was very little loss in power but I didn't like how the exhaust just ended on that side and came out of nowhere on the left. So I plugged the other side and it ran like a pig! I know it was backing up a little in the curve under the bike but the difference was VERY noticeable.

senecagreen

They were just trying to contain their manufacturing costs in my opinion. It would have taken an extra step to cut a round in the side of the pipe they stuck in there before being welded and then they would have to align it with the opening before welding so instead by just sticking it in there that far they gave that section of the header more strength where the Y is and figured it was good enough flow wise.

You won't weaken it by taking a 1 1/2" holesaw and fixing it. They just didn't want an extra step in the manufacturing process because that takes time and time is money. The Japanese are very efficient and cost conscious in their manufacturing processes.

I fixed mine and like the balanced flow out the cans.

thirty_ought_six

so it seems like its a split down the middle as far as if its a good idea.

E.Marquez

and will remain so,, until someone does a before and after dyno run.. with no other mods... on the same dyno, with the same local weather conditions. For comparable results.

It's all just conjecture until then. In theory, it could go either way.. Cost saving measure during manufacture.... designed in, for better scavenging and flow. I’m on the “Cost saving measure” side of the fence…… but it’s just an educated guess.

NOrrTH

I didn't notice any difference in power when I did mine but both pipes seem to flow the same now

yellowstorm

old thread vtr header mod I cut out so call restriction & found that my bike runs to lean at the top end & lost a little power in mid range but as for full throttle through the gears it seem to get to 220km quite quick untill it ran to lean in top gear under load so it seems this mod needs carbs to be rejetted. once again if your bike is running good and its raining for a week leave it alone. **** happens

autoteach

I think, with the experience of my undertail exhaust behind this commment, that the restriction has to do with carburetion, pure and simple. I had my bike jetted after my exhaust and they couldn't get the jets to work everywhere. there just wasn't the offerings that would keep it happy as it came through 6500rpm. There was a hole, actually a black hole, of power. At one point i lost one of my end caps for my exhaust. Iwas leaving for a bike trip the next day, so I replaced it with a shifter kart exhaust tip. My bike regained power in the hole to the point where I hit the rev limiter in 1st gear the first time I took it out, as the power was quite unexpected. I guess I would say that unless you have unlimited fueling capabilities (FI), do not mod this, especially without jetting!