Are there any downpipes > 2" diameter?

[masospaghetti]

Looks like all 2-1 downpipes now for the CB7 have a 2" collector or smaller. Seems like a silly design for so-called "performance" exhaust parts. I would like a 2.25" collector if possible.

I was considering hacking up an old OE downpipe but I would much rather buy a new one if they make them. Are there any available with a 2.25" collector or larger?

EDIT: Here is what i'm working on (since everyone loves some pictures)

[Accrdwgnguy]

I chopped the downpipe from an ebay 4-2-1 header at the collector and welded on a 2.5" pipe. worked well.

[masospaghetti]

Any benefit of using an eBay downpipe compared to the OE pipe?

[Accrdwgnguy]

Oh I doubt it that's just what the car had on it. Intermediate pipes were 2" diameter and so was the after collector pipe, so just chopped the collector back to 2.5in and welded in pipe + flex section. None of this was scientifically tested but it matched up well with the 2.5" exhaust and ran good. I'm sure the same could be done with an OE downpipe, in your 2.25 if you desire.

[cp[mike]]

For a while (years back), it was common to get the best possible, but still affordable, header (all were pretty much the same, which ebay ones are copies of now, and the originals are discontinued) and then cut the collector off and weld a 2.5" one on there. Seems a number of people had the same thought/complaint as you. I'm sure you can still do the same deal with an ebay header - it might be a little simpler to work with, I know the OEM one has extra heat shielding and complexity to the collector/O2 sensor area as compared to other generic headers.

[deevergote]

A generic header will still likely have larger primaries, which will be more effective with a larger collector.
If I were to do this, I'd spend the money for a higher quality header, like DC Sports. Especially since I can't weld, so I'd be paying someone to do the collector mod for me! I wouldn't want thin low-quality steel and weak welds on something that I'd be putting more money into.

A generic performance header with a 2.25" or 2.5" collector (depending on your goals) would be the most effective thing shy of a high end header design such as Bisimoto's (I don't care for the craftsmanship, but I can't deny the quality of the engineering...)
Keep in mind that you'll be losing low end power in exchange for top end. Be sure the rest of your engine's mods will allow it to make power up high.
I think the 2" collector found on most generic "performance" headers is to ensure customers aren't left with a soggy low-end powerband... because kiddies like to trust the butt-dyno, and things that don't "feel fast" don't sell. Low end grunt feels faster to most than high end power.

[masospaghetti]

Does anyone have a generic header they can measure? I would like to confirm that the primaries are larger (if they are, I don't mind buying one - if they aren't, I actually prefer the look/fit of the OE header).

I have a spare cast header I can measure when I get home.

[Accrdwgnguy]

I can pull that header off the shelf and measure it later, maybe snap some pics for you. Nobody never wanted to buy it, maybe because the "high quality" flexpipe I bought from a local exhaust shop was anything but that.

[dj_ender]

You're gonna have to make your own. This is a generic eBay header with a Vibrant 2-2.5" collector mod.

[wagon-r]

A generic performance header with a 2.25" or 2.5" collector (depending on your goals) would be the most effective thing shy of a high end header design such as Bisimoto's (I don't care for the craftsmanship, but I can't deny the quality of the engineering...)

I'll vouch for deever's statements. The build quality on my Bisimoto header was so bad that I had to have the two pieces welded together to prevent leakage and the collector bent so that it wouldn't head off to the side. But the engine is putting down 170 wheel hp with just a Stage 1 cam, H23 intake manifold, 0.025" head mill, Prelude intake, very mild exhaust porting, 2.5" exhaust, and a good tune on 93 octane. Of course, my torque peak is at 5,800 rpm, but what the heck.

[masospaghetti]

Thanks guys.

One more question. is it worth replacing my converter with a real "high flow" like a Magnaflow or Random Technology? Will I gain anything? About a year ago I installed a new Walker cat.

[Corweena]

For the H22, the FGK header I have not only has larger primaries than the DC Sports one, but the collector is 2.36" (60mm) instead of 2". Granted, on a stock motor with the stock ECU, you still won't see a significant power gain, but the potential is there. When I swap the motor in, I may have my fab guy whip up a new downpipe section with a 2.5" collector too, so I can run a 2.5" all the way back.

[masospaghetti]

In the process of fabricating a downpipe. Factory 2-1, chopped off the collector, welding on a 2.25" flex pipe. Reusing that "isosceles" flange to the converter. That factory downpipe really necks down at the collector, no wonder it's a flow restriction.

For now I'll keep my Walker converter but I'm still on the fence about this Yonaka catback exhaust (2.25" also)...

[deevergote]

I'd imagine the stock manifold is fairly restrictive compared to even a cheap aftermarket unit. I assume you're doing the welding yourself?

Yonaka is basically a knockoff company, kinda like OBX or Megan Racing. They're among the better ones. I wouldn't trust anything important from them, but the exhaust is probably just fine. At worst, it may be raspy. If you don't like the sound, you could always replace the muffler with a better one, and just use the piping. I bet you could get $50 shipped for the muffler on ebay.

[masospaghetti]

I'd imagine the stock manifold is fairly restrictive compared to even a cheap aftermarket unit. I assume you're doing the welding yourself?

Yonaka is basically a knockoff company, kinda like OBX or Megan Racing. They're among the better ones. I wouldn't trust anything important from them, but the exhaust is probably just fine. At worst, it may be raspy. If you don't like the sound, you could always replace the muffler with a better one, and just use the piping. I bet you could get $50 shipped for the muffler on ebay.

The secondaries (?) on the stock downpipe are somewhere between 1.6"-1.7", it's hard to measure exactly because the pipe necks down a little bit, and because it's a double walled pipe. Even dual 1.6" pipes should flow at least as much as a single 2.25" pipe (2x1.6^2 = 5.12, 2.25^2 = 5.06).

But Deev I'm sure you're correct and it won't flow as well as an aftermarket manifold but I just thought I'd give it a shot. I like the OE construction quality and I had one sitting around with a bad flex pipe anyway. I'm doing the welding myself.