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Discussion Starter · #61 ·
The exhaust came out very nice, I also have the hybrid racing intake and noticed it makes a very pronounced sound as soon as the TB starts to open. I dig it lol. Iat stay very close to ambient temps when moving as well.
Haven't had a ton of seat time quite yet, to monitor AFRs and IATs, but I've noticed the same. I hear steady little hisses as the IAVC opens and closes to try to keep the idle smooth with that cam too. All in all a nice piece with great fit and finish for a fair price.
 

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The resonator in- and outlet are not clamped? How are the sealed and kept in place?

So, in this car's case at least, a 2.5" straight through exhaust makes a touch less peak power and torque than a 3" exhaust with a chambered muffler imposing a bit more restriction.
I like the high speed cam torque curve on your dyno sheet comparison. Thanks for sharing here 馃啓! For me the 3" exhaust does what is aimed for, lowering the exhaust gas back pressure, what one can see in the better torque there. How much VTC advance was done after swapping to the 3" OD? Normally there is a bigger advance possible of around 5-10 degree in VTC. As well as ign. timing can be advance partly, as less exhaust residuals are suppressing a faster combustion. Please let me know the difference in those two maps.

That 3" thing is all about improving the pressure drop over the engine. If intake and IM can support a better pressure level the gain through lowering it on the exhaust side is of course small. But as VTEC wasn't much changed according the dyno graph I would assume it wasn't fully tuned. So I would recommend first to clarify this before to focus on the intake side. You may share your calibration and last WOT log, just for see what is the status?

Anyway, would be nice to know what your intake and IM setup consists of?
 

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Discussion Starter · #63 ·
The resonator in- and outlet are not clamped? How are the sealed and kept in place?

I like the high speed cam torque curve on your dyno sheet comparison. Thanks for sharing here 馃啓! For me the 3" exhaust does what is aimed for, lowering the exhaust gas back pressure, what one can see in the better torque there. How much VTC advance was done after swapping to the 3" OD? Normally there is a bigger advance possible of around 5-10 degree in VTC. As well as ign. timing can be advance partly, as less exhaust residuals are suppressing a faster combustion. Please let me know the difference in those two maps.

That 3" thing is all about improving the pressure drop over the engine. If intake and IM can support a better pressure level the gain through lowering it on the exhaust side is of course small. But as VTEC wasn't much changed according the dyno graph I would assume it wasn't fully tuned. So I would recommend first to clarify this before to focus on the intake side. You may share your calibration and last WOT log, just for see what is the status?

Anyway, would be nice to know what your intake and IM setup consists of?
It's all welded. The quality of the welding work is pretty stellar!

Unfortunately, I don't have any of that data. As far as the shop indicated, they tuned it as far as it would go with the 2.5" exhaust then fabbed the 3" exhaust and tuned it a bit further. It seems like the VTEC engagement point was a bit earlier on the 2.5" pull. I haven't had a ton of time to tinker with it or peek at the tune yet (or even attach a computer to it at all yet). Hoping to figure all that out once the weather is consistently a bit nicer.

The intake portion consists of the engine's original RBC intake manifold, a KTuned RBC to RRC adapter, and a stock RSX-S (k20a2) throttle body. It's fed by a Hybrid Racing intake. I know 70mm (or bigger) TBs are common with these engines, but I also saw evidence that NA engines are hitting 270+ WHP with the RSX throttle so I didn't bother upgrading it.

--Matt
 

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It's all welded.
Ok, thanks. So sealed, no pressure influence from there 馃啓.

It seems like the VTEC engagement point was a bit earlier on the 2.5" pull
Ok, interesting. Was low speed cam fuel and VTC tuned?
BTW, that dip is common for the DC 2.2 cams, as low and high speed cams are so different and the two torque mountains are more separated, giving a higher gap between them. If VTEC was increased, then, mmmmhhh...the smaller ID must have supported a resonance of the header-exhaust-system, which is now not supported. So more truth of the header came out. Would be interesting to know how long are the runner lenght's of the header. Would you share them?

...RBC intake manifold...stock RSX-S (k20a2) throttle body...Hybrid Racing intake...
How do you adapt the TB and the intake pipe?
 

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Discussion Starter · #65 · (Edited)
Ok, thanks. So sealed, no pressure influence from there 馃啓.

Ok, interesting. Was low speed cam fuel and VTC tuned?
BTW, that dip is common for the DC 2.2 cams, as low and high speed cams are so different and the two torque mountains are more separated, giving a higher gap between them. If VTEC was increased, then, mmmmhhh...the smaller ID must have supported a resonance of the header-exhaust-system, which is now not supported. So more truth of the header came out. Would be interesting to know how long are the runner lenght's of the header. Would you share them?

How do you adapt the TB and the intake pipe?
Yes, they definitely tuned the low speed cam. They indicated that the current tune is at about 35 VTC tapering down until vtec comes on at 5000. Based on the difference in the chart, it seems like it was different on the 2.5" tune. I'm not sure how much, though.

As far as I'm aware, this header is just an RCrew clone. I don't see length specs handy for either, just diameter specs, but I took a stab at measuring it.

A flexible tape measure says exactly 19" from the flange to the inlet of the collector. I'm not sure which spec you're looking for, so I'll let you decide at the collector. ;) I see almost exactly 3" to the start of the merge.
104063


No adapter necessary. It bolts right up without any adaptation.
104062
 

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They indicated that the current tune is at about 35 VTC tapering down until vtec comes on at 5000
Ok, 35掳 VTC from low speed torque peak tapered down thill VTEC sound plausible and is viewable in the graph.

A flexible tape measure says exactly 19" from the flange to the inlet of the collector. I'm not sure which spec you're looking for, so I'll let you decide at the collector. ;) I see almost exactly 3" to the start of the merge.
From the position where actually on the flexible tape measure says 8.0" up to the flange on the cylinder head. That would be the runner length I am looking for.

No adapter necessary. It bolts right up without any adaptation.
Oh, nice, thought they sell only a 3" and a 3.5" mm ID version.
 

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Discussion Starter · #67 ·
Ok, 35掳 VTC from low speed torque peak tapered down thill VTEC sound plausible and is viewable in the graph.

From the position where actually on the flexible tape measure says 8.0" up to the flange on the cylinder head. That would be the runner length I am looking for.

Oh, nice, thought they sell only a 3" and a 3.5" mm ID version.
Gotcha! So that'd be 27" total length including the distance from the collector inlet to the flange on the head.

The intake is 3" throughout, but their clamp setup is flexible enough to fit a pretty wide range of throttle bodies, including the stock RSX TB.
 

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Gotcha! So that'd be 27" total length including the distance from the collector inlet to the flange on the head.
Ah, I see. The resonances of that 4-1 header are not well spread over the revving band: roughly at 3800, 5800 and 11000 rpm. A 4-2-1 header would have 3 more supporting engine speed points, if well designed it beats every 4-1 design. Just as a side note 馃槈. But yes, now we see why the VTEC is in general so late on this engine beside the DC 2.2 torque dip issue. Anyway, seems the 2.5" exhaust supported the 4500-5000 rpm area with an resonance, which is definitely from the header.

The easiest solution would be a right designed 3-way header. In general, those 4-1 headers are too short for a rational torque band design for most Honda chassis. I assume longer = clearance issue in most chassis exhaust channels. So it is anyway better to have a 4-2-1, which has less clearance demand on the floor of the car.

The intake is 3" throughout, but their clamp setup is flexible enough to fit a pretty wide range of throttle bodies, including the stock RSX TB.
Ok, I assume it is at least 600 mm long, isn't it?
 

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Discussion Starter · #69 · (Edited)
Ah, I see. The resonances of that 4-1 header are not well spread over the revving band: roughly at 3800, 5800 and 11000 rpm. A 4-2-1 header would have 3 more supporting engine speed points, if well designed it beats every 4-1 design. Just as a side note 馃槈. But yes, now we see why the VTEC is in general so late on this engine beside the DC 2.2 torque dip issue. Anyway, seems the 2.5" exhaust supported the 4500-5000 rpm area with an resonance, which is definitely from the header.

The easiest solution would be a right designed 3-way header. In general, those 4-1 headers are too short for a rational torque band design for most Honda chassis. I assume longer = clearance issue in most chassis exhaust channels. So it is anyway better to have a 4-2-1, which has less clearance demand on the floor of the car.

Ok, I assume it is at least 600 mm long, isn't it?
A longer 4-1 would actually fit without issues. The Hybrid Racing z3 shift box is tiny in the exhaust tunnel, so there's not really anything in the way on this car.

I picked the 4-1 header expecting some sacrifice in the power band. The low part of the rev range isn't really a huge concern to me, but is surprisingly ample in spite of it! My daily driver has a turbo and enough low end grunt to satisfy my torque needs. I just wanted something that revs happily for this car, and the cam and lightweight flywheel have delivered it nicely!

Yeah, the intake is definitely at least 2' long. The filter sits down behind the bumper.

Don't get me wrong. I'm happy with the results. If there was a magic 10hp hiding in a well known bottleneck, I'd happily uncork it, but so far the swap is exceeding my expectations for this car! 馃槑

I bought/built this car for HPDE, maybe auto-x, and occasional summer driving to avoid the wear and tear on my daily driver. I spent all of last summer and fall removing all the "rice" replacing all the ebay junk the last owner had on it with "good enough" aftermarket or OE stuff. It came with pitch black tints slammed on stock struts, had the cheapest clapped out aftermarket control arms in every position, and had a bunch of extra wiring and LEDs I had no interest in. I replaced every piece of the suspension with new stuff (either OE or middle-of-the-road aftermarket) to get it back to decent spec inside and out.

My goal for this season was to get the d15 out and something more spicy, but still reliable, in. My driver skill and suspension/tires will need additional attention long before this setup's power is a meaningful issue to me, at this point, so I definitely can't complain.

All in all. I'm happy with the state of it. Just need lots of seat time now!

104064


--Matt
 

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Discussion Starter · #71 · (Edited)
Ok, just thought there would be an demand to clarify the differences of the 2.5" to 3.0" exhaust results. But happy is just enough :).
Haha, your explanation makes sense and is appreciated/helpful! By all means, wax lyrical about header theory in my thread anytime!

This is the first reasonably quick non-turbo car I've owned, and I'm content with it so far. It's surely a massive improvement over the I/H/E d16 it had before! My contentness may change in a week, month, etc. but I'm cool for now!

At the very least, I can sleep comfortably at night with solid dyno confirmation that the 3" exhaust with a quieter chambered muffler isn't robbing me of any major amount of power versus the prior setup. I'd be satisfied if it was exactly equal to the 2.5" setup, but that it's even a touch better is just icing on the cake!

--Matt
 

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Discussion Starter · #72 ·
After driving for a few, I do still feel like things could be a little quieter. The shop that did the exhaust seemed wary of putting the glasspack I got on there, and opted to just put on the bullet, but things are a bit loud still when the exhaust is cold. Ironically, since the 2.5" setup was not bad there, idle sound levels are my complaint at this point.

I may try to fit a Vibrant Ultra Quiet resonator after that bullet it the exhaust tunnel will acomodate one, or at least an additional bullet. I think I'm gonna give the setup some time to break in first, though. It's all new, thus not broken in, so the packing in the bullet may improve and a good coating of carbon in that unpacked muffler may help too.

--Matt
 

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Discussion Starter · #73 · (Edited)
My loudness concern is at a super specific frequency, according to the spectral analyzer, of 80-100Hz. I think I'm just gonna seek out a Helmholtz chamber to address it. Everything is really good otherwise!
 

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Discussion Starter · #75 · (Edited)
At which engine speed?
2100-2200 on the dot. With my tire size, it's kinda punishing in 6th from ~47-52mph under any moderate load. I didn't notice it for the first week or so, since I didn't ride on any long uphill 50mph stretches, but I sure did this weekend. Cruising in 6th at 40mph is quiet and tolerable. Anything at 52mph or more in 6th is very pleasant too.

Since I've got an active muffler, it may we'll just be a "not enough resonator" situation...and replacing the bullet with something bigger may sort it out. Haven't picked a plan yet, though, but I did reach out to both StainlessWorks and Dynomax to see if either had an option that'd help me with that frequency.

--Matt
 

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My loudness concern is at a super specific frequency, according to the spectral analyzer, of 80-100Hz. I think I'm just gonna seek out a Helmholtz chamber to address it.
Worse with more load, not so bad at low load.
That is a difficult task compensation that frequency with a Helmholtz-resonator. The spring-mass-transducer section would be very huge to compensate at 80-100 Hz. Helmholtz are better in higher frequencies, where a lower oscillating mass is demanded. Assuming the exhaust gas already cooled down to 300 掳C, the throat volume would be like 0.7 m long, 0.1 m in diameter. This correlates to typical resonators. Not sure if you would fit another one under the floor. But as the frequency is already and almost the double of the engine speed it may be possible to weaken it by obstacles in the flow.
 

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Discussion Starter · #79 ·
Agreed, I'd need ~42" of 2" pipe to mitigate it. It'd be tough to fit in this chassis. I've got a teeny tiny little res now, though, so I'm hoping something bigger there coupled with the chambered muffler should be enough to sort it out.
 

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Agreed, I'd need ~42" of 2" pipe to mitigate it. It'd be tough to fit in this chassis. I've got a teeny tiny little res now, though, so I'm hoping something bigger there coupled with the chambered muffler should be enough to sort it out.
Great, keep us posted .
 
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