Gernby

UPDATE 2: The latest updates to this thread begin at post #234, where I show results of my custom 60mm dual with HFC. I believe this is the best performing exhaust ever built for an S2000.

UPDATE: The conclusions that I made early on in this thread, beginning at post 1 were somewhat wrong. As this thread progressed, I found that the gains from the exhaust were VERY dependent on the diameter of the test pipe or HFC that was used. However, there is quite a bit of interesting test results within this thread if you have time to read it. In the end, there were significant gains with a 70mm single IF it was mated to a 70mm TP or 70mm HFC. Here is a thread about what I learned about the test pipes / catalytic converters. -----------------------------

I've been doing an extensive test of parts on my car in various combinations of stock vs. aftermarket headers, intakes, test pipes, and exhausts over the past few weeks. I've tested them with the stock tune, canned FlashPro tunes, and custom tunes. I've logged the resulting AFR's and the changes in VE, and recorded many "Soft Dyno" results.

My soft dyno is not a conventional dyno (DynoJet, etc.), but has been calibrated by a DynoJet. It is NOT a phone app or Gtech type device that estimates power via accellerometers either. It uses the same method of measurement as a DynoJet, but does this while the car is moving on the road via FlashPro datalogs. The results are repeatable from day to day, all day long, and has SAE correction for climate change. Here's an older thread about it that I really need to update. If you want to argue about the soft dyno, please do it in that thread If you want to ignore the soft dyno results, please do. The AFR plots establish the same conclusions.

I borrowed a popular 70mm single exhaust from another S2000 owner. I'm going to keep his identity and the make and model of his 70mm single private for now. It had 2 silencers installed in it when I got it. One silencer was in the tip, and the other was inside the front of it, just inches away from the flange. I don't know where they came from or who made them, but they were basically just perferated screens formed in a cone.

I started out by establishing "fresh" baseline dyno runs this morning (soft dyno) with my slightly modified stock exhaust (magnaflow cans). It was a beautiful day with cool temps, no wind and low humidity, so all of my dyno results were more consistent than any I've had on a DynoJet. I did several dyno runs so that I could take the average of them. Then I installed the 70mm single exhaust as I received it (with both silencers), and repeated the dyno runs. Then I removed the silencer from the exhaust tip, and repeated the dyno runs again. Then I removed the inner silencer, and repeated them again. All runs were done using the same custom FlashPro tune with VTEC at 3700 RPMs and a flat 12.8:1 AFR (with my current mods) so that we could see exactly what happened to the air / fuel ratio. The other significant mods on my car are a PWJDM intake, T1R Header, Hondata IMG, 60mm non-resonated test pipe, and 630cc Siemens Deka Injectors.

Here are the 3 torque curves showing the the 70mm single with both silencers (red), 1 silencer (blue), and no silencers (green). The silencers clearly suck for performance by looking at the graphs, but I couldn't feel a difference. They did make a HUGE difference in sound though. The 2 silencers together reduced torque by about 8 ft-lbs after 5K RPMs. With some tuning, some of the losses would go away, but it's clear that the silencers are performance KILLERS. BTW, the thin dashed lines under the solid lines are the injector pulse widths from the datalogs adjusted by % offset from target AFR. I like to see this to see how close my torque curve compares to VE. With a good tune, they follow each other pretty closely.

Here are the AFR curves for the same runs.

Here is the most important comparison. With the silencers both removed, there was no real difference in performance between my stock exhaust with Magnaflow mufflers compared to the 70mm single. There was just the slight difference due to slightly different "resonance" in the midrange where the 2 exhausts performed differently.



Here are the AFR curves for the runs above. You can see that the AFR gets a bit leaner for the 70mm single in the same RPM range as it shows more torque above.



All you 70mm single preachers can throw yourselves on your swords now... EDIT: This was too strong of a statement, since I discovered later in the thread that swapping out the 60mm test pipe with a 70mm test pipe did allow the 70mm exhaust to show significant gains.

b.r.i.a.n.

the whole issue with the silencers doesn't surprise me one bit. on my ep3 i had a spoon midpipe and axle back. the spoon axle back had a silencer. i removed the silencer and picked up roughly 3% fuel across the rpm range.

as far as the test goes, did you only play with fuel or did you tinker with ignition timing too? it looks like you targeted 12.8 afr's. did you try targeting other afr's?

if you look around the 5250 rpm range on both graphs you can see that the green line made more power with leaner afr's. looks like it hit 13.1 around 5250 rpm. around 4000 rpm you can see the afr's richen up to roughly 12.6ish and you see a dip in hp on the green line as well. i think you could've picked up hp on the green line if you leaned it out some.

S2K@PR

Very interesting results , good write up!

As for the silencers they really suck performance-wise, but keeps dB at a minimum.

i remember a 2001 Prelude i had with silencer on a Tanabe Exhaust. I tested this on the track.

Gernby

For the purpose of saving time, I have NOT tried to retuning for peak power on these bolt-ons. EDIT: I started with a "base tune" that has slightly less agressive timing than my regular tune (much more agressive than stock. I have just been retuning the fuel for each setup for a FLAT AFR so that I can determine which bolt-ons actually increase flow. If they flow better, and AFR goes lean, then I add fuel until AFR comes back to my target. I just consider this to be a scientific way of determining flow (VE). If you can burn more fuel with the same AFR, then you're going to make more power too. I'm sure I could totally geek out over every configuration to get that last 0.5% of power at each RPM increment, but that would just kill the test. I'm not getting paid for this, so I'm not going to spend 20 hours per setup on tuning. I have full confidence that my soft dyno is accurate, but it isn't "quick". It takes about 30 minutes to find out what each change does to torque.

I have tried lots of different AFR targets, and I've never seen a significant change in power from a 0.2:1 offset. However, I have definitely seen bolt-ons that CAUSE a 0.2:1 offset also CAUSE a 2 ft-lbs increase in torque. This is what we see above.

H22toF20

Thanks for the interesting results.

I do however think you should have tried this with a 70mm test-pipe though. For an exhaust you literally have to think of the whole thing as one. Putting a 70mm exhaust with a 60mm test-pipe isn't going to accomplish much, unless the previous exhaust was an even bigger restriction than the 60mm test-pipe.

This is with my butt dyno but I bolted my HKS 75mm to my OEM cat and felt a slight difference(been proven to make power on the OEM computer). But, what was really a shocker was the huge increase I felt after I installed my Ultimate Racing 3" test-pipe. Probably 3x the amount I felt from just bolting on the HKS.

I believe the HKS 75mm exhaust flows great but due to the OEM cat being small(and a cat lol), you can't see the real potential of the exhaust. It's not until you bolt on a same sized test-pipe that you see it's real potential. I imagine this is what happened during your testing.

It has been proven time and again in the Honda community that 3" makes power on every Honda performance motor made in the last 2 decades. I've also chatted with a couple of tuners that state that "everything after the collector is one big restriction." And to be honest it makes a lot of sense.

S2K@PR

What size is the collector on the T1R Header?

Gernby

The reason why you felt such a gain after installing the 70mm test pipe is because test pipes make huge gains by themselves! The small gain that you felt from the exhaust was just a placebo that got reinforced by the large gain from the test pipe.

EDIT: The next statement wound up being WAY WRONG. The test pipe that I have is larger diameter than the outputs of both of my headers (stock and T1R). I don't believe that a 10 mm increase in diameter on just another 18" of piping would magically create a signficant difference from this exhaust.

dan_uk

I dyno'd my car stock, vs stock with testpipe and VAFC vs 70mm single

https://www.s2ki.com/forums/index.php?act=m...d=si&img=727639

The single made more power and was lean enough to not need any leaning with the VAFC.

punchdrunk

+1

Sold the VAFC as it was useless with the 70mm header back - now have a Spoon ECU.

s2konroids

Good thread Gernby , your finding are consistent with my findings over the years. This is why i run a 63mm single-pipe on my SC setup with HFC . A testpipe made a small difference (around 2bhp) but could'nt pass a MOT/smog test so it had to go.

I used to own two 70mm exhausts and two duals, adding just a 70mm on stock dyno'd will reveal gains on a stock ECU as its simply upping the AFR to be leaner which equals power (if AFR is in target).