It's Saturday! Whether you just finished a disc brake conversion or finally got your decals perfectly aligned, we want to see it.

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It's Saturday! Whether you just finished a disc brake conversion or finally got your decals perfectly aligned, we want to see it.

>

It's Saturday! Whether you just finished a disc brake conversion or finally got your decals perfectly aligned, we want to see it.

>

It's Saturday! Whether you just finished a disc brake conversion or finally got your decals perfectly aligned, we want to see it.

>

It's Saturday! Whether you just finished a disc brake conversion or finally got your decals perfectly aligned, we want to see it.

>

It's Saturday! Whether you just finished a disc brake conversion or finally got your decals perfectly aligned, we want to see it.

>

It's Saturday! Whether you just finished a disc brake conversion or finally got your decals perfectly aligned, we want to see it.

>

It's Saturday! Whether you just finished a disc brake conversion or finally got your decals perfectly aligned, we want to see it.

>

Mine strapped down on the dyno at Westech. First real numbers I've ever seen for one of these.

So if you go looking for how much horsepower a Honda Acty makes, you'll find numbers, they're just all over the place. I've seen anywhere from 30 to 40 hp thrown around, and almost none of it comes from an actual dyno, it's spec sheets and guesses getting repeated back and forth. So I put one on the dyno at Westech and got a real measured number. Figured I'd dump it here since I wish someone had done this when I got into these things.

Quick background on the engine, and part of why those online numbers are so all over the place. The E07A is a 656cc carbed three cylinder. From the factory Honda rated it 38 PS at the crank, which is about 37.5 hp, plus 40 lb-ft. That's the crank rating. What it makes at the wheels is lower, because you lose roughly 18% through the drivetrain. So one guy quoting 37 and another quoting 31 aren't really disagreeing, one's a crank number and one's measured at the wheels.

Here's what mine actually put down at the wheels, bone stock on the OEM Honda filter (17220-PZ3-505):

Metric	Measured Value (At the Wheels)
Horsepower	31.3 hp
Torque	34.9 lb-ft

So the clean answer to "how much power does a stock Acty make" is about 37.5 at the crank, 31 at the wheels. Not exciting, but at least it's a real measured number instead of a guess.

Rear wheels on the rollers, stock airbox and OEM filter for the baseline pull.

Now the mod part, since someone always asks. On a carbed E07A most bolt-ons honestly do almost nothing, the little single barrel carb is what's choking the whole thing, not your intake. I tested the one people ask me about the most, a performance air filter (it's the GhostFlow, I make it, not hiding that). Same truck, same airbox, same dyno, just swapped the filter, no tuning. These are both at the wheels too, so they line up with the number above:

Setup / Test Type	Dyno & Lab Results	Details & Delta
OEM filter	31.3 hp / 34.9 lb-ft	Baseline wheel numbers
GhostFlow	32.0 hp / 36.0 lb-ft	Aftermarket filter run
gain	+0.7 hp and +1.1 lb-ft	About 2-3%
lab side (ISO 5011 at SGS)	8 to 33% less restriction than OEM	Depending on flow, most of it down low

So yeah, a filter on an Acty is a real gain but a tiny one, and that's about the ceiling for ANY filter on this motor. You're not getting around that carb with an air filter. If you actually want power it's carb work or EFI, full stop. I still run a cotton one but only because it's washable and I'm not buying paper filters for the rest of my life, the dyno number isn't really the reason.

I also made a dumb dramatic video of all this where I try to make 0.7 hp look like a moon landing lol. It's in the comments if you want a laugh.

Anyway, if any of you have dynoed an E07A or E07Z, stock or built, drop your numbers. There's plenty of guesses floating around but almost no real dyno data on these, and I'd love to get it all in one place.

EDIT (5/30): Filter is now live. Link in the pinned comment below. Section 6.4 results still pending and will be posted here when they land.

Heard you loud and clear last time. Marketing voice out, independent lab data in. Tear it apart.

TL;DR for the impatient: Independent ISO 5011 flow test at SGS-IBR. GhostFlow shows 8-33% lower restriction than OEM Honda 17220-PZ3-505 in the 20-50 SCFM range (where the E07A actually operates). At 80+ SCFM the OEM wins by 3-6%, but the engine can't physically pull that much air, so that's academic. Full PDF, raw WinDyn screenshot, and flow demo video below. Roast me if the methodology is off.

So a couple days back I posted in here about an air filter project for the Acty platform and got absolutely cooked. Some of it was fair, some of it was personal, and one comment in particular... u/mister_monque's "is this satire? Gale Banks is weeping over his coffee cup" actually made me laugh out loud while it was busy ratio-ing me into orbit. Fair shot. Caught me leaning into marketing voice in a build community, which is exactly the kind of thing this room exists to call out.

The substantive critique was: where are the numbers, and why should anyone trust them?

So I did the only thing that actually answers that. Sent the GhostFlow filter AND the OEM Honda 17220-PZ3-505 to SGS-IBR in Grass Lake, Michigan. A2LA accredited. ISO/IEC 17025 compliant. The same lab a lot of OEMs and big aftermarket brands use for their flow data. Cost was $2,161 for the test. Worth it for the credibility, less worth it for my bank account for a small production run, but here we are.

Test results below. Including the data points where the GhostFlow loses, because if I posted only the favorable numbers half this subreddit would (correctly) would put be on blast.

• Test method: ISO 5011 (2020) Section 6.3 - Restriction and Differential Pressure, modified for custom flow points
• Test date: 22 May 2026
• Samples: Oiwa GhostFlow filter (sample no. 4516) vs OEM Honda 17220-PZ3-505 (sample no. B5S17)
• Test fluid: Air, ambient

Net Differential Pressure (kPa), lower = less restriction:

SCFM	GhostFlow	OEM Honda	Delta
10	0.01	0.01	Tied (measurement floor)
20	0.02	0.03	GhostFlow -33%
30	0.04	0.05	GhostFlow -20%
40	0.07	0.09	GhostFlow -22%
50	0.11	0.12	GhostFlow -8%
60	0.16	0.16	Tied
70	0.21	0.21	Tied
80	0.26	0.25	OEM -4%
90	0.32	0.31	OEM -3%
100	0.38	0.36	OEM -6%

What the data says, honestly:

In the 20-50 SCFM range, GhostFlow has lower restriction. At 60-70 SCFM, the two filters are functionally tied. At 80+ SCFM, OEM wins by a small margin.

Page 2 of the SGS-IBR report. Same data as the table above, plotted as pressure drop vs flow rate.

Important context: Does the 80+ SCFM data actually matter for the Acty?

NO because it's not possible.

This is where I expect push back, so let me show the math.

Honda's own JIS-net published figures on the carbureted HA3/HA4 E07A:

• 38 PS (37.5 hp) at 5,300 RPM
• 5.5 kg·m (40 lb-ft) at 4,500 RPM
• Compression ratio 9.2:1
• Single-barrel downdraft variable-venturi PGM-CARB

Step 1: Calculate BMEP at peak torque.

BMEP = (Torque × 4π) / Displacement = (54 N·m × 4π) / 0.000656 m³ ≈ 10.3 bar

That's the published torque on the published displacement. No assumption yet.

Step 2: Estimate peak VE from BMEP.

Honda never published a VE curve for this engine, so peak VE has to be inferred. A stock single-barrel carb engine producing ~10.3 bar BMEP typically lands in the 80-90% VE range at peak torque (empirical range for naturally aspirated gasoline engines of similar class, era, and tune). I used 85% as a working middle estimate. Real value is probably 80-90% with meaningful uncertainty.

Step 3: Sensitivity analysis — peak airflow demand at different VE assumptions.

Using SCFM = (Displacement × RPM × VE) / (2 × 28,316):

At peak power (5,300 RPM):

75% VE: 46 SCFM
80% VE: 49 SCFM
85% VE: 52 SCFM  (my working estimate)
90% VE: 55 SCFM

95% VE: 59 SCFM

At redline / fuel-cut (~7,500 RPM, where VE drops because the carb chokes the engine):

70% VE: 60 SCFM
75% VE: 65 SCFM
80% VE: 69 SCFM  (probably overstated for a carb at this RPM)

The conclusion is robust to any plausible VE assumption.

Even at the aggressive end of the range (90% peak power VE, 80% at fuel-cut), the stock E07A tops out around 65-69 SCFM. The 80-100 SCFM band in the SGS data is outside what the engine can physically pull, whether you assume 80% VE or 90%.

VE actually drops above peak torque on a carbureted engine because the single venturi becomes the metering restriction, the carb chokes the engine before the cam does. That's why the upper end of the sensitivity analysis at fuel-cut RPM is probably overstated; real VE at 7,500 RPM on a stock carb is unlikely to exceed 70-75%.

The 80-100 SCFM lab data exists because SGS runs ISO 5011 to a standard flow range regardless of target engine. For someone running a turbo'd or stroked E07A (where peak VE can exceed 100% with forced induction) those points matter (not that I know of anyone actually doing that). For a stock Acty carb, they don't (the MTREC Beat variant of this shortblock makes 64 HP at 8,100 RPM, so the breathing potential is there if you remove the carb restriction, different project entirely).

If anyone has actually measured peak VE on a stock E07A (speed-density, wideband, or any direct method), drop the number and I'll redo the math publicly with whatever you measured.

Engaging with the Honda-being-Honda argument:

u/mister_monque made the strongest critique in the last thread: if a less restrictive filter media gave meaningful power on this engine, Honda would have shipped it that way from the factory. That's a real argument and worth answering.

My read: Honda optimized the OEM filter for filtration durability, cost, service life, and a specific NVH target, not for maximum airflow. A small E07A pulling ~47 SCFM peak doesn't have much headroom to begin with, so a more open media element trades a bit of dust capacity for a bit of restriction reduction. That's a different optimization curve than Honda chose. Doesn't make ours better. Just makes the trade-off different.

Corroborating dyno data + the raw screenshot:

Same product tested at Westech Performance Group earlier in May on a carbureted E07A: +0.7 HP, +1.1 lb-ft at the wheels (+2.2% / +3.2%). Modest single-digit gains.

Stock: 31.3 HP / 34.9 lb-ft. Ghost Flow: 32.0 HP / 36.0 lb-ft. (Black curve = GhostFlow), (Red = Stock).

That's the unedited WinDyn chart from the Westech session and the email chain with Evan, the operator. I asked him about the RPM mismatch (Ghost pull ended around 5,450, Stock went to 5,800) because I knew it would come up here. His answer: no tach in the truck, he was watching the power meter and let off when it started going backwards. Posting unedited so you see the methodology, not just the numbers.

Stock pulled 31.3 HP / 34.9 lb-ft. Ghost pulled 32.0 HP / 36.0 lb-ft. Black curve = Ghost, red = Stock.

Sanity check on the dyno setup: the 31.3 wheel HP on the OEM maps cleanly to Honda's 38 PS crank rating once you account for ~18% drivetrain loss (31.3 / 0.82 ≈ 38.2 crank HP). Internally consistent, which is what you want.

What surprised me in the data:

Side-by-side: GhostFlow (left) and OEM Honda 17220-PZ3-505 (right). Both fit the same airbox.

I expected GhostFlow to win across the whole curve. I assumed a less restrictive cotton media would beat a paper element at every flow point. Instead, the OEM Honda filter actually wins above 70 SCFM.

The mechanism is visible if you compare the two filters side by side (photos above). The OEM packs notably denser pleats into the same airbox geometry, more total media surface area, just distributed across thinner per-pleat channels. At low-to-mid flow that doesn't matter because neither filter is being asked to do much. At high flow, surface area starts to dominate over per-area porosity. Honda's engineers earn their paychecks.

Worth noting on the high-flow data: on a carbureted engine, the carb's single venturi becomes the dominant intake restriction as RPM climbs. Filter and carb restrictions add together, so a less restrictive filter still helps total airflow at any RPM, but the carb's contribution grows much faster than the filter's, so filter improvements matter less proportionally at high RPM. The high-flow SGS data points are real, but they're describing a regime where the filter is no longer the primary bottleneck anyway.

Flow demonstration video that my 3 yo daughter performed (visual, not lab):

My daughter doing the visual flow demo. Lab data above is the rigorous comparison.

This is a flow demonstration tool, not the lab test. Visual comparison only. Posting it because some folks asked to see the difference rather than read about it. The lab data above is the rigorous comparison.

Full SGS PDF report:

READ

What's next:

ISO 5011 Section 6.4 (Initial Filtration Efficiency) is currently underway at SGS. That answers the "but does it actually filter as well as paper?" question, which is the next critique I expect (and deserve, since restriction data without efficiency data is half the story).

Heads up on what to expect: cotton-gauze media historically tests 1-3 points below paper on initial efficiency. That's the engineering trade-off baked into the media choice. If results land in that range, I'll post them here with that context. If they surprise me either way, even better. Section 6.5 (Dust Capacity / Loading) is queued after that for the full performance trifecta.

What I'm asking the room:

Honda never published a VE curve for the carbureted E07A. I had to infer the ~85% peak from BMEP at the published 9.2:1 compression ratio. If anyone here has actually measured peak VE on a stock carbureted E07A (speed-density with a wideband AFR sensor or any direct measurement), drop the number. Could refine the operating-envelope math meaningfully.

Also, if you see a flaw in the test methodology, want to call out something the data implies that I missed, or have a sharper interpretation than mine, drop it. The reason I went to SGS instead of an in-house bench was specifically so this data could survive scrutiny. Tear into it.

(And u/mister_monque ... Gale Banks is welcome to weep into his coffee, but if he wants to take a swing at the Acty platform I'll send him a filter. Open invitation.)