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Old 09-09-2019, 04:16 PM   #391 (permalink)
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Quote:
Originally Posted by mpg_numbers_guy View Post
Curious, have you ever tried P&G once to see what kind of mileage you get? 80% load 6th gear, then EOC, etc.
That's how I got my lone 65mpg tank - 5 hours of P&G.

Kill switch will be added soonish, just trying to finish house projects first.

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Old 09-10-2019, 02:53 AM   #392 (permalink)
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Re tuning:

Typically you'll find OEM spark timing to be close to optimal. They'll leave a little bit of margin for bad gas and hot weather and whatever. You can often take this margin out but the gains are pretty small, IMO. What I would personally do is either keep it stock, or use an off the shelf map + PCV catch can to give it more knock resistance.

(if the engine is radically modified then you want to redo the whole thing)

AFR at WOT is again set conservatively so the valves and cat don't cook on a hot day with bad gas. You can remove some safety margin without issues, or remove a lot of safety margin and accept reduced cat lifespan.

I believe all potential low-rpm fuel economy gain comes from EGR and VVT adjustments on 2000-2015 era engines. The oil-pressure actuated VVT is slow-responding, so the OEM doesn't use the full adjustment range to improve response. Hot EGR I believe is limited to reduce intake heat soak (generally speaking every paper I've read suggests 10-15% EGR dilution is a non-issue, but some cars only use a max of 4%, so leaving a lot of pumping losses on the table).

I was able to increase my Scion FR-S's mpg 1% by maxing out intake cam retard for as late valve closure as possible, then retarding the exhaust cam just a tiny bit to get some EGR back (IIRC any more than 5 degrees caused misfiring). Retarding the exhaust cam increases pumping losses though so again there's only so much that can be done without external EGR.

On your Honda K24, you only have intake side VTC available, so things are a little harder, since you increase volumetric efficiency when you try to get more EGR. Since the low cam has low duration to begin with, closing it later probably has only a small effect on VE reduction, so advancing it a tiny bit more is probably the best you can do.

Lean burn or adding external EGR would be your best bets IMO. You'd want to bump the ignition timing advance up a little when doing so. My gut feeling would be increase it by (lambda - 1)*(15 deg - current timing)/2 (pretending that combustion speed is linear in AFR, compensating by 1/2 since friction increases and knock and whatever, comes out to 3-4 degrees max at low load assuming 1.15 lambda).

Last edited by serialk11r; 09-10-2019 at 03:09 AM..
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Old 09-10-2019, 06:22 AM   #393 (permalink)
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Fantastic post, thank you. My only issue is that I don't have access to a stock Honda timing map. I'm basing it from a Hondata map which I've advanced maybe 2 degrees across the board at part throttle.

Yesterday I sat in a parking lot holding the pedal at a fixed position with some loads running (A/C, headlights, defroster) and tried varying timing live to see if revs rose or dropped, but I wasn't able to get any solid data before under hood temps got really out of control.
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Old 09-10-2019, 11:36 AM   #394 (permalink)
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Here are some of the supposedly stock timing I have to work with:

04-05 TSX (in KPro)
07 TSX (in Flashpro) - same engine, same low cam lobes
09 TSX - cams are very similar to 07, has a one-port header
12 Civic Si - physically identical to the 09 TSX










A few points of comparison between these nearly identical engines:

2000rpm / 300mbar
05 TSX: 45 degrees
07 TSX: 40 degrees
09 TSX: 48.6 degrees
12 CSi: 51 degrees

3000rpm / 200mbar
05 TSX: 50 degrees
07 TSX: 40 degrees
09 TSX: 60 degrees
12 CSi: 53 degrees


3500rpm / 1bar
05 TSX: 32 degrees
07 TSX: 30 degrees
09 TSX: 27 degrees
12 CSi: 27 degrees

1000rpm / 1bar
05 TSX: 8 degrees
07 TSX: 15 degrees
09 TSX: 11 degrees
12 CSi: 11 degrees

Again, supposedly "stock equivalent" maps. Physically these engines are all nearly identical, same geometry, with the 09+ engines moving from a 4 port header to an integrated header with one port, and having (I believe) very slightly less aggressive cams. At WOT the timing is similar, but lightly loaded these maps are massively different, 20 degrees difference in ignition timing in some cases.

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