Stock AFR vs. engine RPM for d-series motors - D-series.org

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Old 11-04-2015, 03:52 PM   #1 (permalink)
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Default Stock AFR vs. engine RPM for d-series motors

I have been searching for a while but haven't found anything yet. While I continue looking, has anyone seen or have a graph of what the actual/measured air-fuel ratios are on a stock engine/stock ECU for the 96-00 d-series setups? I have a 99 EX with the d16y8 setup for reference.

I am trying to see at what RPM the stock ECU starts adding fuel, and by how much. I can provide some additional insight on my motives if you are interested
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Old 11-04-2015, 04:29 PM   #2 (permalink)
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Too rich. lol

Its actually hard to be 100% sure. Running on speed density, the AFRs of an old engine are not going to be the same as when the engine was running at its peak. To see how they were tuned by Honda you would need an engine that was in tip top shape.
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Old 11-04-2015, 05:11 PM   #3 (permalink)
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Quote:
Originally Posted by Full_Tilt View Post
Too rich. lol

Its actually hard to be 100% sure. Running on speed density, the AFRs of an old engine are not going to be the same as when the engine was running at its peak. To see how they were tuned by Honda you would need an engine that was in tip top shape.
I was actually hoping for too rich haha.. But I hear ya. I am probably just going to install a wideband soon and watch how the AFRs change through out a full WOT pull to get a baseline for how my car is operating before any tuning. I am running some calcs for a nitrous setup, as well as some boosted E85 setups.
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Old 11-04-2015, 05:34 PM   #4 (permalink)
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Quote:
Originally Posted by Full_Tilt View Post
Too rich.
Yes.

A decently designed engine is usually making peak power around 13-13.5:1. A big part of the reason why intake and exhausts on stock honda engines make more power is because they flow enough more air to lean out the mixture closer to that.

One of my CRXs has a b18a1 (130hp stock) with shortram and 2 3/8" wide open exhaust running on a dead stock P06 ecu meant to run a d15b7 (102hp stock) with a much more restrictive intake and exhaust. The car runs perfectly, you would think the ecu was designed for the b18a1 engine. I believe (dont quote me) that it was aquafina who said that a stock b18a1 with a P06 ecu actually makes more power than a b18a1 with the ECU it came with.

So at a wild off the wall estimate lets pretend a b1a1 running on a P06 ecu is around 13.5 AFR average, and it is flowing around 25% more air than a d15b7 (130/102), that means that a d15b7 is averaging somewhere around 11:1 AFR.

Since the ecu has a little trim wiggle room on both sides I would guess honda was PROBABLY aiming for around 12:1 AFR most of the time.

This is all wild speculation of course.
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Old 11-04-2015, 07:52 PM   #5 (permalink)
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Thx for the insight.. and I am fully on board. I'd see this quite often when tuning in the past and experiencing (as well as hearing about) stock motor/ECU combinations that would yield very rich AFRs at WOT from the factory. It could be as easy as taking out a bit of fuel at the top end to pick up some power, and possibly even a little better fuel economy.

One of the reasons I started this thread was because I read multiple discussions talking about how it is mandatory to add fuel when adding nitrous to any platform. I was thinking if any of these small honda engines was running between 11:1 - 12:1 at WOT (let's assume closer to 11:1) that one could potentially run say a 20hp shot or so without tuning, and that could bring the AFRs up between 12:1 and 13:1 which "should" be somewhat safe for a small nitrous setup without changing the ECU around to add more fuel..

Is that logic correct? Not saying that it is safe, but I would think it could work and be somewhat reliable.
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1978 Camaro Z28 (drag car with multiple motor builds)
1997 C5 Vette (Built for AutoX)
2002 C5 Z06 (Built for Road Racing)
1999 Grand Prix GTP (Built and self tuned on E85)
1998 & 1999 Grand Prix GTPs
2012 Civic SI
2000 Civic EX

My E85 Thread:
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