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Cold start tuning under load

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I’m still working with my tune I inherited from my tuner as I’m still not comfortable doing a full tune on my own yet, but I’m enjoying (sometimes) learning with the touch up work.

My cold start idle is fine, cold cruise is fine too. Cold high load goes very rich to the point where it bogs at times until the engine reaches operating temp.

Hondata s300 doesn’t give me a whole lot of configurability on cold start. I get to set comps for low load and high load. So the low load comps are fine, I think it’s the high load that needs some attention.

My target AFR under high load is 12.5:1. Currently the AFRs I see under high load when cold are 11.2:1 at the leanest and 10:1 at the richest. When warm they are spot on 12.5:1.

I know when the engine is cold richer is required because the fuel sticks to the wall etc... I know at cold idle you can target down as low as 12.5:1 until warm, but is 10:1 typical for cold high load if the normal high load AFR is 12.5:1? The bogging is telling me I can go leaner, maybe try to stay north of 11:1 until warm?

I could guess some AFRs and play with it but thought it was worth asking some of you guys how much richer you go when cold under high load.

Also wanted to ask if there is a potential for knock when cold even with a rich AFR like 12.5 just because it’s still cold?

Hello a little hard to be on the money with how to repy to this with out more info on the build but an example it if i had a car that say ran 14.7 at idle and cruise and 13.0 full load on warm up i would be wanting to see about .5 afr richer at the most on warmup

and no i would not think you will see knock on this

Regards Ross

Thanks Ross. More info: NA b18c with stage 1 cams and all the bolt ons.

Are you saying .5 richer as in your 13 under load translates to 12.5 during warmup, or .5 lambda which is very rich?

When you refer to "cold" my question is how cold? It is one thing to start up the engine from - 25 C ambient temperature and a bit different when starting up from +15 C - the difference in initial AFR would be quite substantial... What sort of ambient temperature are you talking about?

Hi Shota, here in San Diego the coldest I'd ever have to consider is 32F (or 0C) however that is quite rare. A normal cold morning in winter is average 50F. I think the most relevant temps for the sake of this discussion are more like 80F - 150F (26C - 65C) because even it's 32F outside odds are by the time I get off my driveway and get moving it would already be warmed up to at least 80F and the low load/idle comps seem to work fine for me. Operating temp where all comps are to 0 is around 177F (80C).

My idle comps may be richer than necessary too but I don't notice it because there is no blatant ill effect like the high load comps.

Well, to me 12.5 is very safe afr under the high load - i have seen OEM NA calibrations as rich as 12.4-12.2 at high revs and high load whilst we have been running our drag H22A Honda at 13.8-13.5 afr on race gas at same conditions. So if you see it 12.5 fully warmed up and richer when cold i would say it is just fine - that afr was chosen to protect the engine from overheating in case of long load such as going uphill or droving at High speed on high gears...

So the problem I'm trying to solve is about how much richer when cold? If you are running 12.5 when all warmed up, what sort of AFR do you want to see in the same areas when the engine is cold?

This is what HKS suggests for typical settings for water temp and air temp compensations

Attached Files

Interesting, are those examples the same for idle, cruise & high load?

Attached is a screenshot from my calibration. There is a red and purple arrow pointing to the tables I'm focused on right now. On the red arrow the 168F and 177F columns are not default from Hondata but are values my Tuner had put in back when he tuned it. The 177F makes no sense to me at all why you'd still add fuel there as this would affect the whole fuel map at operating temps, even at 200F it will still interpolate and get a little comp. I've actually already zero'd that column so the screenshot is a little bit dated but the rest I haven't changed yet.

Comparing this to what you have from HKS it seems HKS is compensating less across the whole board than all the columns that are still Hondata defaults. Thanks for that gives me some guidance in what may be an acceptable change in comps.

Attached Files

In the initial setup idle air temperature compensation table is the same but can be modified to reflect specific changes and mods. But as i said initially it is the same as for non idle mode. The water temp compensation is the same table for idle and the rest.

Thanks this helped me, I played with it and I've got a better result now.