Rev limit question

s300 and SManager software questions & answers
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Furble
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Joined: Fri Jun 12, 2020 12:55 pm

Rev limit question

Post by Furble »

It says pretty firmly in the help file regarding tuning vtec: “Do not set the VTEC point too high as the high speed cam rocker arm may float on the lost motion assembly, damaging the valve spring retainers. It is not recommended to set the VTEC point over 6500 rpm.”

Ok, so this has me thinking, it is quite possible to rev well past 6500 on the low cam at times when vtec is not available yet, notably when the engine is still cold. My vtec won’t come on until the engine is at least 150F. I could easily go past 6,500 getting on the freeway around the corner when the car is not quite 150F yet. Maybe I should lower that constraint.

Unless I’ve misunderstood something it seems it would be nice to have a separate rev limit per cam profile or by ECT.

Is there an existing feature that can accomplish this?
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Spunkster
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Re: Rev limit question

Post by Spunkster »

You should not drive the car hard until it is fully warmed up, this is recommended for any vehicle.
Furble
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Joined: Fri Jun 12, 2020 12:55 pm

Re: Rev limit question

Post by Furble »

I don’t disagree with that statement but I find it hard to believe there is nothing in the ecu available to prevent this. You’d think Honda would have baked something in there given this risk exists to them for any Honda owner even on a bone stock brand new car. So to confirm there is no way to accomplish this aside from managing the user’s behavior?
spAdam
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Joined: Sat May 03, 2014 5:34 pm

Re: Rev limit question

Post by spAdam »

Use the Advanced Protections to limit rpm when temps are low. I have one for water and one for oil plus one for low oil pressure. Works great.
Furble
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Re: Rev limit question

Post by Furble »

Smart, thanks!
Furble
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Joined: Fri Jun 12, 2020 12:55 pm

Re: Rev limit question

Post by Furble »

Spoke a little too soon though still a smart idea. Some caveats to it... Advanced protection limits RPM to 2k so basically limp mode if triggered. Would prevent the problem but could be annoying if I hit the protection getting on the highway going over 6500 rpm when my ECT is not quite 150 yet haha. I could repurpose the overheating protection that's a traditional style rev limiter and it's based on ECT but then I'm giving up overheating protection which is probably a more important problem to protect against.

If only there was a secondary overheating protection or if the overheating protection could be a 2 dimensional table.
spAdam
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Re: Rev limit question

Post by spAdam »

You can also lift to clear the limiter.
Furble
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Re: Rev limit question

Post by Furble »

You lost me, lift what to clear the limiter?
spAdam
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Joined: Sat May 03, 2014 5:34 pm

Re: Rev limit question

Post by spAdam »

The throttle - the protection clears if you go below 2krpm or to zero throttle. The idea would be that the ecu gives you a slap on the wrist for going above the threshold and you say "oh, I'm still cold" and don't do that again until warmed up, not to ride the limiter until it's warmed up, right?. But it would be nice to have a selectable limiter target for the protections, I agree.

I mean really, there's a few things going on here.

1) It's a production car engine. It will survive occasionally doing this. Doesn't mean it's good to the hardware.
2) Lower the threshold if you don't 'like' it. Then you have to decide, what's worse for the engine? Running it hard when cold, or engaging vtec when cold? Then, 145? 140? 120? What data are you basing that decision on? For race engines at least, those limits are usually determined by durability engineers for based on design parameters and what they've observed in testing. Anything else is just a made up number.
3) Just don't flog the engine until it's fully warmed up. You can get up a highway on ramp without revving to 6.5k. Problem solved.
Furble
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Joined: Fri Jun 12, 2020 12:55 pm

Re: Rev limit question

Post by Furble »

Did not realize that lifting off the throttle had the effect of resetting the advanced protection. For some reason I though the 2k rpm limit on the injectors remained until the car is shut off. If that’s the case then it would work effectively as a slap on the wrist and solve the problem albiet less elegantly than ideal.
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