boostedcabbage's 1995 Dodge Neon

[BenFenner]

Regarding rev limiter hysteresis. I love my 25 RPM hysteresis. It's smooth as butter and a good compromise between the jarring OEM style and the spooky, almost imperceptible behavior of what I imagine a 0.5 RPM hysteresis might be like.

[Fred]

Cool! Good to see another data point. 50 is pretty smooth if you bump it in gear. I had a 0 hyst limit on the hotel with a bug when I first ran it ages ago. That was a solid wall, no perceptible on/off behaviour, just sort of averaging the right number of sparks to keep the RPM constant :-)

[BenFenner]

FYI, I go back and forth on whether or not I think a smaller hysteresis is worse, better, or has no effect on the probability of valve float.

With a smaller hysteresis:
- On one hand you are hitting the rev limiter MANY more times than you used to be. Quadruply so because it feels so smooth. And hitting any "hard" rev limiter causes backlash in the valvetrain which can cause valve float where you otherwise might not have experienced it. This backlash happening at very high RPM is the worst time to experience it. Just because it feels "smooth" doesn't mean the engine isn't more prone to failure.
- On the other hand the backlash could be to a lesser degree and for less time with a smaller hysteresis? It feels good, maybe it is good? With extremely small RPM values (less than 10 or so) it may cross a threshold that actually eliminates backlash altogether?

If you are running an interference engine, you should at least be aware of the potential consequences of modifying this parameter.

[Fred]

If there is any "backlash" (not sure what you mean by this) then it's the same as suddenly lifting off completely from WOT. At cranking RPM you can see the speed variation between firing events. But at higher RPM it's all but completely gone, averaged out by inertia. Hitting a smooth wall and randomly dropping sparks to maintain an exact RPM has to be almost perfectly smooth, with the exception of jitter in the RPM signal causing it to not be a perfect wall.

As for valve float, if your limiter is set anywhere near that, you're doing it wrong :-D Last time I got some valve float it was at ~5000 RPM with a stock single-port 60s VW flat four :-D

Thinking again there will be subtle variations to cross the zero threshold. The granularity being limited by cylinder force and inertia of the flywheel. Maybe dropping a single spark event has a large effect, and bringing it back, likewise. IE, enough to push past the limit level by some quantity, or fall below it by some quantity (likely not this, but the other could be significant).

Fred.

[boostedcabbage]

Received some things in the mail today.

[boostedcabbage]

It runs!

viewtopic.php?f=55&t=2602

[boostedcabbage]

Update:

Pulling engine



#3 Rod is bent from a fuel hydrolock.. I had an injector stay open from a failed FET



Pistons and rods removed



Wiseco pistons and Eagle rods installed. ~9.1:1 CR



Painted the transmission for fun



Built a welding table as I don't have one. Not the most spectacular thing, but it works



Engine as it stands currently



More updates coming soon

[exric]

nice job on that dodge
I have a 1998 Grand Cherokee so it is good to see someone work on a dodge.

[boostedcabbage]

(Still have to widen the ports)




More updates soon.

[boostedcabbage]