Survey of drive-by-wire rev hang (potential) solutions

[francisluu]

I'm super-happy with my recent acquisition of a 1997 NSX 6-speed (IN BRIGHT RED YYEEEE), but the rev-hang *does* bother me a bit. I'm learning how to adjust to it but again, slight annoyance. Just to recap for those of you who aren't familiar — my understanding is that lifting off throttle while driving (to change gear, for example) the ECU will hold the throttle open briefly. This is done primarily for emissions compliance at the cost of a bunch of subjective driving characteristics — response, the ability to change gear quickly and/or smoothly, etc.

I've been trying my best to research this subject and have compiled a list of solutions, some more in the potential camp, some in the confirmed (but expensive lol) camp, some more speculative. I'd love feedback on this:

Confirmed:
– ScienceOfSpeed AEM Infinity + aftermarket throttle body kit (expensive, seems like overkill if you're not going after custom ECU tunes, but has full control over throttle position, not emissions-friendly).
– DBW delete #bringbackthrottlecables (also expensive, parts not readily available, ECU reprogram probably necessary?)

Potential:
– Lightweight flywheel (doesn't eliminate the holding-open-throttle behaviour, but revs do drop quicker between shifts)

Speculative:
– JDM ECU (do they have emissions standards that warrant the holding-open-throttle behaviour?)
– NSX-R ECU (super yolo)
– Mine's ECU (can you even get these anymore? lol, same question as with JDM ECUs)

 

[Old Guy]

I don't know about rev hang; but, most EFI systems have some degree of fuel cut on closed throttle. These systems may completely shut off fuel on closed throttle (not likely) and usually re establish fuel flow perhaps a couple hundred RPM above idle speed. I have another car which has an aftermarket EFI that is user configurable and have experimented with aggressive fuel cut settings (100 % fuel shut off on closed throttle and low RPM value to re establish fuel flow). It was like having a car with a super light flywheel in terms of off throttle RPM change. Might be cool on a closed circuit road course. Made the car absolute agony to drive in stop and go traffic. Even driving in a straight line on a bumpy road was painful. That experiment lasted about 24 hr.

I drive my NSX on public roads exclusively and can't say that I have ever perceived any noticeable throttle hang-up. However, if you do a search on Prime you will find a fair number of people commenting on / asking about the noticeable driveline snatch / noise / banging / lurch in the NSX, which seems to be worse on the Na2. Get aggressive with the fuel cut (or rev hang) and you are going to make the driveline snatch worse. Aggressive ECU settings are like a light flywheel, they might be nifty on the track, not so nifty if you have to drive in traffic.

 

[francisluu]

Interesting. I may be biased having a Porsche 993 that doesn't exhibit any of these characteristics I'm finding in the NSX. That car *is* more difficult to drive every day, but that's where the subjectivity kicks in, heh.

 

[stevenj]

.....Potential:
– Lightweight flywheel (doesn't eliminate the holding-open-throttle behaviour, but revs do drop quicker between shifts)

Your Google search seemed to have missed the QREVS rev hang removing module for Honda engines (K20, K24) which apparently works well. I am sure it could be adapted to suit NSX engine.

 

[francisluu]

Your Google search seemed to have missed the QREVS rev hang removing module for Honda engines (K20, K24) which apparently works well. I am sure it could be adapted to suit NSX engine.

Nice find! I'll look into this more.

 

[MexiRicer]

I know what you mean, though after 6 years of ownership I sort of got used to it. If you havn't seen it already, RF Yamamoto makes a kit for DBW delete.

http://www.rf-yamamoto.com/NSXengine/30.html

 

[francisluu]

I know what you mean, though after 6 years of ownership I sort of got used to it. If you havn't seen it already, RF Yamamoto makes a kit for DBW delete.

http://www.rf-yamamoto.com/NSXengine/30.html

Great find! Anyone know more about this?