3000rpm kick, Why?

[p00t]

For me and Im pretty sure for others as well, the KA24DE gives alittle kick in power once you hit 3k rpm. This happens pretty quick, and isnt gradual.

Ive been wondering why this happens, and I know its been discussed before to no avail. You can rule out cams, and most other rotating/actuating parts in the engine because even if they were optimized for 3k+ rpm, the power would ramp up more gradually.

I think its related to the ECU injector control. I was skimming through the Holy Bible by Corky Bell for some forgotten information and I came across a section talking about Sequential and NonSequential EFI control. It stated there that most EFI systems switch over to nonsequential injection around 3000rpm. This just so happens to correspond with the increase in power.

Hmmmm. Could Nissan have made the non-sequential injector timing maps more aggressive, and made the sequential maps more timid and fuel economy oriented?

If it is indeed related to the sequential -> nonsequential switchover and ECU timing maps, why did nissan do this? I doubt is would be very hard to make the 2500-3000rpm range slightly more agressive to smooth the transition, while still maintaining decent fuel economy.

Also do aftermarket ECUs (like JWT) solve this, or do they still run the fuel exactly the same way with only little injector size and MAF adjustments per request from the consumer?

[pstickne]

Quoting from the 1991 240SX FSM:

EF & EC-19:"When the engine is being started and/or if the fail-safe system (C.P.U., crank angle sensor) is operating, simultaneous fuel injection is used. When the engine is running sequential fuel injection is used."

I haven't seen a KA24DE powerchart, but it might just be getting into the "meat" of the powerband. There are many other factors such as intake runner length, fuel management and all those little "valves" around such as the S.C.V.

[Touchdown038]

I'm pretty sure the powerband for a DOHC starts at 3500... at least I know it does on the SOHC.

[Q45tech]

The torque peak rpm is the point of maximum volumetric efficiency by definition. Below and above this rpm the cylinder receives less air [volume] ...............below because the air is traveling slower [its velocity is too slow] and above the rpm the valve curtain restriction starts to impede the flow [friction].

http://autozine.kyul.net/techn...ngine

[s13sr20chris]

i am tempted to say its ign timing. i have seen this happen on many different makes and models(not any nissans strangly enough) and in some cases i could isolate the ign timing. if you can get it on consult, then you could watch the commanded ign. timing and see if the ign map is ordering more advance at one particular spot.

[Q45tech]

Actually the ignition advance is a function of cylinder air density [VE%].......the advance might be 22 degrees at the torque peak rpm and increase 1 degree per 500 rpm above that.[22>29].......as the valve curtain area creates more restrictions.

At low VE cruise [2,000 rpm 20% filling rate] the advance might be 40 degrees. Because of sensor lag when you suddenly accelerate the advance is dropped to 8-10 degrees then quickly ramped up to 15>20 to avoid tip in knock.Engines with individual BMEP pressure [and EGT and knock] sensors for each cylinder and lots more ecu computer power can be made to accelerate faster.

The whole system is designed to avoid knock starting with our marginal [motor method] octane fuels. There are a few tenths left on the table.A knock on acceleration and retard can ruin your day so its tuned out at least when engines are new and deposit free.

[s13sr20chris]

i can't offer an explanation for the results i have observed, only possible causes. one is in the ckp sensor or sensor wheel. another would be faulty vacuum advance unit or mechanical advance unit. i am very tempted to blame this last one for a particular mazda i worked on one time. on nissans(dist. ign. type) i have seen the rotor plates get a drop of oil on them before and weird stuff happens. i dont specificly remember any 3k hiccup though. those nissan distributors are real good for internal oil seals leaking. i read a honda tech bulletin once that said some accords will clog up the egr passages and bog untill 1900 rpm and then take off like a stuck pig. come to think of it i have experienced a sudden, repeatable, predictable kick in a nissan before. sometimes if the t-chain jumps just so, it will cause a crappy idle but normal performance at high engine speeds. does any of that stuff sound possible to you guys?