My friends and i just installed a JDM 2nd Gen. B16a engine in my car. I am still using my ls tranny until i find an si or gsr transmission. Oh, im also running on an obd1 gsr ecu. My question is why the vtec engages after 5,000 rpm a lot of the times. I installed a vtec light and noticed that it seldom engages at 4.5. I thought the light was slow, but it turned on just about right on 3 other cars that had it. I've been thinking that it could be the transmission and the longer gear ratios.
VTEC Engagement or switch or switchover?
1 - 5 of 5 Posts
Joined
·
31,217 Posts
VTEC engagement depends upon:
rpm
engine temp (temp sensor)
throttle position (throttle position sensor)
oil pressure
vehicle speed (speed sensor).
there are several trigger points or thresholds that have to be met for each of these (not just rpm) before the VTEC solenoid will activate and lock the pin across the 3 rockers. It usually varies by 200 rpm around the main VTEC switchover (4200-4600 rpm for a main GSR switchover of 4400 rpm depending on engine loading conditions) not by 500 rpm. Is your distributor going (rotor or bearing)? The tach is usually off by as much as 600 rpm from the true rpm at the distributor on old cars. When we dyno some older cars we see this difference from the dyno pickup for rpm compared to the tach.
in the dyno tuning basics article, we show you one way to find the best VTEC engagement point for your particular engine and the unique way that it breaths (IM, head, cams, header with no backpressure to work against or not).
another way is to run on the VTEC lobe all the time (ver very early VTEC engagement set by reprogramming or a piggyback VTEC controller) and race N/A engines or high performance street engines with porting and big CR sometimes use this approach but it requires a complete ECU reprogram of the fuel tuning for the car to be driveable on the street and idle properly. You can't do this on a stock ECU with a piggyback VTEC/fuelcontroller because it just doesn't have enough tuning points to adjust the part throttle and full throttle fuel tables and their programs. Plus you need to redo the ignition tables.
rpm
engine temp (temp sensor)
throttle position (throttle position sensor)
oil pressure
vehicle speed (speed sensor).
there are several trigger points or thresholds that have to be met for each of these (not just rpm) before the VTEC solenoid will activate and lock the pin across the 3 rockers. It usually varies by 200 rpm around the main VTEC switchover (4200-4600 rpm for a main GSR switchover of 4400 rpm depending on engine loading conditions) not by 500 rpm. Is your distributor going (rotor or bearing)? The tach is usually off by as much as 600 rpm from the true rpm at the distributor on old cars. When we dyno some older cars we see this difference from the dyno pickup for rpm compared to the tach.
in the dyno tuning basics article, we show you one way to find the best VTEC engagement point for your particular engine and the unique way that it breaths (IM, head, cams, header with no backpressure to work against or not).
another way is to run on the VTEC lobe all the time (ver very early VTEC engagement set by reprogramming or a piggyback VTEC controller) and race N/A engines or high performance street engines with porting and big CR sometimes use this approach but it requires a complete ECU reprogram of the fuel tuning for the car to be driveable on the street and idle properly. You can't do this on a stock ECU with a piggyback VTEC/fuelcontroller because it just doesn't have enough tuning points to adjust the part throttle and full throttle fuel tables and their programs. Plus you need to redo the ignition tables.
Joined
·
25,239 Posts
As far as engine temp with engaging VTEC goes, how does vtec depend upon that? only if your engine is up to operating temp? Don't get me wrong, I don't go above 3.5K RPMs until the engine is up to where it should be.
Joined
·
25,239 Posts
Ahhhh I forgot about that part of the oil locking up the pins, thank you.
![]()
1 - 5 of 5 Posts
Join the discussion
Join now to ask and comment!