Originally Posted by
yourfather
moving VTEC crossover on a stock motor up or down 1000rpm can / may improve your power curves, this is dependant on the modifications you have. It can only be proved while you are on a dyno.
You don't need a vtec controller, or VTEC crossover modifier - it should be part of a fully customizable ecu package, and unless you are using aftermarket camshafts or you've increased the compression, if you've had your head flowed, or some other form of internal work that means that you'll have to get your crossover reoptimized.
since you will be going turbo, you will have a standalone ECU hopefully, like a power FC or hondata, that is when you will need to look at this. - you wont need another device.
Because every car is different, and not just the condition of the motor, but the fuel you use, the weather and moisture in the air is important factor different cars need different points.
Just baseline dropping your VTEC crossover point to like, 5000rpm, or 4,500 rpm, won't really be of any benefit unless you tune it to perfection.
on a dohc vtec motor, you should know, there's a primary and secondary cam lobes for the non vtec, and then a vtec lobe that is engaged by a pin that is placed into a hole on the cam. At the highest range of RPM, the small lobes on the cam cannot let enough air into the motor, or keep them open enough to continue the motor to make more power! It also depends on what kind of turbo you are running, whether you need the lobes open earlier to let more air in. So when the VTEC lobe takes over the close / open cycles from the primary + secondary lobes, it's a more aggressive, longer duration, and taller lobe! so more air, valves open for longer.
So if you were to just dump your vtec crossover to say, 2000 rpm, it makes the lobe that's designed to let heaps of air in, run at a point where a) it is not needed, b) the motor will bog down like a fat pig, and then when it reaches a point where the extra air the motor requires can actually be of assistance to it, it'll jump forward, hence the absolutely ghey "VTEC YO" bullshit.
When you do get your ECU installed, try it one day, set your vtec to like 3000, thats as far is it goes down I think, and see how much of a slut she is to drive. Then set VTEC crossover to like, 7000 rpm, and see how its normal to start, then chokes when it needs more air, and then when it finally does kick in, it'll be like a rush of power. And dont let the butt dyno tell you otherwise, the thing about these honda motors is that they're designed for consistent, linear power delivery. But if you modify your crossover for no reason, your curves aren't optimized to make use of the dual range that the vtec lobe provides.
To sort out the best way to get VTEC crossover, do a dyno run with your turbo setup, with vtec engaged as low as possible, then do one with it engaged as high as possible. compare the graphs on top of each other, and where the two torque / power curves meet up, this is your optimum RPM vtec engagement point.
