Gonna be hitting up the dyno soon, need some suggestions for VTEC Xover on JUN3s. I have a wideband installed with standalone EMS. As it is right now, my VTEC Xover at 6200 is decent in 1st through 3rd, but in 4th and 5th, the cross over seems to bog down, doesnt pull as hard as before it switches to the big lobe, and just makes a lot of VTEC noise lol.

1st through 3rd, the Xover seems OK probably because crosses over a lot faster because the RPMs are rising so quickly, I dont even really notice the dip. But in 4th and 5th, the RPMs arent rising as fast and there is a definite fall-off in power.

If I turn VTEC off(set it to 10K), the low cam pulls very hard(and quiet!) way past my normal VTEC Xover, so Im just kinda wondering if that would mean I should set VTEC later in the RPM band and tune from there. Like maybe I have VTEC set to low in the RPM range. Ive been messing with it some on the street, but its kinda hard to do 4th gear pulls on a public road. I know that Im already running very rich and can see it add fuel at VTEC, but Im wondering if it could be too rich.

Thanks

 

Have you been experimenting on a dyno. I would suggest that you do two extremes. One setting with a really low Xover and the other with a high Xover. Then fine tune from there. It really depends on the motor. I've seen two identical motors with two very different Xover make the same mid and peak power. Don't get too carried away with peak numbers though.

 

Do one pull with vtec disabled. Do a second pull with vtec engaging very early, like 3,000 rpm. Where the 2 graphs intersect is your ideal vtec engagement point for maximum power.

 

if I do that method, should I do multiple runs with and without VTEC? and take the best power/midrange curves from each, and use those curves to find the best xover point? essentially tuning the car as best as possible with and without VTEC, and then combining the best of both. once I have that, I could set VTEC at at that point and tune from there?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RTW DC2 &raquo;</TD></TR><TR><TD CLASS="quote">if I do that method, should I do multiple runs with and without VTEC? and take the best power/midrange curves from each, and use those curves to find the best xover point? essentially tuning the car as best as possible with and without VTEC, and then combining the best of both. once I have that, I could set VTEC at at that point and tune from there? </TD></TR></TABLE>


Ryan, I disagree with the low/ high pulls to see vtec crossover. Always dyno in 4th gear for itr tranny - don't go doing different gear pulls. 4th is most accurate from what I have found - more load than 3rd..... Anyway, just set it at 6200. look at the graph after a pull. Does the whp or tq fall off before picking up at crossover? If the graph is still climbing before vtec, raise the crossover about 500 rpms and try again. If it falls before crossover, then lower it to where it is level or still climbing. You don't want your graph falling off before vtec. You want it to climb - because the engine will gain momentum - don't lose it then gain it back with crossover. 6200 is pretty optimal for a jun3 setup on a 1.8L. If you raise compression and headwork - depending on the flow characteristics of your i/h/e and headwork (and overlap), then you might benefit from al higher crossover - even closer to 7200 or so isn't unreasonable. I don't care what your butt dyno tells you - the graphs don't lie. If you don't feel a vtec KICK, that's because your crossover is so smooth. THIS is what you want. **** the butt dyno.

 

Thanks Ken. The xover now is pretty much tuned out so there is not "KICK" at the xover. Last time I had it tuned on the dyno(just a few runs to get a good base), it was done in 3rd. Next time I get to the dyno I will definitely be doing it in 4th. I think it can be better fine tuned in 4th than 3rd. I guess Ill see how it comes out, hopefully next weekend.

Anyone have any input?