I just recently started doing boosted motors. The first one was an LSvtec and i had no problem determining where the crossover needed to be. The last motor i did was yesterday and it was an h22a4 at 5psi. I don't have the chart yet and due to time restraints and wastegate issues, i didnt get much time to work on the vtec crossover. however, i had set the crossover first at 5000 and it appeared that the crossover needed to be dropped due to the gradual decrease in torque before the crossover. I dropped it to 4700 and there was the sharp drop in torque which told me the crossover needed to be higher. So i changed the crossover to 5200. This graph had a drop in torque starting at about 5000. I had to end the tune there.

I was just wondering what techniques you guys use to determine the best vtec placement for boosted motors.

 

Before you use a boosted vehicle as a vehicle to experiment with, I would suggest you go ahead and complete a boost leak test on the setup along with a compression test to ensure the setup is on par.

Vtec points are going to vary on turbo setups just like n/a setups.
Cam profile, intake manifold, turbo manifold, head flow, displacement, turbo size, exhaust size are all factors that come into play & more....

Simply use a dyno to experiment.
You will figure it out :-)

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mtber &raquo;</TD></TR><TR><TD CLASS="quote">Before you use a boosted vehicle as a vehicle to experiment with, I would suggest you go ahead and complete a boost leak test on the setup along with a compression test to ensure the setup is on par.

Vtec points are going to vary on turbo setups just like n/a setups.
Cam profile, intake manifold, turbo manifold, head flow, displacement, turbo size, exhaust size are all factors that come into play & more....

Simply use a dyno to experiment.
You will figure it out :-)
</TD></TR></TABLE>

yea i figured that much. I didnt have a problem with the LSvtec, but i also was not pressed for time and i got alot more clean runs in. I know I would have figured it out with a few more passes. I guess i could have done the technique like an NA motor. Set vtec really high, then set it crazy low and put it where they meet.

 

I'll do it like you said, low vtec run, high vtec run, where the torque curves meet i'll put the vtec around
but still keep in my mind that the car should always be pleasant to drive

 

Sounds like you had it right at 5000.

VTEC increases valve overlap and that's why you'll see mixed results with boost.


Modified by baller status at 9:11 AM 4/10/2008

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by david974 &raquo;</TD></TR><TR><TD CLASS="quote">I'll do it like you said, low vtec run, high vtec run, where the torque curves meet i'll put the vtec around
but still keep in my mind that the car should always be pleasant to drive
</TD></TR></TABLE>

This is not the best case all the time guys :-p

Use a dyno & experiment, enough said.

 

Since you're boost you should get some adjustable cam gears and dial out some overlap. That's the whole point of having DOHC!

You see VTEC was made for N/A. The exhaust valves open with the intake valves to suck the air into the combustion chamber. But if you're shoving air into the combustion chamber, overlap just means that you're shoving air into the exhaust. So turn the exhaust a couple degrees so the exhaust valves are closed and the boost gets compressed into the combustion chamber.

After that you will find that VTEC isn't so finnicky.