Hondata

'92 eg built LS/VTEC with huge turbo

For now we had tuned it on the road for 20 psi only on street gas, it ran great in 4# (only gear where we didn't lose grip on street tyres)

Tonight we tried it out on the strip, it wasn't to bad but it could be way faster. One reason is the boost is building up to slow.

We are using S300 A11 boost control with MAC solenoid (normally closed).

The wastegata has a 8 psi spring, on the street we found out 83% duty cycle makes 20psi boost. The solenoid is mounted the way hondata recommends (normal vacu?m hose on the bottom side of the wastegate, vacu?m hose with the solenoid on the top of it)

For full boost it works good, boost is very stable. But when building up the boost, it's far from ideal. That's because the wastegate opens before max boost is reached. I noticed when tuning the car, with 20psi max boost, it's way quicker at 10psi, than when boosting 12 psi max. When building up the boost, the wastegate should be 100% closed. Best thing should be 100% pwm duty-cycle before max boost is received, and then go back to 83% (or whatever).

Should it be possible to work this out in the software??

As it isn't for now, i've been thinking for other options. When I use manual boostcontrollers (ball&sping type) I never hook up the top of the wastegate, I just put the controller between turbo and bottom side of the wastegate. 100% closed is max boost, 100% open is spring boost.

So why not hook up the (normally closed) solenoid that way, and set the solenoid activation pressure at 19 psi. The wastegate will be closed till the boost reaches 19 psi.

Or even better: when the boost comes under 'solenoid activation pressure', does the solenoid stop working? If the answer is yes, why not just set the 'solenoid activation pressure' at 20 psi, and the duty cycle at 100%. Solenoid stays closed till 20 psi, then it opens, boost will drop, solenoid closes. There's your fully closed loop boost control. No more experiment with duty cycle, no more temp corrections needed, a wastegate that doesn't open before max boost is reached, wouldn't that be great?

Ok, i guess this way the boost will fluctuate to much, and for now it won't be possible to use boost by gear anymore, but I think it's worth a try.

I'd really like to hear your opinion about this..

First, 83% to get 20 psi from an 8 lb spring is a lot of duty cycle. As a rough guide the solenoid duty should be 30-60%. If you need 83% then start looking at the wastegate and plumbing - nothing in the software will help you. It could be the size of the wastegate, or exhaust backpressure, or it could be something else, but an acceptable solution is to just try other configurations, such as a single line bleed setup as you have already suggested.

If you activated the solenoid at 20 psi with 100% duty cycle then you will get major boost porpoising as the solenoid comes on and off - probably from 20 psi back to almost 0, and then back to 20psi ..

Actually the spring was only 6 psi, and remember, the turbo is really huge..

Till 50% dc the boost doesnt raise, with 60% it makes 8 psi, 75% 13 psi, 83% 20 psi.

I agree on your argument about activating the solenoid at 20 psi.

There won't be to much backpressure, the exhaust is full 4". The wastegate is 44mm, might not be too big, but that will cause more overboosting than to less pressure?

First thing we will do is use a 15lbs spring. Maybe I'll try the wastegate on the bottom side, to see what happens.