Tim Benton

iTrader: (1)

Well I thought I had tuned the PFC for the cooler weather, and I had, it was high 40's, maybe 50 when I took the car out to have some fun. After having the PFS PMS for 2 plus years I knew I'd have to tune for the cooler weather. I did some run at WOT in 3rd and 4th gear, where I was hitting the set boost cut for running .25 above the setting in the PFC. Sucked *** until I got it back down where it needed to be, .84 range for roughly 12.3 psi. Tonight, 1 degree above freezing, got the car out, was hitting the boost cut ceiling every freaking time at WOT (high rpm range 6500+) Started playing with the waste gate duty cycles, lowering them to try and bring the boost down. I'll be damn, I couldn't bring them down. with a .75 prim and waste gate % of 52, 50 ,etc, and the sec of .7, waste gate % 56, 54, 52, etc, couldn't note bring the boost down. Constantly hitting .98 psi, and resulting boost cut. I went all the way down to 20% on the wastegate %, and still no lowering of the boost. I lowered the values to .65 prim, and .70 sec, with the wastegate numbers in the lower 50's, lowered the peak boost number that way, but still was going over the .25 limit and hitting the cut again. Boy think sucks, am I overlooking something simple? Car ran stable boost until the very cold air came, now I can't seem to control it. I'd hate to have to spring for the dawes device as a stop gap measure to keep from hitting the boost cut.

Thanks for any input (Chuck) and anyone else

Tim Benton
thought I knew what I was doing until now

cewrx7r1

iTrader: (2)

Tim,

Part of my background(USAF) was electronics. The situation that you describe really has annoyed me for many years. All of these so-called boost controllers that I know of are crap, and all work by controlling duty cycle of the solenoid without referencing boost. This duty cycle is preset by the user. Even the AVC-R has the same problem. This problem can be solved but is not being done.

All that is needed is a feed back control circuit to monitor the PIM voltage from the engine map sensor or an internal map sensor. You would set the boost by psi or PIM voltage. The circuit would compare this value to what the map sensor puts out. Then it would change the duty cycle of the solenoid to control the WG. Thus with an active compartor circuit, boost would remain constant no matter what the temperature or your altitude.
The altitude example also depends on the capacity of the turbos. Similar control circuits are used everywhere so why aren't they used for boost control?

If you have a pill in your WG line between the turbos an WG actuator, maybe it is too small!

Tim Benton

iTrader: (1)

Chuck,

Thanks for the input and possible fix that no manufacturer has done yet. As far as the pills, they are the stock pills in the wastegate line since I haven't changed them since I've had the car. Our local hop suggested switching them to raise or lower the boost, but pulling that line is a bitch. If I can't get it to lowered, I just might get the dawes device hooked up on the second turbo for 12 psi and have it as a safety boost controller.

Anyone else having boost related problems due to cold weather?

Tim Benton

cewrx7r1

iTrader: (2)

Tim,

Replace the stock WG pill with a larger one.

Chuck

weaklink

what about a popoff valve? one of the guys on the forum, maybe ernie, had one for sale for $50. they are about $108 from RP http://www.rx7.com/cgi-local/3catalog.cgi?cat=9&part=4

Tim Benton

iTrader: (1)

The only thing I don't like about the pop off valve is the surge the turbos would be doing whenever it opens to vent boost. The turbos would spin themselves past what I think they are reliable for at over 140000 rpms.

Chuck, like a .62 or .64 sized pill, sort of like the ones you use for jetting a carb.

Tim

cewrx7r1

iTrader: (2)

You will have to remove the pill to determine it's size, then go with a larger size. Many use Holley carb jets. Another way is to install the adjustable water valve.

SPOautos

If your going to spend your time pulling those 2 vacume lines I'd do the Home Depot controller listed on Rob Robinettes site. I've been using those 2 controlers for 2 years now and they work great. They wont take but 10 minutes to put together and the cost is about $10-$15 for the pair.

Anyway, the good thing is if you just swap the pills and it doesnt do what you want your going to be back in there taking it apart again. If you install the valves the first time you can make adjustments till its exactly what your looking for.

Later,
STEPHEN