Just had a chance to read through all the available info. It seems here you're dealing with surge due to the distance between the compressor output/discharge and where you've chosen to take wastegate reference pressure (waaaaay further down the line close to throttle body). Take a pressure reference RIGHT off of the compressor housing and feed it to the wastegate instead of having a really long hose taken from much further downstream.


Here's my take... almost always with a mechanical wastegate, as RPM goes up; boost falls off a bit due to pressure drop across intake piping and intercooler at high flow. "Some" people like to reference wastegate AT the throttle body to account for these losses after all the piping. I don't like this in practice because there's now a REALLY long column of air and a slight delay. Combine this with a quick spooling turbo (you typically won't get this oscillation issue with that location of wastegate reference with a really big turbo with a lot of rotational inertia) and you'll get some wild oscillations.

If you want boost to not fall off slowly, add a boost controller; sourcing wastegate reference further downstream never seems to get good results.

Yeh - really hard to see what things are doing without instrumentation... I suggested it as a check for the MAP sensor - but I also think it's pretty unlikely that the sensor is reading incorrectly. If the readings aren't insane, it seems far more likely it's showing exactly what it "sees" and working perfectly.

I probably look at the boost gauge more than the tach, a habit I picked up driving from driving with a 3DLZ - as, if it shows vacuum, lets you know how close you are to boost threshold.

The VDO "cockpit" or "vision" series visually match the factory instruments quite well - hardest thing these days is finding ones that only read up to 1 bar (25 or 30 PSI are much more common), especially if you like them to show vacuum as well.

Really appreciate the help with this issue everybody.

I'm not keen on hacking up my clean euro 3 gauge dash for another gauge so will have to look at some canbus options for my Infinity 6. I've got the infinity running my stock oil temp gauge with a lowside output and it rocks ... matches the log data precisely:D

I'll look for 1 discreet digital gauge that can be hidden easily to take care of this ... most likely something from this company .. https://gaugeart.com/product/gaugeart-can-gauge/

You can even configure it with a smartphone ... gotta love technology. I've got the materials to hook up a spare MAC boost solenoid and will tackle it this weekend. Will post an update with the results.

Cheers,

Sandeep

I can make you a custom panel to fit where the radio goes if you don't have a radio any more

Your car; do whatever.

Seems to me having a display of the same MAP sensor info as the ECU is going from is kind of missing the point.

And now I understand your point. I've got a box full of old gauges and need to figure out how to add a small boost gauge to my original tach ... custom job I think.

Sandeep

if 912 gauges (and thus dash holes) are the same size, could borrow a 930 tach and install stock boost sender for a pure electrical connection. Or use a temporarily installed mech boost gauge; on a boosted car could tee off the brake booster, or run a thin hard tube up the tunnel.

Unless you want a permanently-installed boost gauge (I find one useful), primarily to verify that the MAP sensor reading match reality - so you don't spend time chasing down an issue that doesn't actually exist...

Added the boost control solenoid this weekend and noticed some improvement in the MAP fluctuation.

Also noticed that the solenoid acts like a boost vending machine ... need more boost ? Just increase the duty cycle with a few keystrokes http://forums.pelicanparts.com/support/smileys/wat3.gif

Unfortunately (or fortunately), it also showed me how close my stock clutch package was to the edge of holding 0.5bar boost as at 10% duty cycle over stock 0.5 bar spring the clutch slips at 5000 RPM :(

Maybe the G50 upgrade is a little closer then I had imagined :rolleyes:

Sandeep

Which solenoid I'm curious?

The clutch issue is what's caused me a now 15 months of fun and anguish. I pepped up my car 2 years ago and the clutch started slipping when I punched it in 3rd. sigh.

And now I'm starting to re-think a full EFI conversion, I'm most of the way there anyway.

Im using an old AEM truboost (manufactured by MAC) 3 port solenoid. Easy to wire up ... +12v and a PWM ground signal. Its the blue unit behind the red pressure regulator.

http://forums.pelicanparts.com/uploa...1568828897.jpg

Thats why I love this car o' mine ... keeps me busy with mods :D Screw the purists ! :eek:

Sandeep

Cool! Open or closed loop? What hz you running it at?

Heh... Also, overboosting (higher boost target) at lower RPM makes a big difference...

Oh, 915? ZF Sachs Race Engineering pressure plate worked for me as a 4+ year stopgap. You'll come to fear traffic, but it held 350 ft/lbs at the wheels...

Look on the bright side; if you were running more boost, you'd probably find it breaking the clutch free around 3500 RPM on anything over 1/3 - 1/2 throttle, which is a real fun dampener...

Closed loop at 30 Hz. Working on the PID values this weekend as the weather will be nice. Also have a classic car " Petite Grand Tour" at the end of the month through some local back roads and have to be ready to Hoon on demand http://forums.pelicanparts.com/suppo...ys/drummer.gif

Thanks for that. Reading up on how to use this strategy. Maybe high duty cycle below 3000 rpm to help spool and then shut off at about 3000 rpm to preserve the clutch :confused:

Lol .. I've got the majority of items I need for the G50 conversion already ... just need to disassemble the gearbox and take it for shortening. Decided that any money spent now should be put in to the G50 conversion.

Sandeep

In case you'd not seen this: - Boost solenoids

I'm running mine at 25 hz, where 20-80 are apparently meaningful limits for the duty cycle.


Heh. Might as well convert to full EFI and lower the compression at the same time.

Because it sounds like you'll eventually be tempted to run 1+ bar anyway... :D

Thanks for that link. The duty cycle %age was 20% that caused the clutch to slip at 5000 rpm.

Is it a crime to search the want ads for used 930 pistons and cylinders ??? :D

Sandeep

Yeh, season to taste...

I have boost control start at 110 kpa - so almost any boost at all goes to the top of the wastegate to help out the spring. This is what Motec suggest.

With closed loop, it's on/off until you reach target boost, of course.

On the Motec, there's a single-row table of target kpa against RPM (and the usual plethora of other trims/tables which can also modify the calculated value).

I know the PID values do the right thing on the dyno. Eventually. Which really isn't very useful, as I'm almost never WOT in 5th on the Mulsanne Straight...

In practice, I have about a 3 second window of BCV activation, and would like to both avoid overshoot and regulate quickly to the target setting.

That's a WIP, but doesn't seem impossible, just tedious to get perfect.

The boost overshoot to 220 kpa I experienced originally (which didn't cause the Safeguard to get excited) was what clued me in to what a difference it made...

Once the PID is dialed in, I was intending more boost up to 4500 RPM or so, and 1 bar after that. Maybe 1.1, 1.2 down low would be fun.

Wow - 20% is basically "off". But if I interpret that correctly, applying any boost to to the top of the WG is enough to prevent it opening prematurely - and makes enough extra power that your clutch now slips...

My sympathies. I went through 4-5 915 clutches in a very short period of time, once I added the K27/HF, Kokeln & GHLs etc...

It really kinda sucked not to be able to use the power...

Heh. Why, no, no it isn't. 3.2 bottom end, right?

I have my orginal 930 P&Cs left over from the build. I went with 3.4 slip-in Nickies/8:1 J&Es.

Shoot me a PM if interested.

Well, If I trade up to some 3.5l P's and C's

But then I'd need to get new rods, bolts, head studs, rings, port the valves which means new intake and exhaust work, a new turbo to take advantage of that, twin plug the heads.............

I'm shooting for 400 RWHP in my 2200lb car ... should not be difficult with a 3.2L as my base and some 930 P/C, GT3582R and headers at 1.0 bar.

I had a beetle with EFI 2.4L Type 4 turbo, 98mm nickies, 80mm nitrided crank and twin plug heads by Jake Raby / Len Hoffman. That car had a G50 box in it and dyno'd at 375 RWHP and was scary fast to drive. The gearbox, EFI system and turbo I was able to keep.

Looking to have that same feeling again with the 912 :eek:

http://forums.pelicanparts.com/uploa...1568908204.jpg
http://forums.pelicanparts.com/uploa...1568908204.JPG
http://forums.pelicanparts.com/uploa...1568908204.jpg

That’s a sick bug and I’m not really into bugs. What did it weigh?
Tony

Recall about 2100 lbs. Porsche dreams but VW budget at that point in life.