Turbo Fun, and safety weak link.
 

I was out driving my mid mount turbo 928 the other night, and I got on it in 3rd gear.
Everything seemed normal at first, RPMs climbed to around 2800RPM as per normal and then boost came on HARD. Much harder than normal.
I was launched into my seat and it felt like I was strapped to a cruise missile! 3500RPM felt like I was around 550+RWHP. And before I could lift my foot POP.

Pulled over, sure enough MAF had popped out of the boot, and the zap strap I was using to hold it down snapped.

So I pull off the clamp and loosen it up, slide the MAF back in. Tighten the clamp, it spins. :banghead:

Limp the car back to the shop keeping the RPM below 2k and little throttle so it doesnt pull out. Go to the shop put another strap to just hold it a little more. I return home and the next morning (today) returned to the shop (again slow).
I check and see no vacuum leaks, I have good strong vacuum at the hose to the wastegate, but no vacuum at the wastegate.

The vacuum line I ran to the back had gotten a little warm and collapsed under vacuum. So there was no boost actually getting to the wastegate. I imagine that I probably was seeing around 15 PSI before it popped....

The interesting thing was that I saw zero knocks with the higher boost level......

tempting to install a higher spring and have more fun......

LOL.... I was doing something similar in the GT way back with the rear turbo set up on the way to sharktoberfest.... car is pulling strong....and all of a sudden...loss of power and the hood lifts slightly in the rear... I though I blew up the engine. Ended up the maf got blown out of the boot and lifted the air box attached to the boost pipe LOL. I can laugh now..but at the time.. I thought it was done for..

The other name for a Variable Pressure Regulator is Variable Piston Remover. ;)

I hope you don't have the problem I did with my 944T. I took in for service the dealer did something that unlimited the boost, and I drove it for maybe a month before I was dumb enough to ask a question about it and they "fixed it". No fun after that taste.

Wait until you blow the MAF to TB elbow apart - that'll be fun! Not sure what size waste gate you're using, but at 15psi, it needs to be pretty darn big a beefy.

Boost is so much fun, idn'it! :D

Colin,

You saw the wastegate muffler that I made posted on FB. The first cruise after I installed it, I headed out of my neighborhood to the highway. First blast in second gear (auto) flung me back much harder than normal. I peeked over at the boost gauge and was at 10 PSI, and I normally run 7. I turned my manual boost controller all the way down, and got on it again, and the minimum is now 5.5 PSI with the 5PSI spring installed in the wastegate. I had the boost controller on 17 "clicks" open, and now to get the same 7psi, I have to run at 11 clicks due to the muffler restricting the exhaust from the wastegate. And I used a much bigger muffler size than the wastegate exit hole diameter.

With the Meth/water spraying and my normal EZK map, no knocks at 10 PSI. Car felt really good at 10.

Oh,

And, we finally got Pele's mid mount turbo running pretty good. There were lot's of issues, most of which Pele worked through himself with only a very small amount of help from me.

The final issue, which I have never seen or heard of before, was a fluctuating wastegate that would open and close like a sine wave when under boost. It made it impossible to tune correctly. The boost pressure would just ramp up and down over and over again starting at just above boost threshold.

He removed the electronic boost controller stuff, installed a 7.5lb spring in the wastegate, and it runs like it should now.

Colin,

Regarding the MAF popping out of the boot. I had a similar problem with my relocated AFM on my turbo car. I tried many things to get it to stay together but the one thing that helped the most was to cut some grooves into the lip where the boot slides over the AFM ( MAF in your case ). Just grind some fine lines ( I used an air grinder w/ a cutoff wheel and a steady hand ) around the circumference of the MAF inlet and outlet. Theres no need to grind them all the way around, just two or three small "dashes" then skip some space and do it again, then again, all the way around. This gives something for the hose to bite into intead of trying to grip a smooth surface.

As for the wastegate line collapsing :nono: I'm using a small diameter ( 1/4" I think ) braided hose to make this connection. Same with the signal to my RRFPR. It's too critical to use a cheap silicon hose. The only thing I use a hose for is the boost gauge itself.

15 psi must have been fun while it lasted. :thumbup:

I will be converting to VEMS soon running MAP. I hope to ditch that boot Andrew. ;)

It sure was fun though!

I had the MAF popping out issue on Randy's Murf kit, I ended up dremmeling a nice, rough 1/2 inch groove around the seat in to it, leaving a slight ridge and after clamping, it's not come out again.

Glad to hear Pele's issues are solved, my neighbor kept telling me it was waste gate related on the boost side but we didn't listen.

As well I am running a 46mm wastegate which should be fine. I have zero boost creep @ 5.8 PSI.
I will see if there is any at close to 15 PSI.

It was the *gain* setting on the boost controller doing that. You can actually use the controller for how quick you want the boost come up, and if you want it to hit an *overboost* and then come down a couple of PSI.

It could have been corrected in the menu settings however I know quite well how finiky that controller can be...

As for the MAF, I have some straps that are connected to the MAF hose clamp as well as the boot clamp that are crimped after pulled tight. Only way they come apart is if the straps are cut.

There will be a MAP based SharkTuner system available before long..... being tested on a s/c car now...

If you can run a steel line, it would be cheap insurance.

Zeus,
I like the thought of a steel line to the back.
I will look at that soon.

John,
I enjoy the development and progress on the ST system.
But I am wanting full COP ign which is not something that we can do as of yet.
I want this for a much hotter spark, and no blow out with higher boost pressures.
:cheers: