Slant six turbo boost problem

[Altered64]

Im just trying to pick everyones brain while i continue to look for the gremlins that are hiding in my motor.

The motor is a bone stock 64 slant 6
52mm t3/t4 turbo
Intercooler
Methanol injection
Megasquirt EFI
Stock points ignition with a hot coil

The problem:
The car runs and drives fine except when the boost goes over 6psi, it builds boost real fast up to about 10psi but then falls to about 5.
If i keep on the gas it continues to do this up&down stuff 8-5psi
Cant hear any detonation, but there is def a loss of power.:sad10:
This has been happening since the the turbo went on about 8k ago.

Heres what I did so far:
Its getting plenty of fuel!
I played with the timing, the mechanical advance, plug gap and heat range.
Adjusted the tension of the wastegate and blowoff valve.
Nothing changed the problem!

I see others with similar setups pushing over 20psi, why cant I do that.

Any help would be greatly appreciated.

 

[racedodge]

sounds like you have a leak on the boost side.. have you ensured that your gasket/seals around your carb base and tophat are sealing appropriately? Maybe one of the pressurized intake hoses are losing their seal... once it hits 10psi, it blows past a seal/gasket???

 

[Altered64]

Intake leaks was the first thing I looked for and there are none!
This problem has always been there, even with three completly different manifold and intake systems.
I thought it was a carb problem but now its EFI and still does it.

 

[shag766]

it sounds like it is in the turbo side, out. if you figure its getting fuel at a constant rate of pressure.

 

[dryheat]

Please post some detailed pictures of your setup and all the plumbing.

 

[Altered64]

Cant get the pics on here for some reason, but they are in this gallery

http://www.forbbodiesonly.com/moparforum/vbpicgallery.php?do=view&g=1190

 

[racedodge]

have you thought about replacing the blowoff valve or the wastegate?

 

[Altered64]

I have tried jamming bolth of them closed and that didnt change a thing!
So that should prove they are working properly.

 

[IQ52]

At what RPM is all this happening?

 

[dryheat]

I am by no means a turbo or /6 expert so please forgive anything stupid I am about to type.

Is it possible that the crankcase is being over pressurized from some ring blowby? Although, I would think that this would result in leaking seals/gaskets.

 

[Altered64]

At what RPM is all this happening?

It can happen at any RPM the only constant is the boost pressure how wierd is that!


As for the crankcase pressure i was thinking of putting a vent tube on the oil pan, Ill try that later today.

 

[Cranky]

Your crankcase isn't vented at all? Is it blowing your dip stick out or blowing oil out anywhere?

 

[Altered64]

I have the two valve cover breathers that should be venting the crankcase!Maby thats not enough.

The motor does leak a bit of oil but no more than before the turbo.

 

[Moparmatt72]

Have you hooked up a boost leak tester? You can make one really easy from home depo, it dose sound like a leak somewhere, I know on my srt4 when I had a leak it boost but then only hold 5psi and this was on a set up for 25+psi. If you want to build your own tester let me know. Those worm type clamps suck need to upgrade to T-bolt clamps. As far as venting should look into a kit that hooks the valve cover to you exhaust to hold a negative pressure in the crankcase.

 

[Altered64]

Well I did pressure test all the induction pipes after welding by sealing off one end and running shop air into the other and spraying them with soapy water.

I have an exhaust siphon kit i was saving for another project, gonna start fabing up a pipe to link that to the oil pan and valvecover.

 

[Moparmatt72]

Okay you need to do a boost leak test on the whole system, ill find the link from the srtforums to show you what you need to build your own leak tester, you basically need just a lever to hold the psi and have someone just watch your boost gauge and take it to 10psi then spray the whole turbo hoses and pipeing and intercooler with the soap and water. When you welded your pipeing did you make a bead at both ends to hold the clamps and hose from slipping off? Did you check all your vaccum lines and zip tie it all or worm clamp them, for the intercooler pipeing hoses swap to t-bolt clamps, trust me I had some fail of the worm type, they aren't strong enough for boost.

 

[Altered64]

Well I was going to mess with it after work, but its raining cats&dogs here.
Dont have any wipers, defroster, or side glass so driving in bad weather is a nono.
So im hoping tomorrow will be better weather so i can road test.

Oh all the piping is welded at the ends and every line is tied on

Also u gotta understand that some things may be low budget or half ***.
This whole setup was built from spare parts for $500 and I realy dont want to put too much more money into it.
This 6 will be replaced with a big block next winter!
I just want to see how much power i can get out of before it blows or I get fed up and rip it out.

 

[racedodge]

I just want to see how much power i can get out of before it blows or I get fed up and rip it out.

I ABSOLUTELY LOVE THIS STATEMENT! U DA MAN! :headbang:

 

[Moparmatt72]

I understand that, I believe the whole leak tester ran me less then $10 to make, maybe $15. I'm just giving you my .02 and from my experience with turbos. I did low budget stuff with mine but then saved and got better stuff. Can't wait to see your big block build, hopefully in a year or so ill be building mine, just need to do chassis stuff first.

 

[Altered64]

The bigblocks been built its sitting on a stand just waiting.

Like I said before im giving the little \6 a chance to prove itself to everyone who said this was a dumb idea.
Also to my amasement most people think its cool, it was a big hit in carlisle this year!