tedesco

@eclou: What do you think happens with cars that run MAP sensors instead of a MAF or naturaly aspirated engines with open throttle boddies where there is nothing infront of the throttle body? Do you belive that there will be vac infront of the intake? The intake is NOT drawing in the air but the engine (and turbo) does. When the engine is running the pressure you will measure in the intake is determined only by the pressure drop of the air filter and as mentioned by somebody else already above, the pressure drop will be close to nothing at idle and hopefully not too far away from nothing at wide open throttle too if your filter is OK. If you want to have crankcase vac run a vac pump.

Another considderation: The turbo is pressure fed with oil allthough the oil pressure dropps till it reaches the turbo. When the turbo is spinning under load, the exhaust housing sees some considderable pressure too which is build up due to the necessety to run the turbine. That would help to seal the turbo and to keep the oil out of the exhaust.

Rogue_Ant

For giggles I hooked up my map sensor to the banjo bolt, and I measured 3~4inches of vacuum @ idle...yes INFRONT of the throttle plate. Although I still have the stock AFM and a K&N airfilter on. (Chris, I will show you a log ;P ).

Rogue

tedesco

if you measure through the banjo bolt line, you connect your sensor throught the electronic wastegate control valve to the manifold (where you have significant vac at idle). The amount of vac you will read in this place depends on tube diameter and how close you are to the banjo bolt. Try measuring in the original location of the crankcase return.

cpt_koolbeenz

<<<For giggles I hooked up my map sensor to the banjo bolt, and I measured 3~4inches of vacuum @ idle...yes INFRONT of the throttle plate. Although I still have the stock AFM and a K&N airfilter on. (Chris, I will show you a log ;P ).>>>

Awesome! I didn't think there would be much. And 3 inHg is not much... BUT like tedesco suggested, at the crankcase return, I would care to wager a bet that there is even less vacuum if there is any measurable vacuum at all. Is your MAP adjusted for this altitude, or did you measure the difference between atmospheric pressure and the banjo reading? Thanks for checking that out. BTW, are you going to Longmont with us on Sunday?


Thanks for the helpful replies guys and gals! The more info we have the better!

For fun tomorrow, I may hook my crankcase vent up to the intake where the ISV plugs in... See if that helps smoking at idle (I won't dare drive like that!)...

Rogue_Ant

Um, no I don't have the CV hooked up anymore, MBC.


Rogue

tedesco

Rethinking what I wrote, it was wrong anyway, sorry for that. I mixed some tubes while I was thinking about the system. Still I am surprised about the low pressure you ahd and don´t have an explanation for it. Will do a measurement on my car over the weekend.

eclou

Throwing away all the physics, think about it very simply. Air will not enter the throttle body unless it is drawn it by suction. Suction = vacuum. If there was no suction, 500 cfm of air would never be drawn into the motor - molecules would only bounce randomly into the throttle plate through Brownian Motion, and our motors would generate as much HP as a turnip.

Also, if you have a cone filter, notice how the pleats get crinkled? That is suction. If you don't and use a stock filter, notice how it is reinforced with metal mesh to withstand the suction forces.

Rogue_Ant

Hey I think I will be able to go, I will give you a call.

Also its been a few weeks since I took a reading @ the banjo-bolt, but I'm pretty sure that I had altitude comp. on.


Rogue

cpt_koolbeenz

Rogue - Just give me a ring...


Well, I did some testing today... I took off the ISV hose and plugged in my crankcase vent hose. Immediately, there was a loud warbling sound coming from the engine. I think it was internal. I could have caused oil starvation doing that, but I immediately took it off again (any other guesses - I didn't look at the oil pressure while doing this). I cracked the oil fill cap to let some air into the crankcase, and tried again. This time, no warble noise. So, I left it like that for about 6-8 minutes. My boost gauge read about 16-17 inHg. After about 5 minutes, I did notice that the smoking had gotten slightly better (it was windy, so sort of hard to tell and smoke was not too bad to begin with). Which I expected... Then I measured the vacuum just before the turbo on my setup... 0 inHg at idle. At about ~2300 there was about 1-2 inHg of vacuum. So, my intake is not restrictive enough to create enough vacuum in front of the turbo to do any good (as I stated before). So, that leads me to the question, of all the smoking turbos that had their crankcase venting back to the intake and were still smoking, how many were still running the stock AFM? The stock AFM is about the only thing I can think of that would produce sufficient vacuum at idle in front of the turbo to make a difference (as I had to get above 4 inHg to see any difference in smoking).

Also, it takes about a good 5 minutes idling to get smoke. If I have been driving under load at all and let it sit, it doesn't smoke for a while. Maybe that is due to the back pressure in the exhaust holding the seals shut, then at idle, they start to leak due to lack of back pressure?

david fracolli

I ran both the stock AFM and a SFR MAF did not make any difference.

Rogue_Ant

Ok, just did a quick test - I took a reading in the stock J-boot before the turbo.
At idle there is _maybe_ 0.2-0.3inhg
A couple of quick revs made very little difference (slightly more vacuum).


Rogue

cpt_koolbeenz

Yeah, so at idle there is no vacuum... That is what I have been suggesting the whole time. At idle, the stock system doesn't use the vacuum to drain the turbo.

Thanks Rogue for checking that!

Laust Pedersen

Is your turbo a full ball bearing design?
If not, restricting the oil flow is a dangerous game that does no good and can do a lot of harm. If an engine is leaking oil, would you restrict the oil flow to the bearings to reduce the leakage?

Have you done a leak-down or at least a compression test?

Not surprisingly, oil flows from high to low pressure, so if you have lots of leak-down, then the oil may get pushed through the seals in spite of your 5/8” venting. If the seal(s) are damaged, then more oil flows. The delayed idle smoke could simply be the time it takes for the oil to get from the turbocharger to the engine. Is there oil in the IC pipes?

Laust