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Join Date: Apr 2009
Location: Cedar Park,TX
Posts: 2,709
Why run a catch can?

What's the reason for a catch can? It seems like a lot of guys are running the turbo oil discharge right back to their sumps or chain cases and they seem to be fine.

I am having some trouble fitting a catch can to my motor with the custom exhaust and most committed to going with a drain tube/hose (braided with AN fittings) to the sump cover or the chain cover. I've been searching and reading and I haven't seen anyone that says "Don't do it and this this why..."

I need to make a decision on what I'm going to do as we prepare to put the hot rodded turbo motor into my narrow body.

I'm running EFI, EDIS, k27hfs, M&k y pipe with twin wg's, custom grind cams (964/SC) from Dougherty Racing, and RarlyL8 exhaust.

Please help with any insight as I don't want to short cut, there's too much in the motor, but if it's not necessary then why have it?

Thank you in advance,


John- I blame and thank the longhood boys of Austin
84 911 Carrera w/ 930 t/p,efi'd,dizzy free,HFS turbo[/COLOR], 78 930 RoW no option sunroof coupe, 64 Corvette roadster, 71 911T, 73 911E, 67 Bronco survivor. 71 FJ40, 2001 Boxster
"Illegitimi non carborundum"
Old 09-01-2011, 10:23 AM
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Crotchety Old Bastard
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Join Date: Jan 2000
Location: Huntsville, AL
Posts: 14,185
There are periods when the flow is not equal between the inlet and outlet. One of these times is when the engine shuts down and the turbo continues to drain. Another is short periods of boost when the engine rpm increases abruptly causing a surge in oil pressure.
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 09-01-2011, 12:38 PM
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Join Date: Mar 2011
Posts: 471
Hang on, are you talking about the oil catch can that connects to the oil breather tube on the oil tank, or the OIL DRIP TANK under the turbo?

If the latter, the drip tank is there as a reservoir to give it a "chance" for the oil to be sucked up by the turbo scavenge pump, since the turbo pump lags a little against the oil press build up the the oil inlet of the turbo, if you are using a "gravity feed", you should place the turbos high enough for the oil to scavenge properly out of the turbos.

Gravity drain works fine on the 930's. Lots of guys doing it here. Just make sure you are draining to a point lower than the turbo's oil outlet.
Old 09-01-2011, 02:16 PM
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Registered User
Join Date: Jan 2004
Location: Milwaukee, WI
Posts: 3,271
I run a catch can on my m&k y pipe. B&b style. Ben at mk used to gravity drain to the sump pump, but switched to a can as well.

Old 09-01-2011, 02:27 PM
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