Who knows LSs?

adman02

Well-Known Member
Joined
May 15, 2009
Location
Durham, NC
I'm in the middle of an LS swap (going into an '88 Landcruiser). The donor engine is an LM7 from a 2006 Yukon. There's some differences with this engine vs early LS IIIs (e.g,. return-less fuel rail, hydroboost PS pump, different bolt pattern for the oil pan, etc.)

My question is about the vacuum ports, though. I know there's one at the back of the engine for the brake booster. BUT, there's another about midway on the passenger side of the intake. Traditionally, you can break off a plastic tab and voila - you have a vacuum port nipple. With this engine, though, there's no plastic nipple - just a steel block off plug. I need to know the size of that plug so I can buy a fitting. This will power my xfer case vacuum system. 1/4 in is too small; 3/8 seems too big.

Any guesses on size?
 
adman02 said:
I'm in the middle of an LS swap (going into an '88 Landcruiser). The donor engine is an LM7 from a 2006 Yukon. There's some differences with this engine vs early LS IIIs (e.g,. return-less fuel rail, hydroboost PS pump, different bolt pattern for the oil pan, etc.)

My question is about the vacuum ports, though. I know there's one at the back of the engine for the brake booster. BUT, there's another about midway on the passenger side of the intake. Traditionally, you can break off a plastic tab and voila - you have a vacuum port nipple. With this engine, though, there's no plastic nipple - just a steel block off plug. I need to know the size of that plug so I can buy a fitting. This will power my xfer case vacuum system. 1/4 in is too small; 3/8 seems too big.

Any guesses on size?
Click to expand...
5/16 seems too obvious :laughing::laughing::laughing:
 
8mm (.315") or 5/16" (.3125") maybe?
 
If its a truck intake, you can drill and tap it to ¼npt. These are the only intakes I've ran on 5swaps so can't help if its a car intake hope that helps
 
DSCN1215.jpg


You talking about that one?

I'd probably break the tab off the end, drill it out if it's solid, and put some vacuum hose over it. If one size is way too big, but the smaller one will go, I'd put some heat on the end of the hose and shove it on there so it forms/stretches to it and doesn't split later on.

Or just tee off of one of the other vacuum ports.

For the best results, I'd post a picture of what you're dealing with.
 
I'd be willing to bet it's not factory. The cheap asses at GM would have put a plastic plug in it. Steel costs too much 🤣

However, just pull the plug out and match the threads. It's very likely an NPT thread, which is tapered. If ¼ is too small and ⅜ is too big, assuming you checked with straight threads, it's probably ⅛-27 NPT. That uses a 21/64 tap drill, which is .328".
 
Damn, I'm good :D
 
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