Without measuring, my guess would be 3/8".

What issues are you having, and what "oversized" barb are you using?

Vacuum is vacuum. I don't see how barb size (unless restricted) is going to have a negative effect on things, but more detail, possibly pics could help.

 

Happy thanksgiving,

 

Got 3/8 line with the hard lines out of four way split, my vaccum diagram shows a T going to the baro and fuel pressure regulator, does that T stay small like the hard lines?

 

I recently changed most of the underhood vacuum lines on my '86. The vac line coming off the brake booster is 11/32" (Gates 27232):

Amazon.com: Gates 27232 Power Brake Vacuum 11/32 inch x 36 inch (85 PSI) Hose : Automotive

Buy Gates 27232 Power Brake Vacuum 11/32 inch x 36 inch (85 PSI) Hose: Hoses - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

Main vacuum source for that harness is 3/8 as far as I can tell, and that vacuum source that looks like a dipstick tube is just for the pcv valve. On my 89’ I am using that pcv vacuum source as my main source for vacuum for the map, fuel regulator, boost gauge, the original nipple threaded in the intake I am using that hole for the air charge temp sensor since I converted to a T2 setup.

Is your goal to look factory? Or just make everything work correctly?

 

Hello

I appreciate your feedback and I just want it to work properly.

Im giving up on trying to run computer controlled boost and going with a mbc

I do have my pcv running to that dipstick looking
Port on intake and have a T in that run going to charcoal canister and TB with two check valves.

tested that pcv run today to make sure check valves where in rite.

my vaccum diagram shows a T from vacuum source to baro/APR

Can I just run lines from vac block to both and eliminate that T?

 

Here's how we simplified the shit stock vacuum routing.

Cost was about $40-50 from Amazon.

 

Beside your vacuum block on the left side
There is a weird looking 🔌 plug
What is that plugged into?

 

 

A/c low pressure switch

 

Yes unhooked a/c.