Porsche951redt

Hey guys i just wired up my boost/vac guage and at idle i am gettin around 12psi vaccum pressure and when i am at full throttle i am reading 10 maybe 11psi rn't our stock car's suppose to run 14psi? I am not so much worried about the boost pressure it seems right i mean old WG and all that jazz. But i have never installed a vaccumm gauge so is 12 or 10 psi at idle a normal thing?

theedge

10-12 in/Hg of vacuum isnt normal no, assuming it is measured in in/Hg (Autometer gauges do measure in that).

ninefiveone

Stock the cars run 11psi boost.

At idle on a warm engine, people generally see between 14-18in of vacuum. I get 16 on a warm engine, less when it's cold.

Porsche951redt

Well when i just start it up it sits around 11 vacuum when im driving it raises to about 17. Is having low vaccum numbers going to affect how long my car lasts or the power? Yea i see a peak of about 11psi untill redline.

theedge

Low vacuum affects mileage, power, almost everything. Start looking for vacuum leaks. A search on rennlist will turn up lots of info about likely sources, etc.

streckfu's

12 in/hg as a cold idle is not bad and 17in/hg while driving is also OK. That's what I was seeing on my gauge and everyhting was OK.

Stock, your car should boost .8 bar or about 12psi. You may have a weak spring in you WG which can be cured by shimming it or replacing it.

I assume you are completely stock with no chips or boost controller....

If in doubt, change your vacuum lines as it is very easy and cheap.

Porsche951redt

I might just have to end up doing that. The wastegate i will worry about later after i start with performance upgrades. How much work/time would it take to replace all the vaccum hosing?

streckfu's

If your just doing the small lines, about 15 minutes.

If you want to remove the venturi as well, a couple of hours because the intake manifold has to come off (easy).

ninefiveone

Just to calrify... 17in/hg while cruising and off the throttle or after the motor's been warmed up and sitting at idle?

17in/hg while cruising and off the throttle is low and you should have more vacuum. But if at idle on a warm engine, that's a good number.

Porsche951redt

At cold when engine is just turned on. ( i just did it 2 seconds ago) i am running about 10-11hg of vaccum pressure. With a warm engine it raises between 15-16hg.

eniac

I just did a venturi delete in a customer's '86. By carefully cutting a couple of the hoses under the intake I managed to do the whole thing without removing the intake, took about 45min.

What else can cause low vacuum? My car is a little low however I have replaced all vacuum lines and checked for leaks, which I now have none. TB seal leaking before, fixed that but vacuum didn't increase much. I'm getting 11 in/hg at idle warm.

Porsche951redt

Phew ok that is exactly the same reading i am getting. I haven't had leak problems in the past but i will still replace all the minor hosing just incase.

toddk911

I have a fully, dead on rebuilt motor and read 16-18 when cruising and about 14-16 at idle. Although that is with AC on. When in gear and let off the gas and cruise, hits about 20. And trust me, every connnector and hose is new NO LEAKS. That motor is sealed up like a frog's butt.

Also, there is a simple solution to the venturi delete. My mech did it for me after I told him I was going to get the kit and spend all this time to do it, etc.

He simply switched 2 hoses and capped another one at the intake and that was it; it was bypassed.

streckfu's

Where were you last week?

It doesn't make a difference in my case anyway. I already have the head off. May as well do it all.

eniac

You could just bypass the venturi with hoses by why do that when you can buy the kit and get rid of a buch of useless hose in the process?

The kit was <$70, included OEM hose and took me 45 min. on a stock '86. I don't what can be more simple then that. Rip out the entire venturi and pipe/hoses. Install two hoses to replace it.