legacycentral bbs

i finally got a proper boost gauge, when teed into the number four intake runner i see 8-10 psi consistently with the odd spike to around 12. i also have matt's vacuum bypass. my needle shakes slightly when connected this way...


last night, i decided i wanted to see what my turbo is putting out from it's nipple. so i hooked the vacuum lines up accordingly and went for a drive. the td04 was putting out 11-13 psi with spikes to 15 when i let off the throttle. it stuck pretty good around 12 with no needle shake.

all my vacuum lines are fresh from the swap and zip tied well. my intercooler setup is tight and i just checked it for leaks and secured the hose clamps.

i realize ther is a pressure drop through the system njow that it's i/c'd and i would contribute the needle shake to the valves opening and closing when my gauge is hooked up off the runner.

is this normal

and the last thing is when my gauge is off the turbo nipple i obviously dont see vacuum but i do see 2-3 psi while cruising on the highway with steady throttle around 2400 rpm. usally at this point i would see 12-15 on the vacuum side???

thanks for reading
Ryan

mods below

anybody?

I'm interested in the answer to this too

How and where do you have the bypass valve piped in? How long does the spike last when you let off the throttle?

off of that flange on the i/c, hose,elbow,hose,bpv,hose, bhack to stock location

the spikes last 2-3 seconds

now that i have a downpipe in it's even a little higher

bumped

I would say what you're experiencing is probably normal.

What type of gauge are you using? Are you using the small plastic tubing or rubber hose?

rubber hose, i'm thinking maybe i should be using the small plastic hose that comes with it. the needle shake i'm thinking is from the valves opening and closing, actually, i'm going to install right now cus i'm stuck at home on a friday night with the kids in bed and the wife at work!

The needle should be steady. If you have it connected to one branch of the manifold it will pulse a little and the cure then is to put a restriction in the pipe. If you have it plumbed to the throttle body then it should be barely moving at an idle(maybe five inches of slow fluctuation at max), definately steady by 1000 revs. A lot of vibration means something amiss. What exactly depending on the vacuum readings, the speed and range of the fluctuations and what results you get doing other tests with the vacuum gauge..

i hooked up the small plastic line, no difference.

as stated above, i ran it off the turbo nipple with no needle shake.

off the #4 runner where the coolant tank would be is where i'm teed into. it also tees from the bov.

It shouldn't pulse by much at all if the motor is in good order. Have a read here... http://www.classictruckshop.com/clubs/e ... ac/uum.htm
or...
http://www.earlycuda.org/tech/vacuum2.htm

im great on the vacuum side, it's getting into higher boost that i get the shake

Ha, yes I see that now that I read more carefully!

I also see you have it into a manifold runner.... where you would expect a vacuum or pressure to pulse. So that is probably normal.
Have you tried pinching the hose off till the pulsations stop? If you do it carefully you should be able to get a steady, but still responsive, reading. It will wreck the gauge eventualy otherwise.

All the vacuum gauges used to have a little thunb-nut clamp that pinched their hoses to make them steady and pressure gauges used to have restrictors fitted to prevent shock.

Can you not connect to the throttle body somewhere though, which would be better still.?

I think what you are seeing is pretty normal. The amount of shake probably depends on gauge quality and where it is connected.

There are various ways to address the high end shake, mostly aimed at a quality method of boost control I think.

it does not shake off my turbo nipple, my dad has the same gauge just a model lower teed off the number 1 intake runner with no needle shake.

is there somewhere closer to the throttle body i can tee into?

Hook it up to the vacuum/boost port that goes to the MAP sensor. That is what I have used, and have not any issues with the gauge needle fluttering.

I've got my autometer gauge teed off the manifold. Never had an issue with it shaking.

FYI, I hooked up a different gauge, teed off the #1 intake manifold runner, and it was shaking (it is on the same line as the canister and a solanoid).

So, I dropped a brass restrictor pill inline with it that has a TINY hole, and the needle is 100% rock steady now. I can't measure the hole diameter, but it's probably in thousandths.

Gauge response is not delayed, and ZERO shake.

interesting, i have a plenum in there but the hole is probably 1/32 - 1/16th. i'll try that. i guess the reason it wouldn't shake when hooked up off the turbo is because it put's out more consistent off the turbo. the valves opening and closing dont have an effect from the turbo nipple.


josh... when teed by the bcs, i guess i wouldnt see vacuum.
also in vikash's vacuum hose reference, he shows a union between the turbo nipple and the bcs, mine is just a straight hose with no union. should i look into this?



i'm currently teed off line N

in case the pic doesnt work, here is the link
http://web.archive.org/web/200510281912 ... vacuum.png

Mine is teed off line C right after the manifold.

The restrictor that I have is a stock item on my 1998 GF8 (later model 2.2), no idea where in the vacuum system it was originally......

would line I work?

RJ93SS wrote:josh... when teed by the bcs, i guess i wouldnt see vacuum.
also in vikash's vacuum hose reference, he shows a union between the turbo nipple and the bcs, mine is just a straight hose with no union. should i look into this?

That union reduces the size of the hose. There is a restrictor orifice ball in the stock hose somewhere in the boost control lines to help the pulsation issue.

RJ93SS wrote:would line I work?

No that won't work since that line does not see vacuum/boost when the throttle is closed.

thanks guys, i'm going to tery out a few things and post results after.


does anyone know where i can get these restrictors?

update. i just traded my blitz bov for a hks ssq and the hks came with a plastic tee with a plenum.

the hole was probably 1/64 or so.

i rigged it up so both my gauge and my bov ran after the plenum and low and behold my gauge does not shake anymore.

i just hope im not masking some other issue.