Go Back   LS1TECH > SBC-BBC-LT1-LT4 PERFORMANCE > LT1-LT4 Modifications
Sign in using an external account
Register Forgot Password?
Search

LT1-LT4 Modifications
1993-97 Gen II Small Block V8

Opti vacumn reading?

Reply
 
Thread Tools Search this Thread
Old 04-20-2012, 04:49 PM   #1
TECH Addict
Garage is empty, add now
 
Trader Rating: 0
Join Date: Apr 2008
Posts: 2,037
Default Opti vacumn reading?

if you measure vacumn at the blue nipple on intake elbow should it = vacumn from the intake manifold?

I get 18 at manifold. 18 at bottom of hose with 2 check valves that goes to bottom of Opti BUT only 4" of vacumn when reading from the blue nipple.

new opti and vent harness

does the opti itself restrict vacumn or would my reading suggest new opti cap is not sealing?

anyone have a vac gauge and can read theirs to see wtf, thanks

FSM states "until needle slowly reaches manifold vacumn"...which suggests it should eventually read 18" at blue nipple...not 4"
__________________
'96 BBB
383/T56
BALLSS is offline   Reply With Quote
Old 04-20-2012, 05:15 PM   #2
TECH Senior Member
Garage is empty, add now
 
RamAir95TA's Avatar
 
Trader Rating: 2
Join Date: May 2005
Location: South Jersey
Posts: 9,485
Send a message via AIM to RamAir95TA
Default

There is a check valve AND a flow orifice. Orifice = reduced vacuum.
__________________
95 T/A AI 200cc stock castings, 383, Performabuilt 4L60E, Ford 9", Tuned by PCMforless 3340#,
10.81 @ 124.16, 1.43 60' Video of 10-second pass 455whp, 445tq - Dyno Vid

LT1 PARTS For Sale, MSD Opti, steam crossover tube, BMR swaybar, MAF, etc.
RamAir95TA is offline   Reply With Quote
Old 04-20-2012, 07:04 PM   #3
TECH Addict
Garage is empty, add now
 
Trader Rating: 0
Join Date: Apr 2008
Posts: 2,037
Default

Quote:
Originally Posted by RamAir95TA View Post
There is a check valve AND a flow orifice. Orifice = reduced vacuum.
I understand the 'check" valves ....but when I measure vacumn at the end of that line it reads exactly what the vacumn is direct from intake manifold. The line with 2 valves is the "draw" vacumn into Opti. The other vent hose has no valves and goes from bottom of Opti to rubber air duck elbow...it reads 4" there suggesting the "Opti" itself is not holding vacumn

My ? is should the measured vacumn at blue nipple read the same as the draw side after check valves.

In my case it does not

18" in and 4" of vacumn out.

FSM says vacums should "slowly" climb to what intake manifold vacumn is...it stops at 4"
__________________
'96 BBB
383/T56
BALLSS is offline   Reply With Quote
Old 04-20-2012, 09:46 PM   #4
TECH Junkie
Garage is empty, add now
 
shbox's Avatar
 
Trader Rating: 0
Join Date: Dec 2008
Location: Little Rock, AR
Posts: 3,518
Default

I don't think you should be getting 18" going into the opti, but I have not actually measured vacuum there. I would expect the blue valves to restrict and lower the vacuum before it gets there.
I have tested vacuum where the blue elbow connector is on the intake elbow and get a maximum of 8" back toward the opti at any engine running throttle level. I also tested with a vacuum tester at the same spot (engine not running) and was able to pull vacuum through the hose, into the opti and back to the check valves. It held vacuum.
You could test the seal of the opti by using a vacuum tester.
shbox is offline   Reply With Quote
Old 04-21-2012, 01:29 PM   #5
TECH Addict
Garage is empty, add now
 
Trader Rating: 0
Join Date: Apr 2008
Posts: 2,037
Default

Quote:
Originally Posted by shbox View Post
You could test the seal of the opti by using a vacuum tester.
I did my Mighty Vac hooked up to draw side of Opti with other line pluged...it 'slowly" bleeds off to 0. It holds 4" while engine running but won't go higher. The 2 valve line leading to the Opti builds and holds solid at 18"

My old opti would not even let vacumn build up.

should the Opti be 100% sealed?

Since the engine vacumn system is tied into opti I would think it should hold vacumn otherwise a "leak" in the system would effect motor.

I am chasing a stumble under load problem and while this opti not holding vacumn issue may not be related...I want to know if it should be 100% sealed.

would have to pull it and rtv or dialectic grease on inner seal.

I would think the rear bearing on Opti would prevent 100% seal ability...it has to spin???
__________________
'96 BBB
383/T56
BALLSS is offline   Reply With Quote
Old 04-21-2012, 05:52 PM   #6
On The Tree
Garage is empty, add now
 
Trader Rating: 0
Join Date: Jan 2012
Posts: 179
Default

I do not believe it seals 100 percent. I have messed with several opti's on the bench trying to achieve a 100% vac seal and not been able too. The housing it's self has the screen behind the optical sensor I can never get to seal as well as the shaft seal. I can pull vacuum on it but it won't hold vacuum.
Rodinator1234 is offline   Reply With Quote
Old 04-22-2012, 11:03 AM   #7
TECH Addict
Garage is empty, add now
 
Trader Rating: 0
Join Date: Apr 2008
Posts: 2,037
Default

yeah I bench tested the Opti with Mighty Vac and it will bleed off vacumn. The biggest hole obviously is where the 4 pin connector plugs in.

I just skimmed some dialectic grease on cap seal and bolted back togeather and 4 pin plug seal. opti is venting but getting = manifold vacumn will never happen as FSM suggests.
__________________
'96 BBB
383/T56
BALLSS is offline   Reply With Quote
Old 04-22-2012, 11:03 AM
LS1Tech
Pontiac Firebird




Paid Advertisement
Reply


Tags
bottom, check, directly, elbow, hose, intake, lt1, modifying, opti, vacuum, valve, vent


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are Off



Join Ls1Tech

All times are GMT -5. The time now is 08:12 PM.


Powered by vBulletin® Version 3.8.7 AC1
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Advertising - Terms of Service - Privacy Statement - JOBS
Emails & Contact Details