Optispark vent hose assembly
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From: Melbourne Fl.
Optispark vent hose assembly
I've got a clogged filter/orifice in the Optispark vent hose assembly that I need to replace. The part number for this assembly is 12555323 but after doing a search I only see it that it is used for the F body and full size car LT1 applications. Is this also OK for the Corvette? The discontinued assembly specified for the Corvette is 12558921. What is the difference? Can the 12555323 be modified to work in place of the discontinued part?
Warren
Warren
Last edited by Warren Seale; Oct 23, 2018 at 01:31 PM.
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From: Melbourne Fl.
There is one thing that the LT1/LT4 engines with the vented Optispark need and that is a clear functioning vacuum line. I lost a low mile GM (Delphi) Optispark due to the filter being clogged up and not allowing the distributor to vent properly. A word of warning to those with this engine; periodically check to be sure the vacuum line is functioning down at the distributor.
Last edited by Warren Seale; Oct 23, 2018 at 08:17 PM.
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Pull the hose that goes to the intake manifold off of the distributor housing and measure the vacuum with a gauge. There should be manifold vacuum there. As a last resort you can use your finger to see if there is suction. I don't like to measure it on the intake hose side where it connects to the engine air intake because some air flow can enter the distributor at the electrical connector thus you may not see manifold vacuum at that location.
Last edited by Warren Seale; Oct 23, 2018 at 08:18 PM.
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Thanks for the suggestion. I contacted the Optidoctor. He said that the 12555323 will work in place of the 12558921. The difference is minor and is related to the hose lengths being slightly different.
Warren
Warren
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From: Las Vegas - Just stop perpetuating myths please.
Pull the hose that goes to the intake manifold off of the distributor housing and measure the vacuum with a gauge. There should be manifold vacuum there. As a last resort you can use your finger to see if there is suction. I don't like to measure it on the intake hose side where it connects to the engine air intake because some air flow can enter the distributor at the electrical connector thus you may not see manifold vacuum at that location.
Thx.
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Thread Starter
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From: Melbourne Fl.
Le Mans Master
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From: Las Vegas - Just stop perpetuating myths please.
Oh, so you are measuring 15 to 20"Hg on the Opti side of the check valve? I guess I meant to ask between the orifice and the Opti. We may not be looking at the same location. But I am very interested to find out the vacuum reading between the Opti and the downstream orifice. If you measured there it would be nice of you to post what you found but I thank you for your help already. 
Le Mans Master
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From: St. Charles MO
Oh, so you are measuring 15 to 20"Hg on the Opti side of the check valve? I guess I meant to ask between the orifice and the Opti.
Le Mans Master
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From: Las Vegas - Just stop perpetuating myths please.
Thank you very much Warren for your unbiased report. I didn't want to drag you into a heated argument but your independent measurement is very helpful to understand what is going on inside the opti. That should be the same as about 7psi to 10psi differential inside of the opti itself compared to atmosphere. Well I'll leave it at that as I don't want to ruin your thread here.
Thank you again.
Thank you again.
Le Mans Master
Joined: Aug 2015
Posts: 6,103
Likes: 1,986
From: St. Charles MO
Thank you very much Warren for your unbiased report. I didn't want to drag you into a heated argument but your independent measurement is very helpful to understand what is going on inside the opti. That should be the same as about 7psi to 10psi differential inside of the opti itself compared to atmosphere. Well I'll leave it at that as I don't want to ruin your thread here.
Thank you again.
Thank you again.