While does this hole do? (89 TPI pics)
Thread Starter
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
While does this hole do? (89 TPI pics)
I finally started working onthis thing and discovered one in each port. Anyone know the function of it?
BTW, this is NOT finished by any means, just wanted to find out throw a few pics out and get an answer.
This is the pic with the hole Im referring to. Ignore all the metal shavings(dark stuff)
I'll get some more pics when its done. still have a lot of cleanup to do. I dont know how people do this for a living!
BTW, this is NOT finished by any means, just wanted to find out throw a few pics out and get an answer.
This is the pic with the hole Im referring to. Ignore all the metal shavings(dark stuff)
I'll get some more pics when its done. still have a lot of cleanup to do. I dont know how people do this for a living!
Last edited by cv67; Feb 2, 2006 at 09:48 PM.
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Michael S. Palmer
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Originally Posted by 89 Paul in Cal
That's the EGR. It'll dilute the A/F ratio if altered(don't ask how I know 
)
)EGR gases go through manifold to EGR valve , then up small tube by runners through plenum floor and exit at two holes behind the TB.
The holes in question are redundant idle air holes.
On early setups the idle air goes direct from the back of TB , through the base of the plenum (early plenums have two cast in passages underneath whereas late has only one) down a small tube on the drivers side(?) through the manifold`and exit through the mentioned holes directly before the ports.
May pick up cold start as well
In later setups the idle air goes straight in to the plenum
Same base manifold casting is used for all,machined with the holes even though not used.
Although not used in late L98s GM appears to have returned to the port idle air on the LT1 , my LT1 manifold has the holes and a passage behind the TB.
Many posts about poor idle quality on LT1s after fitting aftermarket TB where the new TB is open at the plenum and does not connect to the internal passage.
Last edited by rodj; Feb 3, 2006 at 07:23 AM.
Thread Starter
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
No, Ill try and get one this weekend as Ill try be trying to finish it and get started on the runners.
Interesting, Ive never seen any info on this before. I thought I went through the wall when I first saw it. 
The holes in question are redundant idle air holes.On earlier setups the idle air goes direct from the TB port , through the base of the plenum down a small tube on the drivers side(?) through the manifold`and exit directly before the ports.
In later setups the idle air goes straight in to the plenum
Same manifold casting is used for all.
In later setups the idle air goes straight in to the plenum
Same manifold casting is used for all.
Last edited by cv67; Feb 3, 2006 at 02:34 AM.
Burning Brakes
Joined: Mar 2005
Posts: 1,164
Likes: 5
From: Middle Earth
there are a few holes in these setups that do nothing, when i did my SR install I found places where there were all kinds of build up b/c a line lead to nothing and all the **** flying through it for 16 years had just accumulated.
Thread Starter
Team Owner
Joined: Oct 2004
Posts: 81,241
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From: altered state
St. Jude Donor '05
Originally Posted by BrianCunningham
Sheesh, did you need to get out the vasoline for that one?!
