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Old 11-22-2006, 01:49 AM   #1
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Default polishing LIM runners?

I just had a thought? Would removing the rough casting inside the LIM runners be of any benefit to the engine? I have ported LIM from wbodystore

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As you can see I can reach the other runners because the opening is enlarged so it would be easy for me.

thanks in advance
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Old 11-22-2006, 09:38 AM   #2
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As you can see, the runners are larger at the entrance, closer to the plenum. You need to concentrate more where the runners narrow down before entering the head. If you look closely, you'll probably notice they narrow considerably in the last 1/4" or so. Every LIM I've seen (of 4 different 3800 engine types) have had this problem.

Much to gain? Sure. Any improvement is an improvement. Increasing port velocity is a big benefit to efficiency and power (better fuel atomization and cylinder filling during the intake cycle). But you can also make it worse. SSEiMatt93 had bad results with his. We still don't know why. Mine works like a champ, but I have a mutant setup and not much basis for comparison. BillBoost followed my LIM work on Black94SSEi'* car with good results. I recall they only had an hour to dedicate to it, but they still gained some top-end grunt.

Standard warnings apply. You can screw it up and generate scrap. Don't do it in secret. If you have questions, ask someone who'* done it. Odds of success go up dramatically. Just like the question in the GenV supercharger swap topic in Forced Induction. Standard warnings apply, particularly with an investment like yours.

Some techniques are discussed somewhat in the Tale of 3 Superchargers, pages 2 and 3 in Forced Induction.
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Old 11-22-2006, 09:43 AM   #3
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Quote:
Originally Posted by willwren
As you can see, the runners are larger at the entrance, closer to the plenum. You need to concentrate more where the runners narrow down before entering the head. If you look closely, you'll probably notice they narrow considerably in the last 1/4" or so. Every LIM I've seen (of 4 different 3800 engine types) have had this problem.

Much to gain? Sure. Any improvement is an improvement. Increasing port velocity is a big benefit to efficiency and power (better fuel atomization and cylinder filling during the intake cycle). But you can also make it worse. SSEiMatt93 had bad results with his. We still don't know why. Mine works like a champ, but I have a mutant setup and not much basis for comparison. BillBoost followed my LIM work on Black94SSEi'* car with good results. I recall they only had an hour to dedicate to it, but they still gained some top-end grunt.

Standard warnings apply. You can screw it up and generate scrap. Don't do it in secret. If you have questions, ask someone who'* done it. Odds of success go up dramatically. Just like the question in the GenV supercharger swap topic in Forced Induction. Standard warnings apply, particularly with an investment like yours.

Some techniques are discussed somewhat in the Tale of 3 Superchargers, pages 2 and 3 in Forced Induction.
Thanks for your Advice Will. It is greatly appreciated.
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Old 11-22-2006, 09:47 AM   #4
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No problem.

Maybe Boosty and Black94SSEi can pop in here and give a run-down on that one.

The porting I did on the LIM I'm running right now went a little deeper and complicated, but part of that is because my injector bosses are in the LIM, not in the heads like your S2.
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Old 11-22-2006, 10:15 AM   #5
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Default Re: polishing LIM runners?

Quote:
Originally Posted by OLDsman105
I just had a thought? Would removing the rough casting inside the LIM runners be of any benefit to the engine? I have ported LIM from wbodystore
Bill boost ported my intake when we had it out to do the gaskets and I do feel a noticeable difference. By porting the intake, the engine is breathing better and bringing in more air flow which is probably cooler and less turbulant due to the porting.

Bill did an awesome job and Im glad it was done. just be careful and make sure your port matching to the heads. There was allot of measuring going on.

Heres a pic of my Intake after being ported.

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Old 11-22-2006, 10:22 AM   #6
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And mine (currently on the car):

Before



Measuring:



After:
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Old 11-22-2006, 11:04 AM   #7
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Default Re: polishing LIM runners?

Quote:
Originally Posted by OLDsman105
I just had a thought? Would removing the rough casting inside the LIM runners be of any benefit to the engine?
You can enlarge the port openings, but you want to leave the roughness down in the runners for good fuel atomization. The sand casting takes the large dropplets of fuel and breaks them up into a fine mist. You can tell by willwren'* pics that he enlarged the openings, but left the runners intact.
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Old 11-22-2006, 12:01 PM   #8
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Default Re: polishing LIM runners?

Quote:
Originally Posted by MACDRIVE
Quote:
Originally Posted by OLDsman105
I just had a thought? Would removing the rough casting inside the LIM runners be of any benefit to the engine?
You can enlarge the port openings, but you want to leave the roughness down in the runners for good fuel atomization. The sand casting takes the large dropplets of fuel and breaks them up into a fine mist. You can tell by willwren'* pics that he enlarged the openings, but left the runners intact.
Mac, what you say makes no sense. Can you see where my injector boss is? There'* no atomization taking place in the LIM whatsoever. It'* injecting at the end of the runner. Or in the heads themselves on a S2 L67.

Your car is the same. I have an L36 LIM in for porting (the L36 may benefit the most from this as the runners are UGLY at the exit) and it also injects RIGHT at the end of the runner.
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Old 11-22-2006, 12:31 PM   #9
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Olds.. my findings are that you need a caliper/micrometer set to measure. There'* very little gain on the S2 L67 that I see.
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Old 11-22-2006, 12:41 PM   #10
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Default Re: polishing LIM runners?

Quote:
Originally Posted by willwren
Quote:
Originally Posted by MACDRIVE
Quote:
Originally Posted by OLDsman105
I just had a thought? Would removing the rough casting inside the LIM runners be of any benefit to the engine?
You can enlarge the port openings, but you want to leave the roughness down in the runners for good fuel atomization. The sand casting takes the large dropplets of fuel and breaks them up into a fine mist. You can tell by willwren'* pics that he enlarged the openings, but left the runners intact.
Mac, what you say makes no sense. Can you see where my injector boss is? There'* no atomization taking place in the LIM whatsoever. It'* injecting at the end of the runner. Or in the heads themselves on a S2 L67.

Your car is the same. I have an L36 LIM in for porting (the L36 may benefit the most from this as the runners are UGLY at the exit) and it also injects RIGHT at the end of the runner.
Right it doesn't matter in the Intake manifold due to the injector placement..

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