Porting LIM; do any good for a Series II n/a? - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 02-02-2007, 11:47 AM   #11
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My daughter gave me an idea last night regarding how to determine what needs to be removed on the LIM ports to match up to the head ports...

What if I did this:
1) Roll out two flat rectangles of modeling clay (Plasticene) about the height, width, and and thickness of LIM gaskets.
2) Plug the head ports with rags (to ensure no foreign material enters).
3) Oil the mating surfaces of the LIM and heads lightly (just as a release agent).
4) Lay my clay "gaskets" down as if they were LIM gaskets.
5) Lay the LIM in place, and press firmly.
6) Remove LIM, and gently peel away the clay "gaskets".

As long as I did not stretch the clay, I assume this would give me a perfect model impression of whatever port offset there might be...

Only question is, how can I ensure, in step 5) above, that I'm laying the LIM down in exactly the right place? I suppose I could lightly bolt it in during that step...
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Old 02-02-2007, 11:59 AM   #12
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I suppose I neglected the fact that the heads aren't gasket matched? I assumed if you gasket match the heads and intake, all you need to do is line the intake up properly. My mistake I guess
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Old 02-02-2007, 12:17 PM   #13
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I hadn't intended to port the heads...so that gets me to wondering, since the heads aren't gasket-matched, is porting the LIM going to matter? After all, without gasket-matching BOTH the LIM and heads, isn't there inevitably going to be a sizeable gap (or "ridge" or "lip" or "step," whatever you want to call it) between the LIM-gasket-head no matter what?

I am sure it would be unsafe to try to fil that gap with anything, right?
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Old 02-02-2007, 12:29 PM   #14
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A method you can use to exactly match the head ports is to take a clean white sheet of paper, pencil, and CLEAN heads. Pin the paper over the head using the bolt holes and a couple wood dowels or something similar. Use the pencil (side of lead point) and rub around the head ports. This gives you and exact pattern of the head ports that you can now place over the LIM to see what material needs removing. If necessary, use an exacto knife to carefully cut out the head port openings in the paper. Viola!
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Old 02-02-2007, 12:33 PM   #15
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I was thinking of something similar when my daughter suggested the clay.

Wouldn't it be best if the "paper" was the same thickness as the gasket...maybe some thin cardboard?
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Old 02-02-2007, 12:34 PM   #16
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Alignment of the LIM to the heads after port-matching the LIM isn't critical. The thickness of the gasket gives you an 'alignment buffer'. This is the reason the gasket openings are larger than the head ports to begin with.

Your head ports are 0.9" wide by 1.9" tall. Your LIM ports are fooked. Because of the odd shaped casting, you won't even be able to measure them.
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Old 02-02-2007, 12:52 PM   #17
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willwren,

Thanks for that. It helps greatly to ease my mind about this project.

I think I've got the porting part down...tell me more about polishing the runners.
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Old 02-02-2007, 12:57 PM   #18
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I don't think you really got my point above. This has only been done to one car so far, per my instructions. Results were good. I'm doing the LIM for the second car. After that, we may want to say it'* worth it.

Until then, I'm not taking responsibility for helping anyone else potentially destroy their LIM. My suggestion at this point would be to have patience for a couple weeks.

If you choose to go it alone, you can pick your poison for smoothing the runners. Remember that polishing won't gain you but about 1/2 a percent. The other 99.5 percent will be in smoothness.

Don't modify the geometry around the injector boss. Don't even touch it with a tool. The way the air flows over that is critical for fuel atomization.
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Old 02-02-2007, 01:06 PM   #19
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willwren,

Don't worry, I won't hold anyone else responsible for my actions!

I won't even consider doing this without first getting a backup LIM, just in case I "F" it up, or I don't like the results.
In any case, it will be at least 3-4 weeks before I get around to doing the work.
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Old 02-02-2007, 01:25 PM   #20
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Good reading here:

http://www.bonnevilleclub.com/forum/...ic.php?t=66207


And there were specific reasons why I posted that, as well as specific reasons I removed my Supercharger porting/polishing guide from the Forum and public in general.


Too many people were jumping into it without bothering to really study my work or even ask questions. It also went as far (on more than one project) if someone got a hint of what I was working on next, they'd run out and try to beat me on it, butchering the part in the process. Just because they thought I was working on something, and they either didn't have the patience to wait for my results (which I ALWAYS share after proving the concepts) or were just trying to 'beat' me. Then we have the people who port and polish secretly to 'surprise' everyone. But because they were secretive, they didn't ask the right questions, and screwed up.

So by removing the information from the public eye, I force people to ask the right questions.

I do alot of research and generate a ton of scrap. I'm well-versed in flow dynamics, thermal analysis, and a few other pertinent skills that help me do what I do. I've ported several different parts for 4 different types of 3800 engines in the past. But until now, the L36 LIM has been largely un-touched by human hands. My goal is to prove that SOME people can possibly do this at home for little or no cost.
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