L27 LIM P&P - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 07-05-2007, 10:26 PM   #1
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Default L27 LIM P&P

I got bored. I've pretty much come to a standstill on the SSEi until I get a few extra hands and some good clear weather. So I started looking at the L27 intake manifold that came from the core motor I used last year.

It, like the L67 manifold, could benefit from a decent port/gasket match, and the water passage inlet/outlet could stand to be enlarged as well. But something the L67s do NOT have are long-runner ports. The casting in those ports are quite rough. Not only that, there are some overlappage between the upper manifold sleeve and the lower intake. (For those not in the know, the upper manifold in the L27s actually has 2 parts).

Now, I've got alot on my plate as it is. But I just had to start on one runner, just to see how much material could be removed. No pics available yet, but rest assured there are gains to be had.
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Old 07-05-2007, 10:39 PM   #2
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what year are you porting?
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Old 07-05-2007, 10:45 PM   #3
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Manifold is from a 93. But it will go into the '94 when I do the lower intake gaskets in the fall.
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Old 07-05-2007, 10:54 PM   #4
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oh man neither one of em is a 92 though. well i guess i have to find one to look at myself.
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Old 07-05-2007, 11:19 PM   #5
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I honestly see no reason why this wouldn't work for the 92. I could be wrong, but the lowers I think are the same. And if not, I am sure something could be fabbed up to plug the EGR hole in the composite mani.
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Old 07-05-2007, 11:25 PM   #6
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but i have the aluminum upper
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Old 07-05-2007, 11:26 PM   #7
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The L27 has alot of potential for another reason. The runners are long and EXPOSED. Long runners produce low-end torque. But by polishing them CAREFULLY and meticulously, you can increase the port velocity and gain mid-high range power without sacrificing bottom end.

Because the ports are not as oddly designed (changing shape and size at the same time) like the L36, the work should go easier.

Make sure you don't over-port them beyond the head port dimensions.
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Old 07-05-2007, 11:30 PM   #8
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that would be good. i dont wanna lose my bottom end power just to pick up a few up top.
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Old 07-06-2007, 11:57 PM   #9
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Quote:
But by polishing them CAREFULLY and meticulously
How do you propose one should go about smoothing out and polishing the runners?
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Old 07-07-2007, 12:02 AM   #10
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The same way I've ported and polished umpteen superchargers LIM'*, and cylinder heads in the last year. A dremel is the safest bet for a first-timer. Mistakes don't go as deep as they do with air tools.
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