My L36 LIM Porting (with pics)...NOW WITH DATA! - Page 7 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-05-2007, 02:44 AM   #61
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That is excellent information. Thanks a lot for doing such thorough testing and tuning. Seems to show a great increase as a result of simply cleaning up the LIM.
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Old 04-05-2007, 12:05 PM   #62
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Old 04-05-2007, 12:13 PM   #63
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Not sure why you're calling this 'overporting'. He port-matched to the cylinder head inlets only, not to the gasket frame opening.
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Old 04-05-2007, 01:33 PM   #64
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Old 04-05-2007, 01:58 PM   #65
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Quote:
Originally Posted by Dirthead Racing
I was going to comment on being impressed with your ablity to get a VE over 1.0 :o .....but I read further and understand how now . Nice improvements for "overporting" the intake. Makes me wonder the % difference between properly porting and "overporting". I only say this because people have been "gasket matching"(be it right or wrong), for a long time. Any other peoples results to draw from? Could probably do a % increase comparison over 20-100 points along the curve. Probably going to be hard to duplicate the conditions and mods for two different cars though . Good theory, hard to execute.
Getting a VE over 1.0 is not at all surprising...breathing mods (cams, rockers) do this routinely. After all, if it was not possible to go above VE 1.0, the torque on an n/a L36 would be "capped" somewhere around 240-250 ft lbs (and I'm sure there are some n/a guys around here pulling more torque than that).
Once I put some more mods on this puppy, I expect the VE to climb even higher

While I did not gasket-match, I AM ever so slightly overported. I tried to snap some photos of my head-gasket-LIM port matchup, but my crappy snapshot digital camera couldn't focus well enough to get a meaningful picture. I did whip up this quicky diagram in PowerPoint, though (imagine you are looking down inside the LIM intake runner from the top):



BLUE is the head port.
GREEN is the gasket hole.
RED is my crude drawing of the ported LIM port.

The head port, gasket, and LIM port lined up perfectly across the top and the left.
The head port and LIM port lined up perfectly along the bottom, though the gasket hole was a bit "oversized" there.
Along the right (where I drew the bracket), the LIM port is ever-so-slightly larger than the head port, less than 1/32" at the bottom, tapering up to less than 1/16" near the middle. The gasket is also "oversized" there.
At the top right, where the injector boss is (where I drew the arrow), the LIM port is "outsized" from the head port by a good 1/8"; however, I didn't grind anything away in that area...it was like that even before I ported the LIM.
(I'll bet there would be even more gains if I shaved the head port in the area of the injector boss...but I lack the time, tools, and cojones for that )

BTW, all the before-and-after measurements of my LIM port are in this thread-hijacking I performed on another member'* LIM porting account:
http://www.bonnevilleclub.com/forum/...ic.php?t=74427

What does all this mean?
-Do not gasket match the LIM ports (unless you're gasket-matching the head ports, too)...you'll definitely be overported if you do.
-If I had it all to do over again, I would measure and lay out more precisely before picking up the dremel tool.
-Even my amateurish LIM porting worked out well (so far...knock on wood!)...you are probably right that more precise work would be even better.

EDIT: I will have this all to do over again, because if this mod doesn't blow my engine up or kill my gas mileage, I'll be porting a LIM for the wife'* '04 LeSabre later this year
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Old 04-05-2007, 03:45 PM   #66
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Cool...now imagine if you repeat the proceedure on the exhaust side!! You'll find equal degrees of misalignment there too, even SLP and TOG headers have a significant problem if left untouched

See you over at DHP at some point...

Cheers,
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Old 04-06-2007, 01:48 PM   #67
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MORE RESULTS:

I began MAF tuning on the ported LIM. As predicted, there was little change in the actual MAF curve (i.e., grams/sec vs. MAF Hz)*; however, I am hitting higher MAF Hz values than ever before:

Highest MAF value hit at WOT in scans:
Stock LIM: 8625 Hz
Ported LIM: 9000 Hz

To my mind, this confirms that my engine now sucks more.

*(Except of course, at high MAF Hz values)
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