I put my old LIM back on... - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-28-2008, 11:33 PM   #1
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Default I put my old LIM back on...

... because ZillaMotorsports ported it for me.

I didn't take any pics because... well... I've seen it all before fairly recently. I'll go get a key shot here in a few minutes.

I'm feeling better mid-range power, the kind that rips the tires loose when you mash it and it downshifts to first. My test drive speeds were pretty limited, so I can't tell you about top end power just yet.
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Old 04-28-2008, 11:55 PM   #2
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Here we go. This was a hard pic to get.

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Old 04-28-2008, 11:56 PM   #3
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Center of the pic here (between two nosedrives):
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Bottom right here (custom laser engraving on the bypass cover):
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The work included some corrosion pitting repair around the coolant ports. All in all, it was in pretty good shape to begin with.

If history repeats itself, it'll really come into it'* own in about 100 miles as the PCM learns it. Glad you like it, and I wish I'd turned it around quicker.
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Old 04-29-2008, 10:09 AM   #4
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That */C setup looks nasty. Have you ever had it Dyno'd before? It would be interesting to see what you car puts down now.
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Old 04-29-2008, 10:15 AM   #5
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Your PLIM makes me extremely jealous.

I need to get my *** out to the U-pull it to grab the LIM off a 92 PA Ultra there, and get it shipped out to ZiLLA Motorsports!
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Old 04-29-2008, 11:02 AM   #6
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I got one....


Completely useless to me now


But dammitman...that car felt hella quick before it played the tune "pop goes the piston".
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Old 04-29-2008, 11:09 AM   #7
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Quote:
Originally Posted by sandrock
I got one....


Completely useless to me now


But dammitman...that car felt hella quick before it played the tune "pop goes the piston".
Oooh... PM me with more info and pics.
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Old 04-29-2008, 11:14 AM   #8
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I got no pics of the porting...got installed pics left and right though. My OBD2 thread has a few money shots.

But this is now starting to turn into hijack...so to turn it back around...Wren, did you open up just the ports and the coolant passages (I KNOW you did that much), or did you also include the SC inlet area?
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Old 04-29-2008, 11:52 AM   #9
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Default Re: I put my old LIM back on...

Quote:
Originally Posted by J Wikoff

I'm feeling better mid-range power, the kind that rips the tires loose when you mash it and it downshifts to first.
Every LIM I've ported for myself or others has had the same effect. Including the two we just installed over the weekend. The L36 LIM took me just over two hours, but another hour of 'detail work' in the runners would have been nice. Other work and a tight mod schedule prevented it, but in the long run, would have made little difference:

http://www.bonnevilleclub.com/forum/...ic.php?t=97624

You'll notice in that topic the VERY good alignment of the LIM to the head ports on install. If you don't have your motor opened up during porting, you'll need to rely on very good experience to keep the port spacing right (based on port-port centroids). This is critical to maintain equal port velocity across all 6.

If done correctly, a very noticable midrange pull will be felt. It may or may not raise the HP peak, but it gets into it quicker through the midrange, 'flattening' the HP curve a bit, and provides a much improved throttle snap (response) off the line. This is true for SC or NA LIM'*.

Remember, the WORST from the factory, and gains the most is the L36.
Next is the S1 L67 (and L27).
The best from the factory is the Series 2 L67. This gains the least matching to factory heads, but if you don't mind 30 minutes of cleanup, you will notice it.

There are great variances in match from LIM to LIM of the same type. As well as casting flaws that push one cylinder 'out' a bit compared to the rest on some LIM'*.

There is a little more spooky detail work you can do with the PROPER precautions before installation. AFTER insuring a good port match on the LIM, you'll be left with the ideal dimensions of:

LIM.......0.85x1.85" with corner radius matched to head ports (improved to ~1/8")
Heads...0.90x1.90"

This STILL leaves the gasket cavity at 1.0" by 2.0" (roughly) causing a small mismatched cavity between where the AF mixture can swirl, eddy, and start to expand before necking back down into the head. This can be improved by LIGHTLY chamfering or rounding off the entrance of the cylinder head port. EXTREME caution should be used if this is done with the heads on the car. Stuff the ports, tape everything off, and have a good shopvac and magnet ready for each port. An exaggerated detail I worked up in CAD:

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This is the original concept I worked up a couple years ago.

Refined to the dimensions I port to now (and stated in this topic) it would be this AFTER porting BEFORE chamfer:
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AFTER porting and AFTER chamfer:
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Think of it as not much more than smoothing off the sharp entrance to the cylinder head intake port to ease the transition and maintain port velocity. This has been done on several cars with great success, including the two shown in the link above from this weekend'* work at my house.

DISCLAIMER:
I'm not responsible for a anything you screw up on your car, and I'm warning you now that if you've never done this before, do it the first time with someone who HAS, and has also DEMONSTRATED success with it.
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Old 04-29-2008, 11:54 AM   #10
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Quote:
Originally Posted by sandrock
I got no pics of the porting...got installed pics left and right though. My OBD2 thread has a few money shots.

But this is now starting to turn into hijack...so to turn it back around...Wren, did you open up just the ports and the coolant passages (I KNOW you did that much), or did you also include the SC inlet area?
Opened up the ports to 0.85x1.85 (or a hair over that), cleaned up the flashing on the coolant ports, and lightly broke the inlet edge of the SC port. The large square opening for the SC is typically a non-issue.

FYI, in the pics above, LIM is blue, gasket is gray, head is green.
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