6 good reasons why NOT to supercharge an L27 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-07-2008, 09:40 PM   #1
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Default 6 good reasons why NOT to supercharge an L27

Started the autopsy this evening on the FrankenMotor. First thing done was to drain the oil, of course. Sparkles aplenty in the new crude....so I says to myself, "Oh, spun bearing." So, I pull the pan afterwards and I see silver slivers all in the bottom. Ok, no big deal...kinda was expecting that anyways. Now, its off to pull the caps from the rods.






Every one of the bearings are damaged. Number 2 bearing had ALL of its first layer wiped out, and the rest were on the way. No grooves to speak of, and the journals on the crank look to be in pretty good shape.

Funny thing though...the bearings state they were made in 10/92...which was the same date code the OLD motor was.
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Old 05-07-2008, 09:44 PM   #2
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That says a lot... Those bearings looked like brand new a good while back... I remember looking at them and could not believe how good they looked... Amazing find...

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Old 05-07-2008, 09:47 PM   #3
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My theory is the rods couldn't handle the increase in (effective) compression compounded by boost. L27 rods can't be expected to, and weren't designed to. The rods will give a little, twist, and bend on each cycle, stressing the bearings more than they would with L67 rods.

This may be the answer we've wondered about for quite some time.
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Old 05-07-2008, 09:49 PM   #4
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Do you have another thread on the "FrankenL27"? Something must have went wrong somewhere because my supercharged LN3 had great oil analysis reports
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Old 05-07-2008, 10:03 PM   #5
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Brad put a significant amount of miles on his and fully tested it to the limits that an L67 should be tested.

I don't recall you putting many miles on yours.
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Old 05-07-2008, 10:28 PM   #6
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This L27 initially had the Gen 2 topend on it. Once I did the OBD2 conversion, it went Gen 3 WITH a 2.2" pulley. My fueling was spot-on as evidenced by the color of the O2 and the spark plugs, so there was no running lean...in fact, I was running richer than normal as a buffer zone.

Tomorrow the heads will come off and the pistons removed from the block. We will see what lies beneath at that time...
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Old 05-07-2008, 10:29 PM   #7
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thanks for filling me in...my setup was otherwise stock and ran about 20k miles in that configuration, starting at 152k miles on the LN3
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Old 05-08-2008, 01:52 AM   #8
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It might be able to take stock boost of the L67 setup, but anything more than that is probably too much for it. Were these OE bearings, or rebuild ones?

Most engines can take a reasonable amount of boost and stay reliable. 6 or 7 psi depending on how hard/fast it comes on, is certainly do-able in most lower compression engines.

But a Gen 3 M62 running a 2.2 is definitely going to stress it much more.
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Old 05-08-2008, 08:50 AM   #9
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When I first did the L27 swap, I convinced myself to NOT mod the hell out of the car. But once the transmission got done, reason went out the window

Could it have held together with the stock Gen 2? Almost positive it could, esp. if I put a 2.7 pulley on it...at the most run 6 or 7 psi on it, and it probably would have last as long as I needed it to. But there were...other entities,,,that wanted to see just how far this motor could go.

Now we know

Am I mad or disappointed with the outcome? Nope. It'* actually a blessing in disguise, as I no longer need to rely on premium squirrel pee for fueling. But this isn't the end of the story, as this motor will get rebuilt. My initial findings on this motor tell me it'* easily fixable with just a crank kit...this motor is spotless inside, and the block requires NO work at all. I *might* need to replace the cam bearings and the crank bearings, but other than that...rebuilding this beast should cost me around 600 bucks, if that.
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Old 05-08-2008, 01:13 PM   #10
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My findings for the day:

Piston rings are sharp!!

Now then, the pistons are out. Skirt scuffing on all of them...intake side on the front bank, exhaust side on the rear. This may be normal, or it may not be. All rings are present and accounted for, and show no damage. Pistons themselves are in excellent shape, aside from the scuffing.

Pics will be up later.
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