SERIES 1 L27/L67 COMPARISON - Page 3 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 10-04-2004, 09:20 PM   #21
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Yeah what I was curious about is if maybe the naturally aspriated use press fit pins while I know the supercharged use floating pins. But on to current news:

I've been able to find out some information on differences between years as far as pistons go.

The 1988-1993 piston pictured here:



Has a compression ring height of 1.366 and a head recess 3.100" in diameter at .250" deep. The rings were organized with two 1.5mm and one 3.0mm. The pin diameter was .9054" and offset. This piston was the same between Vin C and Vin 1.


The 1993-1995 piston pictured here:



Obviously underwent some design changes. It has a compression ring height of 1.443 and a head recess 3.100" in diameter at .295" deep. The rings were organized with one 1.2mm, one 1.5mm and one 3.0mm. The pin diameter was .9054" and offset. As far as these specifications apply they were the same between Vin L and Vin 1. More information on this is comming soon.

Note: The difference in ring placement and thickness will not keep you from using these interchangeably. This does not mean there isn't a difference I haven't noted yet. The higher rings help with reduced emissions and the thinner size reduces friction. The change in recess depth, although aparently didn't change CR, may have something to do with flame propigation or other factors that are beyond me...Again, more information is comming soon.
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Old 10-04-2004, 09:32 PM   #22
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So if my wrist pins are stuck in there nice and good they're pressed in right? I pushed on it and it didn't move, but i never really tried either.
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Old 10-04-2004, 09:47 PM   #23
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The STATIONARY pin is secured to the piston at the bosses, and the connecting rod oscillates on the pin.

FULL-FLOATING pins are not secured to either the piston or the connecting rod. Pins of this type may be held in place by caps, plugs, and snap rings, or spring clips which are fitted in the bosses. The securing devices for a full-floating pin permit the pin to rotate in both the rod and piston pin bosses.
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Old 10-04-2004, 10:01 PM   #24
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I'm 99% sure that you're right about the pressed pin then. I'll let you know when i'm out of class.
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Old 10-05-2004, 01:58 AM   #25
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I was reading in the FSM just a bit ago, 93 FSM, Page 6A8-33

L27 has to have the wrist pin pressed out, L67 has to have the clips removed, then the wrist pin slid out.
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Old 10-05-2004, 02:07 AM   #26
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Good work on that dame

So there I believe are our differences, which its an upgrade to the l67 but not something that couldn't be transferred to the l27. There may be more though :P

"Full-floating pistons create less friction and utilize specialized pin retainers. As the engine spins, floating pins allow the rod to compensate for the inevitable slight misalignment of the rod, crank, and piston, and orient itself more precisely with the crank journal and pin. "

So the effeciency of the l27 bottom end is slightly less than an l67 BUT for all intents and purposes they're really the same.

Kind of exciting news, these two engines are more similar than many thought
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Old 10-05-2004, 02:11 AM   #27
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Still alot of work involved in the swap from L27 to Series 1 L67. Now that we have the basics wrapped up (did we ever settle the head issue for sure? And rods?), let'* turn the topic to what would have to be done to make the conversion. It doesn't sound like you'd HAVE to make any changes inside, but it may be desirable. We know the trans is weaker, and again, it would be desirable not to frag a differential.

We still have to satisfy the PCM with boost control, and there'* a ton of bracketry and relocation of accessories. New harmonic balancer, etc......new lower intake, SC, what else? My mind is fuzzy. Too damn many hours at work today.

It might be nice to work up two lists. One bare minimum, and another best practice.
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Old 10-05-2004, 02:23 AM   #28
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Here'* what i've come up with. Frankly all the small bits and brackets etc will be the biggest headache.

You'll need the whole ACCY bracketry. Including the PS pump, alt brackets and such, pulleys idlers. You'll need the harmonic balancer and two belts (right?). (this really turns me off)

Supercharger, lower manifold, fuel injectors/rail, throtlle body gasket.

Electronics - Some sort of boost controller/fuel accomodations. Easiest thing i could figure would be get the L67 conversion wiring kit from ZZP for the BCS and MAF, wire it to your PCM and get a custom PCM with N/A gear ratios, and */C fuel curves, etc, or some sort of piggy back boost device.

That gets you the blower on the motor, the belts driving it, and the fuel to run it with a good AFR.

One question i have, can someone with a 4t-60HD measure the circumfrence of their halfshafts? Damemorder said mine were huge compared to his.
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Old 10-05-2004, 02:32 AM   #29
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Quote:
Originally Posted by BonneMeMN
One question i have, can someone with a 4t-60HD measure the circumfrence of their halfshafts? Damemorder said mine were huge compared to his.
Like 2x.
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Old 10-05-2004, 02:44 AM   #30
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Not sure what'* the deal with halfshafts. I'll look into it. Just don't automatically think that bigger is stronger. They may be tubular. (remember that the base swaybars were tubular for awhile, while the SSEi got solid).

Good point to bring up. The swap doesn't end at the trans.
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