The L27 (1992-1994 (Bonneville), 1995 (U-bodies, Buick LeSabre) and the Series 1 L67 (1992-1995 Bonneville) both share the same ancestor, the LN3, and just by looking at the longblocks, one would be hard pressed trying to determine what engine was what. But this guide should show you just what those differences were.

First, let'* look at the similarities. Both the L27 and the L67 use the same block,camshaft, crank, heads, exhaust manifolds, flywheels, and EGR systems. Timing covers are the same as well. In reality, there is nothing to externally differentiate the long or short blocks of the two engines...with the sole exception of the harmonic balancer. L67s use a two-belt balancer, the L27 is a single-belt design. If the timing cover and oil filter adapter is in place, you can tell the blocks apart that way as well...the L67 uses an oil filter adapter that allows an external oil cooler to be added...L27s did not get this option, but if one were to find this type of cooler in a junkyard, it could easily be fitted to an L27.

Now, for internal differences. THIS is where one can expect to see the most changes. The piston design is different between the two engine models in that the pistons and rods in the L67 use a floating-pin design, whereas the L27 uses a pressed-in pin. The piston crowns of the L67 are also coated in an ablative material...presumably to aid in the reduction of KR. Also, the piston rings are set slightly lower in the L67 for better protection from knock. The pistons and rods are heavier in design to allow them to survive boost. And the bearings...main, camshaft, and rod bearings...are made of a harder alloy for longevity.

On a side note, the 1992 model year saw both the L27 and the L67 use a rocker-pivot design, muck like the LN3 they replaced. Starting in 1993, the L27 and L67 received redesigned heads, and the L27 got new roller-pivot rockers...the L67 soldiered on with the old style pivot-rockers, but can have the roller-pivots swapped in as an upgrade (NOTE that this cannot be done with 1992-spec heads). 1994 saw the roller-pivot rockers on all models.

An attempt to answer this often asked question, and explore alternate possibilities

"Can I add a Supercharger to my car?"

This is one of the most often asked questions on this and other forums. Having a NA (naturally aspirated, as opposed to force-fed) Bonneville and seeing a Supercharged car at a wrecker is enough to make anyone drool. Especially when you see just how easily that Eaton Blower comes off of there! Is it possible to just bolt one up? NO. There are other possibilites, though, and none are cheap.

Please note that there are differences between the Series 1 and Series 2 as you read the rest of this article. Some of the points made may apply to one or both.

The reasons this will not work are extensive. The L27 and L36 NA powertrains are actually quite different when compared to the L67 (SC). The heads are different, the lower intake is different, with different injector placement, the fuel rail is different, and the compression ratio is also different. And pushrods, lifters, and rockers. Now we get nasty. The L67 gets a heavy-duty Transaxle, too. Either the 4T60-E(HD) or the 4T65E(HD). Then there'* the PCM. And the engine wiring harness to go with it. This doesn't even get into the little things. About the only thing these cars really have in common other than outside appearance is the Throttle Body.

So what are my options? First, you can find a salvaged drivetrain, and drop the whole thing in. Engine, Trans, wiring harness, and PCM. You can get one from a Bonneville or a Grand Prix. Very expensive by the time you're done. If you really want this, you could sell your car and buy a SC model for less. And alot less trouble.

Second option would be an aftermarket Supercharger. This mod will run you over $3000 US. You still have the problem of possibly killing your transaxle, 'cuz you still don't have the heavy duty version. Once again, you could sell your NA Bonneville, combine it with the $3000+ you would have spent on this mod, and buy a newer SSEi or SC SSE, SLE or SE (rare, but they're around).

Another option, which is more practical and a helluvalot cheaper is a Turbo. There'* room for it, and they're easier to set up. It would have to be a custom job, 'cuz nobody makes a kit YET.

Now what is REALLY practical? The 3800 NA is no slouch, and it has alot more potential than the little bit Pontiac took advantage of. For less money than we've been talking about, you could do the exhaust, intake, maybe a chip, and possibly still have money to work over the valvetrain. We have a couple members here that have done just that, and they spank stock SSEi'* quite easily.

What'* your preference? It'll have to be something other than just bolting up an Eaton M62 or M90, and everyone will choose a different path, but in the end, you choose the one that'* right for you and your car.

In a nutshell, there are many external and internal differences between the supercharged and non-supercharged models. Adding more brackets and offsetting belt paths with a double-belt harmonic balancer, new PCM programming, and the rest of the drivetrain......this whole procedure gets VERY involved.

Is it possible to add an Eaton M62 to an L27 or an Eaton M90 to an L36? Sure its possible, But is it Practical?


To do this, you have 3 options:

1. Try to add one. Very expensive and could end in engine failure.
2. Do a full drivetrain swap. Engine, Trans, wiring harnesses, and PCM. Slightly cheaper.
3. Sell your LE/SE/SLE/SSE and buy an SSEi. By far the most cost-effective solution.