Originally Posted by radomirthegreat
There was a turbo LN3 here a while back. It is absolutely awesome, and still running today. Not much power, but it is a cool setup.
As rjolly said, you could do an L27 top swap. I suggest a 1995 Chevy/Pontiac minivan should supply you with parts because of the minivan demographic and also since that'* the last year of the L27. The intake would be plastic in that case, I think, but see if you can get a metal one. They crack less easily. That, along with some Yella Terra Series 1 rockers (if they fit), would work great.
An LG3 exhaust should be able to bolt right up. The LG3 came on the 86-88 or so 3.8L V6 engines, and it'* thought to be the engine that came before the 3800 as it'* called today. There aren't many interchangeable pieces, but the exhaust manifolds should work, and if they do fit, please switch over since they essentially are headers. Then, as mentioned, get a high flow cat and all that fun stuff.
Also, I suggest that you take out the cam that'* in there, have a shop figure out its dimensions, and then you should go to some place like CompCams or so and get a new camshaft from them. I don't know why anyone hasn't done that yet.
Probably because for the amount of work and cost it would take to cam and tune an LN3 (and get minimal gains because the heads flow like crap), you could swap an L67 for a couple bucks more.
Let me try to give you an idea of how terrible these heads flow.
3100 (60*v6) heads flow better than S2 L67 heads
S2 L67 heads flow better than L36 heads
L36 heads flow better than L27 heads.
L27 heads flow better than LN3 heads.
A lot of this has to do with casting imperfections, the size of the valves, and the shape of the ports. You can smooth out casting imperfections with a grinding stone and a dremel and that will give a noticeable increase in performance, but you can't get around the fact that the valves are smaller and the ports were not designed to flow high volumes. If you get a cam, you'll get higher lift and duration, but your heads still won't be able to flow well enough. This is why the L27/LN3 is a dead end road, and why porting those heads makes such a big difference.
The L27 front intake manifold is basically the same design as a powerlog. It is much better designed than the Series 2 3800 front manifold, which is cast iron. Not sure what the LN3 has, but I'm assuming its the same.
Want to do an L27 top swap? I have a set of ported heads with lapped valves on 5/16" studs, and a ported lower intake manifold at my buddy'* house in Ohio near Cleveland. I just recently got a S2 L67 swap done, so if you want them, I'll let them go for dirt cheap.