I've been considering an engine swap in my 95 Regal to an L67 for more power, because that 170-190hp (mods included, who knows how much they add) simply isn't as fun as it was 8 years ago when I was 16.
I've been doing some research and came across a few project threads, one of which was a guy named James on a my w-body discussion board who decided it would be beneficial as far as engine design to use Series 2 heads on a Series 1 3800. The advantage would be that the S1 block has a 1" taller deck height, and therefore is more suitable for stroking, but also has a better rod length to piston ratio.
The idea was that Series 2 heads flow better than Series 1 heads, that the belief was that the S1 3800 shortblock was the peak evolution of the 3800.
The major pitfalls to this project was the need for a custom ground camshaft due to the different valve locations, and the 1" extra deck height created extra clearance from the manifold to the heads. Last he posted in that thread, he was still working on it, and I haven't heard from him since.
"Now besides the fact that the SII heads have much better engineering of the port design and excellent crossectional area/flow the SII heads feature 1.8 and 1.52 inch intake and exhaust valves, and they measure 4.7212/4.7133 inches overall length on the intake and exhaust respectively. While the SI heads have 1.71 and 1.487 inch diameter intake and exhaust valves, and measure 4.727 inches overall length each."
My curiosity was peaked when I was given information on 3x00 valve sizes.
"the 3800 and LP3100 exhaust are damn near identical, but the LP3100 flows ~220cfm at .600, while the L67 heads flow ~194 at .600..."
I was told that there are considerable gains to be made by porting L67 heads.
"if you do decide to go 3800, do yourself a favor and port the living **** out of the heads. they suck for flow. large port 3100 heads flow roughly the same air with 22% less displacement, which is why the powerband of a 3800 favors low-rpm while a 3100 favors the top."
"flow tests were done with heads only. the L67 had 1.92/1.57 valves while the 3x00 heads had 1.76/1.42 valves..."
I can now start to see why the L27 has such low performance numbers (170hp) given its displacement in comparison to the 3100.
I don't wish to venture into creating a S1/S2 hybrid as James wanted to do in that thread I posted, but this all got me thinking. How much do I stand to gain from porting my L27 heads? I already have roller rockers on, and the LIM is ported as well. I don't have a flow bench, but I would consider my porting experience to be adequate.
Consider my work with my Jaguar V12 heads and manifolds:
Here'* what the throttle bodies looked like stock:
And after I finished with them:
Ported and polished (after injectors) manifolds:
Stock head intake ports:
Port and polished head intake ports:
Eplanations are in my previous post, but for those who didn't catch it, I didn't really port much of the heads. On the head intake ports, the gasket is 1.5". I gasket matched the ports on the intake manifolds. The very surface of the head ports is a hair under 1.5", but the ports have a sharp taper into 1.25" for the size of the head ports. I smoothed out that taper so it funnels into the bowl of the head port smoothly, thereby increasing velocity and eliminating the turbulence that the stock machining creates. The ridges you see on the sides of the ports are from the factory welds, as these are not cast aluminum heads.
I smoothed the edges of the throttle bodies to also help maintain some velocity and reduce turbulence. They're not beautiful, but they'll be worlds better than stock. The stock throttle bodies are slightly over 2.5" in diameter, while the intake manifold entry is 3", and my new intake pipe will also be 3".
So, what do you think? With roller rockers and a ported LIM, will I stand to gain much from porting the L27 heads if I do work like I did above?