After running the stock Non-PI...
After running the stock Non-PI motor on the dyno, we pulled the heads, cams, and intake manifold. We upgraded the stock head bolts to ARP head studs (we later ran this motor with a Vortech supercharger) and Fel Pro MLS head gaskets.
Now it was time to swap the top, meaning replacing the heads, cams, and intake manifold. Starting with the cylinder heads, the Non-PI heads were replaced not just with a set of later-model PI heads, but PI heads that had been treated to the Stage 2 porting process by Total Engine Airflow. Until Trick Flow Specialties introduces the first aftermarket two-valve head, the only route to improving the factory heads is with porting. The guys at Total Engine Airflow improved the flow rate of the factory PI casting from 177 cfm to 226 cfm on the intake side and 126 cfm to 209 cfm on the exhaust side. This represented flow improvements of nearly 28% on the intake and a whopping 65% on the exhaust. These flow rates were combined with the jump in static compression from 9.3:1 to nearly 10.3:1. This increase in compression not only improves power, but also throttle response and fuel mileage. The compression hike is still well within the range of safe use on pump gas, especially when you combine it with the slightly wilder cam timing offered by the Xtreme energy series we installed.
This shot illustrates the...
This shot illustrates the difference between the PI and Non-PI heads. Both the ports and water passages differed between the heads.
Not content to simply install...
Not content to simply install stock PI heads, we sent ours off to Total Engine Airflow for Stage 2 porting. The flow rates were increased from 177 cfm on the intake and 126 cfm on the exhaust to 226 cfm on the intake and 209 cfm on the exhaust. We also upgraded the valve spring package with the recommended beehive springs from Comp Cams.
Another significant difference...
Another significant difference between the PI and Non-PI heads was the combustion chamber volume. The Non-PI motors relied on a combination of 51cc combustion chambers and 11cc dish pistons to produce a static compression ratio of 9.3:1. The PI motors combined 42cc chambers with 17cc dish pistons to produce 9.7:1. Combining the small PI chambers with small Non-PI dished pistons resulted in a static compression ratio of 10.3:1
Though not strictly a performance...
Though not strictly a performance upgrade, we replaced the stock valve covers with these aluminum castings from BBK.
Part Two: Bigger Bumpsticks
2. Step two of our big three was to replace the factory Non-PI cams with performance grinds. The Non-PI cams differed from their later PI version by way of lift. Where the Non-PI cam offered less than .500 lift, the PI versions stepped up the lift to .535. The lift increase only makes the PI better than the Non-PI, but we were obviously looking for a great deal more power than the mild duration figures offered by either. Leafing through the Comp Cams catalog revealed a set of XE270AH cams that offered not only .550 lift (both intake and exhaust), but a 234/238 duration split. These represented a sizable jump over either of the factory cams profiles, especially considering that our newly ported heads flowed exceptionally well right up to .600 lift. The final performance mod was to replace the factory Non-PI intake with a PI version. Not only was this a performance upgrade, but it was a requirement as the Non-PI intake ports and water passages do not line up with those in the PI head. The PI intake was combined with an inlet elbow and 75mm throttle body from Accufab.
The Non-PI cams offered both...
The Non-PI cams offered both low lift and mild duration figures. The later PI cams increased the lift values, but offered little in the way of improved performance compared to the Non-PI versions.
In the end, we went with a...
In the end, we went with a set of performance cams from Comp Cams. The XE270AH cams offered not only .550 lift (both intake and exhaust), but also a 234/238 duration split.