The goal of this engine build was to make 130 HP in a still streetable package. This meant that the camshaft selection and head flow would be critical in this small displacement engine.
As has been the story in the past over and over, this particular engine came to us after having been worked on by a marque "expert" and it was a mess! Luckily, the engine build hadn’t been completed yet as the previous shop let it sit for over a year without working on it before it was pulled out of the shop by the frustrated owner. And, pretty much all the work that had been done needed to be redone or undone. New 10.2:1 forged pistons were ordered to replace the ones that were in the block, but the block itself was salvageable. The head needed everything.
Part of our build mandate was to convert the head to Big Valve specification. While we were at it, some porting was done as well. This worked out well; the intake flow at 28” went from 142.6 cfm @ 0.400” lift to 156.2 cfm. On the exhaust side, the change was less (the valve size didn’t change), 109.1 cfm to 116.5 cfm at the same specs.
For the camshaft, a moderate duration, higher lift cam was chosen. This cam, known as a 114 profile, has 243° of duration @ 0.050” lift and a maximum lobe lift of 0.413”. Fitting this cam required some special valve train parts and cam lobe relieving on the head.
Basic assembly of this small 4 cylinder engine is straight forward and soon it was ready for the dyno.
After the normal break-in procedure is completed, we were able to start fine tuning the engine to get the most power from it while ensuring it ran perfect. One thing that we insist on at Carobu is dyno tuning the engine with the air filter and muffler system installed that will fitted to the engine when it is back in car. This allows us to tune the air/fuel curve so that it will not change when the car is back on the road.
The twin Cam engine responded very well to the modifications that we performed on it and produced the required power output (see graph below).