A little update on the motor changes this winter.
While I was freshening the motor I decided to change a couple of things. Even though I modified the headers last year to get them to fit in the car, I redid them again this winter. Specifically I raised the collectors to increase ground clearance, rerouted the tubes to better suite the firing order, and added more tube clearance near the starter. First a little background.
Original as delivered Accufab 1 7/8" headers with 3 1/2" collectors.
The main problem with them was that they didn't fit the car, even with the 68' front suspension and notched shock towers. Their attempt to make room for a Zbar failed. In all fairness, no one makes big tube headers for a 351w in an early Mustang that can use a factory Zbar and I had repeatedly begged Joe to give it a try. I figured that once I had them in hand I could make them work.
Here is my last year's redesign that took care of the issues above.
The headers worked great last summer but I didn't like how low the collectors were mounted under the car nor the proximity of 2 RH header tubes that were practically touching the mini starter. With this in mind, this winter I decided to make the necessary clearances plus add a couple of performance minded features.
On the LH header I rerouted the #7 tube from under the bellhousing to over the zbar. This mod allowed me to match all the tubes going into the collector in the rotational firing of the motor:
On the RH side the tubes were moved away from the starter by nearly 1". That side's tubes already matched the rotation firing of the motor so I didn't change how they entered the collector:
Due to clearance issues that made it hard to reuse the old collectors, a set of Cone Engineering merge collectors took their place. Their CE merge collectors consist of a star like device located inside the collector to smooth the exhaust transition as it exits out of the individual tubes and a reduction from a 3 1/2" collector size down to 3". From there it opens back up to 3 1/2". This choke is supposed to act much like car venturi by speeding up the flow and it helps prevent exhaust reversion.
The old cam in the 434w bled off too much cranking compression giving only 170lbs measured with its 11.2:1 static compression. The motor was designed around 185lbs cranking so some power was being left on the table. I contacted Mark at Bullet and he tinkered with the specifications and came up with a slightly different exhaust lobe. The intake lobe remained the same:
Old cam specs:
New cam specs:
Here are both cams side by side:
Because I use a steel distributor gear, I had this year's cam ground on a special 3 piece core with a compatible drive gear:
To better dial the cam to where it was recommended, I installed a Cloyes Quick Adjust timing gear set:
The top gear is 2 pieces which allows the cam to be mechanically moved without disturbing the chain location by loosening the 6 bolts seen on the gear face and using the included tool to make the adjustment. With it I was able to dial the intake opening to be dead on the recommended 106* . Initially I thought that it would be an easy to make adjustment, but a minute amount of movement can create a major change in the cam location so it took a while to get it dead nuts on 106*.
While I had the heads off I removed the valve springs and had them tested to ensure they were up for another race year. I also lapped the valves to ensure they had a good seal. While I had them out I was able to check out the work that the porter did in the valve pockets:
I hope to have the motor completely reassembled and installed back in the car this coming weekend.