273 Commando with Hydraulic Camshaft

[66fs]

I have run a 340 cam in a HP 273 4 speed and it ran great. The first thing to do is check TDC. I have seen early LA engines be over 10 degrees off. Since you are running a 4 speed, 3.23 gears, and 25 inch OD tires you should be good there. If I had to pick a hydraulic cam I'd pick one similar to the old MOPAR Performance P4452759. 260/268 duration .430/.450 lift. 44 degree overlap and 110 c-line. Maybe a step lower. Use 340 valve springs or equivalent and a good true roller timing set. Centerline the cam. Your 920 heads are closed chamber and flow very well at low lift to mid .400's. Distributor is good, just make sure it is working as it should advance mechanical and vacuum, points set right.

 

[PRH]

I agree that a compression test in its current configuration would be a smart idea.

 

[Wyrmrider]

that mopar cam is "similar" to the 268 comp and IMHO is better
add 8 degrees to a mp cam to get similar at comps .006
I will point out that jthe ones 256 cam is 50% bigger than that MP cam at .275 ,,it gives .461 lift
need compression

 

[AJ/FormS]

let's see the compression

agree; the cylinder pressure will lead the diagnosis. You just cannot say it's a 10.5 engine, until you measure it, and you can't measure it until you take it apart.
The compression test is the next best thing.