got a buddy who had a 413 rebuilt by a third party shop and he asked me to help diagnose some driveability issues. The thing has no power... I mean it feels like a stock slant six under acceleration. My diagnosis is the engine builder put the wrong pistons in it and it has very low compression, just thought I'd post here and see if y'all agree with me. Some clues:

- the big one is the static compression test showing about 95-100 PSI across the board.... pretty much tells the story as far as I'm concerned but I checked other stuff below as well

- It runs and idles very smooth and doesn't run hot no matter what you do to it. Verified no vacuum leaks. Starts instantly, no issues with anything like that other than severe lack of power

-the spark plugs are a nice golden brown like they should be, so I feel confident the carb is tuned pretty well

-I played with the timing and ran it all the way up to 30° BTDC (!!!!) but the thing only ran better this way (!!!!) Never could get even a trace of spark knock under load.

- as a check of the above point, I verified timing mark on balancer is correct and showing TDC of #1

- tried swapping known-good carb and distributor just to be sure, same results.

- doesn't burn oil or anything like that so we have some confidence the builder did all the machine work correctly, including the confidence of previous positive experience with this builder


....so add all that up and I'm thinking it has low compression pistons installed by mistake. I recall reading one time about the 413 having a car and a truck piston and you had to be careful about which one you ordered so I'm thinking the builder made this mistake. Would the clues I've described support this? They put 516 heads on this engine, so if it did have the truck pistons with the closed chamber heads, what would we guess the CR to be?