I run one in my 340, stabilizes idle timing mostly and perhaps keeps the cam gear from SOME erratic rotation speeds...but i believe during acceleration, constant or otherwise, already keeps the cam timing steady, 'reasonably speaking'.
Mine, used with a aussie billet dbl set, has wear. I don't like the worn particles going into the pan just like I don't want old valve stem seals bunching up in the pickup.
Steady timing reading at idle is the only noticeable thing. Imo
I'm not saying to run one or not run one.
...I just wish they made a spring loaded gear that meshed with the chain instead of a guide .
4.6 ford... that motor will make you hate chain guides.lol
