Mopar Action On-line – Tech Questions
Terje Carlin, Uddevalla, Sweden, 1971 Plymouth Cuda 340
I have in my garage a ’71 Cuda 340 with only 30,000 miles on the meter. It has been stored in a garage since ’76 and I am about to make it for use in the streets again. The big problem is that the Cuda is an untouched, complete original car.
What to do with the problems of today’s unleaded fuel? I don’t want to use lead substitutes. A Swedish rally engine builder with some experience on American engines told me that there should be no problem to use original heads (with no hardened seats), only change to good stainless valves with chromed stems. This because the low horsepower output of the original motor will not create harmful heat on the seats. Is this really truth?
I’m more into putting on MP head P5249574 and save the original heads untouched. It’s important that the car looks original. What to do?
I disagree with the engine builder on 2 points:
A ’71 340 is not, in my estimation, a low output engine!
The seats usually “go” before the valves – they get pounded into recession – thay are just cast grey iron (with a bit of nickel.)
Having said that, I think it would take many years of “normal” street driving for any problems to surface. My recommendation: just drive it. Then, if you rack up another 30-40K, and begin to notice a miss from a less-than-perfect valve seal (which typically shows up first at idle), you can consider whether to install seats in your original “J”-casting heads, or swap something newer on.