View Full Version : 2.5 or 6.5 power valve for 4160?

Double Overhead
08-30-2005, 08:23 PM
I just tore into my carb for a rebuild and I am wondering what size power valve to use. The rebuild kit that I bought from my marine store came with a 2.5. The carb currently is using a 6.5. I called the shop and they said they always use the 2.5's. Looking online I have heard that the 6.5 is the most current one used in our application. I was unsure what I should use. What are the benefits of one versus the other? Your help is appreciated

dog paw
08-30-2005, 08:50 PM
If memory serves I think mine has a 2.5 It's a 84 S+S Thats a pretty long jump between the two. The difference will be how much engine vacuum it will take to open the valve to allow fuel into the circuit I'm not sure how the numbers go though (I HATE HOLLEYS!!) :D Sorry thats the old school Rochester coming out I'd put back what you have been running if you are not having ongoing driveability problems you are sure you could pin on a powervalve calibration To "strong" of a valve will give you a lean stumble dieing out on hard accel and such

08-31-2005, 01:40 PM
Stick w/what was in there if it was working fine before.

Unless you want to do "jet runs", pull plugs and analyze your A/F ratio, then just leave it where it was before.

09-01-2005, 09:18 AM
I've been using a 6.5 for the last several years and it seems to work fine. Did quite a bit of research this summer on the topic and I found the consensus recommendation, "it depends".

09-01-2005, 12:01 PM
....I found the consensus recommendation, "it depends".
I does. It depends on what YOUR engine wants. You need to feed it what it wants. Stick w/the stocker, or be prepaired to get out a vacuum gauge, get some new plugs and do some jet runs and plug analysis.