exhaust backpressure after performance mods

I'm not sure if anyone is interested in this data, but I had a difficult time finding information on it.

I did some performance modifications to my 351W. I added GT40P heads, a cam research ski boat cam and an edelbrock performer RPM intake.

I noticed that the stock gt40 motors had 3.5" risers on them. This brought up the question whether my 3" risers were restricting exhaust flow after the performance mods. I installed a backpressure pickup in the O2 bung of my riser. From there I attached a pressure gauge and watched it at full throttle.



The exhaust back pressure ranged from 2 to 3 psi. This was good news considering I don't have to spend money on less restrictive exhaust system.

Hollywood wrote: What 02 bung? Sure you weren't measuring cooling water pressure?

I converted my carb to fuel injection. During the conversion, I modified the riser to accept an O2 sensor. I have pictures of the O2 conversion if you can't picture what I looks like.

The O2 bung passes through the water jacket, into the exhaust chamber of the riser.

I'm curious. What was it before the mods? What would you have done if it was more restrictive? Not a lot of choices with exhaust hose size with the current ones using all the room that's available.

Gary S wrote: I'm curious. What was it before the mods? What would you have done if it was more restrictive? Not a lot of choices with exhaust hose size with the current ones using all the room that's available.

I never checked backpressure before the mods.

I should probably mention that this boat is a ski centurion, so it has more room available with the dual exhaust set up.

gun-driver wrote: How is it working for you I was kicking the idea around myself. How about posting the pics of the bung installation. Thanks

The Howell O2 bung kit looks easier to install than what I did. The method I used requires a lot of machine shop work and welding.

I'm very happy with the conversion. Gas consumption went down. Cold starts and warm up is a lot smoother. Throttle response is better.