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exhaust backpressure after performance mods Printed From: CorrectCraftFan.com Category: Repairs and Maintenance Forum Name: Engine Repair Forum Discription: Engine problems and solutions URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=33855 Printed Date: October-08-2024 at 10:52am Topic: exhaust backpressure after performance mods Posted By: mamigacz Subject: exhaust backpressure after performance mods Date Posted: June-13-2014 at 1:28pm 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. Replies: Posted By: Hollywood Date Posted: June-13-2014 at 3:01pm What 02 bung? Sure you weren't measuring cooling water pressure? ------------- Posted By: mamigacz Date Posted: June-13-2014 at 3:20pm 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. Posted By: Hollywood Date Posted: June-13-2014 at 3:33pm I can definitely envision what would be needed. Are you planning on running that modified riser on a normal basis? Bung failure would definitely not be a "best boating moment". ------------- Posted By: Gary S Date Posted: June-13-2014 at 3:59pm 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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport Posted By: mamigacz Date Posted: June-13-2014 at 4:05pm Hollywood wrote: I can definitely envision what would be needed. Are you planning on running that modified riser on a normal basis? Bung failure would definitely not be a "best boating moment". Yes, I run a closed loop efi system. This modification has been done before. Howell efi even sells a kit for it. Posted By: mamigacz Date Posted: June-13-2014 at 4:22pm 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. Posted By: gun-driver Date Posted: June-13-2014 at 6:53pm How is it working for you I was kicking the idea around myself. How about posting the pics of the bung installation. Thanks Posted By: mamigacz Date Posted: June-14-2014 at 12:32am 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.

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