I'm running a pair of hp500 engines with TBS 250 blowers and dual 700 carbs on 5 psi. Both engines are dropping fuel pressure down to 2 psi during WOT and feel like they flatten out at 80mph/5000rpm. I have changed the pumps and raw water pumps to eliminate the cams for the pumps and the pumps themselves as a problem. Is there an upgrade to these pumps that will hold a reliable 5-7psi during WOT or should I switch to electrics? This setup is in a 97 Fountain 35 single step, engines are Gen 5. Any input is appreciated.

Check into CV Products out of one of the Carolinas. They have a marine version that works for your application. It is a Holley HP or at least very close and you can get it with various springs-diaphragms for the pressure you desire.

Mark

I can't seem to find anything on them currently, seems like they are out business maybe.

You can use the bottom half of many different pumps. Holley has a 140 gph version with 1/2” npt I’ve used before. As long as the diaphragm in your top half is ok

I tried to use the bottom off 12-454-20 but it wouldn't prime at all, tried everything including cans of starter fluid but it wouldn't pull any fuel.

Baker 15psi pump and return regulator will do the trick.

I use these and had 9psi . I had the add a regulator to get the pressure down to 7psi. Gauge doesn’t move off of 7psi.
https://www.hardin-marine.com/p-1246...6-engines.aspx

I tried one of those and it didn't work at all. I can't remember the brand I ended up buying, it had better valving than the K&N. Check the threads on mechanical pumps a few people have posted the brand and model. It was basically a stock replacement, it supports 700hp just fine.