You said trimmed to 5. Have you indexed your indicator? At what point are the drives level to the bottom of the hull? 502's and no boxes? Twin step?

No boxes, twin step. Just had a local offshore shop tip to stern the boat, I'd be surprised if its not calibrated properly, I trust they would have done that.

It can't be the valves, for one thing that would be just be too expensive of a fix! Haha seriously though, total hours are less than 400, and had valve job done less than 100 hours ago.

My money says the ancient inline filters are restricting fuel flow.

Index your drives. With a ts you should only be a tick or two above level. Your fuel/water separators should he changed every season. 28's might be a lil big for your boat but should still spin to 4500. I believe they came with 26's from the factory with your setup.

Ok i have the same boat, 353, 502's all stock, 440 hours on them etc....

At 4k rpm and the boat trimmed to 4-5 im at about 57-58 mph or so. ive seen 69.8 on this boat at about 5k and I shut it down, but day in and day out its a 67 mph boat with 3/4 tank 4 people cooler etc....

They came factory with 28's. Your issue is not the trimming.. you are way down on power somewhere.

So what did you come up with?

Both engines are same rpm?

I by passed the inline fuel filters. And still my max RPM is 4000-41000 with same max speed.

Suggestions?

Are your props the original 28s? Any history of props being worked? Could the props be from another boat or props were worked and now too much for the boat? Someone mentioned drive ratio earlier, your 100% sure 1.5s are on there now? Just trying to help, it is a clue that both engines are turning the same low rpm.

This issue with your boat doesn't seem to be a problem that is inherent to only Formula boats. I would post this same question on the Technical "General Q & A" thread, along with an explanation of what you've already tried doing to to resolve it. There are some extremely knowlegeable guys that frequent that thread (some are professional marine mechanics) who might be able to give you additional advice as to what might be going on here... Hope you can figure it out soon!

Do they spin 5,000 rpms in neutral? If so, then it's likely a prop problem. If 4,100 is all they do then you know the problem is in the engine compartment.