You're right it could be the cam, or it could be the builder that installed the rockers wrong and switched out half my Smith bros pushrods for generic crap and still managed to get the wrong length or the machinist who screwed up the bores or the carb guru who built my carbs blindfolded or the professional who spent 20 minutes on the dyno did two sweeps for power and sent me on my way or the professional who rigged the whole thing like an amateur and wired it so poorly 2 connections failed in the harness before it hit the water or the owner who overheated it, or the plug wire manufacturer who didn't crimp the wires, or the brand new engines that melted down at 10 hrs, or the builder that changed the pistons without telling me, or the builder that changed the compression without telling me, or the builder who has special correction factors, a dyno that might have an issue and sweeps at 921 per sec, and has it excessively rich. Yet somehow no names were mentioned, no blame placed and I never go out of my way to bring it up. I just carry on and continue to pay for substandard work because this hobby seems full of incompetence and talk of professionalism that never actually materializes when the work begins. Having a cam problem would be something I haven't experienced yet, it'd be an interesting change of pace.

You are making an excellent case for having zero data to go off of. Skewed data is completely useless for comparison purposes. It certainly sounds like you have been taken for a ride all the way around on your last motors, and that completely sucks. It also sounds like you have paid a huge tuition for the education you have received, and you are smarter for it. Hopefully this time around you have a competent builder that will actually provide you with a package that has been well thought out to work well with all components involved and an honest dyno run that proves you are making the power you are looking for and paid for. I was given the kool aid when I converted my 454's to roller cams. I was told to expect an 80 horsepower gain per motor by only swapping cams, lifters, and pushrods. What I ended up with was a 2 mph gain and 100 extra RPM by refreshing 600 hour motors and swapping cams. They ran well, but I certainly don't feel I picked up the power I was told I would.

The dishonesty in this industry is damn near an epidemic, and no doubt part of the popularity with people to either buy bone stock outboards for their performance boat or pay a huge inflated price for stock Mercury power, because at least then you know what you are going to get and have an idea of how long it will last.

What kind of boat was that in?

Sometimes 100hp will only gain 2-3 mph in a big heavy boat. 80hp might even be a correct guestimate. It's so hard to predict what speed a boat is going to run unless you've built that particular engine for another boat just like it. Otherwise, you're just throwing numbers up in the air.

I tend to be very conservative when I tell people about speed gains and I never make any guarantees. In the end, I tell them it depends how the boat will react to the power. You can't estimate anything without already having the data and experience.

No one made any hp promises in my case so that's not an issue. The only reason I changed any parts from the old combo was just so I could try to get something positive out of a bad situation. Don't forget I started the thread just to talk carb brands. Just want to have a decently thought out package that was put together correctly. I thought I was there until it was pointed out there might be dyno issues going on here. I'm just looking to validate the accuracy of the info at this point. If that means a backup pull on another dyno then that's what will happen.

100rpm gain is no where near 100hp, or 80hp. Prob more like 20-25hp if that

2mph for 20-25hp on big heavy boats ? People would love that.

25hp a side ? I can see that being a 1-2mph gain. He said he gained 100rpm.

If a guy tells you that you can expect 80hp per side gain in a 30ft twin hi perf boat, and you gain 2mph, it was a bs claim.

Theres plenty of 502 mag 415hp 31ft boats, that go alot slower than the same 31ft boat with a pair of 500efis. If 2mph was all you gained by adding 80hp per side in one of them, merc would have never sold a single 500efi package.

Bottom line, a stock 420hp merc 454 , just isnt going to gain 80hp with swapping to a similar cam just in a "roller" wheel design.

We'll agree to disagree.

It depends on the boat, the setup, X Dimension, hull limitations and a whole slew of other factors. There are far too many variables to make a factual statement and assume X HP will equate to X MPH gain.

The claim of power increase from one cam to another is a seperate conversation all together.

I`m sorry to hear about all your troubles BKC, that really sucks!!
I`m lucky to have a guy like Mike around, no BS just great work.
I hope things get better for ya...

don`t mean to derail ( too late maybe )

Just wanted to thank Mike for the great work :

Did Mike do the oilers?