If you can spring for the roller then do it, 240 duration will be no problem with that exhaust it might be with silent choice though. The best flat tappet cam that I used in any 454 was the crane 228/236 .540lift but I never had any 454 with more than 9:1 compression. For a roller go with the crane -731 226/234 similar to the HP500 cam. There is a lot of good stuff in the Dennis Moore book also. good luck.

Ironman, thanks... I might be wrong w/ that cam.
My builder knows what he is doing, so the most I can do is discuss
what is being done, not tell him what to do.
Like i said, I'll post more on the rebuild in a new post, when I have more to post.
thanks again guys...

I agree you are in good hands ,just giving my experiences. Be prepared to spin the engine higher with a 240 duration cam though maybe 5500 to 5800. If the CR is about 9.5 :1 it will make power with the 240 duration cam. good luck.

Iron man,
I am running a 454, bored out to a 468 with 9.8:1 compression, a 561 lift, 306/306 with 240 @0.050 cam with merlin rectangle port heads. What rpm range should I be pulling. Also I have stock mercruiser exhaust with IMCO long risers, will I be ok with that exhaust?

Depending on the centerline of the cam you will probably be ok for reversion with the long risers. with 9.8 cr you probably will need at 93 octane and conservative timing 32 or so max with the iron heads. I would try to prop for 5400 - 5500 with a good ignition system. A friend has a similar engine with a slightly smaller cam in a 22 donzi ,same exhaust riser setup and he can turn 5800+ with a mirage 23 and no problems with reversion.

Jo- What about the New Black 24' SE that is coming to Michigan. What kind of speeds are you expecting it to reach with 550 - 575 HP. I was just wondering the difference in the Salt water and Fresh water. Any difference in the process in Proping the boat. I am a cigarette guy but i really like the product you guys put out. (especially your 36')

Ironman right now I am running 92 octane, with a 23p balistic 3 blade and the thing won't get over 5000rpm at 62 mph, I have a holley 830cfm hp on it, I'm taking the carb. to my carb guy today to go through it and see what is in it. We got the carb off of a 9 second dragster and haven't really done anything to it, other than jets, which right now it has 96's in the prim. and 98's in the secondary. Huge I know but it isn't really running rich. We are thinking carb is the problem, the ignition is the MSD pro billet distributor and the msd 6m-2 ignition box. The cam specs are as follows 306 dur. [email protected], 561 lift and.o20 clearance on a 110 lobe center

With a real 550 HP and strong torque that 24' SE should run in the 85 MPH range on GPS.Between Salt and Fresh water there is an average of a 1-2 MPH difference.There is speed on props. A labbed prop will allow you to turn a larger pitch at the same RPM which will = more speed. In average a labbed prop is worth an extra 2 mph.The 24' with that kind of power and performance is very important to have the correct prop and the proper Hydraulic steeing .The driver is also very important.


With a 500 HP carburated big block rated by Mercruiser at 470 HP the 24' SE on GPS has run right at 82 MPH in fresh water with a stock prop to give you an idea. The torque is more important than HP.

I like the 3 blade Mirage plus prop on the 24' model more than the 4 blade in most conditions.Out in the Ocean a 4 blade Bravo 1 will work well.

Thanks for the compliments,

JO

Jo, why is that?

riverrat i had an 800 holley on a 454 in the past and had a 6.5 power valve in the primary 79 jet and a 85 jet in the secondary with a PV. A mirage 23 will greatly reduce slippage and act like 1" pitch larger than the ballastic after you find more power through tuning. Try going down 2 jet sizes at a time and test for improvement, it is time consuming but you will be pleased with the results.