gmgearhead454

I don't have a problem spinning the engine to 5500 rpms... as it would only be for short bursts, so if I have to go down in pitch to make a 4-blade work, I am willing to do that. I have tried literally over a dozen 3 blade props this past summer, and I just don't like how the boat runs with them. I usually always have 6 adults, plus coolers/gear with me, so its ususally loaded down pretty good, and being able to cruise at a medium speed is a must. Every 3 blade made it pourpose its ass off, the one 4 blade I had made it jump up on plane, cavitate just a tad for a second, and then cruise nice and flat at around 2,900 rpms @ 30mph GPS and only lost 1 mph top speed. Top speed is important to me still, as I participate in poker runs, but losing 1 or 2 mph is something I am willing to sacrifice to make the boat driveable. And I know the engine specs aren't anything crazy, but I've built some 500hp engines before, and I think with some good head work, 9 1/2 compression, and it being a decent size roller cam, close to 500hp should be attainable with a good intake and 850 carb with open exhaust I would think...? 65mph would make me happy as hell

endeavour32

I hate to say it but your not going to get anywhere near 500 hp with vortec heads, not in a boat at least. I'm running a slightly bigger cam than you are going to be running, with the 8.9 compression ratio, performer RPM intake and a holley 800 (the engines were 454 mags) and I'm not making over 430 hp. I know that based on what other formula 292's get for speed. I'm no better than stock 502's, maybe even a little slower. When it had stock 330's in it mine was on the fast side for stock engines (63 MPH now I'm at 68 MPH) so I know it's not that I have a heavy boat. Yes on a desktop dyno the engine should be making close to 480 hp, but this is not the case. I also know what I had to do to make 530 hp and that was far more than what you are planning on. It takes a lot of hp to make a Formula go fast and 65 MPH in a 242 take some power. If you haven't bought your cam yet I would really suggest to you talk to Bob at Marine Kinetics. The price will be close to the same if not the same as the off the shelf Comp but it will be customized to your set up. Bob will also tell you the realistic HP you will be making. If you would like his number let me know, I'll post it. Not trying to be Negative Nancy here, but the posts from the Chevelle site are not really relevant for building a boat engine. If looked back at some of my original posts I wanted to do something similar to what you are describing for my 242. However the more I learned the more I figured out it isn't really possible. Many here have tried on here only to be disappointed in the end.

As for props- did you ever try a Mirage Plus? If not I would try one, for the 242 that is the best prop out there, I'd be willing to bet that is what 90% of the 242 guys are running. Not all three blades are the same but on the same hand not all 242's are the same.

dandercam1

Vortec head 454 build with dyno results

http://www.offshoreonly.com/forums/g...l-results.html

gmgearhead454

Thanks for posting that Dandercam1! I know my build is on the mild side, and I'm well aware of the Formula 242 being a heavy ass boat. Well lets be real, it's like pushing a fat ***** on roller skates through a gravel parking lot. But either way, I know I can make it run a whole hell of a lot better then it is stock (51mph), and to be honest, yeah it won't be the fastest thing in the world, but until I can get into something newer and a little bigger and speed effient years down the road, I don't really like anything else out there for the money I got into my Formula. Yeah I know I could go fast for cheap in a Baja, but I like the quality and ride of my boat. Plus, if that motor is making 460/500 with the same exact build as me, how can I not match that or pass it with a single plane, roller rockers, and long tubes? Just sayin... I think I can get close

dandercam1

My experience with single plane vs dual plane comes from two back to back dyno comparisons. The first of which was a 9.5-1 comp. 468 with Merlin oval port heads a short duration solid flat tappet cam (270* s-s)and a Holley hp750 carb. The Victor jr. made an extra 23hp at 5300rpm over a performer rpm air gap. Torque was the major factor on that motor which was the reason for the test but surprisingly the air gap only made significantly more torque below 3000rpm. From 3500 - 4500 the torque curve was almost the same and from 4500 up the victor jr. started to make more torque. End result 514hp at 5300rpm with the victor jr.

Second experience was a far different combination than anything you would run in a boat but a 12.5-1 comp. 447ci motor with a 296*/304* s-s .714 lift cam and ported 781 oval port heads picked up 41hp with a Dart single plane over a performer rpm air gap. That motor made 652hp and 587tq on 110 octane

There are tons of variables and every motor is different but the dyno is the only way to know what the motor will respond to.
I'm not trying to argue my point but just sharing the experience from which my opinion is based. I would be more interested than anyone to see a back to back comparison on a marine motor with wet exhaust.

dandercam1

I wonder what your motor would make on that dyno .......

Even dyno numbers can be subject to scrutiny