Rob,
Sounds like a good way to go. Tyler Crocket certainly has a great repuatation. Another thing I would look at upgrading would be those $hitty non-adjustable rockers with the 3/8" bolts that come stock on that engine. While the heads are off, look into the possibility of drilling the holes in the heads to 7/16" and installing a good set of ARP studs. Then maybe a set of Comp Cams Pro Magnum roller rockers.
The additional 100 hp will certainly make a difference. However, what also is very important is torque. I dont know what the 454 magnum made for torque or what the curve looked like. I would ask Tyler for those #'s as well. If you look at my upgrade, from stock 385 hp ( which is actually 415 hp) when measuring crankshaft hp like my 540's dyno numbers, I jumped up to 680 hp. So I added about 265 hp and tons of torque. I netted about 14 mph increase of top speed. But, what really feels better is the midrange. If I am cruising at 4000 rpm and hit the stick, I get planted in the seat, the 454 Magnum didnt have the punch. The additional torque from the larger displacement has alot to do with that.


Vinny

Additional head parts include roller rocker arms, rocker studs, roller camshaft, new pushrods, timing chain set, 2.250 severe duty intake valves, 1.890 Inconel Exhaust Valves, valve springs, retainers, locks and seals. Tyler did send a dyno run and peak torque with the kit is 569.7 lbft at 3800 rpm.

Thats what I like to hear, sounds good to me.

fast willy,
alot will depend on what rpm range your running in too,
my 242 convincor would only spin a 23, but i was able to spin it to 5600 rpm where i needed it......so as others have said if you want to keep rpm in check....like 4900 to 5100 then yes a 26 bravo, 25/27 mirage would be good.....

kevin

Since you guys are on the subject, I have a 1991 251 that I'm repowering. Best GPS speed I could get out a modified 454 Mag using a labbed original 23' Mirage was 72 mph. I know that speed sounds high, but the 251 has a very narrow beam and weighs in at only 3700 lbs dry. I'm repowering with a new 540 that Gellner Engineering is building for me. It should make somewhere in the 625 hp range. I need to prop it for 5700-5800 rpm. From your guys experience, will the 27' labbed Hydro your talking about work for my application?
Also, what steering do you guys recommend? I'm considering an IMCO dual ram system. Any feedback is appreciated. Thanks

I would recommend you go with Imco's dual ram full hydraulic steering. What drive are you running? What ratio? Which Hydromotive are you referring to 4 or 5 blade?

Thanks for the feedback.
My drive is a 1.50 Ratio.
For the drive, I was referring to the 27' 4 blade hydro.
How has your drive been holding up with all of that power?
Thanks

Sorry, my drive is a Bravo One. I have only needed to do general maintenance thus far - regular lube changes and greasing the u-joints.

That 27" 4 blade be ok. It depends on where your want to run the engine. You need to look at the dyno sheet. I would try it to get a base line and go from there. Just be careful not to over rev the engine. I have a bit more power than you are planning on. Although are hulls are different, I can run a labbed 26" Bravo 4 blade and get away with it. See post # 10. Remember, a 26" Bravo is actually 24 1/2" pitch.
Drives.... now they are a major problem. I assume you are running a standard Bravo 1. It depends on you driving habits, but dont expect that to last long with 625 hp. Even more than that, is who had their hands in the drive last. I found out the hard way that some people who claim to be drive experts are not. I have broken shafts , worn out gears, had seals leak, wiped out bearings all in 1 season of 60 hours run time. That was last year, the first year with the new power. Disgusted with all that, I learned ( with some guidance ) , how to rebuild and set up drives myself. So far this year, I have 50 + hours without a problem. I am running an XR upper and Imco lower. I run hard but am careful with the holeshots and launching over waves.

Vinny,
Do you think a labbed 26 Bravo would work well on a 259 Convincor with 475 propshaft hp? Peak hp will be achieved between 5100-5300 rpm.
Rob