250ES Refresh - built 454 mag or new 502
 

Hello everyone! I've been a lurker for a while but now I need some help that I haven't found searching:

I want to go faster on a higher hour motor so I am either going to have my gen V 454 mag (365hp) completely rebuilt or sell the long block and buy a new 502 long block then have existing accessories as well as stock manifolds bolted on. The 502 option (see link below) will cost me about $7k+installation minus selling long block vs $4000 to rebuild the 454 so if I do that then I definitely want to get past 70mph. The 454 rebuild would involve boring, higher compression, cams, and rebuilding the stock iron heads to get about 420-440hp vs 502 with aluminum heads at 502hp + 567lb-ft tq.

http://www.eagleenginesales.com/mari...e/view/5026-HP

The 502 cost is a little uncomfortable but may be worth it if it gets me 5-10 mph more than the 454 rebuild. I do not want to mess with (pull) the motor any more after this for several hundred hours (boat gets a lot of use) as my first child is due after this season so I don't know when I'll have the time and money to fool around with the motor again.

Supposedly this boat+motor combo when new went at least 62-63mph on gps. That seems reasonable as I saw 60mph (@ about 4400rpm on labbed 23 solid-hub mercury prop) on gps at 700 hrs . I won't be happy spending the extra cash for a 502 if it doesn't reliably push the boat past 70mph.

Anyone have experience with a similar hull/motor combo?
What can I expect for speed and driveability?
Thanks in advance.

i just bought a 1997 24 ft outlaw sst with a crated 2009 502 ho mag, and a better exhaust manifold, and a m 1 procharger. I think the information is pretty accurate, but the owner i bought it from did not build it, and he was an idiot, But i had my boat up to 78 mph and we had room to hit 80 mph by moving the tabs up more. Contacting the original owner who built the egine, said he would do 80 mph all day and had it gps at 85 one time. I hope this helps,

This summer or next i will have it dynoed, So i will be taking all the uncertainty out of it, and know exactly what i have under the hatch. And the horse power too

Nice... 80-85 with a procharger M-1 sounds solid. I wonder how your motor was built (for supercharging or n/a). Based on my understanding of Procharger's numbers you should be making at least 120-200hp more than the 502 that I am considering for another 7-10+ mph

I bought the boat from the 2nd owner and he was an idiot, but the original owner said that he gained 120hp when he put it on.,, plus a better manifold and not sure what else, i have to ask him, I talked to the owner, and he said he resaerched the procharger, and found that it was the safest and best one for his engine. I talked to the guys who made the procharger and they explaned to me why it was safer then other option, like superchargers and ect.
My boat jumps out of the water like a rocket and roars like a lion when i give it the gas, the nose comes like a sub marine surfacing and comes down quick and takes off like a bullet. You can feel the pull of the boat under you when hit the gas, like driving a 2012 shelby KC cobra mustange with the 5.4 supercharged engine

YUo can definitly feel the power. and then i watch my gas gauge move just as fast in the opposite direction as the mph gauge.

But if i don't punch it aggrressively it cuts down on the boost.
But i am happy with it. And i will never need to go any faster.

Ha ha sounds like fun. I read your post about buying the boat and identifying the motor. I bought this boat and sold a 1990 Baja 190DSR with a 262mag (4.3). Both of them yellow with black graphics with nearly same interior colors (yellow/grey/black to yellow/black white).

I'm tempted to get the 502.

I don't think your going to see a 5mph difference between the 454 and the 502. It's not that hard to get power out of a 454. Doings heads, cam, intake and carb I see people getting numbers very close to the 500 and better mark. With it being very reliable.

Don't feel bad about 700 hours though. I think I am pushing 1300.

The 2nd owner was a real idiot, or he was playing dumb , but how can you have somethhing and know nothing about it.
Do what is best for you. I am happy with mine, what ever it is, next spring i will have it dynoed and find out everything about that engine inside and out.

good luck on your decision

Just as an fyi---

I ran your numbers in the prop slip calculator and there is no way you were hitting 60 mph on gps with a 23 pitch prop and 4400 rpm--you would have to be at 6% slip which is almost impossible..At 15% slip your speed would be 54 mph. If you have the mag motor (you said you have 365 hp) you should be running 4600-5000 rpm. IF you dont rebuild or replace your motor this year you might be wise to drop down to a 21 pitch prop to get your rpm's up to 4800--this will allow you to take advantage of all your hp and might possibly get you going faster.
IMO I would just build that 454 with better heads, a new cam and exhaust and you might be suprised at what kind of speeds you can attain.

I know the tach was off so that was an educate guess, gps was real over and over. I'm curious to know how you calculated?

Easy to calculate, your prop pitch is the number of inches your boat theoretically moves forward for one prop revolution. Multiply by your engine RPM, factor in the drive ratio, and (with a slip factor for efficiency) you can calculate a velocity.