Joe308

I am in the process of upgrading the original Mercury Racing HP500's in my 1999 Formula 353 Fastech and need some advice.
The boat is running 79 MPH on GPS and our goal is 90 MPH which I believe will require about 650 HP output from each motor.
We are running Bravo 1.5 drives (I know - another weak point but that's a whole different conversation) mounted on factory installed extension boxes spinning 30P Bravo 4 blade props.

We did a pre teardown dyno run and although the motors were tired, we were surprised they ran 530 HP on the stand.
My engine builder has recommended we stay with the original 850 carbs and Dart intakes and will port match them to the new Merlin heads we are installing.
Internally, we are basically replacing everthing except the crank. The BBC pistons and rods with Manley pieces, Inconel valves and hydraulic roller valvetrain components for ease of maintenance.
The 502 blocks were decked, bored and honed so they are now 516 CI. Due to durability and cost, we want to avoid blowers and run on pump gas.
We are stuck on whether to reuse the exising camshafts and exhaust with these upgrades in order to acheive the 650 HP goal.
The motors came from the factory with GIL exhaust manifolds and silencer tips with rubber flappers.
This is a major concern since I have read numerous articles on water reversion issues with high overlap cams in this application.
If we move to headers we will tack on 7-10k to our rebuild costs which is not in the budget plus they typically are not a reliable as the GILs.
I would welcome any comments and recommendations on the pieces we have chosen especially in the camshaft and exhaust area.
Thanks!

Eliminator28

You won't be getting 650hp with the stock Crane cam's. I would look into a custom grind for the motors.

The Gil exhaust is fine up to about 600hp (so I've heard)

The stock HP500 carb is only a 800 cfm.

Can you post up the dyno sheet from the stock hp500 pull. That would be some great info to have on here. I know I'm curious.

Dave

88Fount33

Someone with your hull and set up that can run 90, and then find out what it took for them to get there. Maybe an eye opening development.

Sport 280

[QUOTE=Joe308;3389212]I am in the process of upgrading the original Mercury Racing HP500's in my 1999 Formula 353 Fastech and need some advice.
The boat is running 79 MPH on GPS and our goal is 90 MPH which I believe will require about 650 HP output from each motor.

650 will not get you another 11 mph. As a general rule it takes 18 to 20 hp for each additional mph. On a twin engine boat, only hp increase of one engine counts. So if you get 650 hp out of new engines likely will see 5-7 mph increase.

I do not think you will get 650 with stock cam and heads.

Look up rmbuilder on this site and contact Bob, he is one of the best at designing custom cams. If you give him all your information he can get the best set up for your engines.

47EXCALIBUR

BLOWERS,,, Whipple ,,, or buy a complete rotating assy and convert it to a 540cu motor....merlin heads are a bad choice,,,castings are all over the place for alignment,,,Dart Pro1 CNC 335 heads and a 240 248dur 621 632 lift cam and you will go 90+ all day,,, also carb is to small,,,,,,, you can run blowers on pump gas 89 or 93 just depends on how much boost you run,,,,,you can get an Eagle crank and H beam rods that will be fine for this build since your on a budget to build it to a 540,,, do not get headers,,, they all leak,, Stainless marine III is the way to go

augie58

This might help.
http://www.offshoreonly.com/forums/g...-build-up.html

augie58

Try sending to axapowel(l) I believe he did what you are trying to do a couple of years ago. I made a couple of try at searching the thread with no luck. Keep us all posted.

Joe308

Thanks for your replys, heres the dyno run on the original motors - they may have been "touched up" about 6-8 years ago but they were indeed tired and the internal components did not impress us.
It appears I cannot upload images so here it is from Excel. Peak HP 537 @ 5300 rpm, torque 581 @ 4100 rpm test conducted last January @ 60 F with headers.

EngSpd EngTrq EngPwr Fuel A Fuel B FulA+B BSFC A/F_O2 AirTmp
RPM lb-ft Hp lb/hr lb/hr lb/hr lb/hph Ratio degF
3500 560.2 373.3 85.4 80.9 166.3 0.445 14.9 59
3600 554.3 379.9 85.3 84.3 169.6 0.446 14.9 59
3700 563.6 397 85.5 82.3 167.8 0.423 14.7 60
3800 568.5 411.3 87.5 84.7 172.2 0.419 14.3 60
3900 578.8 429.8 90.1 89.3 179.4 0.417 14 58
4000 581.2 442.6 92 93.3 185.3 0.419 13.6 57
4100 581.2 453.7 93.9 95.9 189.8 0.418 13.3 58
4200 578.8 462.9 97.4 100.7 198.1 0.428 13.2 59
4300 578.3 473.5 99.3 99.9 199.2 0.421 13 58
4400 576.3 482.8 103.2 109.9 213.1 0.441 13 59
4500 571.9 490 103.7 114.2 217.9 0.445 12.9 58
4600 574.4 503.1 106.7 114.9 221.6 0.44 12.7 59
4700 571.9 511.8 110.2 122.4 232.6 0.454 12.6 59
4800 560.7 512.4 110.9 122.2 233.1 0.455 12.5 59
4900 561.2 523.6 114.3 123.2 237.5 0.454 12.5 59
5000 546.5 520.3 114.9 122.1 237 0.456 12.4 59
5100 546 530.2 120.2 121.2 241.4 0.455 12.3 59
5200 536.8 531.5 129.6 126.7 256.3 0.482 12.3 61
5300 532.4 537.3 126.5 128.2 254.7 0.474 12.3 60
5400 521.6 536.3 131.1 135.4 266.5 0.497 12.3 61
5500 501.6 525.3 133.6 132.9 266.5 0.507 12.3 60

axapowell

Joe, got your PM. Thanks Augie!

Here's the deal. First of all I have tweaked the set up a little since 2006. In 2008, we bored, honed and decked both blocks to 509's (.030 over), upgraded the rods, pistons, oil pans, pick ups, oil coolers, and the entire fuel system. We are making the max HP for this small cubic inch. The speed is the real proof. I had the boat set on "kill" and ran into the 90's consistently. After denoting a piston at the end of 2008, I decided to back it down a little and again address the fuel system.

So, here we are today with a pair of 509's:
JE Custom Pistons (Teagues recipe)
Manley Rods H-Beam 6.385
Crane 168741 hydraulic roller cam
Crane roller lifters
1.7 ratio roller rockers on the exhaust, 1.8 on the intake
AFR 315 CC CNC'd heads with tulip inconnel exhaust valves and hard anodized coating for marine use
Hardin 10 quart pans with their offshore pickups
Hardin 18" x 3" oil coolers with the stock HP 500 oil filter mount with the thermostat
Mighty Demon Marine 850 Carbs
New this year Merlin intakes for marine
KE mechanical fuel pumps off of the sea water pump
CMI Elbow tops with bunged tail pipes for tuning, FAST wide band O2
XR drives on Imco Boxes
Sportmaster -2" shorties with a 1/2" spacer

I am down to two sets of props and last year decided to turn the props back to outward for handling around the dock. Props are Maximus 5 blade 28 pitch with a 15 5/8" diameter (cut down from 15 7/8") diffusers removed. Second set (faster) 32 pitch Mercury Bravo One 4 blade, also labbed, with the diffusers cut back. Brett at BBlades has the specs, if you use him, you can tell him it's ok to use my set up, it should get you close.

Anything else, just ask!

Dave

axapowell

Couple more things...
Crane Hi6-M Ignition boxes with Crane coils
Stock distributor for the pick up only
Isky Tool Room Springs (9905)

With the CMI's wet, we were in the 650 range!

That's about it for now, ask if you need anything!

Dave