Upgrade small blocks...
 

I would like to get as much power out of my 1999 350magMPI's as possible w/o losing reliability....So where to begin:
I have a valvetrain problem with the port engine so I will have to pull that head for starters....
BTW...It's a 99 Active Thunder 28' w/400hrs on the motors & Bravo drives....Already added new Stainless Marine exhaust systems...got 150-200 more rpms...
Currently spinning 4-blade 14-1/2" x 26" Hydromotives @ 4800rpm's I see 72mph...To get to 80mph I figure I need 400hp each motor.
1. Can this be done (efficiently$$) w/o supercharging? reliability?
2. If I go through the top ends completely & decide to add the Prochargers, what to expect? Reliabilty?
3. Why would the manufacturer say that the hull is not intended for over 80mph? Liability issue? or is it
a handling issue? My Switzer went 81mph w/200hp Merc & not that I recommend it, I felt fairly comfortable (after the learning curve; ie. throttle through the chine-walk @65). This AT hull is exceptionally built; deep, strong, straight lines...why limit it to 80?
4.What can I expect to spend on a sb top end "freshen -up"?
5. Should I consider new cams? New aluminum heads?

I know many will say that the small blocks won't produce enough torque; but I don't want to put BB's in a 28'AT; plus I like the fuel efficiency of these motors....It is such a nice set-up as is; if I can't do any upgrades I'll just fix the valve problem and freshen up both motors and leave stock.

Thanks in advance for ideas...

.....?

stroke 383 or 400 kit, that will give a nice increase in torque good heads so it will breath

400 HP is alot to expect out of 350 cid and ALOT to expect out of the stock short block. Before I tried it, I'd completely go thru the bottomend. You'd most likely be looking at aluminum heads as well much bigger cams- and compression that would require 93 octane. I can't help you on the Merc injection but I'd venture to guess to get to that level, you'll need to go carbureted.

PM Sydways here on the board. he has a relationship with AT and can answer your questions on the hull speed thing.

One thing to keep in mind- these mods won't add value to your boat anywhere near what they're going to cost you. You may want to put honest project cost numbers on paper and compare that with moving into a boat that's more what you want. The market is flooded with bargains.

leave stock motors stock

Nosurprize there!!

What's up Mike?

We did that on our 272 Formula . Made 383's with 425hp went from 54mph to 69.9 on gps. :drink:

Just curious; where do I get these 383 kits & how much $$?

If you have head issues anyway, 1st upgrade to vortec heads, these things are worth 40 hp at lower rpm over what you have now, assuming you have std s/b heads, you have to get matching intake, rockers to make it work, sconnins $ dickey have the complete kit with everything needed, just did one...the prochargers will do wonders and if you keep the boost between 4-5 lbs and the timing at 28 max and no lean condition should work very well and be reliable, have a friend with twin small blocks in a nova III w/ prochargers 4 lbs, runs 85 on radar, and that is not a great hull, Rob

Just put some 502's in it and sell the small blocks.
Reg. 502 ,415-425 HP reliable . Maybe 100 pounds more but alot more tourqe easy fit ,...............done.:eek:

Cool, that is very helpful....

NO Big Blocks
 

I'm not even considering bb's; too many reasons to list. But #1 is the hull is perfecty balanced w/sb's or a single bb; maintenance w/bb's would be a nightmare....then there's the weight!! And the fuel consumption!!!! I get 3+mpg @3800...also my Bravo drives will last FOREVER, if cared for....you get the picture....

The Raylar 550SB would be great if I had an extra 75k layin' around!

Wouldn't '99 350 MAG's already have the Vortec heads?

Here's a kit from Jeg's. It an Eagle cast rotating assembly for 1-piece seal blocks. With Vortec heads and a good roller cam, you should not have a problem pusing 450 HP.

I'm using almost the same kit in my 383 but I have the Competition set up that's all forged with 6.0" H-beam rods. It was about double the price of the cast kit.

http://www.jegs.com/i/Eagle/356/B13005L/10002/-1

This is what I used in mine...

http://www.jegs.com/i/Eagle/356/12010/10002/-1

Don't let the compression ratios throw you. If you're using Vortec-style heads then you can get away with almost 10:1 with premium.

Have you talked to the few engine builders that are well known for their MPI skills what their experience is with the fuel system and reprogramming the ECU? If you want to stay fuel injected (and stay close to that "reliable" 3.8mpg), that's going to be your biggest hurdle and you need to find out what they've done and get their feedback.

With that being said, how about looking at the Merc 6.2 motors to see how they're set up. What about that Scorpion 377? There's no need to re-invent the wheel, just build it better and for less money.

Fix your valve train issue and bolt on a pair of Whipples. The initial cost is quite a bit more then the prochargers but it is worth every penny in the long run. The procharger is an excellent unit, but their "kit" leaves a lot to be desired. If you have a mechanic who is well versed in prochargers then I wouldn't hesitate, but by the time you modify everything to make them run as well as the whipples do out of the box you'll be very close to the same cost.. :drink:

Two Raylar LSM 550's don't cost $75K they are about $51K for twins and for what they are thats a very good price point. One of OSO's good marine engine builders can rework your 350's for an easy 450HP each with the right parts and builds. They would have to replace your stock fuel injection with something like the small block ramjet system and couple that with some good smallblock heads and a blueprint equipped forged short block and headers and a 450HP screamin smallblock would be yours. Buying a Jegs type crate motor and putting it in marine high performance use is like playing "Russian Roulette" with three bullets in the gun!! Don't buy your motors twice !!

Best Regards,
Ray @ Raylar

Mercury reman makes 400hp SBC engines. Mbam on this board sells them. http://www.offshoreonly.com/forums/s...d.php?t=187351

That's true, I did already get a quote....but I was including the new Bravo XR's or Imco's and Props I would need!

I've built quite a few packages like you are looking for. You already have most of the parts you need. Build them into 383's, do some port work on the vortec heads and install larger valves, and the correct roller cam. You should have the older style 4 bbl intakes with a throttle body, which is pretty decent so you can stay with that. I have reprogramed the MEFI3 computers and been able to make 400 HP with this package in complete trim, tested with wet marine exhaust. I would highly recommend tuning it on the dyno or in the boat with an A/F meter.

Recommendation from someone whos been there many times with a SB powered boat-- Fix the broken parts and enjoy it.

IF you really want a BIG project - and it will be a real project. If your going to pull motors then - go for the lower end rebuild with the 383 kit as many have mentioned. Buy a good pair of heads with bigger valves already in them (AFR/brodix) and re cam with a roller ground something like an Engle EP20/22. Tune it on a dyno with an AF meter (also previously recommended) or risk doing it again in 30 hours.

This will get you to 400+hp and you WILL hammer the gimbles they will no longer be "bullet proof" after that - I've gone through 3 of them in 10 seasons, and since yours are already high hour put that money aside right now........

Going BB at this stage means 8K in exhausts alone.

Really dude- just fix it and go boating.


Uncle Dave

Laveycraft 2750 Ilmor 710
Laveycraft 20.8 Sebring 406 SB
Fleetwod nitrous toy hauler
Yamaha raptor 700/Kawi KFX 450
Nissan Titan
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[QUOTE=Uncle Dave;2658296]Recommendation from someone whos been there many times with a SB powered boat-- Fix the broken parts and enjoy it.

IF you really want a BIG project - and it will be a real project. If your going to pull motors then - go for the lower end rebuild with the 383 kit as many have mentioned. Buy a good pair of heads with bigger valves already in them (AFR/brodix) and re cam with a roller ground something like an Engle EP20/22. Tune it on a dyno with an AF meter (also previously recommended) or risk doing it again in 30 hours.

This will get you to 400+hp and you WILL hammer the gimbles they will no longer be "bullet proof" after that - I've gone through 3 of them in 10 seasons, and since yours are already high hour put that money aside right now........

Going BB at this stage means 8K in exhausts alone.

Really dude- just fix it and go boating.

Very well said...I've come to that conclusion after all the "opinions"! To gain 10mph I would have to spend 5 figures and lose reliability and efficiency...what a waste of time and money....fix-r-up and go boatin' sounds good to me.

BTW, I just had the gimbals rebuilt...that wasn't cheap. I need hydraulic steering; esp. if I add any hp.

Yeah what a pain huh? I call it the circle jerk of speed.

motors /Hydraulics/drives/props- its an endless circle of spending that you cant get back when you sell. You already made the #1 call onthe exhausts and you can probably get a few MPH playing with prop tuning if you really want.

IF you dont do hydraulics and you can go 80 a cable failure could kill you and your crew without much warning, or stop you from turning quickly enough to get out of trouble so youd have to do that..............

Your rig looks pretty cool to me and cruising at 55-60 with 12-17 left over is pretty respectable for the dollars per hour your spending to do it. Have fun and let us know what you do either way!

Uncle Dave

Laveycraft 2750 Ilmor 710
Laveycraft 20.8 Sebring 406 SB
Fleetwod nitrous toy hauler
Yamaha raptor 700/Kawi KFX 450
Nissan Titan

Uncle Dave must go. He's too sensible.

If Uncle Dave would only follow his own advice -he'd be a much happier wealthier guy.

I have a habit of learning "by mistake."


Uncle Dave

Laveycraft 2750 Ilmor 710
Laveycraft 20.8 Sebring 406 SB
Fleetwod nitrous toy hauler
Yamaha raptor 700/Kawi KFX 450
Nissan Titan