Small Block performance upgrade suggestions
 

My engine compartment will only fit 2 small blocks. I presently have 2 newer 350 Magnum EFI Mulptiport engines.

Please suggest horsepower upgrades.

Thank you very much. RB

It depends on how much money you want to spend (cubic dollars)
you can put a blower on which is the best but most money or you can stroke it to a 406 or 383 and make a very good motor
there is ton we can do ,,give me the amount ,,,wecome to the board :D :D

Would $4,000 to $6,000 do anything?

both motors alittle ,,each motor alot,,,,, thats worth the money I should say :D

How about $3,000 per engine?
I am considering Stainless Marine manifolds and risers as a start. Any thoughts?

The engines are out of the boat, therefore now may be an ideal time to make some upgrades.

Also...Any thoughts on "lab finishing" the props?

yes that may help a few MPH , I would add a stroker crank and pistons,and port the heads and go to like 9 to one compression and change cams with the stainless exhaust and that would make a potent package for alittle more than you were talking

To start with port the heads and angle cut them to get 9 to 1 comp. add you exhaust and a cam and reprogram the ecu and that will be a good start

Thank you for your thoughts.

Would it be better to trade for Scorpions (340 hp)? My 350 MPI EFIs are newer. I think I can get them on a trade plus $6,000.

what about this 92 350mag pretty stock I just put
K&N filter, K&N snubstack , EMI thunders, and Corsa Q & Q
thur hull. this is in a 25 foot 3800lb dry single step boat
How much to get a reliable 400hp

If your motors don't have them already, upgrade to the vortec heads. Looks as though they will flow nearly 400 hp without a lot of work. Not sure how much as you are limited in cam choices with the wet exhaust. i'll dig up the article as soon as i can.
ken

Thank you for searching for that article on cam choices.

Is it possible to get by with just the Vortech heads and no cam change?

Anyone have a link to research Vortec (sp?) or Vortech (sp?) head availability?

There are about 7 sets of vortec heads on Ebay right now.

I am also looking to hop up a 350 for a friend. Will be real interested in the cam specs also.
Thanks.

The Vortec heads are a good choice for an upgrade but be careful when changing cams. The Vortec head has limited valve lift capability unless they're modified.
The Vortec can only handle valve lifts of about .420 max. The valve guide boss and spring seats need to be machined to gain lift. Several companies offer the Vortec heads already modified so rework isn't necessary.

This article should help you out a little:
http://www.chevyhiperformance.com/howto/97458/

Great suggestions! The article is also very informative.

3 questions:

1) Is there a difference between a Vortec head for a marine application as opposed to a vehicle application?
Can I talk to any Vortec head supplier?

2) Will the stock valve covers still work?

3) Is it possible to just change the heads without porting the heads, changing the cam, pistons, or heads?
Or would it make sense to do the additional modifications while the engines are out?
I would do the additional modifications as long the price and reliability is reasonable.

If anyone is interested I have a new zz4 383 stroker with dyno time only. It already has lighning headers and all the go fast internal parts. Internally balanced and blueprinted.

yes while their out blueprint them and do port work on the chevy vortec heads ,mainly the valve pocket !

Also you could trade them for some other motors

the marine head has innconel exhaust valves and good intakes

1)No difference, except for the exhaust valves. A severe duty type needs to be installed.
2) Yes. I think I saw you have the center bolt style. That's what they take.
3) Yes you could. But, the intake manifold will need to be replaced because the intake ports and bolt pattern are different. Check to see what rocker arms are currently on your engine. The Vortec heads require self aligning rockers. Guide plates aren't used. If you decide to go with roller rockers check into Comp Cams and GM Performance Parts.

Great advice!

As I start adding up the costs, I am starting to wonder if it would make sense to switch my engines with Scorpions. I may be $9k to $10,000 out of pocket after selling my present engines.

Any thoughts?

Actually, after selling my engines, I think I will be closer to $6,000.

get the scorpions for that price of add a coolcharger to each motor best bang for the buck and reliability... i also went through this w/ my 28ss with t 350 mpi's i decided on just getting a bigger boat!!

Why don't you just supercharge them? Any major mod such as cam, heads, manifold, etc. thats done to the engine will require a cal change and theres only a handful that can even do that, even a smaller amount who have the base cal for the 350 Mag.

Is the engine 2002 or later? Does it have the MEFI3 or ECM 555 ECU?

Thanks,
Dustin

Great information! Thank you.

This boat ran 77mph with twin HiPer 320s and Alpha SS drives. The problem is that I kept breaking the Alphas.

The 320s were a Hi Performance engine build by Mercruiser in 1988 and 1989. Powerful engines but they were not reliable. The manufacturer gave me a good deal on these 1995 Mercruiser Multi Port EFI Magnums. I kept the Alpha SSs, but they still kept breaking. So now I am replacing the drives with Bravos, and since the engines are out, I am thinking now is the best time to replace them with Scorpions or do upgrades to these. They have about 100 hours on them.

I think I can switch to Scorpions for a difference of $6,000. Superchargers would cost more than that, right?

Vortech has a supercharger system for the carbureted SBC for about $2400.00 complete.

If you need a set of polished crossover kits with the thermostat housings for those small blocks I have a pair.

Thank you for the information on the Vortech supercharger and the polished crossover kits.

How about this

Another

What exhaust is on that SBC?