Re: Putting a Turbo on a boat engine?
Here's a touch of market research for ya: Prove to me that this bolt-on kit will provides notable extra USABLE power (torque...not HP), WITHOUT sacrificing holeshot. I personally think this will be difficult to overcome as already mentioned earlier, due to the steeper pitched prop (AKA higher gear) it will require to prevent over-revving then outdrive at higher speeds. BUT...once that's proven to me, price the kit for less than $1,000, and I'll buy it for my 3.0 boat. There...you now officially have one interested buyer...just show me it works and keep price in line.
Realize that most of us who own 3.0 and 4.3 motors have less interest in top speed, and more interest in holeshot improvements...we're pleasure-cruisers and watersports enthusiasts. AND, we're operating on a budget. If we could afford to buy a $2,000+ kit to bolt on to our motor, we sure as heck wouldn't have bought cheap 3.0L and 4.3L boats! So recognize that if your turbo kit makes my 3.0 go 50 mph, I frankly don't care if the end result is a boat that takes a whopping 19 seconds to go from zero to 30 and I can no longer use it to water-ski due to slow accelleration.
Which leads me to what I still think the biggest hurdle you'll need to overcome first: The understanding that all boats only have one gear, which is pretty much the equivalent of 3rd gear in your car, and you have no ability to shift.
For reference, take your heavily modded Pontiac (which sounds AWESOME, BTW) out to the strip, stage it at the line in 3rd gear, and launch it. See how much time it takes for your turbo to spool and cover that 1/4 mile without the use of gears 1 & 2. THAT's pretty much the problem you need to figure out how to overcome first...turbos (in gasoline engines...the diesel discussion is completely a moot point here as turbo diesels provide a totally different shaped power curve) need to build RPM first in order to generate power. But boats can't quickly build high RPMS at low speeds because they have only one gear and it's a STEEP bugger. So if you can redesign a turbo that will make your car do the 1/4 mile in 15 seconds or less WHILE LAUNCHING 3rd GEAR, now you've got something that'll propel a boat very handsomely. And yeah, if you don't stall your motor you'll totally smoke your car's clutch when you try this experiment...but there's good news. This won't be a problem on a boat, as they all have built-in, impossible-to-stall, automatic, impossible-to-overheat clutches in the form of prop slipping through water...so you don't need to worry about designing that aspect of the kit, it's already done for ya!
Also remember these outdrives need to keep running at probably 5,000 RPM or less if you want them to live a long life...maybe a touch more would be OK. But a turbo that produces oustanding power in the 5,500 to 6,000 range will be of no value whatsover in the water, despite my strong belief (as you also believe) that the 3.0 and 4.3 motors themselves could easily handle such RPMS without durability probs. The drives I am less certain could handle higher RPMS, even though they could easily handle the power increase you are proposing...Alphas are the predominant drive behind these 2 motors you are inquiring about, and I believe these same Alpha drives are put on 5.0 and even some 5.7 Liter engines. So power handling ability is there, but again I believe they are mostly tuned to make their HP in the sub-5,000 rpm range, and I think that's where you likewise need to cap it. (Oh...which reminds me...when you're doing your aforementioned 3rd gear 1/4 mile run in your car and trying to get it to cover the distance quick, you're not allowed to let your motor exceed 5,000 rpm either...you gotta remember for this experiment you're driving a BOAT that happens to have wheels, not a car!)
Frankly I hope you can figure it out, as I'd LOVE to buy such a thing for my wheezy 3.0L. Power to weight ratios of turbo 4 cylinders are hard to beat...and weight is CRITICAL in a boat, so the turbo argument is strongly in your favor in that respect. But in the meantime while you're doing your R&D, I'm probably going to do some minor airflow mods geared toward increasing low RPM torque in the naturally aspirated version, which is really what these boats need.
Focus your efforts on increasing low RPM torque output of these motors, and largely ignore the calcualated peak HP #'s provided by whatever dyno testing you'll do in the course of your R&D. If you follow that path and show that the turbo will do those things, I think you have a better chance of succeeding.
I also agree you'd have better luck looking toward the supercharger route than the turbo route. Methinks a SC is bit simpler and easier to control through the lower RPM ranges than a TC. But I am much stronger in working with naturally aspirated engines, and I've never personally experimented much with forced induction, so I may be wrong on that.
I wish you the best in your research and quest!
