Turbocharged or Supercharged Gasser

[Bayside Bert28]

My Bertram 28 has the 5.7L Vortec 350's with carburators. These are good for approx 310hp each. I was curious about using a turbocharger or supercharger on these engines to get an extra 100hp or so from each engine. I have not found anything online about this.

[scot]

Either of the two will create the bulk of the additional HP in the upper ranges...4000rpm and above. The gain at cruise (2800rpm-3500rpm)would be more like 20-25HP = not worth the trouble.

Look at "where" your engines are rated 310HP. I think you will find they are rated 310 at somewhere between 5200rpm - 5800rpm. Based on prop HP consumption curves, and engine dyno curves, you are actually only making something like 140-150HP at cruise. This is why many sportfishing boats cruise faster with diesels, they have access to more HP at lower rpms. Many diesels can cruise forever at 80% of WOT. Gas V8 engines tend to really start making power above 4000rpm, the HP curve is very sharp on a gas engine.

Inboard sportfishing boats are all about cruise speed, not WOT because you will spend 95% of your time at cruise speed. B28's are not fast boats by todays standards and your money "might" yield you an additional 1-3kts at cruise speeds. Not to mention the additional load you will be putting on the bottom end of the engine by increasing the cylinder pressures. They are not cars, or go-fast lake boats.

No stock engine will live very long at 4500rpm. So how long do you want the engines to last, and how much is 5-6kts on the top worth?

If you want to make the engines better, upgrade to the fuel injection set up. Better MPGs, more responsive, etc...but the simplicity factor goes out the window.

If you must pursue, the only one that could realisitically be considered is the supercharger. You would have a real exhaust piping mess on your hands trying to turbocharge a V block, raw water exhaust marine engine, and fit it all under the cowling. Get the stock HP curve and compare it to the supercharged HP curve...now look at both of them at 3000rpm.

Just my red-neck opinion, and I like hot rod engines, I've built a few myself.

[Harry Woods]

It is not cost/value effective to turbocharge or supercharge the 350's in your B28. Scot has given you sound advice in the above post. You have been the steward of Third Strike for a few short months and are still in the process of assessing the strenghts and weaknesses of the vessel. Give it a season or so and than review the power options available to you. Before you left New York you took me for a run on the boat and it is a fine example of a well cared Bertram that performed great. Depending on how you use the boat (offshore vs. inshore) you need to assess the amount of hours conditions
will permit the higher speeds and the cost to obtain them.
Harry

[Jeremy]

A single carb root style blower would probably build you the best power in the low rpms. Turbos and centrifigal style blowers/superchargers are gonna need the higher rpms like scott said. Either way, it's gonna be a gas hog. If you want more power in the lower rpms, have you considered swapping cams?

[JeremyD]

How about an Ls3?

http://www.jegs.com/p/GM-Performance/GM ... 6/10002/-1

424 ft lbs torque - crate engine is $7400 6 bolt mains.



dyno chart



Me personally = my B28 runs so much better and smoother at a little faster than cruise - at 28kts - 3200-3400 rpms it really smooths out

[Bayside Bert28]

OK - I get it.

The LS3 might be an excellent choice once the 5.7's get tired. Maybe season after next ...

I suppose the LS3 would be lighter too. I wonder if it's no larger (could fit in the 5.7 vortec space without a whole lot of modification?

The other issue regarding supercharging seems to be octane (which I forgot about) .. I used to run a twin turbo Porsche and I would fuel it myself with race gas from a drum.

Meanwhile, I have had my hands full cleaning up Third Strike II ... the squawk list is getting smaller!

Mike

[Kevin]

Mike,
If you boost a gas engine the fuel consumption goes through the roof. A car at cruise speed on the highway is not under boost untill you put the hammer down. I believe a boat is always under load. I think that would be like never taking your foot off the gas in the porche. Those V blocks would split in half shortly after your wallet runs dry. If you do it make sure you take pics because it would be high on the cool factor.

[JeremyD]

Do you have a Porsche Kevin?

[bob lico]

good advice from jeremyD .that 6" rod makes that engine put out fantastic power. the crank alone is worth 2,000 dollars!! trust me thats one hell of a deal.

[Kevin]

No Porsche here. Don't have that kinda ching. I'm a mustang guy. Tinkered around with boost quite a bit on it though. I was running 17 lbs supercharged with out aftercooler. Lots of methanol spray to keep it cool.

I have a turbo kit ready to install but just to hot to be messing with it. The kit up will support 800+ horse power with proper waste gate and blow off valves. I need to keep it at 550 since I am running a stock block with 2 bolt mains.

Car picture thread maybe?

[Preston Burrows]

Jeremy:

"Me personally = my B28 runs so much better and smoother at a little faster than cruise - at 28kts - 3200-3400 rpms it really smooth"

What motors/trans/props are you running with in your B28 to get those numbers ? Flybridge Cruiser or Moppie model ?

I run my stock B28 FBC at between 3000rpm - 3200rpm for a 22 knot 'normal' cruise......3400+rpm would take me to a 24 knot 'fast'cruise, where the hull runs at flattest over the cruise 'hump' but my motors are screaming and I'm having visions........

[JeremyD]

I have the 260 mercruisers - and that would be with a clean bottom.

FBC - but it's pretty bare bones - bimini no tower -

[DRIFTER31]

The LS motor sucks alot of fuel and looking at the dyno sheet it is not that strong in torque at 3000-3500. Injected 502 big blocks will be faster at lower rpm's due to the torque/rpm factor.

[Bruce]

An auto crate engine ain't the way to go for marine and if your gonna introduce more air into the engine to make power, your gonna need to exhaust it to make apprecable gains. Stock marine exhaust manifolds are poor at best and add to that the resistance of pushing water.


You can garner more speed by going to the next gear ratio if you can swing the prop(clearance and shaft diameter).

IE if your now 1.5:1, goto a 2.0:1.

I've done that trick many times with gassers. The last 28 I did with 300hp MPI gassers I went with the 2:1. Fast was an understatement.

[Carl]

I do not know about putting in boats...
but we fabricate several installation systems for an aftermarket Supercharger company. Centrifical design so they can be located in various positions within the engine compartment with takeoffs from the belts. Simple "Stage One" bolt on setups with electronics and headers just about double the hp and unless "you get on it" they increase the gas mileage in many cases.

Increase the boost and the lower end and tranny needs to be modified to handle the power which may be the case for boats. But the guy I make them for thought with a low boost setup I'd be able to increase economy and cruise speed in the boat. I thought about it, but I didn't need more headaches and he is a car guru with abolutely no experience in boats.

[Bayside Bert28]

You can garner more speed by going to the next gear ratio if you can swing the prop(clearance and shaft diameter).

IE if your now 1.5:1, goto a 2.0:1.

I've done that trick many times with gassers. The last 28 I did with 300hp MPI gassers I went with the 2:1. Fast was an understatement.

I'm not sure what props my boat is running but my max RPM is 3900 RPM WOT ... I think the previous owner set it up this way on purpose. When it comes out of the water in another week or so, I'm going to find out which props it has. I think the max rpm is supposed to be 4900 rpm with these engines.

Mike

[Bruce]

If your engines are in good shape to turn max rated rpm and they because of props are under turning by a grand then thats a real good way to throw a rod through the side of the block.

[Craig Mac]

With the event of higher hp diesels there seems to be no interest in developing a better gas marine motor that has suitable characteristics for fishing boat needs-- maybe they just couldn't get around the efficiency #'s.

But back in the 60's Daytona Marine developed a twin turbo charged big block that was installed in various fishing boats. It advertised 380HP @ 3800 RPM.

Also Seamaster had a 534 cubic inch Ford truck block that developed 277 HP @ 3400.

Turbo Charging, Super Charging, inter-coolers are reserved for high strung offshore racers and too tempermental for fishing boats. But that didn't stop the diesel guys.

[Carl]

Turbo Charging, Super Charging, inter-coolers are reserved for high strung offshore racers and too tempermental for fishing boats. But that didn't stop the diesel guys.

I often wonder about that, just because you can raise the boost to really crank out hp doesn't mean you have to. When the kits we fabricated where 1st put out they almost doubled the hp and had relatively few problems. Soon as they started changing pulley ratio's and bringing that boost up they had issues with items as simple as belts slipping to engines and trannies destructing...

The question is who is going to spend several thousand dollars to to enhance their motors a few HP and some fuel savings just to prove it can be done without killing the motors. Especially when you can just go out and buy proven higher hp motors with warranties. Or go diesel...