MarkRobinson

Hi guys,

Most of you know i've gone bat-chit crazy & plan to place a 951 power plant into my little Porsche speed boat.

I had a turbocharger selected, but feel it's gonna be difficult to plumb evenly: hear me out: my boat has dual exhaust exits out the top of the boat (very rare), & I plan to use them but don't want my little 4-banger to sound like a 4-banger: so I'm contemplating twin turbochargers & of course a completely new exhaust manifold to pull this off. I can get a pair of low-mile GTR turbochargers pretty easily/cheaply, & though they flow upwards of 650hp for the pair, they're sized for a 3.8 liter engine & will probably be too laggy for my little 2.5 or 2.8l motor.

So I need to build my motor to withstand higher boost: 25-28psi on occasion, will be tuned to run on E85 & my lake water (for intercooling) averages 70 degrees. I also want a pretty cammy sound if possible: is there a common grind that provides this? Sadly, boats run about 5-5500 max so you size your prop according to that...a good power spot for the stock 951 cam...maybe just more lift?

I also need to find the correctly sized turbochargers, or maybe build a compound turbocharger kit where one turbocharger feeds the other as that will yield both lower-end torque and higher-end HP flow, but still leaves me with one exhaust. I could always run the WG's to the other side but still have to water-cool.

I'll post a diagram of my engine bay shortly.

Mark

eman930

why not just use the single turbo, Plumb the exhaust to one exit and the wastegate exhaust to the other, This would keep your exhaust easy to make and you wouldnt have to design and package soo much. Plus when that wastegate opens your boat wont sound like a 4 cylinder.... As for the turbo Id see if you can find a 4 cylinder boat that comes turbocharge from the factory and use that turbo, As long as the engine is about the same size you should be ok and that will take alot of the guess work outta it

MarkRobinson

Most boats are not turbocharged...superchargers are more common.

I could keep my Precision Billet 5858 turbo, fast-spooler & upwards of 600hp. Yes that was my initial idea & still on the burner.

Jfrahm

I suggest a single exhaust and a diverter so you can go through-prop. Through hull is kinda fun but pretty obnoxious and tiresome after a while, and some lakes are patrolled for noise so you can get hassled, ticketed, etc.

The main issue with twin turbos is keeping them balanced so you do not fry one while the other is loafing. I do not see the upside of adding more issues to your build. Do you plan to have a kicker to get out of the marina with (and to get home if your main engine fails?)

MarkRobinson

Boat is very rare & designed by an Architect with the dual pips in mind: I plan to utilize them.

txhokie4life

KISS Mark KISS

And might I suggest a back-up plan.....



Mike

MarkRobinson

I'll have you to oar with me right Mike??

txhokie4life

I'm sure I'll be too busy wrenching on some other P-car PITA :-)

But if you really want to use both pipes == drop a 928 engine in there,
turbo charged if you must.

Surely you have a spare one of those lying around.

Mike

MarkRobinson

Yeah I do but that's kinda easy & won't have the exotic appeal I want w/o twin turbochargers...+ considerably heavier than the 951 setup.

Can I get that "loaner 944" block from you this weekend??

Mark

rlm328

The reason most boats run superchargers, as you are probably aware is due to the torque required for coming out of the hole. The supercharger gives you the low end where the turbo does not normally kick in until mid RPM range. With the HP you are talking about will require a fairly large turbo so the spool will be coming later in the RPM curve.

MarkRobinson

Yes though my boat is a mere 2200lbs, & also came in outboard & Jet formats (most common), so if a 115hp outboard get get it out of the hull, a modern 951 with a bit of lag can too. Because of my drive I won't be goosing it out of hole.

Yes on the HP/RPM requirement, hence compounding or twin turbocharging.

V2Rocket

Why not just plumb the single turbo outlet to both pipes? If you ever run a 944 motor open headers, its pretty lumpy...turbo would quiet it down a bit but the sound is still there. Without a muffler you should be OK, plus not much restriction on the turbine dump..

reno808

if your trying to keep up with those chevy v8 boats and fords too GOOD LUCK with that

racerxrick

ahh...a word of encouragement from Uncle Reno!

aglaes

You may want to do a little more research on this. I'm no expert but I have read / heard that low end torque is very important for boat motor performance. Usually boat motors are set-up more like truck motors - to maximize low end torque. Not sure a 951 engine will give the kind of performance in a boat that you might think.