7.3IDI -VS- 7.3Marine IDI

[jayro88]

What else is different? I am assuming (which isn't a good idea) that you are saying that they are able to "Hop-up" the marine engine more since they can dissipate the heat that it produces with these extra mods, correct? If this is the case, then what have they done to the engine to increase it's performance? Different cam? IP/Injectors? Intake/exhaust?

I would think that it would take a lot to gain that much HP (a lot more than hotter IP/injectors). There is a possibility that it has a different cam profile that has moved its torque peak much further out in the RPM range to increase the HP #, but it would need to be a significant shift (I haven't done the math).

 

[fsmyth]

Assuming 275 is the flywheel HP;
275*0.80=220 RWHP.
N/A 7.3's are 185, turbos are 190.
SO, they have added 30 HP worth of something. Probably fuel.

 

[89Laredo]

The number on the sticker is bhp, at the flywheel. They've added 85hp of something.

 

[hce]

The 190hp is net horsepower, power is measured with the engine fully dressed driving power steering pump, alternator, vacuum pump and fan. 275 is probably gross and definitely not driving a fan, and vacuum pump.
Also does marine horsepower use the same correction factors?

 

[fsmyth]

re-read my post.
the equivalent BHP for a stock N/A 7.3 would be about 231 HP.
BHP (flywheel) * 0.8 = RWHP. roughly. with an automatic power train.
Rule of thumb is about 15% loss for geared power trains.

 

[franklin2]

My brother works on the big boats. He told me taking the "lake" water in directly to the engine works ok for fresh water, but is not very good for salt water. A salt water boat still has a closed coolant system with I am guessing a water to water heat exchanger. He told me there are salt water boat trailers also, they use i-beams or some other structural steel, not enclosed tubing.

Fresh water boats are run in the salt water all the time, but there life is greatly reduced.

 

[IDIoit]

and with these being IDI's a closed system is the only way to run them.

 

[jayro88]

re-read my post.
the equivalent BHP for a stock N/A 7.3 would be about 231 HP.
BHP (flywheel) * 0.8 = RWHP. roughly. with an automatic power train.
Rule of thumb is about 15% loss for geared power trains.

If I am not mistaken, all of our power ratings are at the crank. The 185 and 190hp rating comes out to about 150-160hp at the wheels, depending on drive train loss.

I would assume that the the 275hp rating is also crank HP. That would mean that there was an increase of 85-90hp. Since diesels don't rev high, that kind of hp increase would take quite a bit more torque. HP=(TQxRPM)/5252.

With added cooling ability the turbo could be up-sized and fuel added. It would just take a decent amount to get there.

 

[fsmyth]

Well, that certainly would make a difference. I could have sworn that I read
somewhere that the 185/190 ratings were dressed (net) RWHP.
And assumed the 275 was also.

 

[IDIoit]

And assumed the 275 was also.

marine engines have ZERO RWHP

 

[hce]

Well, that certainly would make a difference. I could have sworn that I read
somewhere that the 185/190 ratings were dressed (net) RWHP.
And assumed the 275 was also.

Gross horsepower is taken of the crank no accessories and may not even be standards in the past often skewed.
Net horsepower is taken from the crank with accessories driven. U.S. manufactures comply with S.A.E. standards and corrections to sea level, temperature and other air conditions.
Wheel horsepower obviously is take from the wheels, and really not much testing standards. Not much consistency from one to another, harder to control the testing environment.
There is more to consider than rpm, torque and 5250 when determining horsepower, or comparing.

 

[dunk]

I don't think better cooling opportunity is a big factor for only marginally more power. I think the around +30 HP figure is ballpark of what the marine engine has. Anyone dyno a stockish rebuild engine (not chassis dyno)? Likely just a bit more turbo and fuel than the automotive version. Maybe a different cam, but not necessarily. Marine engines typically have wide LSA and little overlap from the factory to avoid reversion of water in the exhaust into the cylinders. A relatively low output diesel engine is not going to have much overlap.

 

[PwrSmoke]

To which marine engine is the 275 hp being attributed?

I have attached the 7.3L IDI brochure for the Star-Powr, which was a brand name of Marine Drive Systems (affiliated with Navistar), both the TDA (Turbo Diesel Aftercooled) and the NA. They were rated at 260 hp crankshaft (per NMMA regs) for the TDA and 200 for the NA. I have some other info that shows output at the gearbox as well. A second brochure for this engine (not attached) rated the torque at 430 lbs-ft (no rpm given). In any case, the graphs are there.

I have a '99 brochure from Mercury Marine that rates the 7.3L PSD at 270 shaft hp and 300 hp flywheel for pleasure use and 260 crankshaft hp for commercial use (235 propshaft)

AFAIK, the IDI Star-Powr came into being in the early '90s. I have not found any documents on a marine 6.9L. I find references to them but no info on who built them or much on their ratings. There are/were various companies that would do conversions on a small scale. The only power rating I have seen for the marine 6.9L is the standard 170 hp. Still looking for info on the 6.9L marine, so if any one knows of any??

As snicklas said above, unlimited cooling is the great equalizer, so any engine in a marine app can be cranked up. I saw and heard 6.5L marine engines at Peninsular Diesel in Michigan turning 400 hp back in the late '90s. They were being tested for use in Italian military patrol boats. Their standard marineized 6.5L was rated at 300 hp. I used a set of their heads on my built 6.2/6.5L hybrid engine in the old Bum-V. They are offering 310 hp 6.5L conversions for Hummers yet today and I see the 300 hp marines still available too. As I think about this, I seem to recall they dabbled in the IH IDIs at some point. That is a vague, 18 year old memory however.

In the case of the TDA engine above, it is both turbocharged AND after cooled... with a liquid after cooler no less... and rated at 3400 rpm. Remember also that these are probably pressure boat ratings, not commercial which would be lower. In other parts of the marine industry, engine are rated for continuous power and intermittent power. The pleasure side of the NMMA rating are probably nearer to an intermittent rating.

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[fsmyth]

marine engines have ZERO RWHP

You know what I mean. With drive train losses.

 

[IDIoit]

wonder if theres a prop dyno out there....