|At the Baltimore boat show last weekend, I looked at a Supra SSV, Nautique 210, and Mastercraft X2. It is my understanding that all three of these boats use the same GM 350 block, but the Supra has 320 HP, the 210 has 330 HP, and the X2 has 310. What is that accounts for this difference in horsepower?|
|I'm no mechanic, but it could just be a performance cam, etc.|
|One major difference is carburetion vs. throttle-body injection (TBI) vs. multi-port injection (MPI). The latter provides better fuel delivery and more horsepower. |
Other differences that can affect horsepower and torque include:
1. Cylinder head port size & configuration and valve size.
2. Piston design and combustion chamber configuration.
3. Valve timing (i.e., camshaft lobe profiles and separation).
4. Compression ratio (although most marine 350s seem to have the same CRs?)
5. Ignition timing & ECU program.
And, of course, there are two "350s" available. One is the old SBC while the other is the newer engine in late model Camaros/Firebirds (RIP) and Corvettes (LT1? Help me out here, Chevy guys).
In addition, more powerful engines typically produce max horsepower at a higher RPM. If the engine in spinning faster, it is buring more air and fuel in a given time period and thus making more horsepower (which includes time as a calculation factor). Internal changes may be necessary to allow the higher RPMs, such as revised camshafts and stronger pistons, crank, con rods, and valve springs.
The boats you mentioned use different sources of marinized 350s. Supra and MC use Indmars, while CC uses PCMs. There MAY be some differences in the specs for engines delivered to these two "manufacturers."
Finally, there is a fudge factor (or at least a rounding error). Horsepower does not come in discrete chunks of 5 or 10. So how do the marine 350s produce convenient numbers like 310, 320, 330, 370, 375, and 385 horsepower? Those numbers cannot all be "accurate."
(Message edited by fogey on January 22, 2003)
|Yeah, what he said.|
|Ok, thanks. I see that I have a lot more to learn on the engine side. But yes, I found it especialy strange that the Supra EFI Indmar and the MC EFI Indmar differ in horsepower. (I was under the impression that these are both multiport injection). |
|Fredrik, I did some research and found that Merc, PCM, Indmar, Volvo, and Marine Power all buy their engine from a company called GM Power Train. They then complete their marine process to the cooling systems, fuel delivery systems, ECM calibrations etc. There is a window of plus or minus 10% to rate the HP of the engine. In the case of 300 HP engines there is a lot of room for rating. True HP could be blemished by marketing. In the case of Indmar they do not rate their engines on their web site. HP is marketed by Malibu, MC, Skiers Choice etc. The same could be true of all the above engines listed. In the case of 6.0s and 6.2s their is a tear down and modification to achieve greater HP and that comes with a larger price tag.|
|How do you know which engine is the strongest, for example the monsoon(335 hp) and the LS1(375) corvette. Because of the LS1 engines higher rpm range it rates at 375 hp,(torque*rpm=hp) but is the engine faster in the low and medium rpm range or just faster when you talk maximum speed compared to the monsoon.|
|I have not heard good things about the LT1 for boarding. It's a great motor, but the added hp is a waste for us: it's all top-end. |
I have the 325 hp Monsoon, and I'm quite happy with it.
|The displacement of the block has little to do with the overall ouput of the engine. Any major manufacturer can order an engine with a certain output and performance characteristics to match the transmission and final drive (prop) characteristics they want. The big question is WHERE are they measureing the horsepower. At the crankshaft, the transmission, the prop shaft, etc. |
The key to it all is that all hp ratings are derived from the torque of the engine, nothing more, nothing less.
Equation for Brake Horsepower or BPH is:
BHP = 2 times pi times torque times revolutions; all this divided by 550. Pi is 3.1416 and torque is in pounds-feet, and revs is revs per second.
The easier way is HP=torque*RPM/5252.
From HP, you can convert to watts, joules, calories, BTU, etc. I wonder how many Big Macs it would take to operate a wakeboard boat??
|Oh yea, as per a previous discussion, optional engines should be considered carefully. For example, on paper, the Hammerhead option on the Malubu's does not look to be a good value. I haven't been in a boat with one, just saying that the engine specs ON PAPER don't appear to give much of a usable increase in power and warrant the extra money. Actual in-water performance may be a different story.|
|They get different ratings because they measure there power differently. Some take it at the bell housings and other factor in the tranny. PCM uses the 1:23 to 1 tranny that provides a lot more torque and that is about all I could tell you!|
|My Toyota documentation says that my 300 HP engine puts out 224 Kilowatts at 6000 RPM, so I got THAT going for me, which is nice. |
|The difference in horsepower from one 350 cubic inch Chevrolet motor to another is INK! Do not fall for the horsepower wars. The 5.7 multi-port motors whether they be Mercs, Indmars or PCM,s are essentially the same. |
Drive the boats side by side and make the decision based on your criteria not a salesman's.
Whether your five year old boat in the year 2008 has 315, 330 or 335 HP will have no bearing on it's resale value.
|Will throttle-body vs. multiport fuel-injection make a difference in engine performanace overall (not just relating to HP)? I have noticed that multiport is the new thing, but does it really matter that much?|
|I am with you Matt. Our current 275 hp Indmar (with a powerslot) has never left me wanting anything more, even fully weighted. |
Am just tryuing to figure out whether the multiport does anything for you as far as reliability or gas consumption or anything else?
Did some more resaerch on the Indmar Predator, and it is apprenlty throttle-body injection (even though it is mislisted in the indmar site as multi-port).
|I had the 265 hp mercruiser mag. It was in a 3100 lb. boat. The boat ran 41 with one person empty. It would run 40 with 8 people and 800 lb. of ballast. I also never had any pulling problems with a 4 blade. I could run a whole weekend on 30 gallons. I never needed more. I thought about an after market EFI system for better throttle response, but could never justify the $1000 to the boss. Also never had a problem holding speed.|
|Multi-port injection can influence engine life especially in boats where the motor is mounted level in the boat. When the boat is on plane and the front of the motor is higher than the rear, the front cylinders tend to run lean and burn up the rings and valve seats. Not as much a problem when the engine is mounted at a down angle to keep it level when running. Throttle-body injection does little to solve this as the same thing happens but multi-port completely eliminates it. Plus the multiport is more efficient and requires a lot less up keep and adjustment. I'd never buy anything but a multiport injected motor...just a personal preference.|
|By Bob (bob) on Thursday, January 23, 2003 - 6:14 pm:
|Shawn are you serious, you wont buy anything unless its multiport?? What about your lawnmower??|