baz":f9pkaza5 said:
Subject: Volvo D4 260 HP tuned to be 300 HP
When the D4 went from 260 HP to 300 HP I understand this was done with changes made to the engine's ECU in terms of turbo operations and some fine tuning for fuel injections etc. This is much like done for auto engine tuning with 'chip' and/or software changes to the engine's ECU making throttle response different and more responsive, holding in gear for longer with higher RPMs and so on.
Just what affect did this tuning have on the D4 wrt fuel consumption and RPM etc ? Is the 300 HP same as the 260 HP version in terms of fuel consumption ? Is prop thrust different ? Does 300 HP vs. 260 HP mean the boat can cruise a bit faster or what ?
If you do not increase displacement the increase in power is air and fuel. A diesel engines longevity is based on how much fuel is burned more over hours. The fuel burn is a closer gauge to life expectancy then hours. The older large displacement diesels having 1/2 hp to 1 cubic inch turning low RPM and producing less hp burned far less fuel. A basics rule of thumb for a diesel is 1 GPH =18hp. Your fuel burn per hour can tell you how much HP you are demanding from your engine. The new Common rail high speed engines produce more Hp per cu in. burning more fuel producing this HP. I will use the engine that we have for example. D3 2.4 L =146.4 cubic inch producing 220hp that is a ratio of(.665 to 1) displacement to hp. A rule of thumb for diesel power plants longevity is at least 1 to 1. Take that same engine D3 and have it produce 150 hp and now the ratio is .98 to 1. Having that extra HP comes in handy but at a cost. More fuel consumption and less longevity. Using the added Hp for emergency, quicker acceleration is a positive, using it for a continual use is a decrease in longevity. I use a different method of cruising RPM. Volvo says cruise at no more then 90% OF RPM. 90% is 3600 rpm of a rated 4000 rpm. At 3600 rpm our D3 220 is burning 9.3 to 9.5 gph producing approx 171 hp which is a ratio of (.86 to 1) ( displacement to HP) it is also running at 80% load. A rule of thumb is a diesel's runs best at 70% load to maintain good fuel economy, longevity, and as close to the minimum of 1 to 1 displacement to Hp. The D3 in our C26 @ 3360 rpm cruises at an average speed of 14.5 mph burning 8.4 gph, producing approximately 151 hp 70% load and a 9.7 to 1 ratio. Sorry for getting carried away with the explanation!
D4 260hp is a 3.7L =225cubic inch ratio is 8.7 to 1 ( displacement to hp) thats much better then the D3 220hp) But worse then the D3 150 hp. But if run at or close to 1 to 1 or 1+ to 1 you will increase the longevity and burn less fuel.
D4 300 is a 3.7L = 225 cubic inch ratio .75 to 1
More Hp with less displacement is good for the engine manufactures ratings, good for the guy that doesn't care about longevity or fuel burn, and good for the boat builder because smaller engine means easier installation. Its not good for the guy that is buying a diesel for longer lasting great fuel economy. These engines if run at 90 % are no different then the Gas counterpart except twice as expensive. But if run at lower Gph along with the lower load will surpass the gas for longevity and fuel economy.
My answer to your question baz is more fuel burn, slightly faster with a cost to longevity, max rpm will be the same, larger prop installed to use extra power. I would want the bigger engine for the extra power when needed but run it as close to the 1 to 1 ratio. This is entirely my opinion. I am by no means a Diesel mechanic. I just believe in reliability and longevity of equipment. I like to have the most amount of power available and use the least and still achieve the best performance with longevity.
