What have you done on the Engine to improve mileage?

[jezzb]

Hi Folks,
What have you done on the Engine to improve mileage? Any enhancements to the manifolds?
Is a dry manifold better than wet?

Jezz

[gmricketts]

As the price of gas goes up a spinaker is looking better!  Going to need bigger tabs to get it ont a plane though!  (Thats a joke son)

George

[Dave M]

I just got hit up by someone I know that wants me to try this pill or powder that you add to your tank, that is supose to gain upto 30% in your mpg. Sounds like snake oil to me but here's his web site.
   
  http://www.kevinandshelly.mybpbiz.com/

I looked at the web site, but as the old saying goes if it sounds to good it's probably is.

[merwin10]

I the order of most wasteful to least wasteful it goes like this Carburetor, Throttle Body Injection (TBI) and Multi-Port Injection (MPI). Now the Carburetor and Throttle Body Injection are considered wet manifold, meaning that the fuel and the air both pass thru the manifold. The multi – port injection is a dry manifold, only air passes thru the manifold the fuel is injected at the top of the intake valve. There are also variants of each such as the sequential multi-port fuel injection (SMPI). In the SMPI the fuel injectors open just before the intake valve for its cylinder opens. Thus, the system can respond more quickly because from the time the change is made, it only has to wait only until the next intake valve opens, instead of for the next complete revolution of the engine.

The main difference between TPI and MPI is that TPI has one or two injectors mixed with the air too deliver to all cylinders. The MPI has an injector for each cylinder and is only delivering the fuel to that cylinder not air fuel mixture.

Now it isn’t just a simple thing to make a carburetor boat an injected boat. An injected engine needs to have many sensors for it to work properly also you need to have a fuel return for un-spend fuel!

There are a whole host of sensors needed to make the system work, oxygen sensors, throttle position sensor, mass airflow sensor, coolant temperature sensor, manifold absolute pressure sensor, engine speed sensor, fuel flow sensor, and of course the engine control unit (ECU). The ECU is the computer to the system that tell how much fuel and how much air and when.

All in all, it is an under taking to convert a carbureted engine to an injected one. Just remember your boat is in an unfriendly environment to electricity and reliability of the engine may suffer the more you do to it!  

[Sea Saw]

I recently ordered a K&N Marine filter for my 8.1L. It installed perfectly with no modifications. I will wait to see the results. If there are none atleast I have filtered air through the engine.

Also I changed to Lenco trim tab switch with led indicators and an auto retract feature. The dry stack folks have been on me to do this as they can never tell the position of the trim tabs when they get ready to pick up my boat. I think I can improve my mileage by not running with the tabs down as much.

[jezzb]

Thanks to All - and thanks to Merwin10 for the detailed technical explanation which I found very interesting to read.

But besides the carb/Mpi etc. I have read that if you install a stainless steel Manifolds/risers, you will reduce the weight and also improve the performance by up to 30% , as the SS manifolds/risers are desgined in one piece and thus have better water flow.

Can anyone confirm this?

Kind regards
Jesmond

[merwin10]

This comes up ever now and again! SS exhuast manifolds vs stock. The simple answer is yes you will see a improvement! However, isn't there always a catch, you will also see more maintenance. Seems that they have not come up with a SS exhaust manifold that doesn't experience some problems. A friend of mine did this and has wish he didn't. He ahs experienced welds cracking, wrapping, leaking of coolant and exhuast gases. He has replaced the manifold twice now and the manufacture did not stand behind them. He is on his third set, different manufacturer than the first two!

Seems the problem is that SS expands and contracts differently than cast iron. Also there is a procedure to the install and special gaskets. For what he has told me you need to install the headers and torque them down heat the engine up to operating temperature let it cool and torque them again! This procedure is done several times! Then he actually carries a torque wrench on the boat because about every 20 hours they need to be checked. Sometimes sooner it depends on how many times the engine is heated up and cooled in the 20 hours.

The manufacturer of marine engines look at reliability of engine add ons and error on the side of reliability. Yes you can do many things to a engine but at what end cost and I am not talking dollars here. Seems that the more you do the less the reliability is. One thing most boaters want is to use the boat not have to constantly work on it! The more time the boat is laid up for repairs the less you get to use it.

Yea you can build a engine up in HP these days to almost any HP you may want with turbos - Blowers - Cams - special heads - Blue printing etc etc. However, you also need to consider how you use the boat! If you look around on the web you can see special GM 454 putting out 1050 hp they are tricked to the hilt but ask how reliabile they are and you get a different story-

One of my friends has a Donzi 38 ZR has three blown 502's all tricked out, burns about 128 gph, does about 140 mph. Yea he can get to where he is going faster. Cape Cod Canel to Newport RI in 20 minutes on a good day, takes me 2+ hours, maybe 3 if the weather is bad! He replaced all three engines at 380 hours at about $97,000.00. Is it worth it?  IMHO NO!!!

If you ask me - stay with what you have - want something to extend your mpg install a autopilot and couple it to a gps, now that will definately save you gas while keeping you dead on course against any wind or current. How many times have you been on course, so you thought, but had to make slight turns to correct your heading to bring you back on course, you are making "S" across your course line, hence wasting fuel.

If an autopilot will save you 15% on 100 gals of fuel at $3.35 a gallon you would save $50.25 per 100 gallons without effecting reliability, in fact you would be enhancing reliability.

Just my thoughts -

Mike -

[wastewater willie]

Andy:  could you share with us how involved/difficult it was to install the trim tab indicator switches, the cost involved, and if it is an install that a novice "mechanic" (parts changer) could handle? That might be good info for quite a few of us.  Thanks Andy:
Wastewater Willie  (u2willie@aol.com)

[Craig]

I just shut mine off.  I also install a fuel flow system that give you an Idea how much your burning and the best cruise speed.

[jezzb]

Thanks Merwin10 for your imput. I was a bit confused as I will be changing the Manifold & Risers as well, but after having read your posting, I am now convinced. I will install Mercruiser Original Manifold & Risers and not Stainless Steel. The main reasons why I was considering SS were:

1. Less Weight
2. Better Water/exhaust flow
3. Not as bulk in size (which is a main concern for me as the 7.4 Big block took the whole engine compartment).

All the best,
Jesmond

[merwin10]

Yea! the stock manifolds are big but they do have there advantages. Most SS heads allthough not as bulky have tuneing pipes that are hard to fit in a cramped engine space. They just aren't as compact as the cast iron monsters. and they don't have the reliability of the cast ones. You can do much better with other enhancements for your money. Of course there are those of us that 40 mph just isn't fast enough! All fast takes is $$$$.$$, reliability takes good engineering. For the most part I have not seen a 1000 to 2000 engine hours fast boat, they just beat themselves to death. I guess it is the old story "you need to pay to play"!

Mike -  

[Ronnie]

Hey jezzb  ck out the stock risers on the 496's  theyre pretty smooth & I would think they would fit a 7.4l.  Stock mercruiser should hold up better than the stainless