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View Full Version : Carburators vs. Elec. Fuel Injection



James Adcock
08-07-2002, 03:59 PM
Its me again.I was searching EFI vs. Carbs in past posts and I have few more questions.

<font size="2" face="Verdana, Helvetica, sans-serif">Are the boat engines equiped with EFI any more reliable than a carburated version? <font size="2" face="Verdana, Helvetica, sans-serif">I have a fair knowlage of motor mechanics but, I admit to not knowing much about EFI systems.I realize most of the new boats have it but,is it really a big improvement? <font size="2" face="Verdana, Helvetica, sans-serif">Would it be a better system for a first time boat owner? <font size="2" face="Verdana, Helvetica, sans-serif">How well does EFI work with a newer model with some added HP? <font size="2" face="Verdana, Helvetica, sans-serif">Is there a limit to how much HP before a stock EFI system needs to be reworked/replaced? <font size="2" face="Verdana, Helvetica, sans-serif">I am more at home with a carb. Also, Is there any particular time/year when EFI systems starting taking the place of carbs?<font size="2" face="Verdana, Helvetica, sans-serif">Thanks for your patience,Jamie
Starting to narrow down the field and lookin' good!!! wink

Lil Grizz
08-07-2002, 09:17 PM
Best piece of advice I could give you is to stay with what you know. Especially on a boat where a failure could leave you adrift. I am at home with fuel injection but it does have its drawbacks. When a fuel injected system actually fails its usually not somthing that can be repaired without a trip to the parts store, you have more chances of limping home on a carb setup.

The up side to fuel injection in my opinion is that you can monitor everything that is going on with the engine, and you can log all the data and play it back in real time. This comes in handy when trying to chase down some ill behavior and removes some of the trial and error. The EFI setups are more consistant when running in different tempratures and altitudes. Most of the newer systems use a knock sensor and that little feature could save your engine if you get some bad gas. On modded engines the knock sensor generally cant compensate for the added power and therefore not enough timing is pulled out in time.

But since carb setups are still the majority on boat engines and you say you are quite familiar with that setup I would stay with what you know. In the meantime learn about the EFI systems because in a few years you wont have as much of a choice.

Edit: I have seen EFI engines in the 1200 horsepower range with no problems. Thses engines idled just like a stocker.

James Adcock
08-08-2002, 05:26 AM
Griz, Thanks a lot for your imput. I do appeciate your and everbody else's time anwsering my questions. Jamie

Philip47
08-08-2002, 07:02 PM
I think Fuel injections is heads above a carb in starting, at idle, milage & better WOT performance to a carb. the new injection systems can provide more fuel at WOT when needed
I have also read that a few people have clogged a injector and leaning out a cylinder running WOT and melted down a piston, any ideas on this? I read about a ferw cases on OSO

MOP
08-08-2002, 07:19 PM
Most everyone you speak to that has FI seems very happy with it, the local Merc dealer says not many troubles. Did say had some problems with wiring in very wet bilges. Was wondering if anyone still runs non electric FI. Back in the fifties I ran Scott injectors, they looked like throttle bases minus the carb. Weren't much if any better than carbs but did look cool when I opened the hood.

BigGrizzly
08-08-2002, 11:04 PM
AS for idling mine3 will rival any stock fuel injection. The problem with current boat fuel injection is they don't have intelligent engine mamagment, they are dumb computers with no O2 sensors. NowLil Grizz's car he can do anything with on the fly, and usually does, but not his boat. He is the Expert in the family on injection an me on the carbs. The the thing is setup most people run too rich and don't pay attention to Low speed and idle circuit transition.

Randy

Lil Grizz
08-09-2002, 01:47 AM
the marine EFI systems only adjust to 3 refrence points; engine temprature, barometric pressure, and manifold pressure. Everything else like throttle position and low-load/high load are pre programmed tables that have to be set middle of the road just to work in all enviroments. the minor adjustments from diffrent pressures are made across the board and are not very accurate compared to the automotive equivilants. This never poses a problem unless you start modifying the engine and then have to tune the ECU. This is simple to do but since the equipment is so expensive you would have to find someone to "flash" the ECU. If I could do it at home I would but so far demand has remained low enough that an economical tool has yet to surface.

However, in the next few years we should be seing the introduction of smarter EFI systems for marine applications. This would mean that the ECU would see an increased airflow, be able to adapt for lean conditions by adding more fuel(currently the knock sensor just blindly pulls timing), and run even smoother than they do right now. I love my EFI on everything I have ever used no matter what the form(barring pure mechanical). Cold starting is no diffrent than a warm start with EFI, and the system can identify what the problem is by throwing trouble codes. It really takes the guesswork out of troubleshooting.

I have heard about the Magnum MPI engines burning out the cylinder but i dont think it is due to a injector failure. I would bet that the problem is in the intake manifold design. I have heard of the carburated versions having similar issues. That makes me think its an airflow issue and not a fuel issue. I could be wrong but in all my years of toying with EFI its usually the runner length to injector volume that causes the one cyl lean out and not a clogged injector. Simple fix is to run a fatter injector on the leaner cylinders.

turbo2256
08-09-2002, 07:27 AM
I have found a lot of engines have problems with steam pockets causing rich and lean cylinder conditions. Venting of these pockets evens out jetting, plug readings and increases engine life.

harbormaster
08-09-2002, 08:22 AM
How would you vent the steam pockets?
More importantly, how would you diagnose/find them?

Rootsy
08-09-2002, 08:33 AM
on a sbc such as a 350 you'd run a 400 head gasket or similar which has provisions for the steam holes which are on the 400 already...the 400 having siamese cylinders develops steam pockets in the block in the valley where the cylinders join. so in the case of the 400 GM drilled the deck and modified the head gasket to allow these to escape. so on say a 350 you'd need to drill the block deck. OR you could run the rear water crossover on the back of the intake manifold and kinda get the same effect since the end cylinders tend to get stagnant water flow.

Forrest
08-09-2002, 08:47 AM
Hay Lil Grizz, when you and Big Grizzly get together, say at the dinner table, do you guys ever get a chance to talk about carburetors, fuel injection, and other high performance engine topics? :D :D

------------
Forrest - Praying for no stinkin' steam pockets.

turbo2256
08-09-2002, 08:58 AM
On my BBC I run steam lines from the left and right cyl banks to the goose neck (3/8 Aeroquip).
Some just dump them over board thru the transom.
If my home computer was working I could send some pics. I am at this position with my son if he breaks anything I dont replace it. A lot of the newer manifolds have bosses on the rear over the the water port were the crossover would have been.I drill and tap them to 3/8 pipe.
I reciently pulled my heads to check them out. Before both rear cylinders looked to be running hotest, the middle 4 seemed about even fronts looked a bit hotter than middle 4. Now all 6 rear cylinders look even fronts didnt look hot but did look rich. Never finished dialing in the carb due to factory defects the carb needed some machine work to fix it or one of those proform carb bodys.
To busy working on other peoples stuff to play with it right now. This I do know a major engine bulider found that without these lines a big block building serious power would blow on the dino almost every time.

Lil Grizz
08-09-2002, 12:08 PM
Mostly we talk about needlepoint or some new recipie for fried chicken. wink

BigGrizzly
08-09-2002, 03:36 PM
Don't forget the Ribs and the streach and sew course I took last month. How about that new vinergerette chicken dip we got from that German cook.

Randy

HyperDonzi
08-10-2002, 06:13 PM
i read on the merc site that efi is supposed to make a boat start up quicker when it is humid.

no idea, carbs are easy to work with so sticking with them works for me.

Tomahawk
08-10-2002, 09:20 PM
Forrest - having been witness to some of these discussions, let me just say that they are interesting, if you are into motors - or needlepoint. We may see at Eufaula this year.

Forrest
08-11-2002, 10:58 AM
Needlepoint! eek! :D :D