Anyone convert from carb to FI?
 

After burning through $400 in fuel the last time I was out, it got me thinking about FI. I'm running a 1050 Dominator now, so about the furthest thing from fuel efficient. I only have a 60'ish gallon tank, so it feels like I'm constantly running low on fuel.

Has anyone made the swap or have a comparison what to be expected from carb to FI? What are people running for aftermarket FI? In the car space a lot of people were running FAST, Holley, etc. If it's significant change in fuel efficiency a FI setup could damn near pay itself off over a few seasons. Not to mention the manners you get with FI.

Thanks

General rule is EFI is about 5-10% more efficient. It will of course depend on how dialed in the carb was vs the EFI tune.

Its HP to weight ratio = fuel burn
What boat, what motor?

Significantly noticeable gas savings when I switched to Holley EFI.

If carb and FI are tuned to same AFR there are zero difference to fuel consumption. You can install AFR gauge in your boat and tune carb perfectly. I had Baja 29 OL with twin 600hp carb motors, holley 950’s. I tuned it 14.5AFR idle, 3000-4000rpm 13.2-12.8AFR, 4000-WOT 12.7-12.0. Four channel EGT gauge help tuning alot. Egt was in all situations below 700Celsius. It tell how rich you must go.

On average, an in-tune four-stroke gasoline engine will burn about 0.50 pounds of fuel per hour for each unit of horsepower. On a dyno chart theis fuel use would be under the BSFC (brake specific fuel consumption). Typical marine engine around .5 bsfc.
Unleaded gas weighs 6.1lbs per gallon

200hp x .5 bsfc= 100lbs/hr
100lbs/hr / 6.1 lbs/gal = 16.4 gal hr

so 400hp uses 32.8 gal / hr

600 hp = 49.2 gal/hr

It takes some time to tune the carb precisely, but it is well worth it. Only injection i would use over the carb is sequential 8 point injection. Group member articfriends has good info about the fuel distribution problems of the carb intake manifolds, wich i think could be fixed with 8 point EFI. Anyhow there is many in this site that likes their sniper style tbi, much easier to tune than carb.

Since most carburetors AREN'T "optimized" generally speaking a carbureted engine will be ~10% less fuel efficient overall than a fuel injected one. Of course we've all seen cases where the carb was really out of tune and had excessive fuel consumption, but that's a problem unto itself.

My personal experience comes from comparing my Baja 208 Islander to my 252 Islander; both with 454 engines, the 208 was a Quadrajet engine and the 252 a MPI engine. The 252 is ~1000 pounds heavier than my 208. The 208 had a 42 gallon tank, the 252 a 90 gallon tank. Based on historical fuel consumption-to-destination with both boats, running very similar speeds, the 252 actually gets slightly better "mileage" than the 208 did. It amazed me, frankly, to the point I was questioning the fuel gauge when I first got my 252.

Has anyone attempted a lean cruise tune?

I’ve also seen some car guys do it. Apparently the exhaust valve gets hot. Also some Aussie cars were tuned like this from the factory.

I think youd find your common cruising RPM and look at the map sensor to dial out like 5% fuel? Not sure how lean you could go. I’m still around 2/3 max fuel rate at my cruise RPMs.

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