Injector sizing

[Kquaine]

Has anybody changed the injector to a smaller size to save lower the fuel burn rate?

 

[Bob Bradley]

You'll achieve the same result by pulling back the throttles. And, you'll still have the hp there if you need it. Right now I'm helping my daughter and son in law put the correct injectors back into their 671ti engines to fix the problem caused by the prior owner doing the same thing you are suggesting. The smaller injectors are preventing them from hitting their top rpm under a load, and the boat has trouble getting up on plane. I'd strongly recommend against the move

 

[Captain Ralph]

Has anybody changed the injector to a smaller size to save lower the fuel burn rate?

You'll achieve the same result by pulling back the throttles. And, you'll still have the hp there if you need it. I'd strongly recommend against the move

The same horse power is required to move the hull at a same speed.
Horse power requires fuel.
The only thing you would change is top end operation.

Change in operation offers better results.
Changing the throttles to a slower pace does the job better.

I also strongly recommend against the move.

BTW; I'm looking at the next size up in injector size.

 

[Avenger]

Isn't there an FAQ about this subject? If there isn't , we need one. Seems like everyone who can't use the search function has to ask this question.

 

[Timeless72]

Would be cool if a chart did exist for Detroits. Next step up in size for performance gains, if even worth doing. Seems to come up a lot.

 

[Captain Ralph]

Would be cool if a chart did exist for Detroits. Next step up in size for performance gains, if even worth doing. Seems to come up a lot.

I have notes listing the HP & Injectors on the DDC engines. Mostly 12V71**s.

But it is not just injectors on any ole Detroit; #1 concern when messing with injectors on a turbo charged engine, you sometimes have to change the turbos also. That air / fuel ratio thing.

There can be also, cam shaft timing, blower ratios and by-pass blowers.

But wait, there's more; Inter-cooling, After-cooling and on some models both (TIAB)

Always stay stock when you can. Just pull the throttles back.

My problem, tired of slowing down when crawling up the back of a swell when I need to be moving.
It is rare when this happens since we mostly operate in LSD mode but some times we get chased out of the ocean or encounter an inlet at the wrong time, could use some extra ponies.

 

[jim rosenthal]

There probably WAS a chart of injector sizes and performance figures at some point when companies like J&T and Stewart & Stephenson were marinizing Detroit themselves and selling them as OEM engines. The one company I know of which have always been DD dealers and have been around forever is Western Branch Diesel in Tidewater, VA. If anyone would have that sort of information, they would, if they are still around. They are either in Chesapeake or Portsmouth, I think, can't recall which.

 

[bostonhatteras]

my 871N engines went from N70 to N80. no smoke or haze on horizon and no soot on transom. should've done N90.

 

[Captain Ralph]

my 871N engines went from N70 to N80. no smoke or haze on horizon and no soot on transom. should've done N90.

On Naturals (non-turbo), The compression ratio starts taller and you can adjust injectors a little easier.
On a pair of fresh 6-71s, we went from N-60 to N-90s.
No more slowing down crawling over swells.
Full of people and dive gear, you could drive that boat straight up a wall.
We were going to ad pitch into the wheels but never got to it before it sold.

 

[bostonhatteras]

On Naturals (non-turbo), The compression ratio starts taller and you can adjust injectors a little easier.
On a pair of fresh 6-71s, we went from N-60 to N-90s.
No more slowing down crawling over swells.
Full of people and dive gear, you could drive that boat straight up a wall.
We were going to ad pitch into the wheels but never got to it before it sold.

I would definitely need to add pitch if I had gone with 90s

 

[Briankinley2004]

Would be cool if a chart did exist for Detroits. Next step up in size for performance gains, if even worth doing. Seems to come up a lot.

I have it for 8V71's but can't seem to figure out how to upload it here. If anyone wants it I can email or screenshot it and add as an image

 

[Timeless72]

I have it for 8V71's but can't seem to figure out how to upload it here. If anyone wants it I can email or screenshot it and add as an image

That is exactly what I'm looking for. Please send to mwood2580@yahoo.com. Thanks!!

 

[Avenger]

Too bad DD wasted all that money paying engineers when all they had to do to make more power was "turn it up."

 

[Captain Ralph]

I have it for 8V71's but can't seem to figure out how to upload it here. If anyone wants it I can email or screenshot it and add as an image

3 page PDF can not up-load here. I will type in the data of interest to this thread;

8V-71 230Shp N55 @1800RPM
8V-71 296Shp N65 @2100RPM
8V-71 325Shp N70 @2300RPM
Compression Ratio 18.7 tp 1

8V-71TI 340Shp N70 @2100RPM
8V-71TI 450Shp N90 @2300RPM
Compression Ratio 17 to 1

These would be DDC stock figures with normal cam timing.
Please note the lower compression ratios on the TI models.
Dated 9-95
No comments on what turbo is used.

 

[bigbill]

Why dont you people just pull the throttle back a little?

 

[Captain Ralph]

Why dont you people just pull the throttle back a little?

Some minds just can't handle the simple stuff?

I was just trying to be helpful in posting that info.

To be further helpful in case others missed it before;
It takes the same amount of horse power to move a boat at the same speed.
It takes the same amount of fuel to develop that same amount of horse power to move the boat at that same speed.
Slowing the boat down reduces the horse power required to move the boat at a lower speed.
Amazingly, fuel consumption is reduced.
F M
Unloading weight and trimming ship helps also. My second divorce proved this.

Reducing injector size just removes that reserve horse power, if or when you ever need it.

 

[whoover]

Of all the expenses in boat owning, broken things, things that are going to break, upgrades, maintenance, insurance, dockage why worry about fuel consumption. It is the cheapest part of the fun!

Walt Hoover

 

[cww]

What is smaller injectors going to get you that a lower throttle setting won't?

I had a dock neighbor back when I was in Daytona city marina who got angry at me over this exact conversation. He had a hatteras and was explaining that he'd downrated his engines by swapping in smaller injectors to intentionally make it a trawler. I asked that exact question, isn't it cheaper to just set the throttle lower. He started telling me how I didn't understand and it's bad for the engines because of cylinder temps, and he swore he got better fuel economy. I said it's physically impossible that the difference was caused by anything but him running the boat slower, and said temps are a function of the quantity of fuel being burned and either way whether it's smaller injectors or a lower throttle setting all you're doing is reducing fuel. He got super frustrated and acted like I was an idiot.

I'm not sure why this is an attractive idea to people or what drunk dock neighbor is telling people to do this (although I met at least one of them). It literally accomplishes nothing that pulling the throttle back doesn't do. But at least you've spent thousands of dollars on new injectors for no reason, and as a bonus the boat won't plane if you ever decide you want to.

 

[SKYCHENEY]

With the OEM setup, you can always get the temps up by pushing up the throttles. Run it slow all day and at least you can "clean them out" with a good high-speed, higher temp run at the end of the day.

 

[Timeless72]

Man, all these people wanting to go slower. I was hoping to add a few!