Sniper EFI for boat.

[Rajobigguy]

Has anyone done this? What are pluses and downsides? Is there a better choice?
I would really like to swap to EFI vs carb. It’s a 5.7 mercruiser.

 

[Shlbyntro]

dont do it

 

[Rajobigguy]

dont do it

Don’t do the Sniper type or are you just opposed to EFI in general and if so why?

 

[Ace in the Hole]

Has anyone done this? What are pluses and downsides? Is there a better choice?
I would really like to swap to EFI vs carb. It’s a 5.7 mercruiser.

Had it on my cruiser (twins) never worked right and wound up causing an engine fire. Would not do it.

 

[n2otoofast4u]

@wet hull I think just did this.

 

[Dcb.blake]

I did some research before switching and didn’t find much good about the sniper style systems. Ended up going with a port injection style. Cost was more but knock on wood it’s been great so far.

Mine was also a 540bbc the small block might be a different story about headaches with the sniper.

 

[monkeyswrench]

Aside from marine legality, would it be possible to run a TPI intake and injector assembly? Anything from an EEC-IV to a MoTec can control it that way.

 

[DaveH]

holley sniper is the fischer price of efi systems.

much better alternatives out there.

 

[ltbaney1]

i know a few guys who have tried the sniper systems on cars, and 2 of them wound up in the trash and 1 more got sold for pennies on the dollar. if they cant work well on the street, i dont imagine they would work in a marine enviroment. Holleys support in general sucks as well.

 

[bonesfab]

make sure you have a few good oars.. I just took one off a truck and replaced it with terminator. Much better in the first 5 minutes.

 

[Sharky]

The Sniper EFI system is a speed density based system. It looks at RPM & load (intake manifold pressure). It also uses an O2 sensor for fine/small fuel trim adjustments.

Speed density systems are not as accurate with changes in air temp, humidity & pressure.

Besides. . . where are you going to install the O2 sensor?


I would look to see if someone makes a mass flow sensor system. Those use VE to calculate fuel and are extremely accurate in air temp changes, humidity & pressure changes.

I have a couple friends that installed the sniper system on their classic cars. Its OK but nothing impressive. They start every time (hot or cold), idle good with big cams and run just fine cruising on a hot summer day. For performance. . . . not the best.

For a classic muscle car you would like to drive to go to coffee & cars on Sundays, they are great.

 

[Shlbyntro]

Don’t do the Sniper type or are you just opposed to EFI in general and if so why?

well especially a sniper, but I am otherwise generally against modifying an otherwise good stock engine just for the sake of having fuel injection. I've seen these shortcut fi systems kill more engines than they helped. If you are going to do it, do it right with a complete mpi system that uses ALL the engine sensor inputs.

I also don't understand where the hatred comes from towards carburetors. My carbed engines start and run just fine every time even after sitting months at times. Take care of your engine and it will take care of you.





To anybody looking for mpi fuel injection for a 302/5.0 sbf. I have a complete mass air system with intake, ecm, wiring harness, etc. sitting in a box that I dont plan on using. Pm me if you want it

 

[DaveH]

The Sniper EFI system is a speed density based system. It looks at RPM & load (intake manifold pressure). It also uses an O2 sensor for fine/small fuel trim adjustments.

Speed density systems are not as accurate with changes in air temp, humidity & pressure.

Besides. . . where are you going to install the O2 sensor?


I would look to see if someone makes a mass flow sensor system. Those use VE to calculate fuel and are extremely accurate in air temp changes, humidity & pressure changes.

I have a couple friends that installed the sniper system on their classic cars. Its OK but nothing impressive. They start every time (hot or cold), idle good with big cams and run just fine cruising on a hot summer day. For performance. . . . not the best.

For a classic muscle car you would like to drive to go to coffee & cars on Sundays, they are great.

i dunno if a agree that MAF is the way to go. does merc or any other OEM run MAF on anything? not that i am aware of. I wonder why.

there is NOTHING wrong with speed density. the real issue is most want to go the EFI route, which is understandable since its totally superior to a carb, but dont realize whats really involved to make it work correctly.

 

[Rajobigguy]

Well I actually have a Pro-M mass air sequential port system sitting on the shelf but it's for a different project . I was just wondering if anyone has had any success with any of these self contained systems on a boat. I don't have any problems with carbs but I made the mistake of letting a shop screw around with this one years ago and it has never really been right since so rather than me spending days of boating time adjusting the jetting and metering rods to get it performing correctly I was exploring the possibility of an easier/quicker fix.
The current carb is a Edelbrock AVS, maybe I should just switch to the regular Edelbrock Marine carb and call it good (at least until I get around to finishing the other project engine).
Thanks for the input guys.

 

[Nanu/Nanu]

Im running a basic Edelbrock Marine 750 cfm on my 454. Picked up the tuning/jetting kit for it. Super easy to change metering rods and springs. Jets are a bit more work to get to but i think its 8 T25 torx screws to get to the jets.

Of all the folks that ive talked to who have used the Fi-tech and Holley systems im not sold i would try it out on my boat. The juice doesn't seem Worth the squeeze. And that goes for both auto and marine applications. Im sure there are tuners who know their way around these systems but for me its not worth it. You would be better off changing the whole motor in my opinion

Best of luck in your research.

 

[Jonas Grumby]

You guys thing the Holly hp sucks too?

 

[Nanu/Nanu]

Also i don't know how the Edelbrock AVS Carb is set-up how ever with the basic Edelbrock marine carburetor and a tune kit you can go through your carb and match the numbers of your metering rods jets and the color of your meter rod springs and see exactly how your jetted in regards to rich and lean, with the paperwork that comes with the kit. Pretty easy to do In about 30-45 mins. May need a magnifying glass if your eyes get blurry on small stamped numbers.

 

[BBYSTWY]

Everyone seems to hate the idea however I'm on the other end of the spectrum. I had the sniper dual kit on this motor and I luckily found an AMAZING tuner that had it running flawless in about an hour on the water. Get in, hit the start button, and go. No surging in and out of gear nothing....ran like a stock 496. I say HAD because I am upping my boost and I am getting close to running out of injector and there are some things "safetys" I want to monitor and control that the sniper can't do.

The sniper is the base kit when it comes to EFI but with a good tuner and ignition control it will run just like your car. This motor made 993 on the dyno with 4.5 lbs of boost at 6100 and again drove like a stock 496. I did have some issues when I first put it on ALL of them caused by an incompetent tuner that cost me a lot of money and a summer on the water but was no fault of the system itself.

They advertise "self-tuning" as most do and that is just not true. If you think you're going to slap it on and go boating while it tunes you will be severely disappointed as that's just not true, but once tuned she's a wild animal with pussy cat manners lol.

And for what it's worth I am just upgrading holley systems and will still be running holley EFI and ignition control.

 

[Melloyellovector]

We attempted it on my vector, AJ at barrett and brian efi university. Could not get it to hold tune, would get it dialed. Worked great, until cycle the system and start all over. Alexi supposedly has done and can make it work, but fuck that set up.
Brian (B&D) was gonna do a Holley hp for me, but…. RIP buddy
dominator carb it’s been since, w no issues

 

[Blackmagic94]

I run it on my blower 671 jet boat. Works great

 

[Blackmagic94]

Also run it on my 304 cid v8 cj7.

Runs great as well. Did lose a o2 sensor one day and switched the feed back off and drove it back home and swapped it out. No issues post that and it still got me home.

 

[HST4ME]

I've put a few on various type boats. No problems other than little tuning quirks

 

[Jonas Grumby]

Is Holly HP better than sniper?

 

[OkHallett270]

View attachment 1251897

Everyone seems to hate the idea however I'm on the other end of the spectrum. I had the sniper dual kit on this motor and I luckily found an AMAZING tuner that had it running flawless in about an hour on the water. Get in, hit the start button, and go. No surging in and out of gear nothing....ran like a stock 496. I say HAD because I am upping my boost and I am getting close to running out of injector and there are some things "safetys" I want to monitor and control that the sniper can't do.

The sniper is the base kit when it comes to EFI but with a good tuner and ignition control it will run just like your car. This motor made 993 on the dyno with 4.5 lbs of boost at 6100 and again drove like a stock 496. I did have some issues when I first put it on ALL of them caused by an incompetent tuner that cost me a lot of money and a summer on the water but was no fault of the system itself.

They advertise "self-tuning" as most do and that is just not true. If you think you're going to slap it on and go boating while it tunes you will be severely disappointed as that's just not true, but once tuned she's a wild animal with pussy cat manners lol.

And for what it's worth I am just upgrading holley systems and will still be running holley EFI and ignition control.

So as far as tuning the sniper setup, what’s involved with that. Can you manipulate the settings with the handheld device that comes with it or do you need a laptop with Holley software?

 

[ka0tyk]

I’ve always wondered this I just don’t understand how you get an o2 sensor into a wet exhaust. I haven’t ever seen a center rise exhaust setup with an o2 bung at the collector before the riser or a retrofit riser with an o2 bung. Seems a little tough to do it to an existing set. Without an o2 you’re kinda just measuring map or maf input and guessing at what you’re getting out on the other end… little pointless to me.

 

[Racey]

The Sniper EFI system is a speed density based system. It looks at RPM & load (intake manifold pressure). It also uses an O2 sensor for fine/small fuel trim adjustments.

Speed density systems are not as accurate with changes in air temp, humidity & pressure.

Besides. . . where are you going to install the O2 sensor?


I would look to see if someone makes a mass flow sensor system. Those use VE to calculate fuel and are extremely accurate in air temp changes, humidity & pressure changes.

I have a couple friends that installed the sniper system on their classic cars. Its OK but nothing impressive. They start every time (hot or cold), idle good with big cams and run just fine cruising on a hot summer day. For performance. . . . not the best.

For a classic muscle car you would like to drive to go to coffee & cars on Sundays, they are great.

That's absolutely not true at all. Almost everything nowadays is is speed density volumetric efficiency. On applications with MAF it is used for sanity checking and trims, and not relied on for the primary load calc in most systems.

All Merc motors are and have been Speed Density (Manifold Absolute Pressure) going back to MEFI 1 and up to the Motorola 555 stuff.

I can't tell you how many hundreds of different motors i've tuned, all Speed Density (Manifold Absolute Pressure Based). Volkswagen, LS, Harley Davidson, Ecotech, Big block, small block. All Speed Density.

Mass Airflow system are extremely sensitive to intake design, shape etc. Because of this they are almost never used on custom applications. At least any custom application done correctly.

 

[Racey]

I’ve always wondered this I just don’t understand how you get an o2 sensor into a wet exhaust. I haven’t ever seen a center rise exhaust setup with an o2 bung at the collector before the riser or a retrofit riser with an o2 bung. Seems a little tough to do it to an existing set. Without an o2 you’re kinda just measuring map or maf input and guessing at what you’re getting out on the other end… little pointless to me.

Great for tuning, but you pull it out and run open loop after you have gone through the maps.

Closed loop is never good in any performance application, you are put way to much faith and money in the hands of a weak sensor that WILL fail eventually.

 

[Racey]

We attempted it on my vector, AJ at barrett and brian efi university. Could not get it to hold tune, would get it dialed. Worked great, until cycle the system and start all over. Alexi supposedly has done and can make it work, but fuck that set up.
Brian (B&D) was gonna do a Holley hp for me, but…. RIP buddy
dominator carb it’s been since, w no issues

And Brian Macy is a very well respected and knowledgeable guy in EFI, In fact he taught the EFI Advanced class when i went through it probably 15 years ago. If he can't get it to work......

Those cheap boxes have fundamental software issues. The software is the most important part of the box, Electronics have become ubiquitous, so the actual chips, drivers, and ADCs are rarely problematic. Most issues are the result of bad software.

 

[Bigbore500r]

Has anyone done this? What are pluses and downsides? Is there a better choice?
I would really like to swap to EFI vs carb. It’s a 5.7 mercruiser.

As @bonesfab said - Snipers, and most all other "TBI" style self tuning EFI stuff out there are major hit and miss in the reliability / quality department.

I'd stick to a well tuned carb, unless you can find a complete port injected EFI factory Merc setup or similar to plop on there.

 

[85RiverRAT]

I’ve always wondered this I just don’t understand how you get an o2 sensor into a wet exhaust. I haven’t ever seen a center rise exhaust setup with an o2 bung at the collector before the riser or a retrofit riser with an o2 bung. Seems a little tough to do it to an existing set. Without an o2 you’re kinda just measuring map or maf input and guessing at what you’re getting out on the other end… little pointless to me.

The IMCO Powerflows we have an 02-sensor bung in the riser, through and through from the outside, through the water jacket and into the riser. GT inserted a remote 02 sensor on our lake test. I suppose this would be permanent in this situation for running the 02-sensor.

I've seen these shortcut fi systems kill more engines than they helped.

Several have eluted to this, in what sense does it kill/hurt the engines? Bad program, a lean condition that grenades the engine, etc.?

All interesting commentary, it would seem that Sniper-EFI, FI-Tech etc, would be an easy choice. I get the Cars & Coffee comment, kind of why I am considering this for the Camaro, just for the cold/start improvements and off idle drivability on a street car. The claims these companies are making on these kits, the sell, is that they are more then capable in all applications and high HP as well.

Personally, I wouldn't use the TBI style system on the Hallett, I would use a MPI system and get it tuned to the what the motor wants and conditions/environment etc. Been thinking about this for a long time, mostly because the MEFI-1 on our build is so antiquated, would like to have something modern and with more tune capability. Plus Looks!

 

[coolchange]

As @bonesfab said - Snipers, and most all other "TBI" style self tuning EFI stuff out there are major hit and miss in the reliability / quality department.

I'd stick to a well tuned carb, unless you can find a complete port injected EFI factory Merc setup or similar to plop on there.

And Brian Macy is a very well respected and knowledgeable guy in EFI, In fact he taught the EFI Advanced class when i went through it probably 15 years ago. If he can't get it to work......

Those cheap boxes have fundamental software issues. The software is the most important part of the box, Electronics have become ubiquitous, so the actual chips, drivers, and ADCs are rarely problematic. Most issues are the result of bad software.

Merc made a stack type injector like a Hilborn/ Endrele back in the day. I can’t find any info or proof that it even existed.
Anyone familiar?

 

[Racey]

The IMCO Powerflows we have an 02-sensor bung in the riser, through and through from the outside, through the water jacket and into the riser. GT inserted a remote 02 sensor on our lake test. I suppose this would be permanent in this situation for running the 02-sensor.

Several have eluted to this, in what sense does it kill/hurt the engines? Bad program, a lean condition that grenades the engine, etc.?

All interesting commentary, it would seem that Sniper-EFI, FI-Tech etc, would be an easy choice. I get the Cars & Coffee comment, kind of why I am considering this for the Camaro, just for the cold/start improvements and off idle drivability on a street car. The claims these companies are making on these kits, the sell, is that they are more then capable in all applications and high HP as well.

Personally, I wouldn't use the TBI style system on the Hallett, I would use a MPI system and get it tuned to the what the motor wants and conditions/environment etc. Been thinking about this for a long time, mostly because the MEFI-1 on our build is so antiquated, would like to have something modern and with more tune capability. Plus Looks!

The main thing is there is no such thing as "Self Tuning"

You need someone competent enough doing the tuning that understands when the o2 sensor is lying and when to believe it, due to reversion etc. Self tuning will just put 100% blind faith into that sensor. No Bueno.

Proper distributor phasing to match the EFI system is another thing that is commonly overlooked that i have seen DESTROY big money engines.

You also need someone that knows how to correctly set up timing maps, fuel trims for temps, etc. Accel enrichments, yada yada yada.

Self tuning is a disingenuous marketing term

 

[Racey]

Merc made a stack type injector like a Hilborn/ Endrele back in the day. I can’t find any info or proof that it even existed.
Anyone familiar?

800EFI motors if i remember correctly. I don't know what system they were running, might have been EFI technologies? This was wayyyy back in the 90s I remember Brummett had a pair of them down at his shop when i was a kid.

I don't think they were mechanical, but they definitely could have been, it's been 25 or more years since i've seen those motors in person.

 

[coolchange]

800EFI motors if i remember correctly. I don't know what system they were running, might have been EFI technologies? This was wayyyy back in the 90s I remember Brummett had a pair of them down at his shop when i was a kid.

I saw one at Teague for sale about then. Wanted it. Haven’t seen another one.

 

[LargeOrangeFont]

As @bonesfab said - Snipers, and most all other "TBI" style self tuning EFI stuff out there are major hit and miss in the reliability / quality department.

I'd stick to a well tuned carb, unless you can find a complete port injected EFI factory Merc setup or similar to plop on there.

I think another problem is you are relying on a manifold that was not really designed with highly pressurized fuel squirting through it in mind. So there is a high probability that cylinder to cylinder distribution could be way off. And it will always run OK but never great.

 

[Shlbyntro]

The IMCO Powerflows we have an 02-sensor bung in the riser, through and through from the outside, through the water jacket and into the riser. GT inserted a remote 02 sensor on our lake test. I suppose this would be permanent in this situation for running the 02-sensor.

Several have eluted to this, in what sense does it kill/hurt the engines? Bad program, a lean condition that grenades the engine, etc.?

All interesting commentary, it would seem that Sniper-EFI, FI-Tech etc, would be an easy choice. I get the Cars & Coffee comment, kind of why I am considering this for the Camaro, just for the cold/start improvements and off idle drivability on a street car. The claims these companies are making on these kits, the sell, is that they are more then capable in all applications and high HP as well.

Personally, I wouldn't use the TBI style system on the Hallett, I would use a MPI system and get it tuned to the what the motor wants and conditions/environment etc. Been thinking about this for a long time, mostly because the MEFI-1 on our build is so antiquated, would like to have something modern and with more tune capability. Plus Looks!

pretty much. lean conditions grenading the engines and also over fueling washing down the cylinder walls. obviously not both on the same engine.

 

[Bigbore500r]

I think another problem is you are relying on a manifold that was not really designed with highly pressurized fuel squirting through it in mind. So there is a high probability that cylinder to cylinder distribution could be way off. And it will always run OK but never great.

The way they inject the fuel, it attempts to atomize above the throttle blades, squirting thru the throttle bore at the top via multiple holes around the bore. They don't "dump" or spray downward on the blades directly. The main issues seem to be shitty quality control - bad injectors, bad solider joints on ECM's, bad TPS, etc. Then the durability of the units is an issue, with the ECM mounted inside the throttle body they seem to be killed very easily.

 

[Husqy510]

I run a Holley sniper on my blow thru turbo bug and I've been very happy with it, but it wouldn't be worth the trouble for me on a boat. A well tuned carb works great on a N/A motor and you don't have to worry about return style fuel systems and O2 sensors

 

[bonesfab]

Merc made a stack type injector like a Hilborn/ Endrele back in the day. I can’t find any info or proof that it even existed.
Anyone familiar?

I have seen them They were kinsler's. Some were for big chief heads.

 

[DaveH]

The IMCO Powerflows we have an 02-sensor bung in the riser, through and through from the outside, through the water jacket and into the riser. GT inserted a remote 02 sensor on our lake test. I suppose this would be permanent in this situation for running the 02-sensor.

Several have eluted to this, in what sense does it kill/hurt the engines? Bad program, a lean condition that grenades the engine, etc.?

All interesting commentary, it would seem that Sniper-EFI, FI-Tech etc, would be an easy choice. I get the Cars & Coffee comment, kind of why I am considering this for the Camaro, just for the cold/start improvements and off idle drivability on a street car. The claims these companies are making on these kits, the sell, is that they are more then capable in all applications and high HP as well.

Personally, I wouldn't use the TBI style system on the Hallett, I would use a MPI system and get it tuned to the what the motor wants and conditions/environment etc. Been thinking about this for a long time, mostly because the MEFI-1 on our build is so antiquated, would like to have something modern and with more tune capability. Plus Looks!

the problem with TBI, regardless of what electronics control it, is poor fuel distribution per cylinder. this is made worse by most guys that go down this cheap route also want to go cheap on the ignition and retain a distributor, which also has poor consistency. people "get away" with this........for a while....but in the end, longevity of the engine suffers, fuel economy suffers, and the biggest reason people get away with it is becasue they are using them on motors that dont make a lot of HP per cylinder.

when the HP goes up, fuel and spark delivery are all that much more critical. something you cant get with a distributor and TBI.......if it was the hot ticket, you would see the OEMS still doing it and they moved past this technology in the 80's. it cracks me up all the guys spending big money on rotating assemblies and superchargers but for some reason feel the cheapest electronics they can find and get it to run is the way to go. these are the guys rebuilding their engines routinely.

 

[Rajobigguy]

I’ve always wondered this I just don’t understand how you get an o2 sensor into a wet exhaust. I haven’t ever seen a center rise exhaust setup with an o2 bung at the collector before the riser or a retrofit riser with an o2 bung. Seems a little tough to do it to an existing set. Without an o2 you’re kinda just measuring map or maf input and guessing at what you’re getting out on the other end… little pointless to me.

Getting an O2 sensor into a marine exhaust is pretty easy (if you’re a decent machinist).

 

[coolchange]

I have seen them They were kinsler's. Some were for big chief heads.

They weren’t 3”, but they were big! I can’t find anything on them. I’ll search kinsler.

 

[BBYSTWY]

To answer Hallet's question....laptop tuning I would say is a must...comes with the cord just plug it in download the holley software and go. I would suggest either getting some training in that department or paying someone to do it. I paid a guy and have zero issues.

The only thing I would disagree with Racey on is turning off O2's and running open loop. If you do that you basically have a very expensive carb. I run the O2 on the EFI and also a wideband O2 gauge for redundancy. If the O2 is turned off the system can't compensate for changes in air temp, density, etc. It just can't as it has no input to what the engine is doing so I can't make any changes. You are locking in timing and fuel tables and running based on those tables alone which is the same as a carb in my opinion.

Last thing I wanted to ask....how does a TBI efi setup differ at all from a carb if placed on the same manifold when it comes to fuel distribution? You are putting the same fuel through the same holes in the same way. If you have poor fuel distribution in the manifold, I don't care what's on top a carb, efi, or whatever it's going to have poor distribution regardless. Just my thoughts on that.

Is port injection better? Probably, it's certainly more efficient and distributes fuel better. Are you going to see a drastic change on a slightly built motor? Doubtful. If you tune a carb or TBI to run on a given manifold and the motor runs well...why would you try to reinvent the wheel with port injection? A huge cube high HP deal is different obviously.

 

[Shlbyntro]

To answer Hallet's question....laptop tuning I would say is a must...comes with the cord just plug it in download the holley software and go. I would suggest either getting some training in that department or paying someone to do it. I paid a guy and have zero issues.

The only thing I would disagree with Racey on is turning off O2's and running open loop. If you do that you basically have a very expensive carb. I run the O2 on the EFI and also a wideband O2 gauge for redundancy. If the O2 is turned off the system can't compensate for changes in air temp, density, etc. It just can't as it has no input to what the engine is doing so I can't make any changes. You are locking in timing and fuel tables and running based on those tables alone which is the same as a carb in my opinion.

Last thing I wanted to ask....how does a TBI efi setup differ at all from a carb if placed on the same manifold when it comes to fuel distribution? You are putting the same fuel through the same holes in the same way. If you have poor fuel distribution in the manifold, I don't care what's on top a carb, efi, or whatever it's going to have poor distribution regardless. Just my thoughts on that.

Is port injection better? Probably, it's certainly more efficient and distributes fuel better. Are you going to see a drastic change on a slightly built motor? Doubtful. If you tune a carb or TBI to run on a given manifold and the motor runs well...why would you try to reinvent the wheel with port injection? A huge cube high HP deal is different obviously.

Answering your question on tbi vs carb on the same intake goes towards your closed loop O2 sensors. when you have certain cylinders running rich where as others are running normal, the ecm will interpret it as an overall rich running condition and adjust timing/lean out the fueling to compensate. This will cause a lean condition in your cylinders that were running normally before your ecm started trying to clean up the exhaust. The ecm is incapable of seeing the lean condition it just caused in said certain cylinders which in turn results in your engine going boom if run like that too long (burnt valves, grenaded pistons, etc.) This fuel system combined with just a few fouled spark plugs will cause similar results.

Obviously a carburetor isn't going to try to clean up your exhaust, neither is an open loop system. Fyi all oem marine fuel injection has run on open loop up until just very recently.

Here's the difference between a carburetor and open loop fuel injection. In a carburetor, your fuel mixture is determined directly by the airflow passing the venturis at any given moment. your jetting is your "fuel map". So long as your "mapping" isn't out of whack, it's pretty fail safe as to not do anything to hurt your engine no matter what. A MAF (Mass Air Flow) fuel injection system works similarly but MAF does not exist in marine applications; for what exact reasons, I don't know. Your typical open loop MAP (Manifold Absolute Pressure) fuel injection which is most marine systems currently, works based on a calculation determined by your fuel mapping that calculates fuel demand by such parameters as engine displacement, cam profile, manifold pressure, throttle position. Any one of the many sensors in a MAP system failing will cause it to go haywire. Additionally, any low vacuum situation will be interpreted by the ecm as increased load causing over fueling. An engine in need of a simple tuneup is enough to cause noticeable lower engine vacuum to negatively affect MAP fi.

 

[rivermobster]

Well I actually have a Pro-M mass air sequential port system sitting on the shelf but it's for a different project . I was just wondering if anyone has had any success with any of these self contained systems on a boat. I don't have any problems with carbs but I made the mistake of letting a shop screw around with this one years ago and it has never really been right since so rather than me spending days of boating time adjusting the jetting and metering rods to get it performing correctly I was exploring the possibility of an easier/quicker fix.
The current carb is a Edelbrock AVS, maybe I should just switch to the regular Edelbrock Marine carb and call it good (at least until I get around to finishing the other project engine).
Thanks for the input guys.

It will definitely not be easier or quicker to switch over to EFI.

Everyone Always wants to jump ahead of the game without first exploring the basics!

Why is it not running right?

It's it a fuel delivery problem? Ignition system problem? Timing problem? Intake air (vacuum leak?) problem? Engine mechanical problem?

Your best course of action is First diagnosing the actual problem. Cover the basics FIRST!!!

IF you are 110 percent confident it's a carb issue, then sure, replace the carb with a marine style carb and then start fine tuning from there.

I like QFT a whole lot better than Edelbrock carbs, but there is nothing wrong with Edelbrock either.

Always start with the basics.

 

[monkeyswrench]

Mass Airflow system are extremely sensitive to intake design, shape etc. Because of this they are almost never used on custom applications. At least any custom application done correctly.

A few years back I was playing with some efi fuckery, and asked Ryan Falconer about this. He tended to lean towards having a MAF sensor. I asked him why, and what he told me made sense in my carb'd and point fired brain. His logic was that between the map and the maf, you could get a more accurate measurement of the ingested air flow.

This came up as I was questioning the placement of the MAF, pre- or post- supercharger. His comment was to the effect if it were mounted pre-, it would not give accurate measurement. The air would be heated up, making it less dense, and thus a misrepresentation.

Was more of a thought exercise for me. The kid had limited budget, and it ended up being a blow through carb...and he yard saled the car maybe within a few weeks. Some parts are on my shelf still..."lightly used".

 

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To answer Hallet's question....laptop tuning I would say is a must...comes with the cord just plug it in download the holley software and go. I would suggest either getting some training in that department or paying someone to do it. I paid a guy and have zero issues.

The only thing I would disagree with Racey on is turning off O2's and running open loop. If you do that you basically have a very expensive carb. I run the O2 on the EFI and also a wideband O2 gauge for redundancy. If the O2 is turned off the system can't compensate for changes in air temp, density, etc. It just can't as it has no input to what the engine is doing so I can't make any changes. You are locking in timing and fuel tables and running based on those tables alone which is the same as a carb in my opinion.

Last thing I wanted to ask....how does a TBI efi setup differ at all from a carb if placed on the same manifold when it comes to fuel distribution? You are putting the same fuel through the same holes in the same way. If you have poor fuel distribution in the manifold, I don't care what's on top a carb, efi, or whatever it's going to have poor distribution regardless. Just my thoughts on that.

Is port injection better? Probably, it's certainly more efficient and distributes fuel better. Are you going to see a drastic change on a slightly built motor? Doubtful. If you tune a carb or TBI to run on a given manifold and the motor runs well...why would you try to reinvent the wheel with port injection? A huge cube high HP deal is different obviously.

The system absolutely can adjust for changes in altitude and temp in open loop. That is what the VE table is for in a speed density system. If you don’t have speed density with VE then you are correct. But all these modern fuel injections systems we are talking about do.

 

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Answering your question on tbi vs carb on the same intake goes towards your closed loop O2 sensors. when you have certain cylinders running rich where as others are running normal, the ecm will interpret it as an overall rich running condition and adjust timing/lean out the fueling to compensate. This will cause a lean condition in your cylinders that were running normally before your ecm started trying to clean up the exhaust. The ecm is incapable of seeing the lean condition it just caused in said certain cylinders which in turn results in your engine going boom if run like that too long (burnt valves, grenaded pistons, etc.) This fuel system combined with just a few fouled spark plugs will cause similar results.

Obviously a carburetor isn't going to try to clean up your exhaust, neither is an open loop system. Fyi all oem marine fuel injection has run on open loop up until just very recently.

Here's the difference between a carburetor and open loop fuel injection. In a carburetor, your fuel mixture is determined directly by the airflow passing the venturis at any given moment. your jetting is your "fuel map". So long as your "mapping" isn't out of whack, it's pretty fail safe as to not do anything to hurt your engine no matter what. A MAF (Mass Air Flow) fuel injection system works similarly but MAF does not exist in marine applications; for what exact reasons, I don't know. Your typical open loop MAP (Manifold Absolute Pressure) fuel injection which is most marine systems currently, works based on a calculation determined by your fuel mapping that calculates fuel demand by such parameters as engine displacement, cam profile, manifold pressure, throttle position. Any one of the many sensors in a MAP system failing will cause it to go haywire. Additionally, any low vacuum situation will be interpreted by the ecm as increased load causing over fueling. An engine in need of a simple tuneup is enough to cause noticeable lower engine vacuum to negatively affect MAP fi.

No MAF because cams with bigger overlap can cause air reversion which translates to bucking or inconsistent power delivery at lower RPM and load. If you’ve ever driven a cammed vehicle with a MAF you have likely felt it buck.

Also a MAF needs to be placed in a long straight tube because smooth airflow is key to it functioning properly. This is the biggest hurdle.

 

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The system absolutely can adjust for changes in altitude and temp in open loop. That is what the VE table is for in a speed density system. If you don’t have speed density with VE then you are correct. But all these modern fuel injections systems we are talking about do.

only upon key off/on for most marine and aftermarket systems as they take their atmospheric pressure reading from the MAP sensor at key on. They can't change on the fly.

 

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only upon key off/on for most marine and aftermarket systems as they take their atmospheric pressure reading from the MAP sensor at key on. They can't change on the fly.

That’s fine.. I’m not going uphill 2000 feet in the boat

Some of aftermarket stuff does all of that on the fly using a MAP sensor and air temp sensor. With a VE table to interpolate the proper fueling based on pressure as temp. The Holley stuff does this.