Holley Sniper EFI

P

Pdvoor

New Member
Aug 31, 2023
2
Boat Info
1986 Sea Ray sedan 300
Engines
350 Mercruiser
Hi, I'm thinking about replacing the quadrajet carbs on both of my engines on my 300 sedan bridge. Has anyone done this and is it worth it? I'm also thinking about replacing the mercruiser thundevolt ignition system with HEI Does anyone have thoughts on this?
 
This thought has passed my mind on a few occasions but I'm not sure if any of that stuff is certified for marine use. FWIW, last summer I paid a guy $200 to rebuild both of my Q jets and they are behaving beautifully now
 
Keep the carbs and have them rebuilt/tuned and add electric chokes. Install HEI ignition distributors. I have run Qjet carbs with DUI (Davis Unified Ignition) distributors for 9 years with no issues.
 
Agree with @hottodie
I have carbs wouldn’t want add on EFI
The Thunderbolt is getting impossible to find parts. So that upgrade is worthwhile if any issues in ignition.

P.s.
If any mods be sure everything is marine ignition protected
 
Holley makes the Sniper EFI in a marine certified configuration. Actually, all of their EFI systems can be obtained in a marine certified configuration. They are very good systems and have advanced learning capabilities reducing the need to tune on a dynamometer. There is a premium cost to convert so what is to be gained? Provided the system is correctly "tuned" (meaning all of the baseline data, maps, tables, and offsets are correctly populated) you will see improved fuel economy, superior throttle response, better engine starting characteristics, and generally more reliable engine operation. Will you see more engine power? Not empirically - the engine is still naturally aspirated with limitations in induction, compression, exhaust, and displacement. The only gains in power will be from a more precise fuel and spark control.
There are four things the Holley EFI does not provide that are critical to the performance and reliability of the EFI system; if any one parameter is not performing 100% then the investment in the EFI will be soured:
Fuel delivery must be suitable, consistent, and properly filtered.
Ignition system although controlled by the EFI must be 100% accurate in timing and spark delivery with the appropriate spark energy. This is probably the most critical aspect to EFI performance.
Basic engine health in compression, cam timing, oiling, and cooling system.
A solid electrical system with proper voltages and current with clean low resistance connections. EFI systems require significantly higher electrical current than anything carbureted.

I'd say if your engine basics are solid and the EFI installation is correctly implemented and tuned you will be happy with the results. The downside is, if you sell the boat the owners will no doubt have challenges with service if they are not versed in the aspects of the added systems.
 
ttmott said:
Holley makes the Sniper EFI in a marine certified configuration. Actually, all of their EFI systems can be obtained in a marine certified configuration. They are very good systems and have advanced learning capabilities reducing the need to tune on a dynamometer. There is a premium cost to convert so what is to be gained? Provided the system is correctly "tuned" (meaning all of the maps and offsets are correctly populated) you will see improved fuel economy, superior throttle response, better engine starting characteristics, and generally more reliable engine operation. Will you see more engine power? Not empirically - the engine is still naturally aspirated with limitations in induction, exhaust, and displacement
There are three things the Holley EFI does not provide that are critical to the performance and reliability of the EFI system; if any one parameter is not performing 100% then the investment in the EFI will be soured:
Fuel delivery must be suitable, consistent, and properly filtered.
Ignition system although controlled by the EFI must be 100% accurate in timing and spark delivery with the appropriate spark energy. This is probably the most critical aspect to EFI performance.
Basic engine health in compression, cam timing, oiling, and cooling system.

I'd say if your engine basics are solid and the EFI installation is correctly implemented and tuned you will be happy with the results. The downside is, if you sell the boat the owners will no doubt have challenges with service if they are not versed in the aspects of the added systems.
Click to expand...
Great/Interesting to hear there is a marine version!
How is the O2 sensor bunged in?
 
Ok, Holley Sinper EFI, some AFR aluminum heads and intake!
Now all I need is that winning lottery ticket.
 
hottoddie said:
Keep the carbs and have them rebuilt/tuned and add electric chokes. Install HEI ignition distributors. I have run Qjet carbs with DUI (Davis Unified Ignition) distributors for 9 years with no issues.
Click to expand...
This does sound like the most economical. Q-jets are good carbs when they are set up correctly
 
Been there done that. If you have 5 grand to spend, why not, but don’t get too excited about the ”benefits” which you may think you’ll get when installing snipers… starting issues are gone,though, and thats the most acknowledgeable thing you will notest. After all, i don’ think its wise move financially, they won’t pay themself off with less fuel consumption or anything like that.
Lambda sensors i fitted to 1” Thick aluminiumin block between exhaust manifolds and risers. it may be good idea to remove them after sniper has learned enough and created fueling maps, since these sensors fail if they get in touch even slightest amount of salt water(at least I’ve been told so, even though I don’t fully buy that)
 
Zorg said:
Been there done that. If you have 5 grand to spend, why not, but don’t get too excited about the ”benefits” which you may think you’ll get when installing snipers… starting issues are gone,though, and thats the most acknowledgeable thing you will notest. After all, i don’ think its wise move financially, they won’t pay themself off with less fuel consumption or anything like that.
Lambda sensors i fitted to 1” Thick aluminiumin block between exhaust manifolds and risers. it may be good idea to remove them after sniper has learned enough and created fueling maps, since these sensors fail if they get in touch even slightest amount of salt water(at least I’ve been told so, even though I don’t fully buy that)
Click to expand...
I bought and air fuel ratio meter that I use both on my boat and 65 GTO. The manufacturer of the gauge stated for marine applications to not leave it permantely installed (use for tuning only) as the water in the exhaust will shorten O2 sensor life. I left it on my boat for 3-4 weeks last summer put it back in the car with no issues.
 
Scott06 said:
I bought and air fuel ratio meter that I use both on my boat and 65 GTO. The manufacturer of the gauge stated for marine applications to not leave it permantely installed (use for tuning only) as the water in the exhaust will shorten O2 sensor life. I left it on my boat for 3-4 weeks last summer put it back in the car with no issues.
Click to expand...
since Combustion is an exothermic oxidation reaction, where hydrocarbons reacting with oxygen to form combustion products such as water and carbon dioxide, your car engine’s exhaust gasses contains water vapor as well as your boat engine exhaust gasses. So i think the problems which might occur with O2 sensor are not caused by water itself, but in marine applications things like minor leaks of cooling water containing salts, may have some impact on sensor….
 
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