Stack Injection converted to EFI ?

[boatguy222]

I am thinking about converting a Kinsler 2.9 stack manifold to EFI, for a 496-505ci, 10 to 1, pump gas engine for my v-drive daycruiser. I posted this over at the PB forum and It turned in to a 5 page pissing match, with very little useful information.

I have seen stack manifolds done before, all of them have the smaller throttle bores. I am concerned about the 2.9 bores causing issues with low rpm performance, So any thoughts subject are welcome.

Thanks,
Marc

 

[BamBam]

I am thinking about converting a Kinsler 2.9 stack manifold to EFI, for a 496-505ci, 10 to 1, pump gas engine for my v-drive daycruiser. I posted this over at the PB forum and It turned in to a 5 page pissing match, with very little useful information.

I have seen stack manifolds done before, all of them have the smaller throttle bores. I am concerned about the 2.9 bores causing issues with low rpm performance, So any thoughts subject are welcome.

Thanks,
Marc

Hilborn Injection makes a 3" bore EFI manifold
http://www.hilborninjection.com/product.asp?Id=406&CatId=174
If they can get it to run I'm sure you can. The only tough thing will be tip-in, maybe you can come up with an innovative progressive linkage to eliminate the throttle sensitivity right off idle. Sounds like a great project. Have fun, take pictures and post them up so we can all watch your build.

 

[DaveH]

Hilborn Injection makes a 3" bore EFI manifold
http://www.hilborninjection.com/product.asp?Id=406&CatId=174
If they can get it to run I'm sure you can. The only tough thing will be tip-in, maybe you can come up with an innovative progressive linkage to eliminate the throttle sensitivity right off idle. Sounds like a great project. Have fun, take pictures and post them up so we can all watch your build.

x2 but a couple things.

without a doubt, throttle bore diameter will effect how rapidly the engine will accelerate from a small throttle opening. this can be dealt with but makes it hard to drive, "pipey" like a two stroke.

typically stack injection setups are designed to work higher up in the RPM range, something to gain HP up top but performance WILL suffer down lower. If this is a light boat or has a trans then its not that big of a deal, just dont expect it to have the manners of a more modern setup.

take the time to run a small vacuum line from each runner to a plenum and USE A MAP sensor. this is a much better way to control fuel delivery on something like this than using TPS as the main reference for fuel.

Spend the extra money for modern denso or injector dynamics injectors. atomization quality is WAY BETTER than the older style bosch or rochester injectors and your engine will be much easier to tune and run better because of it.

dont skimp on your fuel delivery. you need to make sure fuel pressure is CONSTANT with no fluctuations. there isnt a marine fuel tank out there with good baffles. consider using a lift pump/accumulation system.

use quality wire and connections, all sealed and heat shrinked, or you will chase endless gremlins and it will never run "right".

take it to an engine dyno and try and run it as close to possible in the configuration it will be in the boat.

it like anything else, you get what you pay for.

 

[Racey]

I am thinking about converting a Kinsler 2.9 stack manifold to EFI, for a 496-505ci, 10 to 1, pump gas engine for my v-drive daycruiser. I posted this over at the PB forum and It turned in to a 5 page pissing match, with very little useful information.

I have seen stack manifolds done before, all of them have the smaller throttle bores. I am concerned about the 2.9 bores causing issues with low rpm performance, So any thoughts subject are welcome.

Thanks,
Marc

Exactly what DaveH said plus the length of your stacks will give you some ability to help with the low end performance. The main issues with stack injection is that the air movement has to start and stop each time the valve opens and closes, and air has mass, it takes energy to get it moving, it wastes energy to stop it's movement, this is why you will have such a larger combined throttle valve surface area than compared to a conventional manifold (You probably know this, but I'm just putting it out there for others that may stumble onto this thread) proper runner length will give you somewhat of an ability to help with your low end (it's not the end all, but it does give you some control), longer runners make more bottom end, as it takes longer for the air movement to stop, and at lower rpms you have longer distance between valve events, if you can get the valve to open up before the air has stopped moving it, in laymen's terms, kinda 'rams' itself into the cylinder, it's like a helping hand for the motor instead of having to rely on the piston alone drawing the air you can utilize some of the energy from the air movement of the previous cycle. Shorter helps with top end as there is less restriction/friction, and the higher frequency of valve events, getting air into the motor. Finding that happy length is a lot easier on the dyno :thumbsup.


Most important is referencing vacuum off of all the runners into some type of accumulator (a little can), where you can get a consistent MAP reading, if you just reference one cylinder, the computer will see rapid spikes in manifold pressure as the valve is open then closed (High Vacuum, Low Vacuum, High Vacuum, Low Vacuum) bouncing the computer all over the fuel and timing map, just makes it more difficult to consistently tune. Highly recommend against using throttle position alone as your method of determining load on the motor, Manifold pressure is a far better method. Gasoline engines control speed based on manifold pressure, throttle valves are just a method of controlling manifold pressure, it's better to read the pressure directly than just the valve position.