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Old 04-16-2013, 08:44 PM
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tbi or mpi

I am getting ready to order an efi system for boat. I am curious about pros and cons of each system. The mpi system is about a thousand more than the tbi. This is on a 383 with vortec heads and the gm performance 7395 cam which is the ramjet and ht383 cam. Will there be a noticeable amount of difference between the tbi and mpi? From what i understand the mpi was introduced and widely used due to emission laws, is this true? I'm leaning towards the tbi system because of the cost but i am willing to spend the extra if it's gonna be enough of an amount better. Please help me spend my money. Please i don't wanna hear "what's wrong with the carb system".

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Old 04-16-2013, 08:50 PM
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not fer nothing but pace has a marine efi engine with efi for 1000.oo
sell the 305 and drop the efi on your 383 and reprogram the ecu and maybe bigger injectors.
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Old 04-16-2013, 09:02 PM
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Originally Posted by gearheadslife View Post
not fer nothing but pace has a marine efi engine with efi for 1000.oo
seb
ll the 305 and drop the efi on your 383 and reprogram the ecu and maybe bigger injectors.
What? I can't make sense of any of that. I don't currently have an efi system or a 305 to sell. i am buying a new efi system just not sure what I want to buy.
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Old 04-16-2013, 09:18 PM
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What? I can't make sense of any of that. I don't currently have an efi system or a 305 to sell. i am buying a new efi system just not sure what I want to buy.
pace a chevy dealer, that sells online has a complete marine small block chevy 305 with marine multiport efi for a little over 1000.oo bucks..
I'd look at that, as you can sell the engine. and drop the efi on your 383..
reprogram the ecu and add bigger injectors..
and you'll have a merc chuiser efi system for most likely a grand
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Old 04-16-2013, 09:51 PM
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Could you give me a link to that.
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Old 04-17-2013, 12:39 PM
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Quote:
Originally Posted by crussell85 View Post
I am getting ready to order an efi system for boat. I am curious about pros and cons of each system. The mpi system is about a thousand more than the tbi. This is on a 383 with vortec heads and the gm performance 7395 cam which is the ramjet and ht383 cam. Will there be a noticeable amount of difference between the tbi and mpi? From what i understand the mpi was introduced and widely used due to emission laws, is this true? I'm leaning towards the tbi system because of the cost but i am willing to spend the extra if it's gonna be enough of an amount better. Please help me spend my money. Please i don't wanna hear "what's wrong with the carb system".
What kind of a difference are you looking for?

The MPI will deliver a lower fuel burn (better milage) and lower emissions.

The TBI will stand between a carb and MPI on both issues.

Max power and everywhere in-between there and idle is a tuning issue which in each of these types of EFI systems is going to depend mostly on the control chip and its programming. The largest limiting factor for max power from TBI is the fuel delivery capacity of the injectors where a 2 barrel is used. The max size injector for these is about 90 pounds per hour per injector which figuring at Wide Open Throttle (WOT) the engine will consume about .5 pound per horsepower per hour, this caps the output from a 2 bbl TBI at 360 hp. That compares to an MPI with eight 30 pound per hour injectors which would be able to feed fuel for 480 hp.

Of course in both cases fuel pressures greater than manufacturer nominal and injector ON times greater than an 80% of the duty cycle can be shoved around for greater fuel delivery, but both of these techniques reduce component life. It's one thing to have the engine crap out on the street or track, it's a different thing to have that happen out in the middle of Lake Michigan.

Bogie
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Old 04-17-2013, 01:10 PM
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I basically want a good reliable system. I'm not looking to improve fuelmileage or make a ton more power. I'm not real familiar with carbs so i can never get the thing to run right. I had looked at buying a new carb and distributor then thought i would rather spend a little more and go tbi. I guess my question should be if you drove two vehicles completely the same down to the same bird droppings on them except one was tbi and one was mpi would you notice a difference and if you did would it be enough for a wow factor?
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Old 04-18-2013, 10:01 AM
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Originally Posted by crussell85 View Post
I basically want a good reliable system. I'm not looking to improve fuelmileage or make a ton more power. I'm not real familiar with carbs so i can never get the thing to run right. I had looked at buying a new carb and distributor then thought i would rather spend a little more and go tbi. I guess my question should be if you drove two vehicles completely the same down to the same bird droppings on them except one was tbi and one was mpi would you notice a difference and if you did would it be enough for a wow factor?
If both systems were idealized the only difference one might see is a smoother response of operation at low throttle settings with a high load on the crankshaft from the MPI system. In other words, injection at the valve or better yet into the chamber (Direct Injection) allows the engine to be lugged without bucking and learching that would be seen especially with a carb and somewhat with TBI. Above that regime to WOT at redline the power and functional difference between MPI and TBI, even a properly tuned carb, would be very similar as long as mileage and emissions were not a concern of the evaluation. The other big advantage of injection over carburetion is that injection, either MPI or TBI, is not "g" sensitive as is a carburetor.

Bogie
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Old 04-18-2013, 10:42 AM
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Thank you sir. From your knowledge I think the tbi system will suit my needs just fine. About the g sensitive with a carbd system, is that why you hear about people mounting the carbs sideways?
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Old 04-18-2013, 11:01 AM
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Originally Posted by crussell85 View Post
Thank you sir. From your knowledge I think the tbi system will suit my needs just fine. About the g sensitive with a carbd system, is that why you hear about people mounting the carbs sideways?
That can be a reason though usually it's a space issue with those long Holley style carbs. The Holley and clones of them employed center mounted floats, jet extensions, slosh meshes, cross jetting, etc. as measures to minimize the effects of vehicle movement on mixture ratio and fuel spillage.

Bogie
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Old 04-18-2013, 01:02 PM
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If I was to buy a book on how carbs work and initial setup, tuning, etc. Would you have a suggestion?
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