Throttle Body Injection

[mbhenry]

I have a 1999 5.0 Carb Mercruiser.<br />I have a opportunity to buy an automotive Holly Throttle body injection system with a 2 barrel adaptor for under $500.00. This system is almost new. What modifications must be done to make this work? I have been given the opportunity to try it and if I like it, buy it on easy pay terms.<br />Do you think I would have to change pitch with this setup? I'm now running a Turbo 14.25 X 21 @ 4550 RPMs <br />Thanks

 

[Walt T]

Re: Throttle Body Injection

Sorry, you must use the marine unit. It has steel lines (coast guard lines anyway). There is a difference in the wiring harness for the fuel pump shut off system. As far as differences in the throttle body itself I dont know the differences offhand, if any. There may be differences with the ECM, and the fuel pump may also be different.<br />==============================================<br />I need to edit my above answer. I contacted Holley since I was curious and this is the answer I got:<br /><br />The Marine ECu is potted for water resistance. An the harness is a little longer. The Marine kits come with a flame arrestor. Thanks WW<br /><br />So it would appear that the automotive unit is okay to use on the marine engine.

 

[WillyBWright]

Re: Throttle Body Injection

You mention an adaptor. Are you going from a four barrel carb to two barrel injection? Why would you want to do that??? You'll lose CFM delivery and thus lose power. High Tech does not equal More Power! Not that TBI injection is High Tech. It's nothing more than an electronic two barrel carburetor.

 

[Bondo]

Re: Throttle Body Injection

I wouldn't worry about reproping, until you've got the thing Installed,+ Tuned .....<br />I don't think you're buying alot of new Horsepower, you're getting easy starts,+ Economy.......<br />I Thought about these a few years ago.... <br />Not being able to use an O2 sensor in a Wet Exhaust turned me Off to them....<br />Now that I've figured out How to Tune my Merc/Weber/Carter Carb......<br />I Wouldn't have Anything Else..!!...<br /><br />WillyBWright, I Think he's adapting the 3 legged Throttle body to his 2bbl Manifold.....<br />A 4bbl Swap would Really Wake that motor Up....

 

[mbhenry]

Re: Throttle Body Injection

The adaptor is for the TBI to fit on my 2 barrel manifold. This deal included the ECM and all sensors. I just don't know if this Holly TBI is adaptable to Marine. I don't have the model# yet so I can't contact them directly. <br />I won't do this untill I get all the info, and make sure that it is Marine SAFE!!!

 

[Walt T]

Re: Throttle Body Injection

The Holley TBIs come in various cfms, 625 being the most common. 625 is the same as most 4 bbls. I have replaced 4bbl carbs with the 2 bbl TBI and got much better performance even though the cfm is the same. Most marine units do not come close to needing the full carb cfm. <br />Using the generally accepted formula to determine carb size we find that for a 350 Chevy at 4500 rpm we need approximately 456 cfm. That's a lot less than 625. Cfm is what matters, not 2 or 4 bbl.<br />If you install an 850 double pumper on a stock Chevy 350 what have you accomplished? You've killed your bottom end acceleration because of over carburetion. Over carbureting is the number one mistake amateur hot rodders make. <br />Stick with a 550 or 500 cfm and you will really wake up that engine.<br /><br />Engine size(CID)x Maximum rpm/3456=CFM<br />Carburetor size

 

[mbhenry]

Re: Throttle Body Injection

Thanks DW. I really don't want to go to a 4 bbl setup right now.