Performance questions twin Merc 7.4 vortec
01-23-2019, 04:53 AM
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Performance questions twin Merc 7.4 vortec
Hi !
I have a Tullio Abbate elite 30 with two vortec 7.4 engines ,bravo one with mirage 23 P props and I can not go faster than 50 mph. I did compression test and it came up perfect , I put new plugs , plug wires and distributor caps , etc...
Do you think is the max I will get out of those engines or there has to be something wrong .... my point of view is that it should reach 60 easy... with my previous boat a 24ft and a single engine 5.7 I got close to 50mph
thanks for the help!
I have a Tullio Abbate elite 30 with two vortec 7.4 engines ,bravo one with mirage 23 P props and I can not go faster than 50 mph. I did compression test and it came up perfect , I put new plugs , plug wires and distributor caps , etc...
Do you think is the max I will get out of those engines or there has to be something wrong .... my point of view is that it should reach 60 easy... with my previous boat a 24ft and a single engine 5.7 I got close to 50mph
thanks for the help!
01-24-2019, 06:43 AM
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You have something wrong then.
For reference I have an old 31 foot scarab with twin 454 mags and a few mild upgrades. I am using 25P props and she will do 65MPH all day long.
What engine RPM are you seeing? Do you have it trimmed right after on plane?
For reference I have an old 31 foot scarab with twin 454 mags and a few mild upgrades. I am using 25P props and she will do 65MPH all day long.
What engine RPM are you seeing? Do you have it trimmed right after on plane?
01-24-2019, 07:05 AM
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Thanks for the answer
First I believe that I have 2( 7.4 non mag) but not sure , pain in the ass to find it out since engine has been painted and I only know the engine serial numbers for the documents of the boat. Also I wish I knew if it is a gen 4-5-6. The engine has been upgraded at some point because it has Holley carburetors and aluminium valve covers with electric fuel pump..... so looks like it is a gen V but that’s it. Boat is a 1991
Boat planes almost immediately and then I trim it to get wot , I am looking for a max of 4600 rpm but only reach 4000 , I know I have to drop down to 21 or 22 pitch but I think there has to be something else ....
Thanks
First I believe that I have 2( 7.4 non mag) but not sure , pain in the ass to find it out since engine has been painted and I only know the engine serial numbers for the documents of the boat. Also I wish I knew if it is a gen 4-5-6. The engine has been upgraded at some point because it has Holley carburetors and aluminium valve covers with electric fuel pump..... so looks like it is a gen V but that’s it. Boat is a 1991
Boat planes almost immediately and then I trim it to get wot , I am looking for a max of 4600 rpm but only reach 4000 , I know I have to drop down to 21 or 22 pitch but I think there has to be something else ....
Thanks
01-24-2019, 07:18 AM
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Mine is also a 1991.
I am seeing 5100 RPM with 25P props.
If you are only seeing 4000 then you have problems even if they are not mags. What ignition system is it? Mine had low power when I got it and I found out the timing advance springs where rusted and gone. MSD ignition on mine. This and new plugs wires springs caps rotors and new coils got mine going. I was adjusting the carb with one engine running and the coil shocked the piss out of me through the case so I knew it was bad. Your carbs might need to be rebuilt. I had to adjust all 4 floats in mine (holley 750s) because the previous owner had them all jacked up.
I am seeing 5100 RPM with 25P props.
If you are only seeing 4000 then you have problems even if they are not mags. What ignition system is it? Mine had low power when I got it and I found out the timing advance springs where rusted and gone. MSD ignition on mine. This and new plugs wires springs caps rotors and new coils got mine going. I was adjusting the carb with one engine running and the coil shocked the piss out of me through the case so I knew it was bad. Your carbs might need to be rebuilt. I had to adjust all 4 floats in mine (holley 750s) because the previous owner had them all jacked up.
01-24-2019, 09:39 AM
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Hi thanks for the answer, now I have a place to start
the ignition system is stock and I did not change it neither the coils so I will start from there. I have Holley 4175 CFM 650 and I got a complete rebuild kit that I would put it on as well as new spacers.
I really appreciate your help!
the ignition system is stock and I did not change it neither the coils so I will start from there. I have Holley 4175 CFM 650 and I got a complete rebuild kit that I would put it on as well as new spacers.
I really appreciate your help!
01-24-2019, 10:25 AM
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Don’t know the brand of the ignition however who knows how old it is .... as well as the coils ... yes the boat runs in salt water and it has a layer of antifouling, when I did the speed test it was after some hours of the painting so it was totally clean ... I know it slowes it down a bit ... but I did not test it after 3 months being at the dock
thanks!
thanks!
01-24-2019, 10:44 AM
#8
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If the paint is relatively smooth should be ok. If it's rough can hurt you bad. Ignition normally works or don't if both motors pull the same rpm I doubt it has anything to do with it unless it starts missfireing.
01-24-2019, 11:26 AM
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One sucks at idle but it is smooth on the way to higher rpms at 4000 rpm don’t missfire but it does not go any far (of course trimming the engines ) ....
Thanks for all the help!
Thanks for all the help!
