7.4 MPI (need more speed )
#1
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7.4 MPI (need more speed )
OK thanks for the info. on the Procharger. Since I should not put a Prochagrer on my 7.4 could anyone tell how do get more speed without puting a new motor in the boat
DMH
DMH
#2
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Re: 7.4 MPI (need more speed )
I was where you are last year. I corresponded with many knowledgeable people.
What I was told and what I have now experienced first hand is that the GM fuel injection system will only flow enough air to make 375HP at 4600-4700rpm.
I changed the cam and exhaust to get there. The engine does make a good bit more low end torque now too.
My boat went from 65-66mph @ 4300-4400rpm to 68-69mph @ 4600-4700rpm spinning the same prop...
If you would like a bigger gain than that, you will need to ditch the GM fuel injection.
Good Luck!
What I was told and what I have now experienced first hand is that the GM fuel injection system will only flow enough air to make 375HP at 4600-4700rpm.
I changed the cam and exhaust to get there. The engine does make a good bit more low end torque now too.
My boat went from 65-66mph @ 4300-4400rpm to 68-69mph @ 4600-4700rpm spinning the same prop...
If you would like a bigger gain than that, you will need to ditch the GM fuel injection.
Good Luck!
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Patrick
Patrick
#3
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Re: 7.4 MPI (need more speed )
Originally Posted by Pat McPherson
If you would like a bigger gain than that, you will need to ditch the GM fuel injection.
Good Luck!
Good Luck!
Roby
#4
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Re: 7.4 MPI (need more speed )
Hey Roby,
Are you an engine builder?
I have an extra intake I would gladly donate to your development.
When you come up with a good combo I would definitely be interested!
My engine is a Volvo Penta version so I don't have the gasket behind the TB that I believe you are referring to. I don't have the elbow between the TB and the intake plenum either. Is this better for flow?
I changed the L-29 cam out for a 454/502HO cam, changed the valves and springs, and installed Stainless Marine exhaust. Had and ECM re-calibrated 3 different times by AZ Speed, but the stock Volvo calibration still works the best
This off season I was planning to change the cam out for a ZZ502cam.
I am thinking I have to ditch the MPI for a carb to realize the gains from the larger cam. Would be great if I could retain it! I also have another set of Vortec heads that could be machined and ported...
Roby, I hope you can do what others say can't be done.
Are you an engine builder?
I have an extra intake I would gladly donate to your development.
When you come up with a good combo I would definitely be interested!
My engine is a Volvo Penta version so I don't have the gasket behind the TB that I believe you are referring to. I don't have the elbow between the TB and the intake plenum either. Is this better for flow?
I changed the L-29 cam out for a 454/502HO cam, changed the valves and springs, and installed Stainless Marine exhaust. Had and ECM re-calibrated 3 different times by AZ Speed, but the stock Volvo calibration still works the best
This off season I was planning to change the cam out for a ZZ502cam.
I am thinking I have to ditch the MPI for a carb to realize the gains from the larger cam. Would be great if I could retain it! I also have another set of Vortec heads that could be machined and ported...
Roby, I hope you can do what others say can't be done.
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Patrick
Patrick
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Re: 7.4 MPI (need more speed )
This all sounds great if cost were not a factor. For me it is. I have already ditched the MPI for carburetion and I`m extremely satisfied. I eventually replaced this 7.4 for a stroker big block, displacing 489 ci. Now I have POWER.
#6
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Re: 7.4 MPI (need more speed )
Personally, save your money and do not mess with the 7.4L motor. This motor only has cast pistons and crankshaft. Spinning it more rpms will result in a broken crankshaft. This motor I tell everyone is what it is. Small heads low compression truck motor. Messing with props will get you more out of your boat than spending $2000-$4000 dollars for 50hp. However that is only my opionion.
#7
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Re: 7.4 MPI (need more speed )
I have to agree, I pulled my 7.4 and dropped in a 502. My 7.4 ran hard, but the 502's a blast. It's a stronger engine. Roby1 keep up the good work, get that scarab rippin.
Steve
Steve