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GIL or CMI Headers for 500HP??

Old 04-24-2011, 01:59 PM
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Question GIL or CMI Headers for 500HP??

I'm buying a boat with a GIL headers on the 500HP (is that stock??)


And my boat has CMI, so can swap them.

Not sure if there is any point.

Thanks in advance for the input.
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Old 04-24-2011, 04:58 PM
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Keep the CMI and sell the Gil!!!
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Old 04-24-2011, 06:44 PM
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Wink Manifold is a mnaifold and long tube header is a header

Gil manifolds are manifolds with pipe risers are NOT headers, just good performance manifolds.
Which will help more will depend on which CMI header you have. If the CMI headers are of the E-top type you will not see to much difference between the two, maybe 10HP max. If the CMI's are long tube headers like Sporttube type, then this type of header can probably produce 20-25 HP more than the Gil manifold exhaust and a reasonable amount of additional torque.
Many performance boaters don't understand the difference between aftermarket exhaust manifolds or E-Top headers (with short runner passages 4-10 inch) and single pipe risers versus a true long tube header with 24-28 inch runners and a collector.
On a normally aspirated performance engines there is a definite power difference between the two in use and it is even more significant in higher power engines with deeper breathing heads, cams and intakes, where the scavenging affect of a longer tube header creates more efficiency and produces more power and torque at most rpms.

Best Regards,
Ray @ Raylar
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Old 04-25-2011, 10:34 PM
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Originally Posted by Raylar
Gil manifolds are manifolds with pipe risers are NOT headers, just good performance manifolds.
Which will help more will depend on which CMI header you have. If the CMI headers are of the E-top type you will not see to much difference between the two, maybe 10HP max. If the CMI's are long tube headers like Sporttube type, then this type of header can probably produce 20-25 HP more than the Gil manifold exhaust and a reasonable amount of additional torque.
Many performance boaters don't understand the difference between aftermarket exhaust manifolds or E-Top headers (with short runner passages 4-10 inch) and single pipe risers versus a true long tube header with 24-28 inch runners and a collector.
On a normally aspirated performance engines there is a definite power difference between the two in use and it is even more significant in higher power engines with deeper breathing heads, cams and intakes, where the scavenging affect of a longer tube header creates more efficiency and produces more power and torque at most rpms.

Best Regards,
Ray @ Raylar
Thanks for explanation, have a much better understanding of the difference's.

Greatly appreciated!
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Old 04-26-2011, 01:46 AM
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Originally Posted by 2Slow4me
Thanks for explanation, have a much better understanding of the difference's.

Greatly appreciated!
where do you boat? Salt water GIL just keep an eye on reversion. Freshwater I would use CMI unless you planning on raising the hp a bunch.
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Old 04-26-2011, 05:47 AM
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Originally Posted by Raylar
Gil manifolds are manifolds with pipe risers are NOT headers, just good performance manifolds.
Which will help more will depend on which CMI header you have. If the CMI headers are of the E-top type you will not see to much difference between the two, maybe 10HP max. If the CMI's are long tube headers like Sporttube type, then this type of header can probably produce 20-25 HP more than the Gil manifold exhaust and a reasonable amount of additional torque.
Many performance boaters don't understand the difference between aftermarket exhaust manifolds or E-Top headers (with short runner passages 4-10 inch) and single pipe risers versus a true long tube header with 24-28 inch runners and a collector.
On a normally aspirated performance engines there is a definite power difference between the two in use and it is even more significant in higher power engines with deeper breathing heads, cams and intakes, where the scavenging affect of a longer tube header creates more efficiency and produces more power and torque at most rpms.

Best Regards,
Ray @ Raylar
Don't forget the sound difference The raspyness added to the exhaust note is killer from a header

For me I would keep the CMI's just for the sound. There is a guy on our lake with CMI's on a 454MPI....everyone thinks he has big power
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Old 04-26-2011, 08:08 AM
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Gil's have more of an issue with reversion than does the CMI. Even if your using e-tops they will build a fair amount more torque than the Gil's and like Ray said a bit more HP. I posted several charts on here that compare most of the major manifolds/headers. Here is the link:
http://www.offshoreonly.com/forums/g...no-charts.html
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