454 mag intake manifold help
11-12-2018 | 10:25 PM
#1
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454 mag intake manifold help
I wanted to see if I can get a bit of help. I have twin 454 mag motors that are 1990. Right now they are stock except for I changed over to EMI Thunder exhaust a few years ago with standard risers. I would like to get rid of the stock intake manifold and maybe the Q-jet carb(although the carbs have been overhauled and seem to work well) looking to drop the weight and pick up some extra HP. I’m not sure I want to do the cams because I don’t want to have to deal with changing the new risers. What is the best manifold and carb combo and how much HP will I pick up with out changing the cam. Thanks for the help
Last edited by Railer833; 11-12-2018 at 10:27 PM. Reason: Sent too early by mistake
11-12-2018 | 11:15 PM
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The stock 454mag intakes are already aluminum and are pretty good. You won't gain hardly any hp with an intake and carb.
Being yours are 1990 vintage 454 mags, yours could be the early 330hp version with cast iron intake if they are mated to alpha drives.
Being yours are 1990 vintage 454 mags, yours could be the early 330hp version with cast iron intake if they are mated to alpha drives.
11-13-2018 | 11:07 AM
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I do know that the motors I have are the 365 hp with bravo 1 drives. I didn’t realize they were aluminum.
11-13-2018 | 11:23 AM
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I think the RPM airgap would be a better choice and looks pretty cool. But as Griff said, unless everything is worn out I’d doubt that you’d see much gain if any without a cam change and head work. Merc did a pretty solid job in matching parts. You may actually lose a ton of low end and midrange with minuscule gain on top.
11-13-2018 | 11:32 AM
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I have been there and done that. If you do indeed have the GM high rise dual plane intake as was used in 1995 you will regret changing to the Vic Jr. I tried it, very little if any gain on top end and a TON of loss in the low and mid range. I did not stay on very long until it was removed and the stock went back on. FYI this was with a cam change and exhaust upgrade as well.
11-13-2018 | 08:53 PM
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11-13-2018 | 10:31 PM
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I do not think the 1990 454 MAG was 365 hp. 330 hp if I recall correctly and that was at the crank. 1990 Merc specs did not have prop HP. I can check on that to be 4 sure.
A 750 cfm Q jet is not going to make any less hp than a 750 cfm holley. Actually some of the older carbs flow better than these new out of the box stock carbs. Some carb guys say that the current out of the box stock carbs suffer from core shift when manu plus porosity (spelling ). I am talking about carbs under 900 bucks ( NOT Billet )
A 750 cfm Q jet is not going to make any less hp than a 750 cfm holley. Actually some of the older carbs flow better than these new out of the box stock carbs. Some carb guys say that the current out of the box stock carbs suffer from core shift when manu plus porosity (spelling ). I am talking about carbs under 900 bucks ( NOT Billet )
Last edited by BUP; 11-13-2018 at 10:40 PM.
11-14-2018 | 05:26 AM
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From hands on experience with a 95 Baja with a carb 454 our 1st boat, you are wasting time and $ trying to bolt on a couple parts. Performance gain will be zero to zero +, as many have already stated. Best choice is to do a complete engine build with parts that work together (carb, intake, heads, cam, exhaust) and even then its going to cost you twice what you thought to go half as fast as you hoped. Or leave it alone and enjoy as is.
