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they are way too much money for what you get
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Originally Posted by bobl
(Post 667284)
The MPI on the small blocks and the 7.4 is not good to build on. The mag. engines have a decent system. Not as good as some of the aftermarkets but OK for 500-550 HP. They have 42 lb. injectors so you just need to do a mild remap on the ECU, add an adjustable fuel pressure regulator and tweak some.
I've seen people reprogram these systems - can anyone point me to the software/hardware that is needed? The Holley systems are generic. They're also TBI based, which is fine and functions - but the direct injection systems run better in my opinion based on experience in the automotive world. |
Just to note, we just re-did my 454 MAG MPI. We went with a 30 over pop up piston for about 9.6:1 compression, used Tyler Crockett's camshaft, springs, retainers and such. We went with RHS 320 Aluminum Heads with 2.25/1.88 valves. Then we had to up the fuel system with an Aeromotive pump and adjustable regulator. All this ran on the stock MAG MPI manifold with Crockett's tune. We made 501 hp @ 5200 rpm and 535 lb*ft of torque at about 4600 rpm. It pulls like a monster. We haven't gotten top end worked out yet as I have to prop test, and I think we have a fuel restriction from the tank to the new fuel system. Overall, I'm VERY happy with the setup. We sent the computer back to Tyler for some tweaking as well. Once that's done and the other bugs are worked out, we'll have 501 fuel injected reliable horsepower without putting a big strain on any of the engine internals.
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just to give you my $.02, to give you an idea what you need to to to achieve 500hp + range. This engine was originally a 454 MPI EFI but no one was able to reprogram it for me so I converted it to support the new mods. Sounds like you are on the right track but MAKE SURE YOU remember to include upgrading oil lines and oil cooler.
GM 454 Dart Pro One Chevy Aluminum heads Dart Single Plane Intake Manifold CraneCams Roller Rocker ( I think this is the cam, I have to look it up to me 100% postive) Crane Cams HYDRAULIC Powermax Camshaft Grind Number: HR-306-2S-14 IG http://www.cranecams.com/?show=brows...tType=camshaft JE 9.6:1 Compression Pistons Stock Rods Stock Crank Blue printed and balanced CMI headers 850CFM Carb Mercury Marine 700SCI Oil cooler with all new -10 Oil lines Dyno 550hp. I didn't build it, Gellner did and has all the specs and info on the original build. PM me if you have any more questions I would be gald to help you. |
The difference is the intake manifold and throttle body. The non-mag 7.4 is a gm truck intake system designed to make great low end torque, but won't flow enough air to make much over 400 HP. The Mag uses a Merc intake and throttle body that flows much better.
Originally Posted by dcg9381
(Post 2294033)
What are the differences between the Mag and non-Mag EFI systems that make one good for a modified motor and one no good?
I've seen people reprogram these systems - can anyone point me to the software/hardware that is needed? The Holley systems are generic. They're also TBI based, which is fine and functions - but the direct injection systems run better in my opinion based on experience in the automotive world. |
Originally Posted by Ric232
(Post 665924)
Okay, I'm tired of hearing that I have to ditch my fuel injection for a carb to make any real power. How about this?
-Get rid of the MPI -Replace heads with a good set of aftermarket heads, professionally prepped, ported, etc. -Stock compression (maybe up to 9:1) -Whatever cam would work good with this combo and still idle well (probably no more than 610 lift) with matching lifters, springs, etc. -Holley Commander 950 multi-port fuel injection (I don't wan't to give up the easy starts and smooth idle) Would this work and make some serious (but reliable) power? Are there many good marine mechanics that know how to make the Holley systems work? (Okay, before anyone mentions it, I know all about the blower option and how it's the best bang for the buck, etc., etc.) |
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