Taking a 454 Mag from 385hp to 470hp

[kc0000]

I'm in the process of taking a 454 Mag MPI from 385hp to about 470hp.... new cam and different heads, higher compression, leaving the max RPM at 5000.
Question is, should I buy all new/larger injectors for the MPI or dump it for a carb setup?
Thanks, KC

[DogHouse]

KC, I think that there are some places that can reprogram the Merc EFI system for you, and they should also know what the limit is on the stock injectors. I would call AZ Speed & Marine (in Phx), describe your engine mods, and see what can be done using the stock EFI system. Larger injectors are a viable way to increase power with your other mods but you will need to have the ECU reprogrammed to match. I'm not familiar with the manifold that Merc uses, hopefully that won't be a limitation on airflow.
A single carb setup would easily support the power you're looking for but obviously you would lose some of the benefits of EFI. If you choose the carb route, you'll need a new intake, carb, fuel pump/regulator, flame arrestor, and miscellaneous wiring/plumbing mods to make it all work.
Couple other thoughts for ya: Are you running stock exhaust? Headers or good manifolds (with individual runners) will help get the power you're looking for. Also, you mentioned new cam and heads. Make sure that your valve springs and the rest of the valve trane are compatible with the cam you've selected.
What heads and cam did you buy?
Good luck!
-brian

[kc0000]

The standard Mercruiser heads are bsically left over design from GM, with 325cc Intake, kind of large for a torque monster.
I went with aluminum Dart Pro1 310cc intakes, weight advantage since I have an extra 135lbs of stereo battery in the rear , plus I should be able to run pump gas with and extra point of compression ratio with no worries. My boat has a below water line exhaust, so I needed to keep the LSA angle close, decided upon the GM 24502611 211/230 .511/.540 112 lsa with 1.73 roller rocker arms. Dropped that cam and those heads into my dyno2000 software and decided to retard the cam by 4 degrees so that the more torgue is available above 3500rpm, minor at that.
My motor was a long block that needed a fuel system, bought a 454 MPI off of ebay, ported the intake runners and matched the runners to the heads. I can see that if there is any restriction it will come from the intake runners of the intake, yet Mercruiser uses the same manifold for the 415hp 502 MPI as the 385hp 454 MPI, so it should flow just fine for my HP range.
But now, my heads and cam are breathing much better than the the 385hp setup, and it might be time to upgrade the injectors to the next level to keep up with the air flow.
So I can overdrive the stock injectors with more preasure, or move to the 502 ECU, or install new injectors since my current once need attention anyways. Mercruiser uses the same manifold, same throttle body and same injectors between the 454 MPI and the 502 MPI, - the only difference is that they are driving the injectors for a longer duration on the 502.
Exhaust will be Stainless Marine manifolds, nothing to get too excited about but slightly better than Mercruiser.
So yes, a different ECU would drive the injectors for a longer duration, and the map might be closer to my mods then the stock ECU. Driving the stock injectors for a longer duration is probably not an issue. Either way, the only accurate way to tune is by reading the plugs and adjusting accordingly, since no o2 sensor on the ECU. The stock injectors are probably 24lb, moving to 26lb or 28lb would prevent the motor from running too lean, but the mods still might need a different fuel curve. It is one of those "try and see" situations, I'll call AZ marine and give them the low down to see if they have a solution.
KC
[ November 21, 2002, 10:03 PM: Message edited by: kc0000 ]

[DogHouse]

KC, I just noticed your earlier thread over on LVHB, sounds like you have the EFI thing figured out. Have you considered dumping the stock ECU and going with something you can program yourself using a PC? A friend of mine sells the Electromotive systems and could probably set you up with a good price. If you're interested you can get some info at www.electromotive-inc.com
-brian

[kc0000]

thanks for that reference... I love to tinker. Never again will I buy a "chip" without it being custome made on the dyno. Easy enough to spend a day doing it yourself as long as you have the base maps.
Thanks, KC

[kc0000]

brian....
who is your friend? I'm going to go with their system and could use every discount I can find!
Sent my damper to them today so they can notch it for the crank trigger. Very nice stuff!
KC

[Ric 232]

For your injector issue, have you tried RC Engineering? www.rceng.com
I have not used them and know of nobody who has. I've only seen their ads.
Ric

[DogHouse]

KC, I sent you an email with name/number info.
-brian

[kc0000]

RC is just down the street, going to give them a call soon. From what I am finding, the stock mercruiser injectors might be OK for my application, as long as I can avoid burning them out. If they can push the 502 Mag MPI at 415hp, then they should be able to push mine to 450hp before hitting 100% duty cycle.
I hope to have an HPX direct ignition setup by the end of the month, they will have my damper by the end of the week. Creating a trigger mount for a Gen VI Mercruiser with all accessories will take me a few hours, but then they will have a prototype.
Thanks, KC