454 versus 7.4. any difference?

[Partycattin]

I have a 7.4 in my boat. I read somewhere that the 7.4 is similar to the 496 in that it has 2 bolt main, cast pistons etc. I believe it said that a 454 has 4 bolt main, forged pistons, better rods, etc.
The reason I ask is that I am looking for more power (aren't we all). I invested in some Imco Powerflows that basically produced nothing but a tad more low end.
I'm not sure if my 7.4 is worth adding a supercharger or alum head to if the internals are all lower quality.,
I have heard that the 454 and 502 are good candidates for a bolt on supercharger system with 5-6 pounds of boost.
Any suggestions. Should I just built a big motor from scratch and nix the supercharger idea?

[Beer-30]

The 7.4 is, of course, a 454 (7.4L, 7400cc). Low-perf, cast pistons, small heads. There is a Whipple kit as well as a Pro-Charger kit. I would keep boost low, as your motor will live longer.
You might be better off swaping heads, intake, and cam. Edelbrock has some semi-complete heads that have valves, but no springs (to be matched to cam). Those, a nice cam kit, and even just port-match the intake would get you a very nice performance increase for less $. Motor would live longer, also.

[Party Cat]

I was in a similar position 2 years ago...7.4 330hp merc witha Bravo III
I opted to put together a 509 with Dart Pro 1 heads and a holley 830 carb...Tom at Pro Marine put the motor together and dyno'd at 628hp/652tq
The motor has run great for the past 2 yrs...I once planned on putting some sort of SC on the motor...but I've been so happy with the performance...that I seriously doubt that it's worth it...on a good day...I can hit 60+ with a pretty heavy boat..(Stereo, batteries, Brass Pole)...The best thing has been the boats ability to roll over....Night and day difference :)

[Trigger]

Well after reading your question I am confused. The 7.4 is a 454. There were different versions of it though. 310hp, 330, 365 (I believe) and the 385. The latter were the 454 Mag motors. They had better internals which were more suitable for blowers. Low boost would work well on these. The 496 (375hp) you speak of took over the 454 Mag and the 496HO (425hp) took over the 502. The base 454 was replaced by the 6.2 (320hp).

[OGShocker]

It's that da*m meteric system gumming up the works again!

[Beer-30]

Well after reading your question I am confused. The 7.4 is a 454. There were different versions of it though. 310hp, 330, 365 (I believe) and the 385. The latter were the 454 Mag motors. They had better internals which were more suitable for blowers. Low boost would work well on these. The 496 (375hp) you speak of took over the 454 Mag and the 496HO (425hp) took over the 502. The base 454 was replaced by the 6.2 (320hp).
Very well put. That 310/330 HP model was basically a glorified pickup motor. The MAGs were the forged, heavy duty bottom ends with (I believe) rectangle ports.

[Liberator TJ1984]

The 330 7.4 I had came with 4bolt mains , 3/8" rods ,steel crank and cast pistons....still running the crank and rods in boat today ....had a small B&M 177 and grenaded the pistons at 6# boost and trying to spin past 5500rpms. :wink:

[Beer-30]

The 330 7.4 I had came with 4bolt mains , 3/8" rods ,steel crank and cast pistons....still running the crank and rods in boat today ....had a small B&M 177 and grenaded the pistons at 6# boost and trying to spin past 5500rpms. :wink:
Ah, maybe it was just the 310 model that was cast crank / 2-bolt? Didn't get into those much, so I am just guessing.

[Beer-30]

Even though it says 305 HP, this is the 310:
http://www.cpperformance.com/images/620-8238.JPG
New GM Marine 454 - 305 Horsepower Long Block Engine
305 HP @ 4400 RPM / 435 lb. ft. @ 3200 RPM (PFI)
1987-2001
1-piece seal
4-bolt main
Oval port
Roller cam
8 qt. oil pan
Must use electric fuel pump, No - intake, flywheel, or water pump.
Sale Price $5,980.95 $5,169.99
(Savings: $810.96)

[cdog]

Don't worry about the 2 bolt mains unless your pushing the engine above 7000 rpm. You could easily build a 500 hp 454 with your imco exhaust. If I were you i'd just pick up someones used 496 HO.

[Rev. Williams]

I'd suggest getting the casting numbers off the back of the block, then you'll know exactly what you have to work with. If you have a motor 96 or newer it could be a GenVI block which should give you the ability to upgrade. I took mine from a 454 to a 496 (or should I say Infomaniac did) :D and it makes just under twice the power it once did. Look in the Gearheads section and you'll find the story on the build-up. But start with the casting numbers.
Here's the thread ----> http://www2.***boat.com/forums/showthread.php?t=83319

[Partycattin]

I was in a similar position 2 years ago...7.4 330hp merc witha Bravo III
I opted to put together a 509 with Dart Pro 1 heads and a holley 830 carb...Tom at Pro Marine put the motor together and dyno'd at 628hp/652tq
The motor has run great for the past 2 yrs...I once planned on putting some sort of SC on the motor...but I've been so happy with the performance...that I seriously doubt that it's worth it...on a good day...I can hit 60+ with a pretty heavy boat..(Stereo, batteries, Brass Pole)...The best thing has been the boats ability to roll over....Night and day difference :)
509? Is that a 502 that has been bored out? That seems like a huge about of HP for that motor. 628 hp would be nice. How's that on fuel efficiency compared to the underpowered stock motor?

[dicudmore]

509? Is that a 502 that has been bored out? That seems like a huge about of HP for that motor. 628 hp would be nice. How's that on fuel efficiency compared to the underpowered stock motor?
fuel efficiency will be fine if you can keep it from WOT :wink:

[Partycattin]

fuel efficiency will be fine if you can keep it from WOT :wink:
That's the problem I'm having right now. The boat seems underpowered so I'm constantly keeping it pinned. The motor is surely not going to last!

[dicudmore]

That's the problem I'm having right now. The boat seems underpowered so I'm constantly keeping it pinned. The motor is surely not going to last!
exactly...with more HP you won't constantly have the need to bury the stick, thus better fuel efficiency...
case in point GT's 28 Bullet with ~1000HP is using approx 10 gallons of fuel per hour, that ain't too shabby

[spectras only]

case in point GT's 28 Bullet with ~1000HP is using approx 10 gallons of fuel per hour, that ain't too shabby
Is that between idle and 2000 rpm ;)

[98 Vector 21]

Very well put. That 310/330 HP model was basically a glorified pickup motor. The MAGs were the forged, heavy duty bottom ends with (I believe) rectangle ports.
Your correct with the fact the 454mag and its rated @ 385hp

[Roman 1]

This thread has yuppies written all over it!
R1 :notam: :coffeycup

[C-2]

Your correct with the fact the 454mag and its rated @ 385hp
365 mag
385 mag mpi (fuel injected)
;)
If I ever get my shiat together, I too am having a 496 stroker motor being built by Obnoxious01 from this board. Should be pretty nice...results will follow.
Go to OSO (offshoreonly.com), in the tech section, and you'll see this topic has been beat to death many, many times. Great info over there.

[Party Cat]

509? Is that a 502 that has been bored out? That seems like a huge about of HP for that motor. 628 hp would be nice. How's that on fuel efficiency compared to the underpowered stock motor?
Yes...that is a 502 bored ....
This has made a huge difference in the boat rolling over...especially with a full load of people....
As for fuel efficiency...like any motor...if ya run WOT...it's gonna suck gas...but just cruising at 30-35...it's just as good if not better than before...
I burned 150 gallons at shasta and GPS'd around 280 miles...that was a combination of cruising, pulling kids on tubes and a few quick runs 50-55mph (yeah...I know that's not fast for most people..) from the upper Sac arm to Bridge Bay...
I'm happy with the motor :)

[Jordy]

I burned 150 gallons at shasta and GPS'd around 280 miles...
Holy cow, that's almost 2 mpg!!! :D :D :D
which is really good for that big heavy boat. ;)

[V-DRIVES RULE]

Is this QUESTION OR A JOKE?? just so you know a 496 is an 8.1 liter GEEZ!

[Trigger]

Is this QUESTION OR A JOKE?? just so you know a 496 is an 8.1 liter GEEZ!
Where did someone say it was something other than an 8.1?