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Adam Jaws

454 BBC performance upgrades

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Hey all, new to this page, hope I'm doing this right. I've got a 1990 2550 SX with a 454 with silent choice and bravo one drive. I'm looking for good bang for your buck power upgrades that I can do with my current setup. I'm also curious as to what 454 I have and which heads are usually standard on the merc big blocks. Also what generation Bravo I would have. Thanks in advance guys

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Is the transom hull around the drive plates. Inside & out stress free of cracks ?

Do you know how much torque & horsepower the fiberglass will take repeatedly in a choppy water ? 

I always recommend a crate or custom engine.  Some will be far cheaper than buying the parts of unknown quality. Piece meal.  A warranty ?  Or a DIY with none.

30 year old boat may have any year of engine parts in it.  Need to have someone I D the big pieces. Check all moving bearing surfaces for correctness before pouring money into a stock old 454.

Check all the Valves , compression Timing Fuel system.  Etc.  Lots of etc.

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cam, intake, ignition and carb will take your particular motor up 70-100HP. Its a very proven power adder in the Baja world with the same motor. Best bang is your propeller getting it labbed. 

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14 hours ago, Adam Jaws said:

Resized_20190224_192656_3549_1551054643299.thumb.jpg.ef9df09425ccc411ce1354473de49aea.jpg

Hey all, new to this page, hope I'm doing this right. I've got a 1990 2550 SX with a 454 with silent choice and bravo one drive. I'm looking for good bang for your buck power upgrades that I can do with my current setup. I'm also curious as to what 454 I have and which heads are usually standard on the merc big blocks. Also what generation Bravo I would have. Thanks in advance guys

That vintage 454 was pretty maxed-out in stock configuration. Rod bolts were suspect, as was block oiling, cylinder head flow numbers and even valve train. The secret to getting these things to perform and live is making all the horsepower downstairs. They are torque monsters, but due to the high weight of the reciprocating mass, they do not like high RPMS. Even completely internally balanced rotating assemblies don't like RPM's above 5,700 as the intake valves are heavy and rods are not all that robust on the big end. I have found it better to opt for a crate motor and then add prop to keep the higher output replacement engine down within it's happy place. At times that even requires a drive ratio change. Be careful hot-rodding what you have as it will likely spin a rod bearing or fail a head gasket. Raymar has kits available that address the most common areas for failure.  W

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14 hours ago, cyclops2 said:

Is the transom hull around the drive plates. Inside & out stress free of cracks ?

Do you know how much torque & horsepower the fiberglass will take repeatedly in a choppy water ? 

I always recommend a crate or custom engine.  Some will be far cheaper than buying the parts of unknown quality. Piece meal.  A warranty ?  Or a DIY with none.

30 year old boat may have any year of engine parts in it.  Need to have someone I D the big pieces. Check all moving bearing surfaces for correctness before pouring money into a stock old 454.

Check all the Valves , compression Timing Fuel system.  Etc.  Lots of etc.

Everything around the transom looks solid, there is one crack in the gelcoat on top of the swim platform that I'll be repairing this spring  but that shouldn't effect the transom?

I have no idea what hp the transom is rated for, is there a way to verify that?

There is a lot of original stuff in the boat, the interior is still original and still in pretty good shape, so I'm guessing the boat was taken care of. Do you know what was the standard block, heads and cam would have been from the factory? I've been trying to figure that out and can't seem to find out anything concrete.

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1 hour ago, BajaDriver said:

cam, intake, ignition and carb will take your particular motor up 70-100HP. Its a very proven power adder in the Baja world with the same motor. Best bang is your propeller getting it labbed. 

I've got a mirage 23p on it now and I'm happy with how it comes out of the hole even with 6 people in it. Tops out around 57mph @ 4800 ish rpm. Getting it labbed is pretty much fine tuning the balance and pitch ?

I want to figure out heads are on my BB, I've heard that if it's the peanut ports that I should change out the heads

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1 hour ago, Adam Jaws said:

I've got a mirage 23p on it now and I'm happy with how it comes out of the hole even with 6 people in it. Tops out around 57mph @ 4800 ish rpm. Getting it labbed is pretty much fine tuning the balance and pitch ?

I want to figure out heads are on my BB, I've heard that if it's the peanut ports that I should change out the heads

Send me a pm with a valid e mail addresses and I will send you a PDF file for your engine manual. W

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Calculate out what the slippage of your prop is.  I like props with very little slippage.  Slippage is a wasting of WOT h p.

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50 minutes ago, Mi3sons said:

Wasn't that one rated at 330 hp?

Yep, the old 454 Gen IV beater used from 1988 thru 1991.  W

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32 minutes ago, Wingnut said:

Yep, the old 454 Gen IV beater used from 1988 thru 1991.  W

Any possibility that I'd I've the magnum as stock, or was the base 454 all chaparral used back then 

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1 hour ago, cyclops2 said:

Calculate out what the slippage of your prop is.  I like props with very little slippage.  Slippage is a wasting of WOT h p.

How do accomplish that ???

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6 minutes ago, Adam Jaws said:

Any possibility that I'd I've the magnum as stock, or was the base 454 all chaparral used back then 

No idea, but I do know that the 496 to 496 HO option listed for a 14 grand upgrade in 88 so I would think if you have a high output offering it was pretty rare. As you mentioned on your pm, it's time to go serial number diving. In those years, you could pull the valve covers and the intake runner casting was stamped Hi-Perf.  W

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9 minutes ago, Wingnut said:

No idea, but I do know that the 496 to 496 HO option listed for a 14 grand upgrade in 88 so I would think if you have a high output offering it was pretty rare. As you mentioned on your pm, it's time to go serial number diving. In those years, you could pull the valve covers and the intake runner casting was stamped Hi-Perf.  W

Got it, I'm in Ontario and we just got a nasty snow storm, guess I gotta dig my way out to the barn lol

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I have the service manual for that year BBC and looking through the manual, the obvious difference, looking at the engine, the Magnum had an aluminum intake (per the manual). Also, the serial number of a 7.4 was an "XY" code and the magnum was a "XZ" code.

And rreale is correct, the 7.4 is 4600 RPM where as the Magnum is 5000 RPM.

BBC.jpg

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7 hours ago, Pops said:

I have the service manual for that year BBC and looking through the manual, the obvious difference, looking at the engine, the Magnum had an aluminum intake (per the manual). Also, the serial number of a 7.4 was an "XY" code and the magnum was a "XZ" code.

And rreale is correct, the 7.4 is 4600 RPM where as the Magnum is 5000 RPM.

BBC.jpg

Ya so I'm pretty sure I don't have the magnum as I'm pretty sure I dont have a high rise manifold, my big question is what heads I have, i know it says oval port, just want to make sure the are not the peanut ports, did they ever install the peanut heads on a merc motor from factory?

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I "think" they were installed on some of the later 7.4's. But, considering the std 7.4 configuration, the didn't hurt performance.

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10 hours ago, Pops said:

I "think" they were installed on some of the later 7.4's. But, considering the std 7.4 configuration, the didn't hurt performance.

But not the greatest heads to work with if I'm going to add a better intake, can, carb ect???

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5 hours ago, Adam Jaws said:

But not the greatest heads to work with if I'm going to add a better intake, can, carb ect???

You are 100% correct. They are good for what they are in a stock engine. But add free flow exhaust, a cam, intake and or bigger carb and they will choke off the potential gains.

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And you likely have a cast crank and pistons so be careful doing anything that will twist the monster too tight. Weak valve springs too and the intake valves are huge and heavy. Even the capacity of the oil pans back in those days was suspect and it was easy to suck the things dry in a chop, with just a few hundred extra RPM. The drive will handle up to 600 HP as long as you don't go to a clever style prop that bite too hard and sudden.  W

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