I am interested in doing some upgrades on our 1990 Mach I Condor 22' with a 7.4 (330 HP) Bravo I. The engine is original with 350 hours on the clock. No issues.

Our best speed is with a 14 x 21 three blade SS Stiletto prop per GPS is 54.9 MPH, 4600 RPM, full tank of fuel (55 gallons) two persons, standard compliment of gear. Mach I's are pretty heavy, so I believe that this speed is pretty good for this boat.

I installed a 14.75 x 17 four blade SS Mercury Revolution prop for sking, and the boat runs 44.9, GPS, 4600 RPM. The 17 pitch prop will allow the engine to over rev, and one day I was not watching and found us running at 49.4 at 4850 RPM. The engine sounded great, however the max RPM is supposed to be 4600, so I slowed it down.

Here is the question. What limits the RPM on this setup to 4600? I have heard that the heads are the weak link? Other versions of 454's turn 6000 RPM without any difficulty, so why are these engines rated so low?

Where would you start if you wanted to mod this boat to see 65 MPH? Upgrade the heads? A high performance engine? This is a budget build.

Since the engine runs at 4600 WOT with the 21 pitch prop, I doubt if it will turn a higher pitch prop without loosing RPM.

I understand that the Bravo I is only good for 400 HP, so If I get too radical I will be looking at upgrading the outdrive also.

Thanks in advance,

Charles

I think you're going to find the same thing hundreds of other folks with the 454/330 have found - there's just not a whole lot you can do with that motor. Although the heads are a limiting factor, there are many other components in that paricular package that combine to limit you. Yes, there are a few things you can do to get more power and I'm sure a few of our senior members can help you there, but 65 MPH is going to take a serious injection of steriods.

Welcome Charles,
I'm running 1989 454s (Mark IV) and have broke a couple of them. Like your's mine are cast internals. The Magnums have the forged stuff. My first was a dropped valve which was due to the stock manifolds leaking into the exhaust valve right after I bought the boat. Two others were oil related. High volume pumps in low quantity pans and cooked a rod.

That said they aren't as fragile as most say. I'm a do it yerself on a budget guy too. Some times it haunts us... The guys who reccomend all the top shelf parts required are right about it being the best way to go but usually are made out of un-obtainium materials for me so I do what I can w/what I can afford. I'm a firefighter=no money

My suggestion is an Eldelbrock RPM Air Gap intake and their 750cfm carb or a Holley and a cam. I've been running these cheap cam/lifter set from Summit for under 100 bucks with zero failures. (except when a rod "weed-wacked" one) I just bumped up to the next step 1303 in my new motors. Guys will say you HAVE to have roller set ups... not in my budget. Plus I have to buy 2 of everything.

Stock exhaust is a limiter and the most expensive part of the package. You will want them if you run much cam duration to keep from sucking water (reversion). My boat was fresh water only and a 1989 and the manifolds were rusting thru and leaking. I know your boat is low hours but Rust Never Sleeps(Neil Young) I switched to EMI Thunders with long stainless tails.

I spin mine 4800-5k for long periods of time and are propped to spin 51-5200 w/no load. My machinist says I went wrong by it pumping all the oil to the top of the motor w/ high volume pumps and 7-8 qt pans.

Now I've added Hamburger 10qt pans at a couple hundred each(cheap) and standard volume but higher pressure pumps. Now it takes 12 quarts of oil to fill them up.

I just picked up Aluminum heads for under 1k per set and added 200 more for Inconell exhaust valves.

I was a drag racer for 20yrs and run the crap outa my stuff.
There are some VERY good motor guys here and I'm not one of them. They may tell you I'm full of it but that's what I'm doing to get 80mph. I can't afford to do it all "The right way"
Time will tell how it all works out and holds together. Just got them running this week.

I have some stuff left over which you may want but this is not a sales pitch.
Opinions are like....... this is only mine.
Mark

First off you current speed and prop are normal for your power and weight.
Your boat does not have a rev limiter so you could run it as high of RPM that you want. However your cam runs out of power and your heads run out of flow in the 4800 RPM range. In addition to that you have a cast crank, rods and pistons.
If you want to gain 10MPH get out your wallet because you will have to change out everything but the block. Assume you have 4 bolt mains. I started with a 330 and I am up to about 550HP (crank) now. I thought as you did and wanted to tweek out the stock engine. After breaking parts one by one untill I bought the "good parts". I broke the crank in 2 pieces, ate a flat tappet cam, ext.....
Here is what I did, forged stroker crank, forged rods, forged pistons, large oval head, Holley MPI kit, EMI Thunders with long risers, EMI oil cooler 18x3, Marine DUI dist, RMbuilder custom roller cam with matching components. There are many more parts than this. Before spending 12-14k on parts you may want to leave it stock before the speed bug gets you. I am hitting 74 on the GPS and I am still looking for more.
The stock bravo will run 500HP with no problem, take it easy out of the hole and keep it in the water.

Wow! Increasing a boats top speed gets complicated very quickly.

Thanks to everyone for explaining it all to me.

I thought that maybe I could slap on a better set of heads and have a high performance engine, but that is obviously not the case.

It sounds like Mercury took a plain old 454 light truck engine and marinized it.

Working on the internals are way past my skill level, and I am probably much better off just maintaining the boat as stock, and enjoying it with its limitations. I will also be broken hearted if the engine blows, so its best if I just run it within the specified range.

The previous owner had a Captain's Choice through hull exhaust professionally installed. The boat runs perfect, and sounds really cool. Our mechanic is installing an MSD ignition, mainly because I asked for a rev limiter and he felt that would be the best way to do it. He says that the engine will also start, idle, and accelarate better with that ignition. I guess that is were we will leave it for now.

Heads, Carb and intake will give you some help, but not 10mph.
Again... if you have the original merc manifolds and raw water cooled... watch out for them leaking.
Maybe when you winterize at least pull the risers and have a look for and signs of rust/water in the ports. They can be pressure tested on the boat easily as well.

Is this pressure test somthing that a shop should be able to do?

[QUOTE=gcsprayjr;3227550]Wow! Increasing a boats top speed gets complicated very quickly.

Nothing complicated at all , it just takes MONEY !!!!!

The faster you want to go, the more it costs and the harder it is to get any more speed. You know the saying " Speed costs money, how fast you want to go?" My suggestion is look for a take out engine in the HP range you are looking for. Cheaper in the long run than building an all new engine or engines. Just make sure that you can hear it run if possible or have a return clause from the seller. Lots of stuff is coming available here at the end of the season.

I have no real need to go faster, just thought it would be cool to be able to. 54.9 is pretty fast for me, and more then fast enough for the wife. We are not racers, and never will be. I am just an old fart going through my second childhood, and like the cool factor of having a fast boat. We are a couple of weekend boaters, with two old boats, and 11 grandchildren who love water sports. Not too exciting, but it is the truth.

Anybody have any experience with USEngine?

They offer a remanufactured 420 HP Gen V 454 with forged parts for $3495.00 with a 500 hour/7 year warrenty. Since I am not an engine builder, nor is my mechanic, a complete long block sounds like my best option. They tell me that it is a drop in in place of my 7.4.

Right now I am really more concerned about having the exhaust manifolds tested for leaks.