Possible Upgrades for a 7.4 Merc
 

What would be the most bang for the buck upgrade for a 1990 7.4 Liter/Bravo 1.

The boat is a 1990 Mach 1 22 foot sport cuddy. The engine is the original. Currently it has the simple OEM Mercruiser through-hull exhaust, an MSD ignition, and is otherwise stock. It came from the factory with this exhaust, and has never had a trough-prop exhaust. According to the SN the engine is the 330 HP model.

With the 21 x 3 Stelleto the boat will run 54.9 GPS with a full tank of fuel, tank of fresh water, two people and gear.

With the 17 x 4 Revolution, the boat will run 44.9 GPS, loaded the same way.

With the Revolution 17 x 4 the boat will pull three 150 lb people on the salom from a deep water start, and holeshot is pretty impressive. The thing that keeps nagging me is that my 17 foot bass boat with a stock 115 2 stroke outboard is faster to plane, and although it will only pull two on the salom, it pops them up quicker then the big block will.

My mechanic says that it is running correctly for the beast that it is. Everything checks out, from vaccum to compression.

I am wondering if a marine crate 502 would bolt into the stock location, work well, and not over stress anything?

I would like to get more torque for a better hole-shot with the power prop, and possibly 65 MPH on the top end with a speed prop.

Thanks in advance.

I had a 22 scarab with your same engine, same style boat. Mine couldn't get a holeshot like a bass boat. The big block is a lot of weight in the rear and just heavier than a bass boat. I Had triton bass boat, that would run 67, wouldn't get one slalom skier up! But the boat would leap up on a holeshot. You probably got enough hp/torque. Trick is going to be overcoming hull/weight to pop up on top(tabs?) and propped for pulling, not speed. The engine will most likely swap out, but I hate to see you do the engine swap and still no holeshot.

I disagree, I have seen HP make a smaller boat come on plane like the hull was re-designed. 25 Ft checkmate from 385HP to 600HP, a 271 Formula from 365 to 500HP, and a 24 Baja from 330 to 500HP. All of them "seat of the pants" tested and it was a different world. 2 of the boats required the back seat riders to move forward to plane if fully loaded before the increase. If you are going to go with a 502 go with a 500HP or 500HP clone.

You can get the holeshot and quicker pulling with tabs. I've done it on several boats. But, if you want the speed, you'll need more torque to move the prop faster (or move a higher pitch)- ie, more HP.

That said, you may still need the tabs to get the holeshot and pulling you want. Part of that depends on the hull.

If it was me, I'd try a set of tabs first. Second hand, you can get some good deals. I got a nice set for $250 bucks for a 21' hull. Made a huge difference, and I picked up a couple mph since I could trim for speed and still use the tabs to adjust the hull.

Tabs best bet.A marine crate 502 (guessing 50-75 more ft/lbs more than the 330) won't be that dramatic a difference as the high horsepower options mentioned above. From my past boats, I learned you cannot make bass boats or a performance hull into a ski boat. Can you improve the holeshot with horsepower? Yes, but the engines above are way more than a crate 502. Also V hull with a big block just isn't going to leap up like the shallow hull(shallow draft) of a bass boat. V hull w/ big block also has more weight to lift up and sits deeper(further to leap, and the deeper v will only rise to the top with speed). Horse power won't overcome a hull that is a hindrance to hole shots. Hulls are the most limiting factor in a boat's performance. You can throw as much HP as you can, only to find the gains diminish as you go higher. Most high hp setups with bravos avoid "hole shots" to preserve the drives.The tabs are best bet. Just hate to see a fellow spend a bunch of money on an engine for a little improvement or ripping a drive with a ultra high Hp on a bravo.
es.

I agree with 4bus. I had a 7.4/330 in my '95 23 Nova and it did 57ish. I put a ZZ502 GM crate in it (567 tq/502 hp) and would do 69-70 GPS any day. Best was 73. I only did a few hole shots... just to do/try them. No tabs and it was on plane in no time flat, pun intended. Now I have a 557 in the Humble Little Nova just shy of 700 hp. And no hole shots, won't even bother, want to save the OD.

You might want to try a Mirage 23, the old style, not the "plus". That's what I had on my Nova with the 7.4 and it was a pretty good all around prop. RPM was right at 4600.

Oh, if you change power, might wanna save your 7.4 for when you sell the Mach 1.

Thanks for all of the replies. It sounds, like the boat is not going to be the best boat for sking, regardless of what we do to her.

Just for the record, the boat has factory installed hydrolic trim tabs. They don't seem to make a lot of difference in hole shot. They do make a slight difference in top speed, however it is tricky to get the outdrive trim and the trim tabs set for perfect top end performance. My best speed run to date was with the trim tabs up and out of the water, with the ourdrive trimed up just slighly. The boat would run 56.7 GPS, but feels unstable running like that. My mechanic says that trim tabs are not very effective on boats less then 24 feet. That is why they seem to have minimal effect on the performance of this boat. I have found that the trim tabs work nicely for leveling an unevenly loaded boat, but that is another story.

The Mach 1 is a deep V style hull very similiar to a Well Craft sport hull. The boat is very heavy, 4000 lbs, however it rides very smooth and straight. It is also balanced so that it would be difficult to stuff the bow, which is a good thing for a boat that has multiple drivers with various levels of experience. So it is not all bad.

As for the bass boat, it makes a wonderful ski boat. My family has owned it since new. It is a 1980 model Astroglass 17.6 with a 1150 Mercury (115 HP 2 stoke six cylinder inline) outboard, The prop is a 19 x 3 Quicksilver. The boat has a top speed under ideal conditions of 41.3 GPS, however it will run a consistant 37 MPH all day every day with almost any sort of load. This sounds crazy, but the boat will pop two 200 lb skiers up on the salom without any difficulty at all.

My mechanic says that both boats are performing as they should and that what I have is all that I am going to get from these boats. It sounds like from what you all are saying and also what our mechanic has told us, that is just the way it is.

As for selling the Mach 1, probably not, or the other one for that matter. The Mach 1 is slowly but surely going to get some custom paint, interior, and guage work. She is in pristine like new condition with 350 hours on the clock. The boat has been a pampered garage baby all of her life and has only been used in fresh water. As she ages, I am planning on some custom refinishing to keep her looking her best.

At the age that I am these boats will probably last me as long as I am interested and able to boat.

Thanks to everyone for your honest feedback to my original question.

http://i288.photobucket.com/albums/l...Picture592.jpg

http://i288.photobucket.com/albums/l...Picture638.jpg

http://i288.photobucket.com/albums/l...cture272-1.jpg

http://i288.photobucket.com/albums/l...cture555-1.jpg

Use a Merc High Five prop for pulling skiers. It will jump on plane.

What pitch would you suggest?

What about putting on a Bravo III lower? I know these are usually seen on cruisers, but a friend had one on his 25' Cobalt with a 454 Mag, and the boat would jump up on plane and run mid 60's.

A friend of mine has a Bravo III. While the power transfer is great on the B III, they seem to corrode badly. His fresh water trailered boat is always developing pits in the metal, and they cannot keep paint on the thing. That would drive me crazy just watching it. Our mechanic says the the Bravo I is the best outdrive ever made, and cautioned me about buying any other.

We seem to have worked out a system for water sports with our two boats without making any expensive mods to the boats. A big part of it is learning one's equipment.

First thing, is that some of our skiers have learned to deep water start behind the slower to plane big block. To be honest the skill of the skier has a lot to do with it. The rest of them just ski behind the bass boat which they are use to.

We have two tubes now, and the Mach 1 pulls them perfectly, since time to plane is not important. The tubes are four person each, although we limit each tube to two riders each. The old Mach I lumbers around pulling the tubers without breaking a sweat, where the two large tubes are a challange for the bass boat to pull safely.

Thanks to all for suggestions.

At some point in the (probably distant) future, I want to do a complete rebuild of the Mach I making a GFBL wannabe out of her. I am thinking a custom re-gelcoat, Eagle on the bow deck, and interior, with an Amarican Flag theme. The seats will be red and white stripes, and the sunpad will be blue with 50 stars on it. For power I and leaning towards a 572 Chevy crate engine, marine of course, and a B 3 outdrive. Right now it is just a dream.

The BIII will provide a heck of a holeshot, and pull like an ox. However, it provides another benefit besides just the increased hookup on the props - it give a lot of lift to the stern. That allows me to plane my 26' Powerquest in about 3 seconds, and hold plane at 12 mph (gps). Great for watersports, and I still get 56-58 mph top end depending on weather & water conditions (300 hp 7.4).

A healthy 572 will give you the torque you want and in a 22' perhaps the the low speed planing ability. But, it will be more expensive than switching outdrives.

If someone is having problems with corrosion on a BIII, they need to check the Mercathode system - it it is not working, the paint will blister and pit. Ask me how I know :eek:

I loved the BIIIs I had on my 280ss, pulled hard out of the hole with 350s and climbed all the way to the top @ 55mph in Denver.
Does anyone know why they are not used more on performance boats? Is it that they are not as strong as the B1, or do they have issues when the speed reaches more than 60 due to increased drag.

I've always heard drag, speed for that varies by person giving the info, but seems to be somewhere in the '60s. They are also reverse rotation, and so get hotter than a std rotation BI, so a good drive shower is a plus when running high speeds.

The most bang-for-your-buck (the original question) would be a camshaft change. The camshaft used in these engines is the same camshaft used on the 396/325 horsepower Impala, Chevelle and Camaro engines from the late 1960's.
The camshaft has 213/217 intake/exhaust duration with a wide 114 degree LSA. Not a very powerfull camshaft for the late 60's, really not a powerful (or modern) camshaft for a 1990 boat engine.
You would see a real performance increase with a modern Comp Cam and no drawbacks as far as fuel consumption and idle quality. I suggest a camshaft with 218/224 intake/exhaust duration and a 110 LSA. You will be pleasantly suprised.

Install a modern dual plane high rise intake manifold (retain the stock carb) and throw the MSD ignition overboard (re-install the stock Mercruiser Thunderbolt IV for best performance).
Use RV15YC4 Champion spark plugs gapped at .045 and a K+N flame arrestor.
Good Luck
Dennis

A 572 will tear the B3 apart. So yes, it'll be expensive. And don't think a XR will make it better. A 600 hp 572 pushing 600+ hp and torque will detonate the B3 pretty fast.

Get an Arneson #7M

Many have. There is more to it than the Mercathode system. Too much steel. Also, if someone is in your habor, and has a screwed up electrical system, he can be a huge problem too,

It's not that easy.

Well, owning one that is not corroding now, yes it was that easy. Know of quite a few others with no issues also. Stray electrical current from bad installations are another issue.

It sounds like a 572 is too much engine. I may be better off to have the 454 built with a forged crank, roller cam, rectangle port heads, matched intake, and be happy with those mods only. As for the MSD/Thunderbolt ignition, it has been flawless so far. Our mechanic swears by them.

Right now, we are just going to maintain the boat and enjoy it as is. A 7.4 in a 22 footer with a 1:50 ratio B1, and a 17 x 4 Revolution prop is is sprited ride. I will not be making changes until repairs are needed. I figure that once it has to be repaired, I might as well add some mods to it. Since it has 360 hours, is stored on the trailer in the garage, and is only run in fresh water, it could last a while.

A preventive for corrosion on a B3 may be fairly easy, I don't know. What I do know is that when we were boat shopping, I only looked at fresh water boats, and there were many B3's with lots of corrosion problems. One friend of ours who keeps a boat dry on a lift at Lake Wylie SC has been fighting this issue since his boat was new in 1997. I have driven the boat, and it does out perform my boat on holeshot, however my boat out performs his boat on top end. The two boats weigh nearly the same, and have the exact same engines.

His boat has no shore power, inverters, or other items that can cause stray power. His dock is at least 250 feet from the nearest neighbor, and his boat is out of the water on the lift when they are not using it. Why the thing is corroding, nobody has yet to determine, including Mercury Marine.

During our boat shopping, our mechanic, who also provided our survey, told us that the B1 is the best outdrive available. It is easy to maintain, simple to repair, and pretty much trouble free. He strongly urged me in the direction of the B1 as first choice. So when we found the time capsule of a boat we have now the choice was clear. We had found our next boat.

A lot of this stuff is learning one's equipment, how to use it, and what to expect from it. Once the operator has an understanding of their boat, it all gets easier.

If your interested I've got a BBC with 50 hrs on it that puts out 525 hp and around 525 +/- tq that I'm selling for $6000.00. It was professionally built by Wesco Racing. http://www.wescoracingengines.com/
You could sell your engine for $3000 or so and for $3000 have a far superiour engine. I've got it for sale in the swap shop and all the specs are listed there. If your interested or have questions let me know.

Don't forget, if you choose to build your current 454 as you mentioned, you will have to ditch the stock exhaust for something better flowing to notice any big difference. Many others have chimed in on this in other threads............plus I am currently building my 1990 454's and without changing exhaust will probably only get to around 375hp.
9.4 cr
049 heads
mildly upgraded cam (no reversion issues) 224duration .510lift 114lsa
edelbrock performer intake
match porting