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View Full Version : upgrading merc. 7.4l



seascarab
08-16-2005, 10:05 AM
I have a ´97 22ZX with a mercruiser 7.4l engine. I bought the boat with this engine, which has a cmi header and an aftermarket air-filter. I am wondering what could I do to improve the performance of my boat ( at the moment doing about 63+ mph with a bravo I 24` lab-finished). An engine swap to a 502 Magnum is in Germany very expensive ( over 10 k$). I was thinking about other carburetor or ignition or ??Because I am travelling to the United States in October /November I thought I could buy me some "souvenirs" :biggrin.: . I was thinking about spending about 3-5K$. Any suggestions, please advice.

The Hedgehog
08-17-2005, 01:32 AM
Is that thing bone stock other than that flame arrestor and headers?

seascarab
08-17-2005, 04:28 AM
Yes, except for the flame arrestor and the headers everything is bone stock.

Pismo
08-17-2005, 06:49 AM
That engine has the ultra low performance intake and very mild heads and cam. Swap those to add some significant hp.

turbo2256
08-17-2005, 07:24 AM
I would go with some Edelbrock oval port heads, a Torker II intake and a 750 Barry Grant Sea Deamon carb. For a cam I woud go with a stock 502 Mag Merc marine one. Were in the States are you visiting?

turbo2256
08-17-2005, 07:29 AM
A 502 mag ignition control module woud give you a few hundred more RPM.

turbo2256
08-17-2005, 07:32 AM
You will need a new prop too

seascarab
08-17-2005, 11:10 AM
I am visiting a friend in Florida in the Fort Myers area.
Is there a shop in the Florida area known with a good reputation or is it better to go via mail order in advance. I think I need some technical advise not to forget something to buy.After my return I have to convince my italian mechanic to modify my engine, so everything must fit. Another problem is then the difficult availability of performance parts in Italy.

I was thinking about a new prop too. Which one should be good and what performance could I achieve with this setup.
At the moment my engine is turning 4600RPM with the lab-Bravo 24´.

turbo2256
08-17-2005, 12:44 PM
My shop has done work for and sent parts to one of the scandinavian contries (a turbo Cevelle). What are your restrictions? Best might be mail order could send you part numbers take at least the big stuff back. Is your motor a roller cam of flat tappet hyd.

FUELPOWERED
08-17-2005, 01:47 PM
Watch out for the cast pistons, crank and small connecting rods. These do not take kindly to mods. Best bet is to look for a carbureted "magnum" version of this engine.

mrfixxall
08-17-2005, 01:47 PM
I have a ´97 22ZX with a mercruiser 7.4l engine. I bought the boat with this engine, which has a cmi header and an aftermarket air-filter. I am wondering what could I do to improve the performance of my boat ( at the moment doing about 63+ mph with a bravo I 24` lab-finished). An engine swap to a 502 Magnum is in Germany very expensive ( over 10 k$). I was thinking about other carburetor or ignition or ??Because I am travelling to the United States in October /November I thought I could buy me some "souvenirs" :biggrin.: . I was thinking about spending about 3-5K$. Any suggestions, please advice.

i have a 415 502 for 4000.00 with 100 hr on it?????

seascarab
08-18-2005, 03:16 AM
I thought about going to a shop or mail ordering and taking the stuff with me. We have about 100 lbs free and all what fits into two big Samsonite suitcases. I am no mechanic, so where is the difference to be seen roller cam vs. flat tappet hyd.

How difficult is it to bring this engine to some greater numbers? What I see there great concerns about it (pistons, crank etc.).

What is about installing a blower? Same problem?

What is about reliability? Idle?
So a engine swap to 454 magnum or better a 502 magnum might be the best for reliable performance?

Does my cmi headers fit to a 454 magnum or a 502 magnum?

I am a little confused now.

502 Magnum would be nice. I have to check the Cost for transport.

cneidhart
08-18-2005, 10:14 AM
I have the same boat. I went with a Pro-Charger, Custom Carb, MSD 6M iginition, New fuel system and new Bravo 1 28" prop. She is hitting 74+ MPH on fresh water. Total cost installed was $6,500. (the fuel pump was $1,100.:kaioken: )

The engine now has 217 hrs on it blown and no issues with a boost of 5# at WOT. I think I made the right choices because when it does go (and it will), I'll stab a 540 CI in and it's just a bolt in.

The 7.4 is to weak to upgrade. Poor crank, heads suck, and cast pistons.

How fast do you plan on going. Mine was a mid 50's boat before the upgrade.

seascarab
08-18-2005, 10:58 AM
70 to mid 70´s in Fresh water sound good to me and would be my target.
I saw a procharger m1 interccoled kit for 4470 $and the msd ignition for about 800 $ this would just fit my budget.
Are a procharger or a other supercharger "easy" to install?

Has someone experience with a supercharger like a whipple and this engine?
What is more to prefer? Procharger or supercharger? The boat is on a lake in fresh-water.
Last question would you prefer upgrading the engine, turbo or supercharger or better wait and swap to a 502 Magnum?
My engine has about 160 hours on it.

cneidhart
08-18-2005, 12:39 PM
70 to mid 70´s in Fresh water sound good to me and would be my target.
I saw a procharger m1 interccoled kit for 4470 $and the msd ignition for about 800 $ this would just fit my budget.
Are a procharger or a other supercharger "easy" to install?

Has someone experience with a supercharger like a whipple and this engine?
What is more to prefer? Procharger or supercharger? The boat is on a lake in fresh-water.
Last question would you prefer upgrading the engine, turbo or supercharger or better wait and swap to a 502 Magnum?
My engine has about 160 hours on it.

Let me say first I did not install it.



I think I could have but crawling in and out of that hull did not excite me. The hardest part from what the Installers told me was the fuel tank. Another inlet had to be made, while the tank was in the boat.

I bought the carb already setup and dynode. Don’t try and do this yourself. It must be dynode under pressure.

If I would have just built a better Engine, I don't think I would have had the same increase in speed for the same $.

Stay with an intercooler blower. It fits under the hatch and runs much cooler. I keep the total timing advance less then 30, run 91 octane pump gas. We use it at LakeMohave which today will be 110 degrees.

It is a grossly noisy blower without a hatch. But with the hatch down you will hear a faint whistle noise.



Making that boat or ANY boat go faster is not cheap. Once you add one thing you’ll find you need another. The difference of 10-20 mph will cause handling issues, insurance cost (if they find out or you have a claim), fuel consumption doubled. If you get air and land hard the Bravo 1 will be toast. Take all of these factors in consideration before you start. I don’t regret ours, but I’m sick. Boat sick!

seascarab
08-19-2005, 04:06 AM
Thank you all. I will collect some information about the different systems. I am also sick in this matter. I think it started when a Stingray 23 feet with a small block and a supercharger was faster last weekend. Not much but a 2-4 MPH.
So I think about going faster.
The Procharger systems were advertised to be complete bolt-on packages. Is there something else I need.
DOes anybody know a store in Florida with good experience where prochargers or whipples can be bought?

Pismo
08-19-2005, 08:46 AM
Get the blower install it and drive the 7.4l until it blows up then move the blower and CMIs to a nice 502 Magnum and really go.

seascarab
08-19-2005, 11:20 AM
That´s exactly what I am thinking about and will do. I am not sure what toprefer Procharger or whipple. At the moment I tend to Porcharger.
Thank you all for you help.

Pismo
08-19-2005, 05:50 PM
The CMIs will bolt up to any big block. May have to adjust the exit thru hull holes for a tall(er) deck block though.

mrfixxall
09-06-2005, 05:20 PM
super charged marine engines have half the life expectancy as a naturaly asperated engine and you always have to use preimum fuel,,,do you know what your really getting at the pumps???????

Mudball
09-07-2005, 07:40 PM
Be careful!
The motor pictures that I saw sure looked a lot like a reworked 7.4mpi motor.
The valve covers give this away.

The bottom end of these is very weak. They can be improved by doing what your motor has, as in exhaust, intake, and switching to a carb.

BUT, you will grenade that thing if you try to do much more.

Too many people have tried that and failed.

If it was my boat, I would look for a mag motor or better, and sell yours.

Just my 2c.
Kent
PS: I had a 7.4mpi in my 22zx, and wanted more power. After lots of research, I ended up buying a used HP500 and redoing it, and then selling my 7.4mpi...I am one happy camper now...

seascarab
09-17-2006, 09:12 AM
I just want to share my experience upgrading the engine of my boat with a b&M 176 (?) blower.

I had the oportunity to get a complete kit from a friend of mine.

First of all:
After installing the kit and dialing it in, the 22ZX was a blast to drive. I reached at 600ft altitude (northern italian lake) about 73 mph at 4500 mph but there was more in..... I was turning a Bravo 1 26".
I think the boat could have gone faster, but I needed more seat time to get used to this speed and the boat.
The torque of the prop forced the boat to lean to one side at that speed.

Unfortunately the srews which hold the lower wheel of the drive belt of the supercharger to the engines wheel... broke twice.
That forced me to pull the engine twice in my holdiay....so we could only boat a week in a 3 week holiday...

Sad but true my girlfriend wants me now: " ...put that thing off...."

Next year I want to swap the engine - 496 mag ho -or the boat - a used 26 ZX or a if availiable 27ZR - ...so will do her the favour...

I was wondering If I just change the intake manifold. Has someone experience with a WEIAND STEALTH and the stock setup?? Or better leave everything stock?

Thank you for you help...

Ed Donnelly
09-17-2006, 01:23 PM
cneidhart; No need to tap into the fuel tank on a procharger installation.
Install a tee before the fuel pump and run the return line there..

Seascarab; If your 174 is the low profile, single carb, I know someone that will trade you even, his unit has extra pullys,belts,carb hat and box, rebuild kit for supercharged carb.. He even has a spare MSD really cheap. P.M. me
if interested......Ed

BigGrizzly
09-17-2006, 01:53 PM
Sea scar That is BS about Blown Marine engine have half the life Of Normally asperated engines If the engines ate set up correctly and you just drive it sanly yiour fine. I don't want to tell you that a number of stock NA engines have been blown up every year. Most of the engine failures are done by the driver and not fault of the engine or builder. I have a blown 502 and my son has the a 99 22ZX with a wipple and thwe stock 7.4 engineand neither have had any trouble in years. In fact to my knowlege all the board members with blown engines none have had failures do to the blower or the extra power. As for preimun fuel that motor you have needs it anyway and so does any of the merc mag series. If your future plands are a 502, your half way there to the 80MPH club.

Mudball
09-17-2006, 08:15 PM
I just want to share my experience upgrading the engine of my boat with a b&M 176 (?) blower.
I had the oportunity to get a complete kit from a friend of mine.
First of all:
After installing the kit and dialing it in, the 22ZX was a blast to drive. I reached at 600ft altitude (northern italian lake) about 73 mph at 4500 mph but there was more in..... I was turning a Bravo 1 26".
I think the boat could have gone faster, but I needed more seat time to get used to this speed and the boat.
The torque of the prop forced the boat to lean to one side at that speed.
Unfortunately the srews which hold the lower wheel of the drive belt of the supercharger to the engines wheel... broke twice.
That forced me to pull the engine twice in my holdiay....so we could only boat a week in a 3 week holiday...
Sad but true my girlfriend wants me now: " ...put that thing off...."
Next year I want to swap the engine - 496 mag ho -or the boat - a used 26 ZX or a if availiable 27ZR - ...so will do her the favour...
I was wondering If I just change the intake manifold. Has someone experience with a WEIAND STEALTH and the stock setup?? Or better leave everything stock?
Thank you for you help...

With my 1999 stepped 22zx:
I can tell you that with a box stock HP500 carb motor (freshened last year), that I have hit a top end of 78.2 on GPS (5,100 rpm, stock Bravo 28, 1.5 drive).
I do have a brand new labbed 28 Bravo from Throttle Up that has not been tested, as our lake is now GONE, due to a major drought.

My every day speed is 76-77 with a full tank of gas and another in the boat.

I do have full hydraulic steering to the helm, and have superb handling.
Take care,
Kent

farmer tx
09-17-2006, 10:10 PM
Kent, Why don't you bring your 22ZX to Possum Kingdom next weekend and treat yourself to some great boating? The Texas Roundup V is being held at Bass Hallow. There is information in the events and gathering section.

Come on over,
Mark

Mudball
09-18-2006, 08:13 AM
Hi Mark:
Thanks!!
I'll check with my wife and see if we can make that...

I've never been to Possum Kingdom lake, but have heard great things about it!

Take care,
Kent