bajalome

Hello everyone.....I just got a 1997 baja 252 with a 7.4 merc...not a magnum. Can anyone tell me about the engine...What kind of crank, Heads etc....? I guess what I want to know is can I build a 400+ HP engine with the existing crank and pistons. The boat only has 230 hours on it and runs great. Also it has a mirage 19p prop on it....doesn't sound right. As soon as it warms up I will get some speed numbers on it. Until then any suggestions would be greatly appreciated. Thanks

Howie

ohiobaja

In 1997, Merc manfg. several versions of the 7.4 with different hp. There was the 7.4 L, 7.4 LX both at 300 hp. Then there was the 7.4 LX MPI at 330 hp. The 454 Mag MPI was 385 hp. If you give me your engine serial number, I will check my manuals to tell you exactly what you have. If you cannot find the numbers on your engine flame arrestor, look on your title. Then give me a shout.........easy problem to solve. Awaiting your reply!

ohiobaja

38KV

As far as I know, the 7.4 300hp is almost similar to the old 330. Which means 2 bolt mains, cast crank and pistons, 3/8" rods, cast iron intake, Rochester carb and small port (oval) heads.

This is a great engine as stock,It will almost run forever if you take good care of it. But I don't think it is the best base for big power.
If you are looking for 400+ hp and your motor is in that good condition I would sell the complete engine and build/buy a new longblock with four bolt mains, forged crank and pistons, 7/16" rods and largeport heads.
May be you can find a 365 or 420 in good shape to start from,these engines have all those features.

Good luck.

crmax

if you want to make more power, head work new cam, intake and carb will get you a few more ponies but you have to watch where you make all your power to dont want to run that motor over 5000 rpms (400 hp is pushing it with out beefing up the bottom end with better rod bolts)

mcollinstn

400 horses is no problem.
You'll need to spend some money on your heads, or find a good deal on some large oval port heads.

A cam swap, a performer RPM intake, and headwork will get you to 400 horses pretty easy.

Don't spin it over 5000 rpm, and prop it for 4800.
All of the above can be done without taking the motor out of the boat (assuming you can remove the rear seat or cut a hole to swap the cam out).

Sure, rod bolts are an issue, but 4800rpm and 400 horses is not a borderline application.

Not sure how extensive you want to go, or what your budget is, but 400 is a reasonable number.

You have cast crank, pistons, 3/8 rod bolts. Small oval port heads. Should be a 4 bolt block for a 97.

tomcat

I used to have one of these engines. I used a Performer RPM-O intake, opened up the intake ports in the heads to match and cleaned up the ports behind the valves. Reused the Qjet with richer secondary rods. These changes plus switching to a cam with the 454 Magnum specs (224/.510") added 5 mph to the boat, so I figure it added ~65 HP. Keeping the lift fairly low allowed me to leave the rest of the valvetrain alone. Thru-prop exhaust.

The original engine spun a 21 Mirage prop @ 5000 RPM in a lighter boat than yours; the new engine did the same with a 23 Mirage. You could call these changes "Phase I". Phase II would be more cam and valvetrain changes to match, maybe roller rockers, and thru-transom exhaust. Should be good for another 35 HP or 100 HP total gain.

bajalome

Thanks for all the input. It is a 7.4l carb 300hp engine. I do have upgraded Stainless Steel marine 4" thru hull exhaust so I guess it should be about 330 hp total. I guess I'll run it in a few weeks and see how it performs. Thanks again for all the input.

mcollinstn

lome,

Enjoy your new exhaust, but I doubt you'll see more than 100 rpm from the change. The 300 horse motor simply doesn't flow more than the stock thru hub exhaust can handle. At least it will SOUND faster.

Your motor's restriction is primarily in the camming. Not the exhaust.

Whiteknuckle

This subject on increasing the power of this type engine is one of the most talked about subjects in the forum. Do a search and you will find all kinds of good info on the subject. Your engine will have 4 bolts mains, but that really does not make much of a difference. 400 hp is easy to get. If you can change the rod bolts to a good quality like a ARP, do it. The rest of the bottom end is good to well over 400 HP. The cast crank and pistons will hold up better than most people think.

Pat McPherson

I have a set of GenVI Large Oval Port Vortec heads that will help wake that engine up. They are off my 1999 7.4MPI that I am reworking....
$250 plus shipping and they are yours.