Madmax

Not sure why the Mercruiser page is telling ya that, but a 96 is a Mark VI engine. Shouldn't have a rev limiter, cause it should have a Thunderbolt IV ignition. Just speaking from experience on my friends boat that has a 96 232 with the 454. My 97 has the Thunderbolt V and it has the rev limiter.

Maybe your engine has been replaced somewhere along the line with an earlier model? You should be able to take the serial # and look it up on the Mercruiser page. Externally the difference between a Mark IV and V is easy to tell, the Mark V has the aluminum valve covers, the mark IV has the old style stamped steel. Mark VI is a lil harder to tell from a Mark V externally. It will have a 6 bolt timing change cover instead of an 8 bolt, made of aluminum also. That's if memory serves.....i'm getting old so don't quote me on the # of bolts.

Chris288

96 is the year they switch but it was mark V to mark VI, so realistically I could have either one.

One thing for SURE is I have a rev-limiter, going hard into a turn if i'm not trimmed all the way down I will cavitate and hit rev-limiter, If I had to take a guess, I would say its somewhere around 4,800 or so, hard to tell when it bouces off, and I am almost 100% positive I have the thunder-bolt V ignition..

I will check to see which block I have...

Madmax

Sounds about right. Mine kicks in at 4750. You can get a module off of a 454 Mag and that will increase it to 5050. Not sure of the part #, but they are EXPENSIVE new. I found mine used on this board for 100 bucks...

I dunno if i would worry about the internals unless you wanna tear the engine down. If you are gonna tear the engine down, then i retract all previous statements and think you should go for a crate motor or a used 454 Mag or 502 Mag. The comments I made on upgrading only make financial sense if you keep the stock lower end. Otherwise, don't waste money on that motor, start with something better.....

Chris288

If I upgraded the cam, heads, intake, re-jetted the carb, went with forged pistons and rods, what do you think my hp increase would be ???

Budman

I would consider keeping the bottom end stock, and applying the money that you save on the bottom end rebuild towards a better exhaust system. This way you can run a more aggressive cam without as much concern about reversion. The forged pistons won't buy you any speed, just a little more insurance against detonation, which shouldn't be a problem if you don't go too high with the compression. You already have the forged rods, but 7.4's have the 3/8" bolts instead of the 7/16" that the mag's and 502's have. Shouldn't be an issue if you keep it under 5000 RPM. As someone else mentioned, if you are going to completely rebuild the engine, why not go with a crate motor, and then sell your old one (or keep it as a spare)?

Just to give you a point of reference, I installed a beefed up 454 in my Baja Force 235. It is .030 over, has forged TRW's, stock 3/8" rods (with ARP bolts, beams polished, stress-relieved & shot-peened). I went with a set of large oval heads with some minor valve bowl porting, 2.19 intake valves, Comp Cams Xtreme Marine 262 hyd flat tappet Cam (226/236 @ .050, .540/.550, 112 LSA I think), Comp Cams roller rockers, Edelbrock Performer RPM, etc. I am still running the stock Q-jet, but I have jetted it richer. I don't have much of a baseline to compare it to (boat came out with a 350 mag/Alpha), but I am running around 60 - 62 right now. I think there is a few more MPH available with some tweaking - so far I have just dropped it in, set the timing, and run it. Have not experimented with spacer plates, flame arrestors, carb jetting, props, etc. Also, I am running the stock Merc manifolds with Silent Choice. If I had it to do over again (and the extra $$$), I would have run a set of Lightnings with the Teague switchable tips like my buddy cpqtim has on his boat. My point is, the forged pistons really didn't buy me much. I am not really running any faster than some stock 7.4's. Spend your money on the heads and exhaust - paired with the right cam, this is where most of your performance gains will come from. One benefit of the aftermarket exhaust will be less worry about reversion, and you eliminate the ****ty design that Merc gave us with the water jackets going through the riser flange - ask Jayl13 about that one!

The other way to make power is though cubic inches. This is where the crate 502 comes into the picture. But keep in mind that I think my friend cpqtim didn't get over the magical 70 MPH mark with his 502 until he added the Lightnings - I think, so go figure.

I hope I have muddied the waters up real nice for you with my rambling!

Back4More

Try the Merlin 509 or 540.
They come with a marine warranty.
509 c.i.d. 540hp/ 575tq $7,495.00
540 c.i.d. 580hp/ 625tq $8,495.00
www.theengineshop.com/engine3.shtml

candyman35

Back4More,
They had a slight price increase. $12,000.00 is the new price for the 540. I liked the old pricing better.
Dan

Back4More

Don't they know times are tuff now!?
Well, that sucks.

Chris288

by the time I spend 5 or 6 grand on a crate motor and then another 2 to get it set up properly, 7 or 8 grand is TOO much, even if I sell my motor for 1,500 to 2,000, 6 grand if more than I wanted to spend.


Looks like I will be upgrading my my heads, pistons, intake, cam, carb, and maybe the exhaust. whatever hp increase I get, is what I will live with.

HOPEFULLY it will be atleast 425hp..

I went to the speed calcualtor and if I plug in the new setup running at 4,900 rpms, I get almost 66 mph. which would be an increase of about 7 mph. not quite where I want to be...

cobra marty

If all you want is 425HP I would go to the 1800runnew for under $5000. with that long block you can pull your motor and transfer the accessories and back in in two days. How long and lost memmory and parts to get yours built up and back to you. There are never any shortcuts.