glassdave

iTrader: (1)

Ok peeps . . . i know this has probably been discussed a gajillion times on here but i have a few questions about some mods i want to do on the engines in my Scarab. They are bone stock 89 454 Mags that are in great shape with relativly low hours and currently run well and are trouble free. i have them out of the boat right now while i am doing the transom and stringers and was thinking about cams and intakes before they go back in. They are getting a good inspection and pending everything looks good, fresh oil pumps and a few other things. I am only looking to wake them up a bit and bring them up to the 400/450 HP range (is that realistic?). i was thinking Edlebrock AirGap intakes but what cam would be good for what i'm trying to acomplish? Also will i need to go to a different carb over the stock ones? should i toss some valve springs on it while its out?

MILD THUNDER

iTrader: (3)

You could upgrade the cams, to the stock crane 400, 420,425,525SC cam, install a better intake, roller rockers, new valve springs and holley 800 4150 carbs. Basically build yourself a pair of 425's. Oh, and upgrade the manifolds to Gils, Revolution Marine, etc. I have a pair of 425's, and they run great, they push my 40' Excalibur to 60.

My buddy has a 1988 Scarab III. His came with 370HP mercs and TRS. He installed 420 cams, roller rockers, but left the stock intake, quadrajet, and Exhaust. It runs good, but I think he would benefit from a better set of manifolds and intake/carb.

You could always convert to a hydraulic roller cam, and get in the 450-475HP range, but i believe the conversion is about 700 bucks per motor.

I think with 425-450HP a piece, that Scarab should run about 64-66.

RJBBC

Tyler Crockett has a good update kit for your motors. He can send the parts you need to make 90 or 110 HP over what you have depending on the cam specs. We put the 90 HP on our boat last year and gained 7mph top end with his kit and a different prop. Our motor is fuel injected but I am sure he has a carberated setup.

KAAMA

iTrader: (1)

The old Merc 365's had all forged parts in them including a 4-bolt main block. If you're only looking to warm those 365's up a bit you could proabably still make 425hp with the stock GM aluminum intake manifolds that already come on the Merc 365's.

If it's in your budget some hydraulic roller cams/lifters and even something like a set of Crane Gold roller rocker arms would be a good thing for power and reliability. Add a Holley 750cfm carb and a set of aftermarket exhaust manifolds like some Stainless Marine or GIL exhausts. My opinion, but if you really want to wake the engines up a bit then at least buy the aftermarket exhausts if you can swing it. A set of good breathing exhausts should really come first when doing mods. They will help the induction side do its job much better than if you were to leave the old stock Merc cast iron exhaust manifolds on your engines.

Do just a little bowl clean-up/short side radius work in the ports of the heads you have---nothing extensive. A cam in the 222*/230* duration on a 112* lobes would probably work well, but will depend on the type of exhaust system you;re using. Or call Bob Madara/RMbuilder of Marine Kinetics and he will get you the right cam the first time for your application and has helped several guys on here. Have fun!

MILD THUNDER

iTrader: (3)

Like Kaama said, get some better manifolds. I would also swap cams and install roller rockers while they are out. You can still run the stock intake and quadrajet with the bigger cam and exhaust. You just may have to richen up the q-jet metering rods a bit.

glassdave

iTrader: (1)

Thanks, great info guys. i am not looking to get to deep into these engines as i have another pair i may put in next season. So far i am pretty set on the AirGap intake and bigger cam (anybody got a part # thay can recomend?) also thinking about Dana Torque flow exhaust. Would i benafit from 1.7 roller rockers over 1.5's? what is the up and down side of the 1.7 rockers?

Payton

The Crane 241 is a slight improvemnt over the stock Merc 420 cam. Mine runs very strong with a set of Gold roller rockers the 241 cam Air Gap or similar intake and an 800 Holley. The stock alum intake with a little more spacer and the stock 750cfm Qjet carb is still a very good combo with that cam.Also some better than stock exhaust.

My stock springs were fine and good enough for this cam.

jeff1000man

Merlin oval port heads, Edelbrock 454-o victor jr intake, Leave everything else alone. Possibly install ms-6 box into your merc system. It will knock your socks of when you feel the diference. Just did them in my 38 scarab and there is at least 10mph diff and I havn;t gotten into changing the props yet. This sombo makes power through 5500. If you want more then install 800 marine carbs from holley. They are less then 750 through JEGS. You could also upgrade roller rockers, pushrods and install new lifters and do both engines for under $4k if you do all of this yourself.

glassdave

iTrader: (1)

sounds like a great combo i'm a big fan of the Merlin heads. i'm not lookin to get quite that deep into these engines though. i have a deal going on a pair of low hour 525SC's that may find there way into my boat. i probably wont have this boat for more than another season or two, want to step up to a 38 Scarab but in the mean time i would like to wake them up as long as there out of the boat. i will most likely just warm these up a bit as the 525's wont increase the value of the boat much these boats are only worth just so much no matter what power. its a very nice turn key boat as it is though. i am seeing about 56-57mph with the stock 365's hoping for 64-65 with the above mentioned mods.

Griff

The 241 cam referred to is Crane #134241. It comes in a kit with lifters using the part # 134242. Very close in specs to 420cam. I used one in my 454 mag afew years ago. I used the stock intake with a 1" open spacer and a holley 800. It will get you into 425hp range.

I also think you would need to add exhaust to see real gains and that adds a lot of $$$ . I would say if you're not ready to spend 3k per engine, then leave them alone

Here is a dyno proven rebuild using that cam.
http://www.offshoreonly.com/forums/s...light=nobudget