KAAMA

iTrader: (1)

Rookie, with those Merc 425hp engines you have they should have the GIL exhaust manifolds on them although they may actually say "MerCruiser" on the sides of the manifolds. If you have those as Patriyacht has mentioned, then you are pretty much good to go with a cam, and hi-perf upgrades/mods. It's got to have an exhaust system that breaths well such as a GIL exhaust to help realize your cam/head, etc, mods----and having the GILS is at least a significant chunk of money that you DON'T have to spend as you do your mods. Have fun.

Rookie

iTrader: (4)

Kaama, I have Stainless Marine.

Rookie

iTrader: (4)

cstraub,
1. goal would be 100-125 HP increase. 2. budget is unknown as of yet. I wanted to get info from people to get a realistic amount to see what I needed to budget for. 1. price for a specific roller cam and lifters needed for either 454 or 496, 2. heads $1000-$1500 3. stroker kit $1200-1400 and machine work $400-600. (which I see that you had broken down on another thread concerning 496's).

But, after doing some reading on some other stroker threads it might be bigger bang for the buck to do the roller cam switch and stroke it, then to do the roller cam switch and new heads. My heads are bowl ported and after doing some research they will flow but are just overkill on my 454's. from what I have read.

JJONES

100 hp will not make your boat go much faster if at all unless its an 18' jet or v drive!Ive done what your trying to do in a different way and it wasnt worth it!Save all your money until you can go big!Youll have more fun boating and using some of your money on gas untill youve got the dough!

Rookie

iTrader: (4)

JJONES, 100-125 x 2 = 200-250 HP
Thats no difference? oh.

JJONES

You Might Gain A Few Mph But Not Much,if Your Boat Is A Big Deep Vee,it Takes Alot To Push Them!then The Next Thing Youve Got To Think About Are The Props, Once Youve Got That Figured Out Youll Need Stronger Drives!theres Alot That Goes Into Makeing A Boat Faster Than A Couple Hundred Horses!i Just Upgraded My Boats Engines Maybe 150hpx2 And It Only Made A Slight Diferance Once I Found Props That Worked Ok!believe Me,if I Could Take It All Back,the Money And Hard Work I Would And Save Until I Could Make Big Hp!what Kind And Size Boat Are You Working With?

Rookie

iTrader: (4)

JJONES, I'm thinking everyone might be right, I liked the reliability factor that I had last year, oil, gas and go. I did burn down some valves last year but that was cause the carb floats went lean, out of adjustment. caught in time and only had to weld the head and resurface, new valves and springs. it isn't to deep of a vee i don't think, scarab panther. I would stay in the hp ratings of the drives, 550hp on a twin 6800 lb boat shouldn't shouldn't be to much. Maybe I'll pull the engines and just put new gaskets in to stop the oil leaks and leave them together. Just had some money laying around that I would like to use on some upgrades.

JJONES

I Used To Own A Scarab Panther,good Boat,probable Has Borg Trans With Trs Drives,it Shoud Be Spinning Cleavers Also.when I Had Mine I Blew An Engine,ingested Salt Water!i Ended Up Building Two New Engines Hence I Wanted More Power And Both Engines To Be The Same.i Started With The Same Setupas The Boat Had In It But I Increased The Com,used Big Valve Heads,demon Carbs,edlebrock Manifolds,a Cam To Complement The Comp And Heads,hei Ign,power Torque Exhaust,eliminated Circ Pump And Used Crossover!what A Differance!i Did Blow A Trans Though!i Also Tryed Alot Of Differant Props From The 21 Cleavers That It First Had To Bravo 1 23 All The Way Up To 25 Mirageplus,and Each Time I Went Back To The 21s!the Hull Seemed To Like This Set Up The Best!i Cant Remember The Specifics Of The Engines But It Was Great,i Did It All At Home On 2 Stands For About 8k!believe Me It Was A Rocket After All The Work!

cstraub

The OEM heads on the mags are plenty for a 496CID engine. Adding a .250" of stroke can really broaden the powerband giving you more useable power all over. Unless you want to knock off 140# off the back end of the boat I would use the heads you have since they have some work already.

For your power goals a nodular cast crank will work just fine. These are very budget friendly and will easly support 550HP. This along with a cam change would make for a couple of nice pieces that would give you some long hours with low maintenance.

Rookie

iTrader: (4)

JJONES, thanks for the info on the cleavers. I run quicksilver 25's at 5250 @ 70-71mph gps. i tried some hydro-motive 25's but could only get 4800 out of them. I have a set hydro 24's that I am going to try next summer. did you have any problems planing out with the cleavers. I had problems planing with my quicksilvers when the cupping was washed out, but it would also spin 5400 @ 73mph. I will be looking for some cleavers to try out. and yes the 425 TRS package. I think if I can get 100-125 extra ponies/engine, and my prop slip from 17% to 12-13% I should be in the mid to upper 70's that is the goal, shoot it could touch 80.

Thanks Chris, that is what I wanted to hear about the heads. Do you believe that stroking these engines, with a cam change, and the existing large rectangle bowl ported heads chevy heads will be over the 500-525hp range? you still haven't brought up a cam selection that you would feel would work for these mills, the 731 does sound like a good choice. would I have to worry about piston clearance? I know my heads are 118cc, but they have been milled down to 114.5cc. the compression is high 175lbs on one engine, and 185-190 on the other.

Also I was reading up on some intake threads, and was thinking of going with a single plane intake, I have a friend that has a 496 with a brodix single plane that seems to work well for his setup and runs good on the top end. I have Weiand stealth dual plane intakes and was thinking of upgrading. I have no issues with low and midrange twins in a relative light boat. but at 5000 rpms it hits a wall, it takes forever to get that extra 200rpm's.