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rocketman
12-27-2001, 09:52 PM
I am rebuilding a 1981 30 foot Thunderbird, Formula which originally had twin 330 mercs. I am a newcomer to boats and am having a hard time trying to figure out which engines to power with and what size. Just wondering if maybe someone else out there has already gone through this. Also looking for any other info on rebuilding this boat.

25OUTLAW
12-28-2001, 08:20 AM
Originally posted by rocketman:
I am rebuilding a 1981 30 foot Thunderbird, Formula which originally had twin 330 mercs. I am a newcomer to boats and am having a hard time trying to figure out which engines to power with and what size. Just wondering if maybe someone else out there has already gone through this. Also looking for any other info on rebuilding this boat.
Rocketman, I would go with Big Block chevy's with bravo 1 drives. Post this in the Hot Boat Hot Spots forum and you can get more response. THere is a guy called Old Rigger who knows tons about building/rebuilding. Good Luck!!!!
Larry

spectras only
12-28-2001, 12:54 PM
Rocketman, I've been in a few Formulas,and there's one thing about them.Heavy!The 302 was their first to enter offshore big boat league.The 27 foot model that John Connor succeded in racing was a more recognizable.The model I really liked was the 233 Liberator [single BBC].The 255 Liberator with twin 350's were difficult to service[very cramped engine compartment].Your 302 has the same problem as space goes inside the engine well.The 302 has an 8 foot beam whis is perfect for offshore applications.What you have to check out seriously is the stringers and transom.The T-birds used a lot of wood that's prone to rot.I have tons of old Boating mags,and I'm positive to have an article on your model.I'll try to find the issue,and if you care I'll scan it and e-mail it to you if you wish.So long for now http://free.***boat.net/ubb/biggrin.gif

sea buddy
12-29-2001, 12:02 PM
OLne of the choices you have is to re-balance the boat with todays drives or use what you have.
Most likely you have a 330hp rated at the engine 454 with a TRS merc drive. This has a transmission that sets the heavy engines in that narrow boat about a foot forward as compared to a Bravo drive. The tranny itself also weights abolut 150 lbs.
If you use a Bravo 1 drive the engines can be moved back that foot and the weight shift will rebalance the boat. It will be just a little more tail heavy coming out of the hole but a dep vee will gain speed if it can "dance on the transom" at wide open throttle. And this weight shift allows for more of that.
Went though this with a 30' Scarab. Gained about 4-5 mph with same hp on the Scarab.
Engines- there is a world of difference betren a standard and magnum 454 or 496 for heads, and internal parts. If you want to cruise above 3,400 rpm you will have alot more life with the magnum. and if you want to "hot rod" later, it is the right base.
The 375 hp stock motor is showing about 10-15 hp less than the older 454 385 hp as instqalled in boats. the 420/425 hp 496 is showing about 20-35 more hp than the old 415 hp 502, again ibstalled in boats.
Remember, the engine builders can rate an engine within 10 percent plus or minus of its true power.
The 420/425 is underrated compared to were the 415 engine was rated.
Within the next six months Merc may come out with a 496 rated at 515-540 hp to replace the current 500 hp 502. This is not yet ready to be announced by merc yet.
Final thought, most 30'pleasure versions of deep vee offshore racing boats such as yours gain 10-11 mph if the complete cabin interior is removed. This is not only the weight but also where the weight is, in the bow. Think about any and all weight placed in the back from the front as the cheapest way to more speed.