275 horse Cosworth?

[searaycer24]

Good bad...yay nay...found a smokin deal on one of these motors, looking for some background info.

[ChrisCarsonMarine]

Big heavy solid workhorse motor,not a racer,hard to find/expensive parts,

[Raceman]

They are very durable, dependable and torkie IF they're used within their limitations. Try and twist one hard or make a race engine out of it, and you'll have a box full of parts for the scrap man. If you're NOT twistin' on it, the gearcase is the weak link. Good for deck boat, big V bottom, center console, etc, etc. Like CCM said, NOT GOOD for a high perf application. I've always said they're more like a good plow mule than a thoroughbred racehorse.

[searaycer24]

Will the controls off my 2.0 work?

[ChrisCarsonMarine]

every thing fits

[Capt.Insane-o]

Great motor when used as advertised.

[INXS]

I've picked up two in the last month. My mech said I got great deals on them, seems that if you price a new 250 you can't go wrong. I plane on mounting mine on my 24' Banana and to have it mounted to a swim platform with about 18" of set back. This well give me the speed W/O working the motor as hard. As stated here, if you search the fourm, you can not turn over 5800-6000K without taking a good chance of blowing them up. I think if I prop it right it should give me some decent speed, with the new Merc prop and set back. I could have gone with twins or a 300 but what would I pick up, 4 mph?

[searaycer24]

I am planning on mounting the one I picked up on a 21 checkmate starflite..I will prop it for 5600 max

[INXS]

I am planning on mounting the one I picked up on a 21 checkmate starflite..I will prop it for 5600 max

I think the new Merc props give you am extra 1.5-2 mph, setback is inportant on Starflites, check with the Mate guys before you buy. Also I think the Corsworth weights a bit more then you average V6 some you may need a heavy duty, Bobs has them, jackplate if you go that way. If you have a notched transom you may be able to get by with less. I think Junipter has a Starflite with 14" of set back? anyway the guys on Chris's site can tell you better.

[150aintenuff]

they are a heavy work horse.... on a 21 dont exceed 8" setback or they weill be to flighty... and can break the transom... they are a big motor with lots of torque... but also very thirsty... if the units have oil injection disable it and mix 50:1.... or even 32:1.... they were pronme to injection failure more so than even the 2.0/2.4/2.5.. not so much the crank gear.. but the oil supply pump couldnt keep up with the flow rates and reduced oiling.. and burned down the few ive seen that were spun above around 5600.. the best application i ever saw for one was a 25 boston whaler.... a single 275 pushed that thing faster than a set of 150 twins... and rolled a 21 Mirage right to the upper end of its recommended range... a 24 progression or similar would be right a t home with one.. cool motor but dont break the gearcaase.... they are NLA and hard to find..... VERY HARD TO FIND.. id love to see that motor again with modern fuel system and a 3.0L tower and lower.. .weight was around 565 lbs for a 25" motor... but the kicker was the midsection could hold another 100 lbs of water so figure a similar setup to equal power verado

[SPRKY01]

3.4 300+ hp 150# comp balanced alu fly wheel massaged exhaust holley fuel pump 10" of set back prop shaft 1" above pad 6,800+rpms 85 hours. I have owned 10 3.4s also cosworths the holley fuel pump really helped at start up and the entire rpm range i run #82 main jets 40to1 PENNSOIL FULL SYNTHETIC Turn a standard 3.4 5,800 rpms with 93 and good oil a water/ fuel separator and enjoy the beast! PS. the 275 hp cosworths have a very durable lower unit. The original 3.4 300hp lowers werent as well built.

[SPRKY01]

Bussines end!

[150aintenuff]

is that a 89 or 90 cosworth

[INXS]

3.4 300+ hp 150# comp balanced alu fly wheel massaged exhaust holley fuel pump 10" of set back prop shaft 1" above pad 6,800+rpms 85 hours. I have owned 10 3.4s also cosworths the holley fuel pump really helped at start up and the entire rpm range i run #82 main jets 40to1 PENNSOIL FULL SYNTHETIC Turn a standard 3.4 5,800 rpms with 93 and good oil a water/ fuel separator and enjoy the beast! PS. the 275 hp cosworths have a very durable lower unit. The original 3.4 300hp lowers werent as well built.

Are you saying that the alu flywheel exhuast and jetting gave your 275 another 25 hp? And did you do anythink with the heads, cutting?

Oh, can you suggest any propping if I do your mods, I'll be pushing a 24' Banana boat with a little over a ft of set back, maybe less with all that weight.

[SPRKY01]

The block is a 84 3.4 300hp the heads are cut approx 60 thousandths .I have a 21' chase marine which is like a rally sport barron ,shadow/challenger /with 29" set back with a 300hp 3.4 that topped out at 75 mph I also have a custom 31' center console that topped out at 74 mph with twin 3.4 300hps I have run thousands of gallons of fuel thru these engines so i have alot of hands on( experience )with these engines. I like to run a bravo1 four blade on the v bottoms. I run a 32" mazco four blade on the mirage I need to step up to a 34".

[150aintenuff]

the engine may be ann 84... but what year cowls.... have to be 89 or 90??

[INXS]

What does a balanced Alu. flywheel cost and where can I get one? Seems you your set-up, 25 more hp, is a decent up grade for the cost, about $1,200 maybe?

[SPRKY01]

I have 7sets of clam shell cowls and just sold a lift of race cowl (rare). A alu fly wheel could be hard to find? the motor response is very noticeable i picked up aprox 400rpms. well worth the investment. I also run the cosworth heads they are enginered much better than the original heads along with the carbs with the thin venturas and rubber reed blocks with fiber reeds.

[searaycer24]

the one I picked up is a 1992 Cosworth 275 20" mid, it has one hole that got water in it....relatively clean, I will let it go for a 1000.00 dollars...will post pics later after it quits raining.

[arrowwaves]

Blew up my cosworth at 5500 on a 24 progression with 89 oct fuel.Nice hunk of cylinder gouged out and a big hole in the piston.There is a guy in Baldwin LI that is pretty expert at keeping them working , he has a shed full of them.

[INXS]

" I also run the cosworth heads they are enginered much better than the original heads along with the carbs with the thin venturas and rubber reed blocks with fiber reeds."

I guess that standard is just the block and the Cosworth are non Merc parts? Any idea who sells those alu. flywheels?

[150aintenuff]

um... werent alll the 3.4 blocks COSWORTH blocks and heads... because wasnt the 300/275 3.4 engine a joint venture between merc and cosworth engines... thus your statement about cosworth heads being better be a moot point... like saying gm makes better heads than gm... the later 275 heads may be better than the 300 heads... but saying cosworth is better than cosworth is a bit off isnt it ???

[INXS]

I read that Merc had them do the blocks, could it be that that was all they did for Merc?

[SPRKY01]

I stated that i have a 84 300 HP Balanced block which is a totally different animal. the porting isn't the same the exhaust isn't the same etc. Cosworth totally redesigned the pistons , rods, wristpins,block,heads,starter,stator,lowerunit,electronics,reedblocks,etc,etc.

[SPRKY01]

NO not all 3.4 blocks were cosworth appx 1990 is when the cosworth blocks were designed.So appx 1983 to 1989 were the original merc blocks , heads , carbs,reed cages etc.

[plasterer tim]

no not all 3.4 blocks were cosworth appx 1990 is when the cosworth blocks were designed.so appx 1983 to 1989 were the original merc blocks , heads , carbs,reed cages etc.

so any one know howmany 3.4 cosworth motors were made?

[SPRKY01]

I have no idea! Merc used some of the cosworth improvements in their future engine designs.

[searaycer24]

if anyone knows of someone looking for a real Cosworth with a good foot...mine is going in the classifieds tonight...1000.00 dollars....one bad piston, other than that in good shape.