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Thread: first engine need advice

  1. #11
    waterbum
    Since you plan on assembling the engine yourself,make sure to pay strict attention to the manufacturers specs for piston to wall and ring end gap.Not enough piston to wall in a marine engine and sieze will result,not enough ring end gap and the ends will butte,seize and tear the top's off your piston's!!!An information sheet should be supply'd with your pistons.I'm runnin aluminum heads with 10.3 to 1 comp. on 91 octain. You can get away with more compression with alum. head's because they dissapate the heat faster=no detonation. Make sure you have a good torque wrench,cover underside of headbolt heads and threads with a good assembly lube,O.M.C.gasket sealing compound or equivilent on any threads that enter a water jacket this will give you true torque readings.Hope this was a help. The Bum

  2. #12
    Infomaniac
    I would not use the Vortec heads unless they are free. They are very thin and light weight. Crack very easily.

  3. #13
    tahitijet
    Thanks,
    So can i get away with 10.5:1 with cast iron heads? Also on the piston spec sheet will it have a spec for clearances for marine applications? or do i need to ad 3 thousandths myself?
    thanks

  4. #14
    waterbum
    10.5 to 1 with iron heads will probley result in detonation cause they won't dissapate the heat. Iron heads maybe 9.5 or 9.7 at most. Aluminum heads,10.3 to 1 no problem. I used Keith Black hyperutectic pistons and they did come with all pertnant info for marine applications.Have a blast,there's no better feeling than being able to say I created this beast you had to buy yours.Ha Ha Didn't mean to offend anyone. The Bum http://free.***boat.net/ubb/biggrin.gif

  5. #15
    DOHARA
    I WILL HAVE TO DISAGREE W/WATERBUM. THE PROBLEM WTIH JET BOATS IS GETTING ENGINE TO
    RUN WARM ENOUGH, JETS RUN TO COOL. I RUN CAST
    IRON HEADS W/ 10:1 COMP. AT 36 DEG ADVANCE AND NEVER HAD A DETONATION PROBLEM ON 91 OCT.
    I'M ALWAYS HAVING TO CLOSE WATER VALVE LITTLE BY LITTLE TILL I GET IT TO RUN AT 160-175 DEG.. JETS ALWAYS HAVE FRESH COLD WATER RUNNING THRU THEM. ANY ENGINE BUILDER WILL TELL YOU A ENGINE THAT RUNS TOO COLD WILL NOT PERFORM PROPERLY AND WEAR OUT JUST AS IF IT RAN TOO HOT.

  6. #16
    Tinkerboater
    Why don't you jetboat guys run a thermostat housing and piping like the i/o boats. I dont see any reason why it wouldn't work.

  7. #17
    waterbum
    You know something DOHARA,it's ok to dissagree with me but you didn't have to DISS me by CAPPIN me out!!!As long as your engine is running warm enough to burn off moisture(a byproduct of combustion)it is fine.Furthermore it's been proven on the dyno that a cool running marine engine will make more horsepower(also read this fact in a past issue of Hot Boat)although it may produce a little more carbon.Also on the compression thing,how do you know your not detonating?Is it mabe because you think you can hear it?How do you know that that 91 octain your buying is really 91 octain?What makes you think your jetboats run cooler than my I.O.?My 500h.p. and my 383 stroker both run around 140 degree's with no problems !! The man asked about runnin 10.5 to 1 iron heads your runnin 10 to 1=lots of piston heat,HARD on your oil.Remember this ain't 1965 fuel were runnin.Yo man,you gave me the thum too and I'm still tryin to be nice,mabe you should try that!! The Bum http://free.***boat.net/ubb/biggrin.gif http://free.***boat.net/ubb/biggrin.gif
    [This message has been edited by waterbum (edited January 01, 2002).]
    [This message has been edited by waterbum (edited January 01, 2002).]

  8. #18
    DOHARA
    HEY WATERBUM, I'm not dissing anyone, I just think your a little off thats all. I don't think a half point in comp. will determine detonation or not. It depends on fuel. If you run high comp., you need to run higher octane fuel. Every engine is different so if he runs 10,10.5,11.1 etc. it may detonate at 10.1 or may not. also depends on how you tune your engine. I know what your saying about engine temps, I am simply saying that too cold of engine temps can cause loss of performance, so can a engine that runs too hot. What do you think a thermostat is for? A thermostat is to control temp. and assure a quick warm up, and to keep it operating at the most efficient and safe temp. for performance and engine life. If your engine runs too cold, fuel can condense and rob the combustion chamber of fuel required for performance, also causing a lean condition that will also causes detonation. Also, yes I know my engine isn't detonating cause I can't hear it. The definition of detonaton is: the explosion of the mixture in the engine cylinder, becomes audible through the combustion chamber walls, usually caused by fuel with too low octane rating FOR THE ENGINE,ignition timing too advanced,high engine operating temp., or excessive carbon buildup in the combustion chamber. So, the man asked if he can run 10.5.1 comp. I personally think he can. Ya aluminum dissapates heat faster but marine engines run pretty cool water thru the heads all the time so why would it make that much of a difference on a mild engine. I also know that I can run my engine colder than your 140 If I choose to. I have run it so cold that the temp gauge didn't budge off 120 deg., until I adjusted the water pressure going into the engine. What's with all the "HOW DO YOU KNOW" BS? SO let me ask you how do you know? I know enough, I have grown up in a family that has had plenty of high performance toys we have built, all my friends either race cars or build and dyno engines, I myself am a ASE certified mechanic that has been wrenching for many years. I don't know everything but, I know when someone doesn't know what they are talking about. All I stated was that a half a half point will not be a reason to buy aluminum heads when you can run a little better gas and get away with it. You think someone needs to buy aluminum heads if they jump out of your 9.7.1 comp. range that you stated before? I say your wrong thats all....ENOUGH SAID http://free.***boat.net/ubb/smile.gif

  9. #19
    77charger
    If you run a bigger cam you can get away with 10-1 comp with cast iron heads using 92 octane.I my self run a 11-1 motor and it gets by well on av gas timing is at 38 also.if i back it to 32 i can get by on 92 with octane booster if i had to.but it wouldnt survive at 38 this i already know.the theory you have on aluminum heads holds true for cars as they are under load but i have gotten away with a 10-1 small block that was well built on 87.nainly because it ran cool 160 degrees.But a jet boat is not really under load.If you tied it to a dock you will still get max rpm you just wouldnt go anywhere.but they do take torque to get past a certain point (your max rpm)I pretty much agree with dohara on the comp issue i've been there myself and know from experience.

  10. #20
    waterbum
    Well maybe I took you wrong.I too have been doing all my own wrenching for many,many years.I have never owned a squirt boat so I didn't understand that they aren't under the same load as an I.O. I am man enough to admit when I may have been wrong.The load factor would play a big role when deciding what comp. to run.Also my h.p. has a crossover(no circ pump)and no thermostat,lake water blows straight through,takes a while to heat the oil but never any sign of moisture in the oil.Guess maybe I learned somthing about squirt boats.Got kinda pissed at the thum and CAPS though.By the way,the cooler the fuel,the dencer the charge=horsepower! The Bum

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