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Torque peak at 6000 rpm will need cam to be something like 282/288° at .050" and .740"+ intake/.660" exhaust lift 111-114° lobe seperation. What you have now will torque peak about 4300 rpm, it is way too small, belongs in an 11-1 compression engine.

You are aware that torque peak of 6000 rpm will mean hp peak is 8100-8400 rpm and shift point will be 8800 or so -- Are you prepared to run it that high??
 

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JOHNNY
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Discussion Starter · #5 ·
i want to be real sure here before i get pixxed off with the guy that ordered it for me so here are the numbers in full--- @ 050 242 - 248 668 at full lift intake 19--43--ex 54--14 lobe sep 106
 

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crowerjunky said:
i want to be real sure here before i get pixxed off with the guy that ordered it for me so here are the numbers in full--- @ 050 242 - 248 668 at full lift intake 19--43--ex 54--14 lobe sep 106
Other than the fact that it is a solid roller, the duration #'s are virtually the same as a 370 hp 1970 LT-1 350 Chevy stock cam, What does that tell you??... IT'S TINY when taken in context to your 18° headed 15-1 comp 406.

Are you sure you didn't have a communication mix-up...? You said torque peak and he heard horsepower peak??
 

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JOHNNY
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Discussion Starter · #10 ·
ericnova72 said:
Torque peak at 6000 rpm will need cam to be something like 282/288° at .050" and .740"+ intake/.660" exhaust lift 111-114° lobe seperation. What you have now will torque peak about 4300 rpm, it is way too small, belongs in an 11-1 compression engine.

You are aware that torque peak of 6000 rpm will mean hp peak is 8100-8400 rpm and shift point will be 8800 or so -- Are you prepared to run it that high??
looks good but what would the valve timing numbers be
 

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Just to get you in the ballpark, a Comp 12-814-9 solid roller with 278/294 @ 0.050" with a 114 LSA would be...
Intake opens 25 degrees BTDC @ 0.050"
Intake closes 73 degrees ABDC @ 0.050"
Exhaust opens 81 degrees BBDC @ 0.050"
Exhaust closes 33 degrees ATDC @ 0.050"
The cam is rated to make power 6000 to 10000
 

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your tq does come on around 4000 RPM and your HP peak is at about 6000 RPM, so I'da say it was a good cam choice. If you want a TQ peak at 6000 why are you even concerned with 4000? Your conv. will still be slipping its little heart out at 4000, for drag racing your stall should just about match your tq peak which means any numbers below that are essentailly useless- circle track is another story.
 

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JOHNNY
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Discussion Starter · #14 ·
thanks for all the help :thumbup: the cam is not for a race car its for a airboat that is built for racing if you want go to photobucket an look at my pics --their under --(stephull) to show ya what im talking about --- i did call the cam comp an they said the same as what yall are saying 2500---4500 with the torque i can tell ya thats not what the cam should be :spank:
 

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Now that you have let the fact that this is going in an air boat, isn't there a critical or max rpm you want to turn the prop?? Something to do with prop diameter and rpm and the speed of sound/tips of prop blades going supersonic, at which point the blade rapidly loses efficiency??
 

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JOHNNY
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Discussion Starter · #17 ·
ericnova72 said:
Now that you have let the fact that this is going in an air boat, isn't there a critical or max rpm you want to turn the prop?? Something to do with prop diameter and rpm and the speed of sound/tips of prop blades going supersonic, at which point the blade rapidly loses efficiency??
YES THERE IS A MAX RPM IT WILL RANGE FROM 2300 TO 2700 DEPENDING ON HOW WIDE THE PROP IS THEY RANGE FROM 12IN TO 15IN WIDE THE 12IN YOU CAN TURN 2700 AN THE 15IN 2300 --WE PUT WHAT WE CALL GEAR DRIVES ON THE BACK OF THE MOTOR THEY HAVE DIFF RATIOS FROM 2/1 UP TO 3/1 JUST LIKE A RACE CARS GEARS THEY MULTIPLE ENGINE TORQUE ---FOR A RACE BOAT IT IS VERY INPORTANT TO START YOUR TORQUE IN THE RIGHT SPOT AN TO PICK THE RIGHT RATIO AS A EX IF MY TORQUE IS FROM 3000 TO 5000 YOU MIGHT PICK A 2.37 AN TURN THE MOTOR 6500 WHICH WILL GIVE A PROP SPEED OF 2700 THE CAM I HAVE IS NO GOOD FOR A RACE BOAT THE TORQUE RANGE IS JUST TO LOW I NEED ONE THAT HAS A TORQUE RANGE OF 3500 TO 5500 OR 4000 TO 6000 AN I NEED ALL THE TORQUE I CAN GET OUT MY MOTOR BECAUSE THAT IS WHAT HELPS TO TURN THE PROP I KNOW YOU GUYS RUN MORE CAMS THEN I WILL AN HAVE MORE EX THEN I SO ALL THE HELP I CAN FROM YALL WOULD BE GREAT :thumbup:
 

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You are really getting out of the area of my knowledge, I've only ever helped one person with an airboat application and he was using about a 40" diameter low speed propeller.

In your case, the cam I referenced would be too big, it is a drag race or circle track spec for 18° 406 engine that was being used in a powerband of 5500-8800 rpm on track and didn't see anything lower except in the pits. Your application is a whole different planet.

Maybe I'm looking at it wrong, but given a 6500 rpm engine speed to reach 2700 rpm prop speed it seems like you would want a cam that made torque from down low to about 4500-5000 rpm and had a horsepower peak at the 6500 max you want to turn the engine for your 2700 rpm prop speed. You want the engine to be making max horsepower just lower (a few hundred rpm)than your max engine rpm for prop rpm speed. Torque is what will accelerate the prop up to speed, but hp is what will keep it turning once you get the rpm up

All this makes the original cam choice sound not too bad, maybe only a little small depending on the gear reduction ratio you are actually going to use, and the second cam you listed may be right on.

Correct me if my thinking as far as turning the prop is wrong.
 

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You're line of thinking is kind of wrong, but I'm sure it make sense to a lot of people. What you really want is your hp AND tq peak to be close to your maximum engine speed, or to atleast have a flat torque curve right before your peak hp point which depends on your final prop speed and gear drive. I thin khis gear drive example was just an example and not what he has, he's probably looking closer to a 3 for a gear drive ratio.

You're going to need a custom cam and just about no one on this board is qualified to spec it. I would call up Isky and see what they have to say.

An air boat application is unique in how the load increases with engine speed.
 

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JOHNNY
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Discussion Starter · #20 ·
ericnova72 said:
You are really getting out of the area of my knowledge, I've only ever helped one person with an airboat application and he was using about a 40" diameter low speed propeller.

In your case, the cam I referenced would be too big, it is a drag race or circle track spec for 18° 406 engine that was being used in a powerband of 5500-8800 rpm on track and didn't see anything lower except in the pits. Your application is a whole different planet.

Maybe I'm looking at it wrong, but given a 6500 rpm engine speed to reach 2700 rpm prop speed it seems like you would want a cam that made torque from down low to about 4500-5000 rpm and had a horsepower peak at the 6500 max you want to turn the engine for your 2700 rpm prop speed. You want the engine to be making max horsepower just lower (a few hundred rpm)than your max engine rpm for prop rpm speed. Torque is what will accelerate the prop up to speed, but hp is what will keep it turning once you get the rpm up

All this makes the original cam choice sound not too bad, maybe only a little small depending on the gear reduction ratio you are actually going to use, and the second cam you listed may be right on.

Correct me if my thinking as far as turning the prop is wrong.
THIS WHERE YOU ARE RIGHT ON IT--TORQUE IS WHAT WILL ACCELERATE THE PROP UP TO SPEED--THE SPEED BEING THE TORQUE RANGE AN THE MORE TORQUE I HAVE THE MORE PITCH I CAN PUT IN THE PROP ALSO WHICH WILL HELP ME GAIN SPEED ON THE WATER--NOW AFTER THE PEAK TORQUE THE GREAR TAKES OVER ---I NEED A TORQUE CURVE LIKE THIS(LETS SAY FOR A EX MY TORQUE IS 500FT AT 3500 ---AT 5500 IT NEEDS TO BE 550 AN AT 6500 ITS 500 AGAIN
 
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