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MIKE , DAVE , RICHARD

F

fatboy0054

Well-known member
TRIED TO TUNE MY MOTOR DOWN ! BUT ANYWAY WENT FROM 540 LIFT CAM TO 488 ! CHANGE CARB WENT FROM 850 TO 750 DP ! WALLARDED MY 76 CC HEADS OUT TO 88 CC 10 TO 1 TO 9TO1! DROP MY VALVES ABOUT 1/8 INCH !CUT THE HEADS TO FIT MY FLAT PISTON AREA ! SO WHY DID I GAIN ALMOST 1000 RPMS !BETTER MILEAGE ! I KNOW YALL CANT REALLY ANSWER THIS DEAL !BUT WOULD LIKE YOUR OPINON ! TRYING TO LOSE HP AND FINDING MORE OF IT ! YALL SELECTION ON PLUGS REALLY HELP BUT NOT THAT MUCH, I HOPE ! ALL THE STUFF I GOT INTAKE V-TRAIN SET UP SHOULD STOP AT 4800 OR SO !BUT I GUESS IT DIDNT CARE ! SORT OF GOT SOME OF US WONDERING ! NEED ANOTHER BLADE I GUESS ! GOING TO SLOW IT DOWN A LITTLE DONT WANT TO BE BANGING AIR ! THANKS YALL ! THESE HDY LITERS WONT LAST AT THIS RPM ! I DO VALUE YALLS 411 !!
 
:D -ya motor guys .........some of us would like an explanation on why with less compression-less lift -and whatever could equal more rpms and more pitch?
whats the story??????????????

another question-why would a hyd.lifter not be able to survive at 5,500rpm?

as always thanks in advance,Tom.
and thanks fatboy for the post-now lets get some answers we can all learn from!
 
I'm lookin forward to the answer too, Fatboy. My guess is that the changes you made increased volume and built torque but I'm anxious
to hear what Potter and Felber think.

A lot of times we can learn a lot of lessons from an old Allis-Chalmers or Case tractor when it comes to these airboat motors.

olf
 
I don't know all the details about your changes but a few things you did can make a huge difference and it sounds like from your description you drastically improved your quench area if so that’s a major change and is one of the areas that will wake an airboat motor wake up the most! Need more details sounds like your cam change improved cylinder pressure. You can run less compression and have more cylinder pressure and you will end up with a stronger motor.
 
T-REX":2c3rr9zd said:
:D -ya motor guys .........some of us would like an explanation on why with less compression-less lift -and whatever could equal more rpms and more pitch?
whats the story??????????????

another question-why would a hyd.lifter not be able to survive at 5,500rpm?

as always thanks in advance,Tom.
and thanks fatboy for the post-now lets get some answers we can all learn from!
Click to expand...

That's because, as engine speed increases, the hydraulic lifter's plunger depresses further into its body due to the increasing forces of trying to accelerate the valve off the seat. The cam begins to act like an aggressive solid design from the lash that's created, but now has a shorter duration as the result. The more aggressive the cam acts, the harder time the valve spring has controlling it. As it approaches max speed, the valve bounces off the seat and oil rushes into the lifter to take up the clearance that's now been created at the plunger. This effectively holds the valve off the seat, (valve float), bleeding off compression and power, and limits the high-rpm capacity of hydraulic designs. :wink:
 
There are limitations with a hydraulic lifter as lift and lobe profiles become more aggressive generally, unless you spend a fortune on certain parts your valve spring pressure must also go up. Thus compounding the problem! I can see several things that may have helped your motor improve performance. It's all a combination and it only takes one minor detail to mess it all up.
 
Waterthunder":3l9me9pt said:
I don't know all the details about your changes but a few things you did can make a huge difference and it sounds like from your description you drastically improved your quench area if so that’s a major change and is one of the areas that will wake an airboat motor wake up the most! Need more details sounds like your cam change improved cylinder pressure. You can run less compression and have more cylinder pressure and you will end up with a stronger motor.
Click to expand...

This read goes real good with a cup of coffee. !!!
 
Cylinder pressure in an airboat is a very fine line and there is only one way to find the line! Hence one reason I run the coolant temps I do! Just like piston to head clearance I run a different piston to head in an airboat motor then I do for any other application! There are many, many pieces to this puzzle and I'm sure me or Mike ain't going to blurt out the big ones! We both have worked years on many different types of airboat motors to find these parameters!
 
Waterthunder":3rejks4j said:
It's all a combination and it only takes one minor detail to mess it all up.
Click to expand...
that is quite correct after racing at polluted i had a couple of people tell me my exhaust was horrible i had welded hard angles in my exhaust for convienence,i was told it was majorly screwing up my exhaust pulses.so after smoothing out the exhaust i had to re-pitch the prop another 1/2 pitch mark deeper because of the energy it released.(i assume). gained around 375 engine rpm on top.now i am out of prop ,pitch mark 3 -5100rpm.

so i want one more chance terry :lol: i still dont think i could beet ya i just want to be less than a boat. :D
 
Waterthunder":28g0y8ko said:
If you picked up that many RPM's I don't know if I want to run ya! It's all in the details!!!!!!!!!!
Click to expand...

oh com'on dave get the fuel tank and the prop fixed,and spot me 200ft on a 400 ft run
and i might be able to stay within a boat lenght or two of ya. :lol:
 
i worked with a sprint car team back in the day , drove some wrenched some , im convinced that quinch and head pressure is key , we would take a 2000 dollar set of pistons and do some nasty things to them reducing compression somewhat but improving the burn,air and fuel in the burn and gas out , wish it was as simple to do as it is to say , but when you get that right you got the stuff, how do ya think dave gets550 out of a ls motor its the tricks hes perfected,which its hard thing to do is make #s like he does with dependability an no excessive heat build up ,if i ever get the gumtion to build a race boat , and that would take some sanction races on a circuit it would be a hilburn powered acohol on a step hull , but thats been done aint it 8)
 
QUENCH AREA THE SAME !.JUST INCREASE VOLUME ! SHAPE THE CAMBER TO LOOK LIKE MY PISTONS ! CAM SPECS 114 - 488 LIFT! LOST THE CARD ! ALWAYS BEEN RUNNING STOCK EXH VALVE WITH A 219 INTAKE VALVE ! HEADS ALWAYS BEEN PORTED ! ALL WE DID IS HOG OUT TEN CC IN THE CAMBER ! DONT KNOW ANYTHING ELSE ,JUST GOT LUCKEY I GUESS ! GOT TO BE THE CAM ! ITS FROM CAM TECH ! TOLD THE GUY WHAT I WANTED !HE SAID I ONLY THINK ON FRIDAYS ! HE CALL ME TUESDAY I SAID TRY THIS IF YOU DONT LIKE WE WILL MAKE YOU ANOTHER ! TOLD HIM ABOUT GEAR NOISE HE SAID I WILL TRY ! WELL HE FAIL ON THAT PART ! :shock:
 
If you reshaped the chamber you have changed your quench! Quench isn't only the distance between the head and piston it's also the shape and design of your chamber, chamber shape directs and effects combustion! Look at a 1970's chamber and then look at the modern Sprint Cup style AKA heart shape chamber!
 
fatboy-this could be the majic formula you stumbled on to!!! 8)

what material you removed from the combustion chamber-where exactly did you remove it from? did you smooth the chamber out as well-or just grind material away?

potter do you have any ideas on why this would work so well?

i know we need to know the exact cam #'s,but how is it possible there is now more cylinder pressure-with less compression and less lift(not that lift effects pressure) but lets hear all of guys!

c'mon yall!!!!!!
 
I THOUGH THE POP UP PART OF THE PISTON AND THE FLAT SIDE OF THE HEAD WAS MY QUENCH AREA WHICH IS 0 DIDNT TOUCH THAT ! IF I GO TO DISH PART ON BOTH IT WOULD BE OVER 1/2 INCH ! I AM SORRY !JUST TRYING TO LEARN ! MY CRANKING PRESSURES WERE 185 NOW 170 !TALK TO THE CAM GUY HE DOESNT WANT NUMBERS KNOWN , SORT OF GOT TO RESPECT THAT PART ! AND I AM USING MY BAD HEADER SET UP ! ! GOT TO GET THE GOOD SET COATED (SALT WATER THING )!
 
another thing out this is fatboy is saying he is getting much better fuel mileage....

its fine that there are proprietary cam info, but how is there more hp (or torq)with less cylinder pressure?
 
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