Advantages of high crankcase compression

[Jay Smith]

MY TAKE of crankcase compression advantages

7:10 AM 11/25/2011

Reply Edit


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To clairify a question it is not that you have too much air induction its refers to the speed of that COMPRESSED fuel charged air BEOND the reed. The reed works as a valve allowing air OR air mixed with charged fuel vapor to enter with the induction or draw of the piston as it makes it UPWARD movement. The inlet air after being drawn in ( reed open ) is now to be compressed as the piston reaches TDC and combustion occurs the driven down piston begins to compress this charged vapor, the reed is now closed and completely sealed or should be to stop the charge from backing up.. PAY ATTENTION NOW IT GETS GOOD !
The compressed vapor begins getting compressed by the pistons travel on its UNDER side , this area of the piston and the surrounding area is refered to crank case compression and its is AS IMPORTANT as top of the piston motor compression on any 2 cycle.

The piston drives the fuel vapor to a compressed state farther and farther raising the compression poundage to around 5 lbs the at the peak of this compression with NO CHARGE being able to escape via sealed reeds , sealing rings, piston rings and no hole in the bore opening , wa la the piston passes an intake port and the vapor rushes tru the port and as the piston travels to BTC the remainder of the charge loops around the piston crown ready for compressing on the top of the piston and combustion occurs about 25* before TDC and the cycle begins again..

REMEMBER I TOLD YOU ITS FIXING TO GET GOOD ? The tighter or LESS volume you can have in that sealed crankcase area the more crank case compression is made and the higher the compression number is say arount 7 psi instead of 5.. This more higher compressed vapor makes a noirmally lazy moving charge to the top of the piston now like a racehores increasing velocity .I achieve this condition by stuffing areas with epoxy as well as cutting the front half, machining ( reed side ) to reduce the volume and increase crank case compression and air speed, thus like supercharging a 4 cycle.. Believe me it works..

I've had some claim that after I machine the front half and epoxy target voids the difference in their motor before and after mods is like stepping on a firecracker verses a grape before the work is/was done..This is done to 99% of the WINNING drag race engines out there the ones that don't do it are in the looser's bracket .., I've done a zillion to motor that belong to my customers as well as others that I don't build their motors, that along with big compression and light hulls make a drag race boat LEAVE the line so snappy....

Hope that answers any questions and you enjoyed the reading ,

Jay

[andymac]

Hi Jay,your knowledge is second to none.keep it comming .

[Germansaleen]

Thank's for sharing your knowledge with us

0.500 to 0.600 front half cutting , that's right ? to get the room tighter in the front half(less Volume).
and 0.??? machining ( reed side ) ? ,that's new to me.
machining just the gasket area to get the reeds deeper into the front half ?

i do have also a carb intake and it would be difficult to machine just the gasket area on the intake around the reads.

but to deep cages will contact the inner of the front half and how close is it to the crank ?

michael

[Jay Smith]

If you remove too much off the reed side of the front case half the connecting rod bolt in its rotation will contact the reeds cage. If you cut .100" it can make that surface brittle and prone to crack and break. I always cut .050" off the front and never have an issue....It is a noticeable pick up in torque and HP on the bottom and mid range.. You laso must machine the pockets where the attachment bolts screw in the reed ncages as well as dragging an end mill across the place where the reeds attach and will contact the case half before it gasket seats..

Jay

[maz928]

Great reading Jay

would you change (go up) the jet size on a carb motor and would it effect the fuel burn rate ?

Steve

[Jay Smith]

Steve ,
You would need to do a plug check to see how the added fuel vapor speed effected the crown temp and burn quality... As this mod will effect HP it could be creating more heat and may need additional fuel to prevent detonation....

Jay

[Jay Smith]

Michael,
Mill the COMPLETE FRONT case half of the block itself .050"... Where the reed with reeds attached slips into the block half. You would NOT touch the reed plate surface leave as stock. To do this mod you must have the motor completely torn down ( split the cases )NEVER under any circumstance cut or remove metal where the two case halves fit, that is a ground joint fitiing where the bearing fit and is line bored. Any removal of metal in that area will results in the front half of the block assembly being rendered UNUSABLE and JUNK !

Jay

[Germansaleen]

Thank`s Jay