MY take on crank case compression increases

[JaySmithRacing]

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 BEYOND 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

 

[hemi2005]

Jay, you are an overflowing fountain of knowlege! Thanks for the education. I hope to send you my ProMax sometime for some needed mods.

 

[hullbilly]

MY TAKE of crankcase compression advantages

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 ..,Jay

I will respectfully disagree with the comment that 99% of winning drag race engines have cut front halves and epoxy filled factory voids. I do however, basically agree with your general explanation and appreciate you sharing it.

The most winning engine in drag racing (DSRA & ODBA), certainly since 2005, but probably before then, is the stock drag motor. It will take a better than stock fuel curve and slightly higher compression than 21cc's to win consistently, depending on who shows up. Otherwise, the volumetric effeciency and porting of the stock drag was nailed by merc engineers for its intended purpose.

Just read some of Dave Bush's comments on merc drag porting.

 

[JaySmithRacing]

Thanks for the kind words Hemi....

Jay

 

[JaySmithRacing]

"Jay, I would like to add one more thing.
Since the reduced crankcase volume is now reduced, the swept volume to total volume is higher. This means a stronger "pull" as soon as the piston starts upwards, increases velocity even thru the reeds. and when the piston reaches top dead center, this additional velocity also packs more air/fuel into the crankcase.
So, not only are you compressing it more, but you are compressing a larger air/fuel volume more. (More total mixture into a smaller space)"...

Another great bit of information thrown in the mix by John Jackson,
Thanks John....

 

[suicidealli]

You can tell it is the off season!!!! Lol


i agree jay, it works great. this is the reason some guys run the bigger chatfield rods also. takes up area, and adds strentgh. i still prefer the small rods for a lighter rotating mass. i do the mods similar to jay, it has been proven many years ago to work. after you cut or grind on some block to change some angles for the fuel to get there quicker, well then your adding more volume. you need to have a the best of both worlds, or atleast a happy medium. THAT IS THE TRICK!!!!JMO

roy

 

[suicidealli]

I will respectfully disagree with the comment that 99% of winning drag race engines have cut front halves and epoxy filled factory voids. I do however, basically agree with your general explanation and appreciate you sharing it.

The most winning engine in drag racing (DSRA & ODBA), certainly since 2005, but probably before then, is the stock drag motor. It will take a better than stock fuel curve and slightly higher compression than 21cc's to win consistently, depending on who shows up. Otherwise, the volumetric effeciency and porting of the stock drag was nailed by merc engineers for its intended purpose.

Just read some of Dave Bush's comments on merc drag porting.

the merc drag porting really makes some hp. the eyebrow drag is a little better than the older style. i agree fuel curves, but also props win races..

roy

 

[hullbilly]

the merc drag porting really makes some hp. the eyebrow drag is a little better than the older style. i agree fuel curves, but also props win races..

roy

Roy,

You are correct, but I was only referring to engines.

In a straight drag motor class (weight and modification rules) within the DSRA or ODBA, setup and prop (which are related) trumps all.

All the block mods in the world don't produce much dyno hp with the drag motor anyway. It's already there from Merc. Plus, many common mods disturb the volumentric efficiency, which exacerbates itself in holeshot performance, and the race is over. More is not always better down low, which is where heads up drag races are won and lost.

Some good info. in this discussion. Thanks

 

[suicidealli]

Roy,

You are correct, but I was only referring to engines.

In a straight drag motor class (weight and modification rules) within the DSRA or ODBA, setup and prop (which are related) trumps all.

All the block mods in the world don't produce much dyno hp with the drag motor anyway. It's already there from Merc. Plus, many common mods disturb the volumentric efficiency, which exacerbates itself in holeshot performance, and the race is over. More is not always better down low, which is where heads up drag races are won and lost.

Some good info. in this discussion. Thanks

i agree merc hit a homerun with the drag motor. it is what i call a balanced motor, referring to the volume with the exhaust, and fronthalf. merc had it going on designing the drag.
excellent read!!

roy

 

[RBT]

Not enough crank case volume kills top end power. It is a careful balance.
Too much compression also kills power, it might feel snappy but it has nothing after the snap. There is A LOT of power in combustion chamber design how the radius's in the ports and crank case are designed.
It a a total package, to get the combination right, or even better than a stock merc is difficult.
Merc left a fair bit in the motors for us to find...

RT

 

[JaySmithRacing]

Agree Rob,

Drags are GREAT motors BUT IMO can and are made better by many people you being one of them..

I see more and more racers using 280's now days !

I've built quite a few 260's thats had some of Ruck's and my ideas on port mapping done to them thats been hard to beat..

Lets say when one of these 260's is totally healthy ( not down on leak down because of a water pump failure and getting hot = egged) it has not been beat yet by ANY drag motor its come against....

Thanks for your input Rob, you guys were flying in Jasper....

Jay

 

[K.Kiser]

i agree merc hit a homerun with the drag motor. it is what i call a balanced motor, referring to the volume with the exhaust, and fronthalf. merc had it going on designing the drag.
excellent read!!

roy

Mercury can thank the Eaves' from Tennessee for the little gem weve come to love and know as the drag motor...

 

[JaySmithRacing]

Jr. Eaves was one smart cookie for sure..

Jay

 

[RBT]

I like the 280 block, more metal to carve on......
Merc can thank about everyone but themselves for what is running today. And they SURE LOVE TO CHARGE for other peoples development!.

RT

 

[JaySmithRacing]

Rob ,
You don't have a nice 280 block and matching Front half do ya ?

Jay

 

[patches]

You are so right about Mercury charging for others development work. The 2.5 was built by Mercury and perfected by racers

 

[suicidealli]

I'm going to try the 280 very soon. I sent a 2007 280 block to ruck last week. Had 10 hours on it, and a circle clip came loose. Going with drag elec. I might try super stock.

Roy

 

[hullbilly]

Lets say when one of these 260's is totally healthy ( not down on leak down because of a water pump failure and getting hot = egged) it has not been beat yet by ANY drag motor its come against....
Jay

Wow, what drag cut 260 is this?

Only one I know of to be dominant in sanctioned DSRA/ODBA, was the one Galen Burden did for Jason Smouse on his Lakeracer boat that has been the macdaddy forever.

 

[JaySmithRacing]

Jr. Eaves' Drag Motors:

If I remember correctly and some old timer correct me if I'm wrong Tommy Huges was the first one or two guys to run the Jr. Eaves cut early development Drag Motors in 1994-1995 ish time frame then Mercury got wind of the success and power it was making and copied it. Tommy's was very quick..

I worked with Tommy along with Richard Hammontree, and Willy Atwood and built them a complete alky fuel system that used the Mercury ECU's . Lotta machine work involved building custom rails and mods to the front half but the system worked GREAT on all 3 rigs... Brad at Kinsler Fuel Injection Co. was a big help and still works there to date and is one smart guy about fuels and injection systems.

Jay

 

[RBT]

Jay I don't have any 280 blocks, I do have a Diamond 280 that will be for sale.
It is funny, I have been reading this thread, and I got to thinking of all the engine builders motors that I have had come across my bench. It is amazing how different ideas are between all the builders. I really wish I had a dyno to run them all. I have a good idea what does what on boats but it would be interesting to see what the dyno says. I would love to know the real numbers that give the changes in performance.
The motor that ran at Jasper wasn't that exotic, but it did have one hell of a good tune on it, add that I got super lucky with the air... it was almost exactly what we run here at home.
RT