2.5 Head Mods.

[popslavaz]

A friend brought over a set of 2.5 heads to cc. The chambers
have notches(chamfers)towards the exhaust ports.We do
the same thing to big block chevys(top of block) to un-shroud
the valves.Ever see this on 2 stroke?
Mike

[T-REX]

I have seen sumpthin like that...in sum ov tha fastest boats on ODBA...Chuck Goodman does sum head magic that kinna sounds like what U iz explain'in...thro it on tha scanner and letz look at it and I kan tell ya if he dun it!!...REX:cool:

[lavazhole]

Here's the pictures of the heads, if it's good for a few don't tell G-Train...lol

[Superdave]

Not an expert, but exp in 4 strokes. I would think the unshrouded area would be towards the intake side of the motor. Reasons are to direct the flow of the fuel mix, cooler intake charege for the spark plug. Looks like it would be similar to the old smallblock chevy 300 fuel heads being converted to angle plug heads. The spark plug is angled towards the intake valve to promote flow, smoother and more complete combustion. Just my 0.02.
DAve

[G-Train]

I've noted your comments, and you will pay the penalty.

Your dad's car is purdier.

G

[TB21]

IMHO that notch was cut to aid in allowing the flame front to travel into the exhaust area of the squish band....in hipo 2 strokes theres always been a 2 sided arguement on this and they are (1) one group believes that most of the air/fuel charge stays in the squish area never making it to the chamber for a complete burn....this group usaully makes an effort at doing things "such as radical squish angles to try and get the flame front into the squish band thinking there will be a more complete burn "it is my belief that is the purpose the notch over the exhaust port , to burn that charge before its gone" . (2) Now the other group makes all efforts to use angles and very tight squish clearances to get most all the charge traveling into the chamber thinking the flame front cant travel into the squish band area. Like I said this is my opinion....I wont say to which side i agree with......but I will say this , ive raced and built very hiperformance 2 strokes for over 25 years and with what ive seen the... stock flat squished merc heads would get laughed at in a real 2 stroke hipo world. TB

[G-Train]

Are you saying in this statement......

... stock flat squished merc heads would get laughed at in a real 2 stroke hipo world. TB
That the Merc 2.5's are not "Real" Hi-Perf 2-strokes?

What is your opinion on how the heads should be cut for them to be "Real" hi-po heads? I'm not being a smart-ass, could you show a little diagram?

G

[TB21]

G-Train
In no way did I think you were being a smart ass......when I said I think stock merc heads were junk I figured someone would counter....after all them junk heads sure are on alot of fast engines. Anyway to answer your question..yes they would be laughed at where i came from...sorry thats the facts!

Now if the mercs had the digital ignition like some of the real hipo 2 strokes use and we were able to advance & retard ign timing through out the rpm band then hell yes go with the more efficiant flat squish band.

But I refuse to be mildly conservative on compression and sissy ignition timing just to make a motor live because mercury does the heads that way...thats what milling machines are for.

Unless your very understanding of how changing the ( MSV maximum squish velocity) affects an engine I'd leave it alone.

How many guys you know that can run 175.lbs of cranking pressure and loads of ign. timing on pump gas dependably? My heads will.

Anyway you asked my opinion on how they should be....this image will give you some ideal...though its not a merc its a real race engine LOL . hope the image works Thanks TB

[popslavaz]

Jay T-Rex US1
What do you guys think??
Do you think any HP gains in "TRICK" heads

[G-Train]

What do you think a completely Symetrical Dome would do for these Merc heads? With the Dome covering the whole cylinder opening, with no squishband needed?

BTW: Very nice diagram

G

[Jay Smith]

Most of the F-1 guys are on the cutting edge of whats hot and whats not and I haven't seen any movement going that way. My opinion is that the pistonsin these motors are junk and with the notch I think you would not get an uneven push off the explosion at time of firing and have an undue wear on the piston skirt on the off side as the notched area has less volumn on that side. I relize it would equalize but I like the even umbrella or hemi style combustion chamber.

I would have to test with the stop watch to make an educated desision that is the real true benchmark of either improvement , staying the same, or loss in performance.......

I know thats beating around the bush but not having run them I cannot knock em or prase em.........

Hope that was politically correct , I have gotten jumped on in the past for choosing one product over another and even been terribley misquoted! But like I've said in the past this place is not for black and white it is just what folks like and to share constructive suggestions and knowlege , you even have some people that like a 2 cycle oil for the way it smells when it burns and make a desission to buy that product on that basis alone , if people don't like what I say , what I choose to endorse, or believe in then put me on ignore, thats what I have done to more that one poster on this board that I have witnessed in the
past and my opinion is that they have nothing constructive to offer....

My feelings only .....

[Dave@DunnWright]

You show in your schematic the top of the piston being domed or crowned at approximately, just by eyeballing, the same angle as the squish band is cut. It also shows what appears to be a hemi type chamber. This is classic two stroke design. My question is where would one acquire such a piston? I don't think there is enough material on a stocker to accomodate that kind of radiusing and it would be a booger to machine as it would need to be hemisperical in shape also. I have seen many "classic" two stroke tried and true performance mods tried on these V6's and they seem to fall short in performance compared to the time and expense. I would mention "The great expansion chamber debate" but I am not going there!!!! My experience is limited but I will offer that in any, and I mean any, high performance marine application that 5-10 hp located somewhere in the powerband you may never figure out can be more than offset, and more cheaply, with set-up, prop selection and huge doses of nitrous. Just kidding about the nitrous. Happy New Year and safe boating for 2003!!!!!!

[us1]

I totally agree with TB21. We work with and use different squish band mods and combustion chamber mod which allows us to run more compression more timing and lower octane fuel. The stock mercury heads are not so good. How ever I have not experimented with the head design being discussed in this thread.

[us1]

What is the angle difference between the dome of the piston and the squish in your diagram?

[TB21]

Guys first off read my post and you'll see that I stated that diagram was not a MERCURY...that it was a REAL racing engine. LOL

And I have only been toying with boat engines for about 3 years now.....my 2 cycle knowledge all comes from karting (which is many years ahead of boating) regardless of what anyone thinks....Now there are some of you thinking you cant compare boat engines to kart engines..."BULL CHIT" they use no gear box and must have a wide power band to acomplish pulling the 1 drive ratio. Every thingthing I've applied to my merc that i learned from karting has worked...including the port timing and flow patterns for the ports...right down to the (collision porting) of the transfer ports. But I doubt if the mercury world has heard of collision porting yet?

G-TRAIN
By eliminating the squish band completly the chamber would have to be so shallow to achieve good compression I think it would be impossible to get it to that point with out hitting water passages......But I have seen guys cut heads to the point of almost no squish band for use on road coarses with good results.....really kill lowend torque though.

As far as what F-1 guys run I dont care....I dont monkey see monkey do. Besides I dont for one minute believe that the top F-1 teams would share what they run (if they do they are stupid). And as far as this place not being for black or white I totally disagree...its for black , white , yellow , red or whatever , even chrome guys like me because there aint none of us right or wrong its just our opinions.anyone that modifys a part from info on this board should always research the mod completely because its just someones opinion.

Dave you are right about the domed piston crown in the diagram and i wasnt referring to do a merc like it.....just showing what a non-parallel squish looked like (But it does have about 2 1/2 degrees tapered squish.

US1
The angle in the diagram is about 2 1/2 degrees more than the piston dome. BTW dont you race something like F-1? Sounds like you to are constantly looking for an edge on competition....seems ur heads are on the right track.

Just to prove the power thats lost in heads a couple weeks ago at a race i was at a good friend of mine that happens to be in my OPINION probaly the best there is on 2 strokes (dont ask his name) showed me a head with a squish and chamber design and i laughed at it....well he proceeded to tell me it was a head that got the original race cut ruined by a blow-up , so they put it in the mill and played with it till they came up with this stupid looking cut , all by accident , that he showed me....i told him it was rediculous...until he stated the dyno results I know this is hard to believe and i wouldnt have believed from anyone but him , it picked up 12 % almost over the whole curve....thats kinda un-heard of . Now im sorry but dont ask for the design because I swore not to discuss it...Edges are to hard to achieve in racing and you have to keep em....and besides the guy has been very helpful to me for 20 years and i aint about to stick him.

Happy new year guyz. TB

[steve]

an important item. The squish area also cools the piston.
G-train--- If you make the chamber too wide especially with the poor quality Merc pistons you don't allow the piston some much needed cooling. The newest carting, snowmobile and PWC designs look very intriguing.

[TB21]

your excactly right......the squish band does act as sort of a heat sink for the piston crown.....But dont forget (heat is and power is heat). TB

[us1]

Thanks for the info. That goes hand in hand with what I believe. I like the way you think.

[T-REX]

Now Bein 2 cycle stupid, I juss couldn't hep putt'in my findingz/nonfindings...az far az F-1, dunno...Kartz...mmm, so so...Model plane engines, dun it all.....Drag motorz, well, let me say this in this manner so'z I don't piss nobody off or git misunderstood....I have taken my lil 2.0 from stock 135 to maxed to tha limit, plus sum!!...difrent pistons, heads ov ever kind shape and color, combustion chambers of all sorts, and squish bands of difrent shapes and sizes and even a shot at no squish at all...I will say(juss to clerify) no squish don't work...anythang over .040 starts dropping bottom end punch...BUT, Dragz muss not be compared to nuttin else, cuz nutt'in I have learned about 2 strokes have made a bunch of differnce in any OB I've fooled wit...I have a lil book "Super tuneing performance 2strokes", and anuther thats very informative "performance 2 stroke technoledgy"....There are several illistrations such az the one in the upper post...and I have tried most of everthang in them books(not counting other books that pozed ta have all the performance secrets)...Most of the performance 2 stroke books are motorcycle orentied,and mostly 1 cyl...When U start intergrating cyl's into each other(exhaust resanating in same chamber) and sharing the same intake track up to reeds...then, ever thang starts to change, and sum things change drastically....Well, any way, what I wanted to say iz this...In a drag motor U burn the good fuel, shove az much fuel/air mixture az U kin git to tha reedz, step up tha crankcase pressure, and pour on tha Compression...The shape of the squish band may meen a lil, but if U keep it in retrospect to the original size of the engine used, then enuff compression will over cum any loss(if any) that the stock squish will take away...COMPRESSION=POWER!!...I never stop experimenting, but till I stumble across that mirical combonation, STEP UP THA COMPRESSION if ya need a lil mo go!!...My 2 centz, T-REX

[TB21]

us1
Thinkin like i do will get you in trouble and wanna try to make things that work perfect work better....and that tends to make junk.....but seriously, thanks for the comment.


T-REX
If someone gets pissed of by your 2 cents then they should just go to www.getalife.com......cause as far as im concernerd you are one of the heros on this board....you kinda remind me of , hmmm well me. You take what high $dollar$ joe throws away and whoop his ass with it......being poor is the best teacher I ever had "know what i mean?"
Though I disagree with you on the importance of proper squish ,chamber and head design I will argee that compression is the cheapest horsepower there is...but if you happen to ever find that magic cut on squish angle , width , transition radius and chamber shape I think you'll be suprised.

Now back to the original question about that notch....theres been several opinions on it , and who knows which is right "hell we probaly all wrong"....but only 1 thing to do , run it...then run another set of stock heads of same cc without notch , under exact same conditions and measure the results.
Goodluck TB

[popslavaz]

TTT
Here it is John!!

[sho305]

Maybe you could get these guys to mod your Merc heads:D :D

http://www.psiperformance.com/catalog_2003/page8.htm
How much compression today?....hmmmm:cool: