Porting Timing for Torque

[Merc 2.5]

Well funny thing is. I just had hr long conversation with james perry bout blow down angles, port heights etc , not 10 min b4 i got on here and seen this thread, and seeing what Forbes posted was just dead on. If ur boat can support a 3.0l or better then go that route but if u need the weight savings , I'd got with the ee and yes cut heads to the 135ish mark , it will help torque but not to much that it will hurt it if u lug it , just run decent fuel. Play with props little for ski or cruise, id say they prob have hard time just holding the rope if u was to hammer down, especially of its on little bit lighter boat

[Chaz]

Another item not mentioned is the angles on the ports. The top roof angle on the intake ports also has an effect on where power is made.

That's the advanced class ...






P.S. I know why you said it ...
But how do I put the carbs directly on the transfer ports and block the intake / reed / disc valve / use ta be intake port ... Inquiring minds ....

[Merc 2.5]

That's the advanced class ...






P.S. I know why you said it ...
But how do I put the carbs directly on the transfer ports and block the intake / reed / disc valve / use ta be intake port ... Inquiring minds ....

Lol. Huh? I wanna learn all I can so plz go in detail in English if no one else does, fir dummies like me , im n process of doin builds for lite boat and heavy boat and just tryin maximize what i got. After light porting my motor degrees at 34% blow down. The 245 measured 30 or 31% blow down stock and rated at 7500 rpm? I know there's alot goin on in there on angles tho. Has anyone got same or close when measuring on 245? Stock 2.5 200 bout 28 29% just curious on others findings

[Chaz]

I didn't see where I said .. LOL in that post.

For better or for worse, here it is in plain English. To continue using the wrong name for anything in the long run does no one any good. Racer knows the difference, but used the wrong name .. to maybe be understood without going into detail.

No where will you see a transfer port, no matter the location being referred to as an "intake port" ... The transfer ports sole job is to move (transfer) the fresh charge from the crankcase to the cylinder above the piston ...

The "A" port is considered the main Transfer port.
"B" is the axillary Transfer port.
"C" is called the boost port.
Early two strokes , (1880 thru the early -mid 1900's) had neither the axillary or boost ports ...




An "intake port" has the sole purpose of bringing fresh air into the crankcase from the outside world..
At some point, be it the piston skirt, reed or rotary valve, it must close to build pressure in the crankcase to activate the transfer ports.

Obviously , blocking the intake, and mounting the carb on the transfer port directly would push air out of the carb in one direction and try to get it back in the other. If you could keep it from catching on fire .. it might run .. Make sense ???



Although somewhat dated, as is the port layout of the "modern" 2-stroke outboard. The port timing, timed area relationship, location and effects of port roof angles are all written and applicable in this book.

http://www.amrca.com/tech/tuners.pdf

[Glastron1987]

Thanks for that book. Looks pretty complicated, but will give it a try.

One other question... it seems the EPA really drove manufacturers to develop the DFI engines mainly for emission standards. Are there porting things that can be done to make the traditional 2-stroke better or worse in this regard?

[FORBESAUTO]

Would like to add, the original question was a basic port timing and effect on low end power. Tried to answer question as basic and use terms that everyone regardless of two stroke knowledge would understand. Did not use transfer and boost ports,(well actually did use transfer with “intake” to tie it together for the beginners) understanding a lot may not know the difference. Realize probably wasn’t best choice of words, but pretty sure was put where all knew what I was saying. If thread progressed, then we would go into detail. Sorry if I confused anyone.

[Chaz]

I guess your asking about improving fuel mileage. I normally say, buy a Kia or Hyundai at this point ..
The DFI motors , inject a spritz of gas as the exhaust port is closing, so little chance of escaping without going thru the process. It's also the reason you cant clip the heads, the excess cylinder pressure will push the fuel back where it came from or not let it in the chamber in the first place.

Outboard carbs are two circuit. Idle feed restriction and main jet. As long as air is moving thru the carb the idle circuit is active. Most emit fuel into the venturi thru a series of holes under and behind the closed throttle blade. As the blade opens, it uncovers another hole. I have drilled them out, epoxied them shut and redrilled them. You can clean up the bottom end a bit, but keep in mind that is also like an accelerator pump shot for carbs not equipped with one.
The main jet starts to move fuel as the blade has transitioned past the idle circuit and carries the fuel load to WOT. Old Webber carbs and people like Braswell have built more transition circuits into their carbs. The good thing is that they are adjustable. It also bad, because they are so adjustable. Easy to get lost. But also good reading to get a good understanding on how carbs really work.

EFI, The best you can do is put the higher flowing injectors in the hot holes and the weaker ones in the cold ones, and then adjust the fuel pressure globally.

Aftermarket ECM's allow you to tune the pulse width to each individual cylinder. You can even blue tooth your phone to the box and do it on the fly with the better units.

I use a EGT probe in each log. It would be better to have one in each exhaust port rather than read an average of the three in each bank. I also started using a O2 sensor in one bank. Both give me a general idea of where I'm at. Until we get a little guy to go inside and make it out alive to tell us what he saw .. the end result will always be to monitor sparkplugs and piston wash.
Never lose sight of the fact that gas and plugs are cheap ... pistons, not so much

[Chaz]

Would like to add, the original question was a basic port timing and effect on low end power. Tried to answer question as basic and use terms that everyone regardless of two stroke knowledge would understand. Did not use transfer and boost ports,(well actually did use transfer with “intake” to tie it together for the beginners) understanding a lot may not know the difference. Realize probably wasn’t best choice of words, but pretty sure was put where all knew what I was saying. If thread progressed, then we would go into detail. Sorry if I confused anyone.

Forby .. I'm so corn~fruzed ..

I think you called it .... transfer/intake . So you covered everyone.

Just make sure they know what your talking about before you hand em a grinder with a brand new aggressive carbide ...

[FORBESAUTO]

Forby .. I'm so corn~fruzed ..

I think you called it .... transfer/intake . So you covered everyone.

Just make sure they know what your talking about before you hand em a grinder with a brand new aggressive carbide ...

Ya just got me to thinkin. Was being conscious of words I used to include everyone, then noticed after your post, would have been more constructive to use proper terms and use the explanation like you provided to get all on the same page. But when ya postin ina phone, you get lazy and short cut as much as ya can.

[Glastron1987]

Would like to add, the original question was a basic port timing and effect on low end power. Tried to answer question as basic and use terms that everyone regardless of two stroke knowledge would understand. Did not use transfer and boost ports,(well actually did use transfer with “intake” to tie it together for the beginners) understanding a lot may not know the difference. Realize probably wasn’t best choice of words, but pretty sure was put where all knew what I was saying. If thread progressed, then we would go into detail. Sorry if I confused anyone.

The simple basics answered my questions for now even if terms were not precise. Precision is good for those advanced. Thanks.

[Chaz]

My response was more of an inside type joke to Racer .. I was asked to explain, I said .. for better or for worse, because I knew it was going to go off the rails.

Should I have said .. sorry it's a private joke .. No

Should we call things what they really are and if someone doesn't understand .. would any of us say .. go away kid .. ya bodder me .. NOPE . I would hope that someone would take the time to explain.

If people get butt hurt and want to close a thread over nothing .. I think I want their life.. Mine seems to have real issues to lose sleep over ..

Pick a port .. any port .. do's , don'ts .. should-a, kould-a, fixin to on the next one ..

[Glastron1987]

I guess your asking about improving fuel mileage. I normally say, buy a Kia or Hyundai at this point ..
The DFI motors , inject a spritz of gas as the exhaust port is closing, so little chance of escaping without going thru the process. It's also the reason you cant clip the heads, the excess cylinder pressure will push the fuel back where it came from or not let it in the chamber in the first place.

Outboard carbs are two circuit. Idle feed restriction and main jet. As long as air is moving thru the carb the idle circuit is active. Most emit fuel into the venturi thru a series of holes under and behind the closed throttle blade. As the blade opens, it uncovers another hole. I have drilled them out, epoxied them shut and redrilled them. You can clean up the bottom end a bit, but keep in mind that is also like an accelerator pump shot for carbs not equipped with one.
The main jet starts to move fuel as the blade has transitioned past the idle circuit and carries the fuel load to WOT. Old Webber carbs and people like Braswell have built more transition circuits into their carbs. The good thing is that they are adjustable. It also bad, because they are so adjustable. Easy to get lost. But also good reading to get a good understanding on how carbs really work.

EFI, The best you can do is put the higher flowing injectors in the hot holes and the weaker ones in the cold ones, and then adjust the fuel pressure globally.

Aftermarket ECM's allow you to tune the pulse width to each individual cylinder. You can even blue tooth your phone to the box and do it on the fly with the better units.

I use a EGT probe in each log. It would be better to have one in each exhaust port rather than read an average of the three in each bank. I also started using a O2 sensor in one bank. Both give me a general idea of where I'm at. Until we get a little guy to go inside and make it out alive to tell us what he saw .. the end result will always be to monitor sparkplugs and piston wash.
Never lose sight of the fact that gas and plugs are cheap ... pistons, not so much

Are those Webber and Braswell carbs a viable alternative? I always hear about WMH and WMV, but never those. Do you have a website to look them up for a 2.5 Merc?

[Chaz]

I guess anything is possible ... What I said was --->

Old Webber carbs and people like Braswell have built more transition circuits into their carbs. The good thing is that they are adjustable. It also bad, because they are so adjustable. Easy to get lost. But also good reading to get a good understanding on how carbs really work.

Weber's have been around since 1914, I'll bet if you googled that .. you could read for a month .. or more.

Braswell and Bo Laws (BLP) have taken the understanding of clean , efficient carburation to way past the next level. Neither will come out and say .. do this, do that .. but even if you just look at their work .. you will find subtle little differences that add up .
The carbs you mentioned have crude entry/exit machine work that makes air tumble. I've done epoxy work around the air bleed stands in the past to smooth out the air.
Big square headed throttle shaft screws wont do you any favors .. button head allen screws are worth a little ..
Five circuit Braswell ... plus the squirter .. They dont come like that from Holley



BLP .. closes the throttle blades and meters idle air thru the two brass jets in between the 4 barrels. It also closes off the idle transfer slot . You ever stand next to a car while the carb guru keeps turning in the idle adj screws and it loads up even worse .. ? Its cuz the slot starts to activate the main boosters and starts dumping in excess fuel .. The Merc toiletsons .. err tilleson.. might not look the same , but have the two same basic low/high circuits. (this one has an intermediate as well)



I'll bet this bad boy flows like Niagara Falls ...




Enough "intake" stuff ..

The two ~ stoke guys favorite .. has got to be the exhaust port .

Is it because it's "majic" ... ???

Because the others are hard to get too .. ???

OK .. real questions .. How wide should a guy go with the exhaust port.

#1) Good power with excellent reliability ?

#2) Max power, who cares how long it lasts ?

[Smalltownbassin]

I guess anything is possible ... What I said was --->

OK .. real questions .. How wide should a guy go with the exhaust port.

#1) Good power with excellent reliability ?

#2) Max power, who cares how long it lasts ?

#1) 75% of the width of the piston
#2) As wide as possible without snagging a ring

[Chaz]

Anybody else have a "go to" number .. ?